School Science Lessons
Topic 12D
2024-06-24
Bases, Hardness
(topic12D)
Table of contents
12.7.0 Bases, alkalis
12.5.0 Hardness in water, water hardness
12.4.0 Tests for water hardness
12.9.0 Prepare soap
Soap
12.2.0 Soaps and synthetic detergents
12.6.0 Surfactants
12.7.0 Bases, alkalis
12.7.1 Bases, properties of bases, alkalis
12.7.2 Solubility of alkalis
12.7.1 Feel of alkalis
12.7.4 Alkalis with acidic oxides, carbon dioxide
12.7.5 Alkalis with amphoteric oxides and hydroxides
12.7.6 Alkalis with basic oxides, copper oxide
12.7.7 Alkalis with metals, sodium hydroxide
12.7.8 Alkalis with salts, hydroxides
12.7.9 Alkalis with sodium carbonate
12.7.10 Sodium hydroxide with zinc sulfate solution
12.5.0 Hardness in water, water hardness
12.5.1 Hardness in water, water hardness, soft water
12.5.2 Detergents in place of soap solution
Experiments
12.5.3 Make soap suds using hard water and soft water
12.5.4 Prepare hard water
12.5.5 Remove water hardness
12.5.6 Soften hard water by boiling
12.5.7 Soften hard water using chemicals
12.5.8 Tea, Prepare cup of tea (See 3.)
12.5.9 Tea with dilute sulfuric acid
12.5.10 Tea with iron (II) sulfate
12.5.11 Tea with limewater
12.5.12 Tea with iron (III) salts
12.5.13 Temporary hardness and permanent hardness
12.5.14 Tests for metal ions in water, EDTA chelates
12.5.15 Wash in hard water
12.5.16 Water softening using ion exchange resin
12.4.0 Tests for water hardness
12.4.1 Tests for hard water to form a lather
12.4.2 Tests for water hardness
12.4.3 Tests for water hardness in different water samples
12.4.4 Tests for water hardness using standard soap solution
12.4.5 Test for water hardness, EDTA titration, Calmagite indicator
12.4.6 Tests for water hardness, EDTA titration
12.4.7 Tests for water to form a lather
12.2.0 Soaps and synthetic detergents
Anionic detergents
12.2.1 Soaps and synthetic detergents (syndets)
12.2.2 Bleaches, disinfectants, deodorizers
12.2.3 Detergents in washing powders
Wetting agents in detergents
Builders in detergents
Bleaches in detergents
Enzymes in detergents
12.2.4 Detergent phosphates
12.2.5 Drain cleaners
12.2.6 Laundry detergents
12.2.7 Machine dishwashing detergents
12.2.8 Scouring powders
Experiments
12.2.9 Oxidation of glycerol by potassium permanganate
12.5.9 Prepare detergent, alcohol-based detergent
12.3 Tests for glycerol
12.9.2 Tests for soap
12.9.0 Prepare soap
Experiments
12.9.1 Prepare inflammable soap with methylated spirit
12.9.2 Prepare soap by neutralization
12.9.3 Prepare soap by saponification
12.9.2 Prepare soap with animal fats
12.9.5 Prepare soap with fats or oils
12.9.6 Prepare soap with vegetable oils
12.9.7 Prepare soap, household soap
12.6.0 Surfactants
Surfactants in detergents.
Surfactants, surface active agents, are organic molecules with a lipophilic end and a polar end that emulsify and disperse oil and grease.
Surfactants also lower the surface tension to improve the wetting of clothes so that dirt may be more easily removed.
Surfactants do not precipitate in hard water.
Cationic surfactants may act as fabric softeners, e.g. aminoethylethanolamine, AEEA, C4H12N2O, surfactant, fabric softener, fuel additive, chelate.
Detergents or soaps contain surfactants, surface active agents, which reduce the surface tension of solvents used for washing.
When the distance between solid and liquid is less than 10-8 m, molecular forces between them will apply.
The attraction between molecules of solid and liquid forms a liquid layer attached to the surface of the solid.
When the action of the solid molecules on the liquid molecules of the liquid layer is stronger than the interaction of the liquid molecules, or force of cohesion.
The interface spreads and molecules stick to each other between liquid and solid.
It is called adhesion, force of adhesion.
Surface energy, surface tension - the force of attraction for itself that gives a liquid, e.g. water, an apparent skin.
The "skin" contracts to form drops rather than sheets on surfaces it does not wet.
On some surfaces, e.g. clean glass, the attraction of the water is greater for the glass than for itself, so the water "wets" the glass.
Water spreads out smoothly on clean glass, but remains in droplets on dirty glass.
So wetting refers to the covering of a solid by a liquid with a thin film.
The contact angle the liquid makes on the solid is small.
12.6.1 Surfactants in washing powders
12.6.2 Amphiphile
12.6.3 Bleaches in washing powders
12.6.4 Enzymes in washing powders
12.6.5 Fillers in washing powders
12.6.6 Fluorescent whitening agents in washing powders
12.6.7 Foaming agents in washing powders
12.6.8 Inorganic builders in washing powders
12.6.9 Ionic surfactants in washing powders
12.6.10 Non-ionic surfactants
12.6.11 Organic builders in washing powders
12.6.12 Synthetic fatty alcohol ethoxylate, ethylene oxide
12.7.1 Bases, properties of bases, alkalis
A base can dissolve in water to form hydroxyl ions and react with acids to form salts.
The term "base" includes the alkalis basic oxides and basic hydroxides.
The strong bases are lithium hydroxide LiOH, sodium hydroxide NaOH, potassium hydroxide KOH, rubidium hydroxide RbOH, caesium hydroxide CsOH.
Most bases dissolve in water releasing hydroxide ions (OH-) and react with acids to form salts.
In the reaction with dilute sulfuric acid, the base copper (II) oxide the oxide accepts hydrogen ions.
So you can say that a base is a proton acceptor.
CuO (s) + H2SO4 (aq) --> CuSO4 (aq) + H2O (l)
O2+ (g) + 2H+ (aq) --> H2O (l)
NaOH (s) --> Na+ (aq) + OH- (aq)
A basic oxide is a metal oxide, e.g. CuO.
A basic hydroxide is a metal hydroxide that is insoluble in water, e.g. Mg(OH)2.
Alkalis
(Arabic: al-kalī, calcined ashes)
An alkali is water-soluble base yielding a caustic solution, pH > 7.
In the later eighteenth century, the word "alkali" referred to any potash needed for glass and soap manufacture.
The "alkali" needed for making soap was formerly produced by burning wood charcoal or dried seaweed.
Alkalis are bases that are easily soluble in water.
The most commonly used alkalis are sodium hydroxide (caustic soda) calcium hydroxide and dilute ammonia solution.
An alkali is a hydroxide that dissolves in water to form a solution with pH > 7 and contains hydroxyl ions (OH-), e.g. NaOH.
Alkalis are good electrolytes, turn red litmus blue, and feel slippery.
Strong alkalis: ammonia solution, KOH, NaOH.
When strong alkalis dissolve in water, they completely ionize.
Be careful! Strong alkalis may burn the skin and cause blindness if splashed in the eyes!
Use safety glasses and nitrile chemical-resistant gloves.
NaOH (s) --> Na+ (aq) + OH- (aq)
Weak alkalis do not completely ionize in water, e.g. pass ammonia gas through water to form dilute ammonia solution.
NH4OH (aq) <-- NH4+ (aq) + OH- (aq)
or, using the more modern way of representing this reaction:
NH4OH (aq) <-- NH3 (aq) + H2O (l)
This solution is shown as NH3 (aq) + H2O (l), because while "NH4+" ions and" OH-" ions can be detected, "NH4OH" cannot be detected.
Experiments
1. Add a little solid sodium hydroxide, potassium hydroxide, calcium hydroxide and barium hydroxide separately to a little water in separate test-tubes.
Shake the test-tubes.
Which of the substances are soluble? Place your fingers around each test-tube to see if heat is being produced.
You will have noticed that the alkalis are not equally soluble; the order of decreasing solubility is sodium hydroxide, potassium hydroxide, barium hydroxide, calcium hydroxide.
2. Prepare sodium hydroxide solution, potassium hydroxide solution, calcium hydroxide solution and barium hydroxide solution.
Test each solution as follows:
2.1 Pour a small amount into a test-tube and place in it a piece of red and a piece of blue litmus paper.
2.2 Add a few drops of methyl orange solution.
2.3 Add a few drops of phenolphthalein solution.
Record what happens in each case.
The alkalis turn red litmus paper to blue, colourless phenolphthalein solution to red and methyl orange solution to yellow.
2.4 Add a little solid sodium carbonate.
Observe any changes in the solutions.
No gas forms when sodium carbonate is added to solutions of the alkalis so they do not behave like acids.
The white solids formed in the calcium hydroxide and barium hydroxide solutions are calcium carbonate and barium carbonate.
A solid formed, because of a chemical reaction in solution is called a precipitate.
12.7.3 Feel of alkalis
1. Feel some soap.
It feels slippery, because it contains alkalis.
Prepare very dilute solutions of each sodium hydroxide, potassium hydroxide, calcium hydroxide and barium hydroxide.
Moisten your finger tips with each solution and rub your fingers together.
What do you feel?
2. Wet your finger with the sodium hydroxide solution, feel it between your fingers, then wash them afterwards.
Describe the feel.
The solution has a soapy feel.
12.7.2 Solubility of alkalis
Add to the same amount of water in test-tubes solutions of: sodium hydroxide, potassium hydroxide, barium hydroxide, calcium hydroxide.
The relative solubility is in that order.
Feel the heat of reaction.
12.7.7 Alkalis with metals, sodium hydroxide
Most metals do not react with alkalis.
However, zinc or aluminium reacts with alkalis to form soluble zincate and hydrogen or soluble aluminate and hydrogen.
Strong alkalis should not be stored in aluminium or zinc containers.
Experiments
1. Add 5 mL of concentrated sodium hydroxide solution to test-tubes containing: copper, iron, aluminium, zinc.
Heat gently if no reaction is observed.
Test any gas from the reaction.
2. Add a small piece of aluminium foil to quarter of a test-tube of sodium hydroxide solution.
Heat until bubbles of a gas appear, but do not boil the solution.
Test the gas by first trapping it in the test-tube and holding the mouth of the test-tube to the flame.
The gas at the mouth of the test-tube explodes with a squeaky pop sound.
The gas formed is hydrogen gas.
Aluminium reacts with sodium hydroxide to form sodium aluminate and hydrogen gas.
12.7.3.1 Recycle aluminium drink-cans as potassium aluminium sulfate, alum
Waste material can be converted to new substances, but full recovery is seldom attained, because of incomplete reactions and loss of partially soluble materials.
In this experiment, conversion of aluminium scrap metal to alum crystals requires large quantities of sulfuric acid and potassium hydroxide.
Be careful! Use safety glasses and nitrile chemical-resistant gloves.
Experiment
1. Use 4 g of pieces of an aluminium drink-can cut into thin shavings.
Put 150 mL deionized water in a 400 mL beaker.
Slowly add 50 ML of 6 M potassium hydroxide solution.
Add the shavings, put the beaker on a tripod stand and mat inside a fume cupboard, fume hood.
Heat the mixture gently over a small flame for 30 minutes to dissolve most of the aluminium metal.
Adjust the flame to keep a controlled bubbling rate in the beaker.
Use a glass stirring rod to prevent the metal shavings floating on top of the froth.
Be Careful! Keep your face away from the caustic spray!
When most of the aluminium has dissolved, turn off the Bunsen burner and filter the hot mixture through a funnel and glass wool plug to remove suspended paint, varnish and unreacted aluminium pieces.
Collect the filtrate in a 400 mL, beaker.
Cool the filtered solution to room temperature.
Transfer the liquid to a 250 mL graduated cylinder to record the total volume of solution.
Pour one quarter of this total volume into separate 150 mL beakers.
With continuous stirring, acidify each portion of the solution by slowly pouring 20 mL, of 9 M sulfuric acid into the beaker.
Be careful! Considerable heat is produced!
If any lumps of aluminium hydroxide precipitate are present after adding the sulfuric acid, heat the mixture gently with stirring.
Remove the heat when the mixture becomes clear.
Cool the solution m an ice bath for about 20 minutes with frequent stirring.
Crystals of alum, KAl(SO4)2.12H2O, form in the beaker.
Set up a Buchner funnel with all the holes are covered.
Clamp the flask to a ring stand, and connect the flask to a water aspirator.
After the alum crystals have fully formed in the ice bath, turn on the aspirator and transfer the alum crystals from the beaker to the Buchner funnel.
Wash the beaker with 20 mL of 60% ethyl alcohol / water solution to transfer any crystals remaining in the beaker.
Add these washings to the Buchner funnel.
Run the aspirator for several minutes, allowing the crystals to become moderately dry.
Remove the filter paper and alum crystals from the Buchner funnel and put on a watch glass.
Divide the mass of alum crystals recovered by the original mass of aluminium present in the solution to show the mass of alum crystals obtained per gram of aluminium metal.
2. Theoretically, 17.5 g alum crystals can be obtained from 1.00 g of aluminium metal.
Calculate the percentage yield: = Actual mass alum recovered per g Aluminium / Theoretical mass alum recovered per g Aluminium
1. Dissolving the aluminium
2Al (s) + 2KOH (aq) + 6H2O (l) --> 2KAl(OH)4 (aq) + 3H2 (g)
2. Acidifying with sulfuric acid
2KAl(OH)4 (aq) + H2SO4 (aq) --> 2Al(OH)3 (s) + K2SO4 (aq) + 2H2O (l)
2Al(OH)3 (s) + 3H2SO4 (aq) --> Al2(SO4)3 (aq) + 6H2O (l)
3. Forming alum crystals
K+ (aq) + Al3+ (aq) + 2SO42- (aq) + 12H2O (l) --> KAl(SO4)2.12H2O (s).
12.7.8 Alkalis with salts, hydroxide ions
Hydroxide ions (hydroxyl ions) form precipitates with most metal ions.
All metallic hydroxides are insoluble in water except sodium hydroxide, potassium hydroxide and ammonia solution.
[Not "ammonium hydroxide, NH4OH".
Ammonia solution is shown as NH3 (aq), because "NH4+" ions and "OH-" ions can be detected, but "NH4OH" cannot be detected.]
Calcium hydroxide and barium hydroxides are only slightly soluble.
However, all substances dissolve in water to some extent so there is no sharp distinction between soluble and insoluble substances.
Experiments
1. Add drops of 2 M sodium hydroxide solution to 2 M solutions: copper (II) sulfate, copper (II) chloride, copper (II) nitrate.
In each case, a blue precipitate results.
These solutions contain only the copper (II) ion in common so this ion is the cause of the blue precipitate.
Add drops of barium chloride solution to: sulfuric acid, sodium sulfate.
In each case the white precipitate is caused by the sulfate ion.
Ba2+ + SO42- --> BaSO4 (s).
2. Prepare solutions of collection of salts in separate test-tubes, e.g. magnesium sulfate, copper (II) sulfate, iron sulfate, potassium nitrate, calcium chloride.
To each solution slowly add a small quantity of sodium hydroxide solution.
Note the colour of any precipitate formed and any other change you may observe.
copper (II) sulfate (aq) + sodium hydroxide (aq) --> sodium sulfate (aq) + copper hydroxide (s)
copper ions (aq) + hydroxide ions (aq) --> copper hydroxide (s).
12.7.6 Alkalis with basic oxides, copper oxide
Basic oxides do not react with alkalis.
Add a small quantity, about the size of a split pea of sodium hydroxide solutions to: copper (I) oxide, calcium oxide, magnesium oxide, iron oxide.
In each case there is no reaction.
12.7.4 Alkalis with acidic oxides, carbon dioxide
Acidic oxides react with alkalis to form salt and water.
1. Pass carbon dioxide bubbles through sodium hydroxide solution in a test-tube.
Note the size of the bubbles.
If the bubbles decrease in size as they rise through the solution, carbon dioxide is being used in a chemical reaction.
Carbon dioxide combines with water to form carbonic acid, so a reaction of this acidic oxide with the alkali occurs.
NaOH (aq) + CO2 (g) --> Na2CO3 (aq) + H2O (l)
Add dilute hydrochloric acid.
Test gases that form from the reaction with: moist litmus paper, a lighted splint, limewater.
The production of carbon dioxide confirms that the reaction forms a carbonate.
HCl (aq) + Na2CO3 (aq) --> CO2 (g) + 2NaCl (aq) + H2O (l).
2. Pass a slow stream of carbon dioxide bubbles into the bottom of a measuring cylinder containing sodium hydroxide solution.
Note any alteration in the size of the bubbles as they rise through the solution.
After five minutes stop the flow of carbon dioxide and add 5 mL dilute hydrochloric acid.
Test any gas liberated with a lighted splint, pieces of damp red and blue litmus paper, and limewater.
The gradual decrease in the size of the ascending carbon dioxide bubbles shows that a reaction involving carbon dioxide occurs.
Carbon dioxide and sulfur dioxide combine with water to form acids so you expect a reaction of these acidic oxides with dilute solutions of alkalis to occur.
The production of carbon dioxide after adding hydrochloric acid to the solution in the measuring cylinder confirms this view, because no gas is produced when hydrochloric acid reacts with sodium hydroxide, the only substance other than water originally present in the cylinder.
2NaOH (aq) + CO2 (g) --> Na2CO3 (aq) + H2O (l)
sodium hydroxide (aq) + carbon dioxide (g) --> water (l) + sodium carbonate (aq).
3. Pass carbon dioxide through barium hydroxide solution in a test-tube.
Filter off the precipitate.
Add dilute hydrochloric acid to the precipitate.
Identify the gas liberated.
The reaction forms barium carbonate.
Ba(OH)2 + CO2 (g) --> BaCO3 (s) + H2O (l)
BaCO3 (s) + 2HCl (aq) --> BaCl2 (aq) + CO2 (g).
12.7.5 Alkalis with amphoteric oxides and hydroxides
Oxides and hydroxides of Al, Pb, Sb, Sn, and Zn are amphoteric.
An amphoteric oxide or hydroxide will neutralize an acid to form a salt and water, and will neutralize a base to form a salt and water.
When amphoteric substances react with alkalis, they behave as acidic oxides.
When amphoteric substances react with acids, they behave as basic oxides.
Aluminium hydroxide, Al(OH)3 solution, is amphoteric: A.
As a base, aluminium hydroxide with acids forms aluminium salts, B.
As an acid, aluminium hydroxide with bases forms aluminates, [Al(OH)4(H2O)2]-.
Experiments
1. Add dilute sodium hydroxide solution to: aluminium oxide, zinc oxide, aluminium hydroxide, zinc hydroxide.
Heat gently.
Note any reactions.
ZnO (s) + 2NaOH (aq) --> Na2ZnO2 (aq) + H2O (l)
zinc oxide + sodium hydroxide --> sodium zincate + water
Al2O3 (s) + 2NaOH (aq) --> 2NaAlO2 (aq) + H2O (l)
aluminium oxide + sodium hydroxide --> sodium aluminate + water.
2. Repeat the procedure, but using dilute sulfuric acid instead of dilute sodium hydroxide solution.
Al2O3 (s) + 3H2SO4 (aq) --> Al2(SO4)3 (aq) + 3H2O (l)
aluminium oxide + sulfuric acid --> aluminium sulfate + water.
12.7.10 Sodium hydroxide with zinc sulfate solution
The addition of aqueous sodium hydroxide to a test-tube containing zinc sulfate solution will result in the formation of zinc hydroxide, white precipitate.
2NaOH (aq) + ZnSO4 (aq) --> Zn(OH)2 (s) + Na2SO4 (aq)
On addition of excess aqueous sodium hydroxide, the precipitate reacts with the sodium hydroxide to form a complex salt, sodium zincate.
Zn(OH)2 (s) + 2NaOH (aq) --> Na2ZnO2 (aq) + 2H2O (l) (insoluble --> soluble)
zinc hydroxide + sodium hydroxide --> sodium zincate + water
The resulting zincate is soluble and so dissolves to give the colourless solution.
Dissolve
However, many secondary school chemistry teachers, chemistry textbooks, and handbooks on qualitative analysis, would describe the above reaction of zinc hydroxide with excess sodium hydroxide as:
"a white precipitate forms that dissolves in excess sodium hydroxide to give a colourless solution".
Students are taught that dissolving is a physical change as the solute can be recovered easily and that no new substances form.
Thus the use of the word "dissolve" in the above situation may give students the notion that the disappearance of the precipitate is a physical change,
when, in fact, it is a chemical reaction that occurred.
The word "dissolve" has also been erroneously used to describe the following phenomena:
1. The reactions of excess aqueous sodium hydroxide with aluminium hydroxide, result in the formation of soluble sodium aluminate.
2. The reactions of aqueous ammonia with silver chloride, zinc hydroxide or copper (II) hydroxide results in the formation of soluble complex amines.
3. The reactions of acids with metals, insoluble bases, carbonates and sulfate (IV)
Chemists use the term "dissolve" loosely to mean the disappearance of a solid in a liquid, but they are aware of what is happening,
i.e. whether a reaction occurred or whether it is just solvation.
However, secondary new substances form.
The use of the word "dissolve" above may give students the notion that disappearance of the precipitate is a physical change, when it is a chemical reaction that occurred.
12.7.9 Alkalis with sodium carbonate
Add solid sodium carbonate to alkaline solutions.
No gas forms.
White precipitates of carbonates form only in the barium hydroxide solution and calcium hydroxide solution.
Na2CO3 (s) + Ca(OH)2 (aq) --> CaCO3 (s) + NaOH (aq).
12.2.1 Soaps and synthetic detergents (syndets)
Saponification is the process where fats are broken up by sodium hydroxide to form soaps and glycerol (glycerine, propane-1,2,3-triol).
Soaps are the alkaline salts of fatty acids.
Most soaps are a mixture of sodium stearate and sodium palmitate.
Palmitic acid C15H31.COOH) is found in vegetable oils.
Octadecanoic acid, stearic acid [CH3(CH2)16.COOH] is found in mutton fat.
Cis octadec-9-enoic acid (oleic acid, red oil, C17H33.COOH, cis-9-octadecanoic acid) occurs as glycerine ester of fats and oils and oxidizes
on exposure to air and turns rancid yellow colour.
Soft soaps are made from potassium salts and hard soaps are made from sodium salts.
Metallic soaps are compounds of fatty acids with metal bases and used for waterproofing.
Resin soaps are alkali salts of resins.
Soap is not soluble in salt water.
Soap dissolves in water to form sodium ions and stearate ions containing along chain of carbon atoms with a negatively charged group at one end
that attracts water molecules.
The other ends of the long carbon chains do not attract water molecule, but can mix with non-polar compounds, e.g. oils and grease, and surround small
oil droplets to be taken away in the wash.
Dirt particles suspended in the grease and oil are also washed away.
The small oil droplets become negatively charges, repel each other and so remain suspended in the washing water.
Sodium stearate is a salt of a weak acid so it produces slightly alkaline solutions, harmful to certain fabrics, when dissolved in water.
R(C=O)O- Na+ + H-OH <--> R(C=O)-OH + Na+OH-
In acid solutions, sodium stearate forms insoluble stearic acid and forms insoluble salts with Ca2+, Mg2+ and Fe3+ that precipitate as a curd-like "bath scum" and dark ring around shirt collars.
C17H35(C=O)O-Na+ + H+Cl- --> C17H35(C=O)OH + Na+Cl-
sodium stearate [soluble] + HCl --> stearic acid [insoluble] + NaCl
C17H35(C=O)O-Na+ + Ca2+ --> C17H35COO-)2Ca2+ + 2Na+
sodium stearate [soluble] + Ca2+ --> calcium stearate [insoluble] + 2Na+
or
Ca2+ + 2CH3(CH2)16(C=O)O --> [CH3(CH2)16CO-]2Ca2+.
Anionic detergents
The first anionic detergents were sodium salts of alkyl hydrogen sulfates
1. 3[CH3(CH2)10(C=O)OCH2] + 6H2 --> 3CH2(CH2)10CH2OH + HOCH2-HOCH-HOCH2
Glycerol trilaurate reduced to 1-dodecanol (lauryl alcohol) + glycerol
2. CH2(CH2)10CH2OH + HOSO2OH --> CH2(CH2)10CH2O(SO2)OH + H2O
1-dodecanol + sulfuric acid --> alkyl hydrogen sulfate + water
3. CH2(CH2)10CH2OSO2OH + NaOH --> CH3(CH2)10(S=O2)O-Na+ + H2O
Alkyl hydrogen sulfate neutralized with NaOH --> sodium lauryl sulfate [lipophilic chain: CH3(CH2)10,
hydrophilic chain: (S=O2)O-Na+] + water
Modern detergents are straight chain alkyl benzene sulfonates that are biodegradable and do not accumulate in the environment.
RCH=CHR' + benzene --> [AlCl3 catalyst] RCHCH2R'- benzene --> + H2SO4 -->
RCHCH2R'- benzene-SO3H --> + Na+ OH- --> RCHCH2R'- benzene-SO3-Na+ [lipophilic: RCHCH2R', hydrophilic: -SO3-Na+]
Also, detergents may be cationic, e.g. C18(CH3)3N+Cl-, neutral, e.g. C8 - benzene ring - O(CH2CH2O)5H,
amphoteric C18(CH3)2N+CH2CO2-.
12.9.5 Prepare soap with fats or oils
Soap is made by using a double displacement reaction of a strong base, e.g. sodium hydroxide, + many fats and oils.
Castile soap, seafarer's soap, is made from vegetable oil, usually olive oil, but also coconut oil and other vegetable oils.
Experiments
1. Dip the tips of two fingers in < 0.1 M dilute potassium hydroxide solution to feel the soap made.
Rinse hands thoroughly after this experiment.
2. For this experiment, wear safety glasses and the area must be well-ventilated.
Dissolve 2 g of sodium hydroxide or potassium hydroxide in 25 mL of methylated spirit in a small beaker.
Heat the solution on an electric hot plate or in a water bath.
Pour 10 mL of olive oil into an evaporating basin, add the sodium hydroxide solution then stir with a glass rod.
Put the evaporating basin on a large beaker filled with hot water.
Leave the methylated spirit to evaporate until a soft semi-solid mixture of soap and glycerol remains.
Dissolve the mixture in 25 mL of hot water and pour it into a 50 mL beaker.
Add 5 g of sodium chloride and stir.
Add 2 mL ethanol and warm the mixture, not to boiling.
Leave the mixture to cool, then cool remove the top layer of soap and test it by shaking with water.
3. Be careful! Do not touch the solid sodium hydroxide or the solution, because both are caustic.
Use safety glasses and nitrile chemical-resistant gloves.
Use animal kidney fat from a butcher.
Boil this fat in water and the oil will separate on the surface.
When cold, the fat will solidify and it can be separated from the water.
Melt the fat again and strain through several layers of cloth.
Weigh this fat and then weigh out one third as much sodium hydroxide pellets.
Heat the fat in an iron dish.
When it is molten, slowly add the sodium hydroxide solution with continuous stirring.
Heat with a small flame to avoid boiling over.
Allow the fat and the sodium hydroxide to boil for 30 minutes.
Stir the mixture frequently.
Weigh sodium chloride using twice the weight of the sodium hydroxide pellets.
After the 30 minutes boiling, stir the sodium chloride into the mixture and leave to cool.
The soap separates as a layer at the top.
Separate this soap from the liquid below, melt and pour into matchboxes where it will solidify again as small bars of soap.
4. This preparation can be done with beef fat, mutton fat, lard, or olive oil.
Put an basin of beef dripping (which must be free from salt) or olive oil into a beaker with three times as much dilute sodium hydroxide solution.
Add three or four small pieces of broken tile or flower-pot to ensure steady boiling and to prevent the beaker from bumping.
Cover the beaker with a small watch glass and pour cold water into the watch glass.
The purpose of the watch glass is to condense the steam produced in the boiling and prevent the liquid from drying up.
Heat the beaker very gently at first, moving the flame.
When boiling begins, continue the heating with a flame, the tip of which touches the tripod.
Keep the contents of the beaker boiling for half an hour.
Then turn out the flame and leave the beaker to cool in a container of cold water.
When the beaker is quite cold skim off any fat, or pour off any oil, which remains on the surface of the liquid.
Add two teaspoons of salt to the beaker and dissolve the salt in the liquid by stirring.
A white jelly-like precipitate separates out.
This is soap.
Run off the liquid from the beaker, keeping back the soap with a spoon.
Stir the soap in the beaker with two or three lots of cold water to free it from alkali and salt, pouring away the liquid after each washing.
Test the soap by rubbing between the fingers.
Note the soapy feel.
Put a small piece of the soap into a test-tube with water and shake the test-tube.
An abundant lather forms.
12.2.12 Tests for soap
1. Dissolve a small piece of house- hold soap in half a test-tube of hot water.
Tests the solution with red litmus paper.
The paper should not change.
Add one or two drops of phenolphthalein solution.
The liquid turns pink.
A solution of good quality soap is a very weak alkali and, although it affects phenolphthalein, it s usually too feeble to change litmus.
2. Dissolve a piece of soap the size of a pea in half a test-tube of hot water.
Cool the test-tube and add 5 mL of salt.
When the test-tube is shaken the soap separates out as a white precipitate on top of the water, because it is insoluble in salt water.
This explains why it is very difficult to obtain a lather when you wash the hands in sea-water with soap.
3. Add drops of limewater to a solution of soap and shake the test-tube.
A precipitate of calcium stearate forms as a scum on the surface of the water.
This precipitate is important in connexion with hard water.
12.9.1 Prepare inflammabl soap with methylated spirit
Prepare inflammable soap from ordinary household soap and methylated spirit.
Put two or three small pieces of soap into a test-tube and add an inch of methylated spirit.
Hold the test-tube in a pan of hot (nearly boiling), water for a minute or two and gently shake the test-tube.
The methylated spirit dissolves some of the soap.
Pour the liquid from the test-tube into an basin, where it immediately solidifies and forms a small cake of soap.
Remove the cake with a penknife on to a metal lid and apply a light to it.
It burns for a long time.
12.9.2 Prepare soap by neutralization
RCOOH + NaOH --> RCOO-Na+ + H2O, R = CH3(CH2)10-16
fatty acid + base --> Salt (soap) + water.
12.9.3 Prepare soap by saponification
ester + alkali --> salts of carboxylic acids + alcohols
RCOOR' + NaOH --> RCOO-Na+ + R'OH
RCOOR' + OH- --> RCOO- + R'OH
Substitute KOH for NaOH to produce semi-solid soft soap.
Substitute heavy metals to produce heavy metal stearates for lubricating oil, detergents and plastic manufacture, e.g. PVC
ester (fat) + base --> salt of fatty acid (soap) + alcohol, e.g. glycerol (glycerine) CH2OHCH(OH)CH2OH
Salt of fatty acids from beef tallow, sodium stearate CH3(CH2)16COO-Na+
Salt of fatty acid from palm oil, sodium palmitate CH3(CH2)14COO-Na+.
Experiments
1. Alkalis react with fats and cooking oils.
For this reason sodium hydroxide (caustic soda) is used to remove fats and greasy deposits.
Add a very small piece of lard (pig fat) or olive oil to half a large test-tube of sodium hydroxide solution.
Boil very for a few minutes, keeping the test-tube moving over the flame so that the liquid does not spurt out.
Wear eye protection and protective clothing.
Pour the hot liquid into a clean test-tube, and add a quarter of a test-tube of clear, saturated, sodium chloride solution.
Leave to cool.
A white precipitate of soap settles out from the liquid.
When this process is done on a large scale in a soap factory, the soap is separated from the liquid and pressed into blocks.
When sodium hydroxide reacts with fats, soap and glycerol (glycerine) form.
2. Use double decomposition to make metallic soaps.
Separately boil a strong soap solution and an equally strong solution of a metallic salt, e.g. chloride or sulfide of Al, Cu, Fe, Mn, Zn.
Mix the solutions and gather the soap on a linen cloth.
Metallic soaps are used for varnishes, and waterproofing.
3. Make laundry soap.
Melt lard at low heat and add sodium hydroxide solution, 200 g per litre, while stirring at constant low heat until saponification occurs.
If the soap does not separate from the solution, add more sodium hydroxide solution.
To purify the soap, after separation pour off the sodium hydroxide solution, add water to the soap mass and heat until it dissolves and separate again with concentrated sodium hydroxide solution or common salt, sodium chloride.
Melt the soap again in a water bath.
Heat gently to expel water then pour into moulds.
4. Make a hot stirred soap with potassium hydroxide.
Olive oil 100 parts, solid potassium hydroxide 20 parts, deionized water 100 parts, 90% ethanol 20 parts.
Boil the mixture in a steam bath until oil is saponified.
Dissolve the soap formed in 300 parts deionized water then "salt out" the soap by adding 25 parts solid sodium hydroxide and 5 parts solid sodium carbonate in 80 parts deionized water.
12.6.1 Surfactants in washing powders
A surfactant is a molecule attracted to the surface of water and capable of changing the properties of the surface, generally by lowering the surface tension to make a solution more wettable.
Surfactants, surface active agents, lower the surface tension of water on an item and allow more entry into tiny clacks and holes.
Then other chemicals in the solution can react with the item.
CH3-CH=CH2 propylene --> CH3-CH(CH3)-CH2-CH(CH3)-CH2-CH(CH3)-CH=CH(CH3) propylene tetramer
--> CH3-CH(CH3)-CH2-CH(CH3)-CH2-CH(CH3)-CH=CH(CH3), benzine-SO3-Na+, alkylbenzene sulfonate (ABS), i.e. RSO3-Na+, similar to soap, RCOO-Na+
Surfactant molecule = hydrophobic, water insoluble chain of fatty acids + hydrophilic, water soluble, charged end.
Anionic surfactants
Anionic surfactants have negative charge at the water-soluble end.
They are used in most domestic detergents and especially for washing glass, e.g. sodium dodecyl benzene sulfonate, CH3(CH2)11C6H4SO2O-Na+.
Anionic surfactant molecules concentrate on the surface layers of water to lower the surface tension and allow the water to wet hydrophobic surfaces.
The long hydrocarbon tail is soluble in non-polar substances, e.g. oil and the sulfonate group at the other end is soluble in water.
So the surfactant molecule can lie across the oil water interface.
The molecules aggregate into micelles with the hydrocarbon tails towards the centre leading to emulsification of oily dirt and its removal from the fabric being washed.
Cationic surfactants
Cationic surfactants have positive charge at the water soluble end.
Used in mild antiseptic throat medicine, algicides, fabric softeners and washing plastics, e.g. CH3(CH2)15N(CH3)3+Br-
3. Non-ionic detergents have polyethylene oxide group in the molecule.
The non-ionic polar groups in the molecule, e.g. -C2H4-O-C2H4-OH, form hydrogen bonds with water.
4. Amphoteric surfactants have positive and negative charge depending on pH.
Used in hair conditioners.
Surfactant system
1. Ionic surfactants | Non-ionic surfactants
2. Inorganic builders | Organic builders
3. Fluorescent whitening agents | Foaming agents
4. Bleaches
5. Fillers
6. Enzymes.
12.6.9 Ionic surfactants in washing powders
Sulfonation is the addition of the function group -SO3H to a molecule.
Aromatic ring-H to aromatic ring (-SO3H), a sulfonic acid, e.g. sulfonation of benzene.
LAS (linear alkylbenzene sulfonic acid, CH3(CH2)11C6H4SO3H, dodecylbenzene sulfonic acid), is the most used synthetic surfactant, because of low cost, can be dried to a stable powder and has a straight chain so it is environmentally friendly when degraded after use.
LAS is an mixture of anionic surfactants with molecules having hydrophobic and a hydrophilic groups.
LAS is a mixtures of homologues of different alkyl chain lengths C10 to C14) and phenyl isomers, each containing a sulfonated aromatic ring attached to a linear alkyl chain.
The starting material LAB (linear alkyl benzene) is produced by the alkylation of benzene with n-paraffins with aluminium chloride (AlCl3) catalyst.
LAS is produced by the sulfonation of LAB with sulfuric acid.
The LAS is then neutralized to a salt (sodium, ammonium, calcium, potassium, and triethanolamine salts).
LAS is mainly used to produce household detergents, laundry powders, dishwashing liquids and emulsifiers for agricultural herbicides.
Other anionic surfactants are alpha olefin sulfonates (AOS) and alkyl sulfates (AS), nonvolatile compounds produced by sulfonation.
α-olefin + benzene --> alkyl benzene + sulfuric acid (sulfonation) --> sulfonic acid + water.
12.6.10 Non-ionic surfactants
Coconut diethanolamide
RCOOH + H2NCH2CH2OH -->RCONHCH2CH2OH + H2O (condensation reaction)
coconut oil fatty acids + monoethanolamine --> coconut diethanolamide (alkylamide) + water.
12.6.12 Synthetic fatty alcohol ethoxylate, ethylene oxide
RCH2OH + (n-1) CH2OCH2 --> RCH2(OCH2CH2)nOH (condensation polymerization)
fatty alcohol + ethylene oxide --> fatty alcohol ethoxylate.
12.6.8 Inorganic builders in washing powders
1. Sodium tripolyphosphate, STPP, buffers water to milder pH and sequesters hard water ions, deflocculating action to keep clay-type dirt in suspension surface active agent surfactant
2Na2HPO4 + NaH2PO4 --> Na5P3O10 + 2H2O
disodium monohydrogen phosphate + monosodium dihydrogen phosphate --> pentasodium triphosphate (sodium tripolyphosphate)
However, zeolite / sodium carbonate / polycarboxylate builders, e.g. "Zeolite NAA" may replace polyphosphates where there is concern that adding phosphate to polluted water will cause growth of algae that cuts off the light to waterweeds and lead to fish death.
In some countries there is an agreement to limit to < 5% phosphorus in detergents.
2. Sodium silicate (water glass) removes magnesium and some calcium and inhibits corrosion in washing machines.
12.6.11 Organic builders in washing powders
cellulose + sodium hydroxide + chloroacetic acid --> sodium carboxymethyl cellulose
It acts as an anti-deposition agent on cellulose based fabrics, e.g. cotton and rayon, by increasing the negative charge in the fabric, which then repels the negatively charged dirt particles.
12.6.6 Fluorescent whitening agents in washing powders
Fluorescent whitening agents, optical bleaches, optical whites, fluorescers, "washing blue".
Blueing refers to the practice of adding "washing blue" to the washing water of sheets to neutralize any yellow colour by adding more blue colour so that the dry sheets would appear whiter.
Cotton naturally ages to a yellow colour, which does not fully reflect blue light from incident sunlight.
These chemicals convert invisible ultraviolet light to visible blue light to give fabrics greater uniformity of reflectance and appear "whiter".
A white shirt on sale in a shop may already contain fluorescers, but they get washed out.
12.6.7 Foaming agents in washing powders
Foam may be important in some detergents to hold up particles of removed dirt, e.g. in carpet and hair shampoos, but the suds may cushion the impact of blades in front loading washing machines and may expand up to cause shot circuits.
Some detergents contain a "low suds" foaming agent, because people think that a non-foaming detergent is not doing anything!
Some detergents include soap to act as a water softener and surface active agent and also to rapidly collapse foam during the rinse cycle after wash.
Soap for these purpose my be replaced by silicones.
12.6.3 Bleaches in washing powders
The enzyme catalase catalyses the oxidation of substrates by hydrogen peroxide and, if no substrate, it breaks down any hydrogen peroxide to water.
Sodium perborate in water releases the powerful oxidizing agent hydrogen peroxide that removes most stains without harming textile fibres or removing dyes.
However, sodium perborate is effective only at high temperatures and the enzyme catalase in some stains may destroy sodium perborate at low temperatures.
The boron in detergent runoff in sewers may be poisonous to citrus crops.
Bleach activators can bleach at lower temperatures, e.g. penta acetyl glucose, tetra acetyl ethylene diamine (TAED), sodium percarbonate, nonoyloxy benzene sulfonate (NOBS).
TAED activates "active oxygen" bleaching agents, e.g. sodium perborate, sodium percarbonate, sodium perphosphate, sodium persulfate, urea peroxide, to release hydrogen peroxide in the wash cycle by reacting with hydrogen peroxide to release peracetic acid, a fast-acting bleaching agent.
[CH3C(O))2NCH2CH2N[C(O)CH3]2 + H2O2[CH3C(O))2NCH2CH2NH(C(O)CH3] + CH3CO3H.
12.6.5 Fillers in washing powders
Calcium carbonate and other components provide bulk to the product.
Fillers include solvent-based fillers, wood grain fillers, water-based fillers, acrylic fillers, and plastic fillers, e.g. Poly filler, Space filler.
They are toxic if ingested.
12.6.4Enzymes in washing powders
Enzymes include alkaline proteases coated with polyethylene glycol that melts in the wash, amylases to breakdown starch glue and lipases to hydrolyse dirty fat.
12.6.2Amphiphile
An amphiphilic molecule is both hydrophilic (loves water) and lipophilic (loves fat), e.g. "soap molecule", saponins, cholesterol, detergents, sodium dodecyl sulfate.
12.2.3 Detergents in washing powders
Detergents washing up detergent, "Teepol", "Trix", anionic, washing-up liquid
Detergents have the same action as soap, but do not form precipitates with calcium and magnesium salts and so can use in hard water.
Detergents use polyphosphates or zeolite to make calcium inactive in the system.
Wetting agents in detergents
Wetting agents, e.g. sodium laureth sulfate, sodium lauryl ether sulfate, SLES, sodium dodecyl sulfate, CH3(CH2)11OSO3Na, foaming agent, allow soap suds to form easily.
Builders in detergents
Sodium tripolyphosphate, STPP, removes calcium and magnesium ions as a complex through chelation or by exchange these ions for sodium ions.
Other builders used to avoid phosphate pollution by wastewater are sodium carbonate, sodium citrate and sodium silicate.
Also, sodium aluminium silicate, a zeolite, may be used for calcium ion exchange.
Bleaches in detergents
Bleaches may be hypochlorite bleaches that allow chlorine to act as an oxidizing agent, or, to avoid pollution by residual chlorine, e.g.
sodium perborate, NaBO3, may be substituted to allow bleaching by hydrogen peroxide produced by hydrolysis of the sodium perborate.
Enzymes in detergents
Enzymes may remove stains, e.g. protease enzymes to hydrolyse protein stains and amylase enzymes to dissolve starch based stains.
12.2.4 Detergent phosphates
Detergent phosphates, as polyphosphates, mainly sodium tripolyphosphate (STPP), Na5P3O10, are used in detergents for different functions.
Without using polyphosphates several different chemicals would be needed to replace them.
There are also used in ceramics and are an authorized food ingredient.
Phosphates occur in sewage from detergents, human foods (transferred into human wastes) animal manure and food industry wastes.
These phosphates can be recovered and recycled back into fertilizers and the detergent industry.
Phosphates are the only recyclable ingredient of detergents.
12.2.6 Laundry detergents
Dose 25 g / 30 L TO 100 G / 64 L
Percentage formulation:
Anionics 15 to 35%,
Non-ionics zero to 15%,
Surfactants 15 to 49%.
Phosphate (% STPP, inorganic builder sodium tripolyphosphate) zero to 30% (being replaced by zeolites) typical 4.5 g P per wash, self-regulation maximum 7.8 g P per wash,
Zeolite (%) 10 to 30%,
Alkaline builder 15 to 30%,
Calcium carbonate mostly zero, used as a filler,
Sodium carbonate to break up fatty soils,
Sulfate zero to 30%.
Enzyme zero to 1.5%,
Bleach activator zero or various including perborate,
Water 3 to 15%
Observe the labels of soaps, detergents, shampoos and washing powders and list their contents.
12.2.7 Machine dishwashing detergents
Example 1.: Phosphates >30%, Oxygen based bleaching agents 5-15%, Polycarboxylates <5%,
Non-ionic surfactants <5%, Phosphonates, enzymes protease [may produce allergic reaction] amylase <5% Detergent may be classified as an irritant [irritating to eyes and skin] With extremely hard waters above 26oC.
Example 2.: Anhydrous sodium tripolyphosphate >30%, Anhydrous sodium metasilicate 30% [dangerous if swallowed!] Anhydrous sodium carbonate 37.5% [ may dissolve glass] Low foam non-ionic surfactants < 0.5%, Sodium dichloriisocyanurate (56-64% available chlorine) 2% [may dissolve plastic] Corrosion inhibitors 9.5% [Includes aluminium salts, otherwise aluminium may be dissolved in machine dishwashing detergents].
12.2.8 Scouring powders
Abrasive powder 80% (screened silica, feldspar, calcite, limestone) sodium carbonate, surfactant + (chlorine bleach).
12.2.5 Drain cleaners
Sodium hydroxide + aluminium filings, e.g. "Drano"
They react in water to produce heat and saponify fat to release hydrogen gas.
Drain cleaners may contain crystals of sodium hydroxide (lye), sodium nitrate, sodium chloride (salt), and aluminium pieces.
The sodium salt dissolve in the drain water to generate heat of solution.
The sodium hydroxide solution reacts with fats in the drain to form soap.
The aluminium pieces cut hair and dislodge deposits then react with sodium hydroxide to generate more heat.
Sodium hydroxide solution removes the alumina (Al2O3) surface layer on the aluminium that reacts with water to produce hydrogen gas.
2NaOH + 2Al + 2H2O --> 2NaAlO2 + 3H2
Pressure from the hydrogen gas may also unclog drains.
The hydrogen reduces nitrate ion to ammonia.
2NO3- + 9H2 --> 2NH3 + 6H2O
The water and sodium ions then regenerate sodium hydroxide and hydrogen.
12.2.2 Bleaches, disinfectants, deodorizers
Sodium, potassium, calcium, magnesium hypochlorites.
Household bleach is usually 5% sodium hypochlorite NaOCl (made from chlorine gas + sodium hydroxide solution until pH = 7.).
Use bleach, calcium hypochlorite, to clean deodorize and remove mildew and bacteria from garbage bins, butcher's blocks wooden chopping boards with garlic smell, coffee stains on pottery, baby clothes, coolers, thermos bottles, china cups with coffee or tea stain, mops, bathtub and shower caulking and grouting, porcelain sinks, toilet bowls, sink mats, shower curtains and dishes, sponges.
Use bleach bottles to make hot caps for seedlings on cold nights, megaphones, scoops, buoys, funnels, bird feeders, and to store salt and corrosive substances
Bleaching powder is a mixture of calcium chlorate, calcium chloride and calcium hydroxide as a white powder, used to bleach fabrics and sterilize water
Experiment
Extend the life of freshly cut flowers.
Add one quarter teaspoon (twenty drops) of bleach to each quart of water used in your vase.
12.9.4 Prepare soap with animal fats
Do not prepare soap in containers made of aluminium, because aluminium reacts with sodium hydroxide.
Use clean dripping from a butcher shop or boil hard animal fat (tallow) in water and remove the separated oil from the surface.
Clean the separated fat by strain heated fat through layers of cloth.
Weigh sodium hydroxide pellets equal to one third of the weight of fat.
Weigh sodium chloride equal to twice the weight of fat.
Melt the fat and slowly add sodium hydroxide solution with continuous stirring.
Heat gently to avoid boiling over.
Boil for 30 minutes then add the sodium chloride while stirring.
This is called "salting out".
When the mixture cools soap separates as a floating layer, skim off the soap, heat it again, and pour it into moulds, e.g. trays of matchboxes.
The reaction is much quicker if the fat is already dissolved in methylated spirit before adding the sodium hydroxide.
12.9.6 Prepare soap with vegetable oils
Pour 5 mL olive oil, 5 mL 30% sodium hydroxide solution and 3 mL ethanol into a small beaker.
Put the small beaker into a larger beaker of water.
Heat the larger beaker while stirring the smaller beaker for 20 minutes.
Take out the small beaker and heat it directly to form a creamy paste.
Add 5 mL hot saturated sodium chloride solution and stir.
This is called salting out and it removes excess alkali.
Leave to cool.
Remove the solid that separates on the top of the mixture and wash the solid with water.
Shake the solid with water and note whether it behaves in the same way as common soaps.
Repeat the experiment with potassium hydroxide instead of sodium hydroxide to saponify the fat.
Compare the behaviour of the two soaps when used for washing.
Use vegetable oil + salt crystals to clean oily pans.
12.9.7 Prepare soap, household soap
1. Add to a tin can half full with water, 2.27 kg dripping (animal fat) free from salt, 0.45 kg resin.
Boil for 30 minutes then add 1 tablespoon borax or kerosene and 0.45 kg caustic soda.
When bubbling stops (from adding the caustic soda) boil for two hours.
Leave in tin for two days then cut into slabs with a tight wire.
BE CAREFUL! Add caustic soda gradually to avoid boiling over!
Soap
Soap (Commercial)
Models, organic Soap, "Scientrific" (Commercial)
River Bell Cottage, soap making, candle making
Soap, soap bubbles:
"Super Bubble Concentrate", 1 L, "World’s Largest Free Floating Bubble” (toy product)
"Touchable Bubbles in a Test-Tube", free-floating long-lasting bubbles, (toy product)
Blow soap bubbles: 19.220
Blow soap bubbles (Primary): 1.40
Blow soap bubbles at a van de Graaff generator: 31.4.3
Bubbles in water and aqueous solutions: 19.1.2
Bubbles in the air: 19.0.2
Burn butane bubbles: 19.1.2.1
Count bubbles, dilute hydrochloric acid with zinc: 17.1.1
Make soap suds with hard water and soft water: 12.5.3
Move a boat with surface tension, detergent, soap: 19.1.3
Prepare soap: 12.9.0
Soap as an emulsifying agent: 7.8.3.4
Soap film and sliding wire, soap film minimal surfaces: 19.3.22
Soap and surface tension: 4.212
Soaps and synthetic detergents: 12.2.0
Soap bubble support: 19.221
Tests for water hardness using standard soap solution: 12.4.0
Soap
Soap, bulk liquid soap, hand soap bars, hand sanitizer, abrasive soap (contains sand)
Soap, white Castile soap powder, Clarke's soap solution, Wanklyn's soap solution
Soap, bulk liquid soap, hand soap bars, hand sanitizer, abrasive soap, (contains sand)
Soap was formerly manufactured from beef and mutton fat, but nowadays mainly vegetable oils are used, e.g. olive oil, palm oil, coconut oil.
These oils are compounds of glycerine with three organic acids, stearic acid, palmitic acid, and oleic acid.
When the fat or oil is boiled with sodium hydroxide solution it splits into glycerine and the three organic acids.
The organic acids combine with the alkali to form soap, i.e. a mixture of sodium stearate, sodium palmitate, and sodium oleate.
Equation for stearic acid: glyceryl stearate (fat) + sodium hydroxide--> glycerine + sodium stearate (soap).
When the boiling is complete the soap is precipitates and made to float on the surface of the solution by adding salt.
The soap is separated from the underlying liquid and left to set.
After it has dried it is cut to the needed size, stamped, and packed.
Use soap to lubricate zippers, prevent soot sticking to pots, stop insect bites from itching, lubricate furniture drawers and windows, make a pin cushion for sharp instruments, lubricate hand saw blades, nails and screws, fill small small holes in walls.
12.2.11 Tests for glycerol
Neutralize 10 mL of the sodium hydroxide solution with drops of dilute hydrochloric acid and filter.
Evaporate most of the filtrate in a watch glass over boiling water then add 5 mL ethanol.
Evaporate most of the solution.
Heat the residue with solid potassium hydrogen sulfate.
The sharp odour of acrolein, burning fat odour, confirms the presence of glycerol.
CH2OR1-CHOR2-CH2OR3 + 3NaOH --> CH2OH-CHOH-CH2OH + NaOR1-NaOR2-NaOR3
triglyceride fat + sodium hydroxide --> glycerol + soap.
12.2.9 Oxidation of glycerol by potassium permanganate
Be Careful! Do this experiment either in a fume cupboard or outdoors.
Using larger crystals of potassium permanganate slows the reaction.
Use 15 g of potassium permanganate and < 3 g glycerol.
Put the potassium permanganate in a small metal dish and pour the glycerol on top.
The mixture slowly warms then ignites with a purple flame.
Flames may rise from the dish as the unreacted glycerol pyrolyses to form flammable vapours, which burn above the dish.
These vapours are extremely acrid so do not inhale them.
Do not leave the mixture unattended as delayed overnight reactions may occur.
Dispose of surplus reaction mixtures by washing with 100 volumes of water.
14KMnO4 + 4C3H5(OH)3 --> 7K2CO3 + 7Mn2O3 + 5CO2 + 16H2O
potassium permanganate + glycerin -->
This reaction between a strong oxidizing agent and an easily oxidized substance may be used to initiate the thermit reaction.
12.5.1 Hardness in water, water hardness, soft water
1. All natural waters contain dissolved cations and anions.
Water dissolves many ions as it flows through minerals.
Although water hardness is defined as the quantity of cations with a +2 or +3 charge, calcium ions and magnesium ions are the most common of such ions in natural water.
The formation of solid calcium carbonate is an endothermic process.
Thus, when water containing both carbonate and calcium ions are heated, calcium carbonate can precipitate out onto the walls of pipes, boilers, and household items such as tea pots.
This can shorten the life-time of some of these items.
Hardness indicates the tendency of water to precipitate soap or form scale on heated surfaces and is expressed as the sum of Ca and Mg and usually reported in equivalents of Ca carbonate.
Fe, Al, Zn and Mn also can contribute to hardness and should be considered if present in unusual amounts.
Hardness in water is a nuisance, because it makes washing difficult and causes a precipitate of "fur" in kettles and "scale" in boilers.
However, hard water is not dangerous to health.
Some water authorities add salts to the town water supply to prepare it harder, because it is believed that this may precipitate some harmful bacteria and other micro-organisms.
Also, hard water may supply calcium in the diet.
Natural spring water is often hard.
The salts of fatty acids are insoluble in water except the sodium and potassium salts.
When soap is added to water containing metal ions, other than sodium and potassium, ions, insoluble soaps form so removing the fatty acid ions from solution, but forming a floating scum on the water.
2. The five units of measure commonly used in water analysis work are as follows:
2.1 milligrams per litre (mg / l)
2.2 parts per million (ppm, 1 ppm = 1 mg per litre)
2.3 grains per US gallon (gpg)
2.4 equivalents per million (epm)
2.5 grains per imperial gallon (gpg imp).
3. In the USA, hard water contains dissolved hardness minerals above 1 GPG (grains per gallon).
USA levels of hardness:
| soft water < 1 grain per gallon | slightly hard =1 to 3.5 grains per gallon | moderately hard = 3.5 to 7 grains per gallon | hard (very hard) = 7 to 10.5 grains per gallon | extremely hard > 10 grains per gallon |.
GPG (gpg) is a unit of weight, 1 / 7 000 of a pound, 1 gpg = 17.1 ppm or 1 grain per gallon is equivalent to 17.1 mg / L.
4. The hardness of water is a measure of the amount of minerals, primarily calcium and magnesium, it contains.
Water softening, which removes these minerals from the water, may be desirable if large quantities of detergent are needed to produce a lather when doing laundry, or scale is present on the interior of piping
or water tanks, laundry sinks or cooking utensils.
Water that contains more than 200 mg / l (200 ppm) as calcium carbonate (12 grains per gallon) is considered to be hard and may cause plumbing and laundry staining problems.
Three grains per gallon equals about 50 ppm.
Methods used to soften hard water for home use are zeolite softening and reverse osmosis.
5. Hardness expressed in mg / l as CaCO3:
0 to 100 soft, 100 to 200 moderate, 200 to 300 hard, 300 to 500 very hard, 500 to 1 000 extremely hard.
6. Zeolite softening, ion exchange, exchanges calcium and magnesium ions in the water for sodium ions in the zeolite grains.
When the exchange capacity of the zeolite is exhausted, it can be regenerated by passing a strong sodium chloride solution through it causing it to give up the calcium and magnesium ions and take up a new supply of sodium ions.
However, only calcium, magnesium and small amounts of iron will be removed from the water so people on salt restricted diets or with high blood pressure may not be able to drink it.
Reverse osmosis units remove water hardness through a straining action as hard water passes through a membrane that allows water molecules and only trace levels of contaminants to pass through it.
Reverse osmosis units are slow and produce more waste water.
7. Hardness should not be confused with salinity.
Water can be very soft with low levels of Ca and Mg, yet have a high salinity value from dissolved Na salts.
Most ground waters have hardness values of less than 2000 mg / L.
Hardness range in mg / L: 0-60 soft, 61-120 moderately hard, 121-180 hard, >180 very hard.
8. Hard water containing calcium ions that form a scum in black tea caused by reactions with the polyphenolic flavonoids,
e.g. Catechin, which has both (+)-catechin and (-)-epicatechin (cis) forms, (+)-catechin is a polyphenolic antioxidantflavonoid, and is found in woody plants.
By adding lemon juice to black tea, the neutral pH is reduced, the calcium ions are removed by formation of covalent soluble sodium citrate.
12.5.13 Temporary hardness and permanent hardness
Temporary hardness occurs when calcium hydrogen carbonate or magnesium hydrogen carbonate dissolves in water.
When water with temporary hardness is boiled, the hydrogen carbonates decompose to form insoluble carbonates.
They precipitate from the solution to leave "soft" water that forms a lather easily.
calcium hydrogen carbonate (aq) --> carbon dioxide + water (l) + calcium carbonate (s)
Permanent hardness in water occurs when calcium sulfate or magnesium sulfate dissolves in water.
Boiling water with permanent harness does not affect the hardness.
12.5.5 Remove water hardness
Remove permanent or temporary hardness in water by adding sodium carbonate crystals to precipitate the calcium ions or magnesium ions as carbonates.
Other methods are used for removing metal ions:
1. Add calcium hydroxide.
2. Add sodium hexametaphosphate, NaPO3(Na2O), e.g. Calgon, which reacts with the calcium and magnesium ions to produce soluble substances that do not react with soap.
3. Add chelating agents, e.g. Versene, the tetra sodium salt of ethylene-diamine tetra ethanoic acid, EDTA, that combines with unwanted metal ions.
4. Pass water through an ion exchange resin in an ion exchange column, e.g. zeolite (Permutit) that removes the calcium and magnesium ions from the water as insoluble solids.
These chemicals "soften" water by removing all minerals to form demineralized water that is as free from ionic substances as deionized water.
The last two processes do not form a scum that can discolour laundry.
The Permutit process is the best for producing drinking water.
The hardness of water depends on how much calcium and magnesium salts are present.
In natural stretches of water, these salts are mainly hydrogen carbonates, besides sulfates, silicates, chlorides, nitrates and phosphates in much smaller amounts.
On boiling, the water, the hydrogen carbonates are almost entirely precipitated as insoluble carbonates, so the hardness caused by these salts decreases.
The remaining hardness is non-carbonate hardness, permanent, hardness.
Ca(HCO3)2 --> CaCO3 + CO2 + H2O (in boiling water)
The sum of the carbonate (temporary) hardness and non-carbonate (permanent) hardness is the total hardness of water.
It is expressed in degrees of hardness.
One degree of hardness corresponds to a content of 10 mg of calcium oxygen per litre of water.
In Germany, this is symbolized by dH.
Water with a hardness less than 4o dH is described as very soft.
Water with a hardness of 8 to 12o dH is described as moderately hard, between 12 and 18o dH fairly hard, between 18 and 30o dH as hard, and above 30o dH very hard.
Water hardness is important technically and from the point of view of health hygiene.
It affects the taste of food and drink.
Water with a hardness greater than 25o dH acts as a laxative.
An increase in the hardness of water causes an increase in how much soap is used, because of the formation of insoluble calcium and magnesium soaps that neither foam nor clean.
Hardness also causes precipitation of chalk, boiler scale, in pipes and vessels.
Very soft water tastes insipid and exerts a bad effect on tooth and bone formation.
12.4.2 Tests for water hardness
The test-tube of the water hardness test set is filled up to the 5 mL graduation mark with the water sample, a level spoonful of indicator powder is added, and the mixture is stirred.
If calcium or magnesium salts are present, the water sample turns red-violet, in their absence it turns green.
If a red-violet coloration is produced, i.e. if the water possesses a definite hardness, the tablets, each corresponding to 5o dH, added in succession until the colour of the water sample turns to green.
Each individual tablet must be completely dissolved before the next one is added.
To help this process, the tablets are crushed with the special tamping rod provided for this purpose.
Since one table corresponds to 5 degrees of hardness, the exact end point from red-violet to green will usually be greatly exceeded.
Repeat the test by first dissolving in the water sample one 5o dH tablet fewer than used in the preliminary test.
As many 1o dH tablets are then added until the colour of the water sample just turns green.
The degree of hardness of the water is obtained by adding up the hardness values of the tablets used, e.g. if three 5o dH tablets and two 1o dH tablets were used to produce the colour change, the water has a total hardness of 17o dH.
The hardness value of the tablets is shown on the package containing them.
To find hardness exactly, i.e. to within 0.5o dH, fill the test-tube to the 10 mL mark, add two level spoonfuls of indicator powder.
Stir, and add tablets with half the hardness value, i.e. 2.5o or 0.5o dH, until the colour just turns green.
12.4.7 Tests for water to form lather
1. Prepare soap solution by dissolving 1 g of shavings of plain laundry soap in 100 mL of methylated spirit.
Put 5 mL of deionized water or demineralized water in a test-tube.
Test the solution by adding one drop of soap solution to the water.
Put a stopper on the tube and shake the tube vigorously.
If no lather occurs, add another drop of soap solution and shake again.
Continue until a lather appears.
Record the number of drops of soap solution needed to prepare a good lather.
2. Add soap flakes one by one to 25 mL of the water in a test-tube with a stopper.
The flakes are usually uniform in size.
Count how many flakes must be added to the sample to form a good lather by shaking.
12.5.4 Prepare hard water
1. Temporary hardness
1.1 Add 5 g of calcium hydroxide, Ca(OH)2, to a litre of water, shake it occasionally over a day and leave to settle, pour off the clear solution on top, leaving a saturated solution of fresh limewater.
Pass carbon dioxide gas from a gas generation apparatus through the lime water to turn it milky, then clear again to form a calcium bicarbonate solution.
2. Permanent hardness
2.1 Dissolve 1 g per of magnesium sulfate-7-water crystals, Epsom Salts, in water.
2.2 Dissolve 1 gram per of calcium sulfate-2-water crystals in water.
2.3 Dissolve calcium chloride or magnesium sulfate, or both in water, to make an approximately 0.1 M solution.
2.4 To prepare hard water similar to what occurs naturally, use 3 volumes of the temporary hard water and 1 volume of the permanent hard water and add 2 volumes of distilled water.
12.5.15 Wash in hard water
Only the sodium and potassium salts of fatty acids are soluble in water, but most are insoluble.
If soap is added to water containing metal salts, insoluble soaps form as a greasy scum of calcium or magnesium stearate on the water and the soap cannot be used to remove grease and oil.
The scum requires the use of extra soap to remove it and the dirt.
This water is called "hard water", because it is hard to prepare a lather in it.
Try to wash the hands with hard water and soap.
Use three samples of dirty cloth.
Wash each simultaneously and with the same amount of soap in: tap water, hard water, groundwater or stream water.
Dry the cloths and compare the results.
12.4.3 Tests for water hardness in different water samples
Test different liquids for formation of a lather:
1. dilute solution of magnesium sulfate-7-water crystals,
2. dilute solution of calcium hydrogen carbonate,
3. suspension of calcium carbonate, tap water, rainwater or tank water, mineral water.
12.4.1 Tests for hard water to form a lather
1. Boil for 5 minutes, 5 mL of:
1.1 temporary hard water, containing calcium or magnesium hydrogen carbonate
1.2. permanent hard water, containing other soluble calcium or magnesium salts.
Test the liquids for formation of a lather.
2. Add sodium carbonate crystals (washing soda) to 5 mL of: 1. temporary hard water 2. permanent hard water.
Test the liquids for formation of a lather.
3. Add a water softener, e.g. Calgon to: 1. temporary hard water 2. permanent hard water.
Test the liquids for formation of a lather.
12.5.6 Soften hard water by boiling
Boiling temporarily hard water softens it by decomposing the calcium or magnesium hydrogen carbonates
1. Test tap water for hardness.
Boil the water sample for 5 minutes.
A precipitate of calcium carbonate may form.
2. After cooling the water, test for hardness again.
Note if a lather forms with less soap than before boiling.
3. Prepare temporary hard water and repeat the experiment.
4. Prepare permanently hard water and repeat the experiment.
Ca(HCO3)2 (aq) <--> CaCO3 (s) + H2O (l) + CO2 (g).
12.5.7 Soften hard water using chemicals
Adding sodium carbonate crystals (washing soda) removes both temporary hardness and permanent hardness in water.
1. Temporarily hard water: Test the harness.
Add sodium carbonate crystals (washing soda) and shake.
Note whether a precipitate forms.
Test the hardness again.
Ca(HCO3)2 (aq) + Na2CO3 (aq) --> CaCO3 (s) + 2NaHCO3 (aq)
2. Permanently hard water: Prepare permanently hard water.
Test the hardness.
Add sodium carbonate crystals (washing soda) and shake.
Note whether a precipitate forms.
Test the hardness again.
CaSO4 (aq) + Na2CO3 (aq) --> CaCO3 (s) + Na2CO3 (aq)
MgSO4 (aq) + Na2CO3 (aq) --> MgCO3 (s) + Na2SO4 (aq)
3. Repeat the above experiments with Calgonor other chemicals that soften water.
Enter the results of the experiments on water softening in the table below.
What can be concluded about the hardness of the different types of water used every day?
What is the best way to treat the water used every day?
Type of water used and number of drops of soap solution to form lather
1. Untreated deionized water
2. Untreated tap water
3. Untreated temporary hard water
4. Untreated permanent hard water
5. Boiled temporary hard water
6. Boiled permanent hard water
7. Add sodium carbonate crystals (washing soda) to temporary hard water
8. Add sodium carbonate crystals (washing soda) to permanent hard water
9. Add Calgon to temporary hard water
10. Add Calgon to permanent hard water.
12.5.2 Detergents in place of soap solution
1. Wash clothes with 1. soap solution 2. household detergents.
Compare the results.
Some household detergents do not form lathers, so test the detergent before using it in this experiment.
2. Use two strips of cotton fabric weighted at one end.
Put one strip in pure water and put the other strip in 0.1% surfactant solution.
The pure water does not wet the cotton fabric so the strip remains upright.
The surfactants wets the cotton fabric so it sinks.
3. Pour an equal thickness layer of olive oil into jars of pure water and a 0.1% surfactant solution.
Close the jars, shake them and leave to stand.
The oil rises to the surface of the pure water, but remains emulsified and dispersed in the detergent solution.
12.2.10 Prepare detergent, alcohol-based detergent
1. Mix 3 drops of dodecan-1-ol (lauryl alcohol) with 2 drops of concentrated sulfuric acid in a test-tube.
BE CAREFUL! Dodecanyl sulfate gel forms.
Add 2 mL water and 1 drop of phenolphthalein solution.
Add drops of 10% sodium hydroxide solution and stir until the solution is just alkaline.
Evaporate to dryness on a watch glass to prepare solid detergent.
Shake the solid with water and note whether it behaves in the same way as common soaps.
2. Prepare dodecanyl sulfate and add phenolphthalein as before.
Neutralize with 10% solution of triethanolamine.
Shake this liquid detergent with water and note whether it behaves in the same way as common soaps.
H2SO4CH3(CH2)10CH2OH --> CH3(CH2)10CH2OSO2OH
dodecan-1-ol --> dodecanyl sulfate
NaOHCH3(CH2)10CH2OSO2OH --> CH3(CH2)10CH2OSO2ONa
dodecanyl sulfate --> sodium dodecanyl sulfate.
12.4.4 Tests for water hardness using standard soap solution
Standard soap solution is of such strength that 1 cc contains sufficient soap to exactly neutralize one milligram (0.001 g) of dissolved calcium carbonate.
Soft water contains no mineral impurities.
Rain water is the purest kind of natural soft water.
Waters for domestic uses may be divided into two general classes, hard waters and soft waters.
Hard waters can be either permanently hard, temporarily hard, or both permanently and temporarily hard.
By hardness of water is meant its soap destroying or neutralizing power, which is due to the presence of carbonates or sulfates of or magnesia.
A large degree of permanent hardness indicates a bad water.
Permanently hard waters contain sulfates of lime or magnesia in solution.
Temporarily hard waters contain carbonates of lime or magnesia in solution, and both permanently and temporarily hard waters contain sulfates and carbonates of lime or magnesia in solution.
1. Prepare soap solutions for estimating of hardness in water
Solution A: Dissolve 100 g of pure powdered soap in 1 litre of 80% methylated spirit.
Leave it for a day.
Solution B: Dissolve 0.5 g of calcium carbonate in hydrochloric acid, density = 1.19.
Add dilute ammonia solution so that litmus paper just turns blue.
Dilute to 500 mL.
(One mL is equivalent to 1 mg of calcium carbonate.)
Titrate the solution A in the burette against solution B.
Dilute solution A with 80% ethanol until 1 mL of the resulting solution is equivalent to 1 mL of solution B, after making allowance for the lather.
This is the amount of standard soap solution needed to form a permanent lather in 50 mL of deionized water.
One cubic centimetre of the adjusted solution is equivalent to 1 mg of calcium carbonate.
2. Mix 25 g of finely shredded castile soap (olive oil soap), with 1.0 litre methylated spirits and 0.5 litre of deionized water.
Leave to cool for half a day with occasionally shaking, then filter.
Test the solution with water of known hardness.
Dilute with a methylated spits and water mixture until the strength is correct.
3. To determine the degree of hardness in water, put 70 cc of water in a clean 2 litre glass bottle and slowly add standard soap solution
while shaking the mixture.
If a lather forms that disappears in soft water or remains as a curd in hard water will form, add more standard soap solution while shaking the bottle until the lather formed can stand for five minutes.
The number of cc soap solution added, less one, indicates the hardness of the water in degrees.
The 1 cc is deducted, because even distilled water requires a small quantity of soap to make it lather.
4. Hardness of water is measured in degrees Clark, and each degree of hardness corresponds to one grain of carbonate of lime or magnesia to one English gallon of water.
Table 12.5.10
Water character
 Hardness as
degrees
(Clark-Wanklyn) 		Hardness as
parts per 100, 000 		Hardness as grains CaCO3
in UK gallon 		Hardness as grains
CaCO3 in USA gallon
Very soft 1 degree 1.4
 1.0 0.8
Moderately soft
 6 degrees
 8.6
 6.0
 5.0
Hard
 9 degrees
 13.0
 9.0
 7.6
Excessively hard
 16 degrees
 23.0
 16
 13.4

5. Originally the hardness of water was defined as the capacity of water for destroying the lather of soap.
The hardness was determined by a titration with a standard soap solution.
Metal ions have the ability to cause hardness.
Nowadays, water hardness means the total calcium and magnesium ion concentration expressed as calcium carbonate concentration.
However, with an electrode, the total water hardness can be determined directly in the range of 1-1000 ppm as calcium carbonate.
12.5.14 Tests for metal ions in water, EDTA chelates
The different forms of hardness are expressed as "calcium carbonate hardness".
EDTA is [ethylene diamine tetra-acetic acid, HOOCCH2)2N(CH2)2N(CH2COOH)2].
The disodium salt of EDTA combines with metals to form chelates.
Chelates are compounds where a multidentate ligand, e.g. as an enolate anion of a diketone, is bound to a central atom of a co-ordination complex.
EDTA is a complexone and is used in special soaps to remove metal contamination and as a chelating agent for analytical determination of metal contamination.
It is available as "EDTA (0.5 M)", which is a concentrated volumetric solution for dilution to prepare 1 litre of 0.5 M standard solution.
1. Prepare a 0.01 M EDTA solution by dissolving 1.861 g in 500 mL water.
2. Prepare pH 11 buffer solutions by adding 7.0 g ammonium chloride solution to 57 mL of concentrated aqueous ammonia solution.
Dilute to 100 mL.
BE CAREFUL!
3. Prepare an approximate 0.01 M solution MgCl2.6H2O by dissolving 2 g in 1 litre.
4. Eriochrome Black T or Erio T indicator is the indicator for determining Ca2+, Mg2+ and Zn2+ with EDTA.
Dissolve 0.2 g EDTA powder in aqueous ammonia solution.
Pour 100 mL of the water to be tested in a conical flask on white paper.
Add 1.0 mL of the Mg2+ solution, 3 drops of "Erio T" indicator solution and 1 mL of the buffer solution.
Add drops of EDTA solution until a blue colour appears.
1 mL EDTA solution / 1.0 mg CaCO3.
Ca2+ + H2EDTA2 <--> CaEDTA2- + 2H+.
12.4.5 Tests for water hardness, EDTA titration, Calmagite indicator
The usual form of EDTA used for measuring water hardness is Na2EDTA.2H2O, the ethylenediaminetetraacetic acid disodium dihydrate salt.
In this ion exchange reaction, the EDTA is in the sodium form and only the cation Ca2+ is removed.
Let RZ = the ion exchange resin.
2RZ-SO3- Na+ + Ca2+ <--> (RZ-SO3-)2Ca2+ + 2Na+
Make the following solution: 5.0 mL of water sample, 1.0 mL of 1.5 M NH3 / 0.3 M NH4Cl buffer, 0.1 mL of 2% ascorbic acid solution, 1.0 mL of 0.01 M Na2MgEDTA / 0.1 M NH3 solution, 3 drops of
0.1% Calmagite indicator.
The buffer keeps the hydrogen ion concentration of the solution at the optimum value.
The ascorbic acid solution prevents oxidation of the indicator.
Titrate the solution with 0.01 M Na2EDTA (Na2EDTA.2H2O) until the colour of the solution changes from red to blue.
Repeat with a blank titration 5.0 mL of deionized water instead of the water sample.
Subtract the volume the blank titration from the volume of the water sample titration.
1. Calculate the water hardness in units of millimoles per litre, i.e. the sum of the calcium and magnesium ion concentrations.
2. Calculate the water hardness in units of parts per million of CaCO3 (ppm, 1 ppm = 1 mg per litre), i.e. milligrams of CaCO3 per litre, assuming that the ions titrated came from CaCO3.
Magnesium usually also occurs in hard water, but this second calculation is often used by water engineers for convenience.
(mg CaCO3 / L) = (mmol Ca2+ + Mg2+ / L) × (1 mol CaCO3 / mol Ca2+ + Mg2+) × (100 g CaCO3 / mol CaCO3).
12.4.6 Tests for water hardness, EDTA titration
Eriochrome, C20H12O7N3Na, solochrome black, toxic if ingested
1. Use Eriochrome Black T indicator and titrate with EDTA.
Check that the pH is 10 when adding the buffer, using a pH meter.
Use Eriochrome black T indicator that has been ground with salt rather than a liquid.
EBT is blue in a buffered solution at pH 10.
It turns red when Ca2+ ions are added.
At the blue end-point, sufficient EDTA has been added, the metal ions are chelated by EDTA, to leave the free indicator molecule.
Eriochrome Black T, C20H12N3O7SNa, is blue in protonated form, but turns red when forming a complex with Ca2+, Mg2+, and some other metal ions.
EDTA, Ethylenediaminetetraacetic acid, aminopolycarboxylic acid, [CH2N(CH2CO2H)2]2.
2. Hardness Ratings (mg CaCO3/L equivalent): < 15 very soft; 15-50 soft; 50-100 medium hard; 100-300 hard; > 300 very hard
3. The quantity of hardness ions will be determined by titration.
EDTA, a weak acid, will be used as the titrant.
In its ionized form, it is able to form soluble complexes with calcium and magnesium cations.
The indicator added to the sample is Eriochrome Black T.
Initially, the indicator will form a complex with the cations.
When complexed it is red in colour.
As the EDTA is added dropwise to the sample, it replaces the Erio T and forms more stable complexes with calcium and magnesium.
When the indicator is released by the metal ions, it has a distinct blue colour.
Therefore, the endpoint of the titration is marked by the colour change from red to blue.
To determine the hardness of water by measuring the concentrations of calcium and magnesium in water samples by titration.
The titration should be completed within 5 minutes of buffer addition.
Some metal ions may interfere in the titration by causing fading or indistinct end points.
Experiment
1. Clean a 25 mL volumetric pipette by rinsing it with 10% HCl, then 2 washes of distilled water.
Hold the pipette horizontally and rotate it so that the liquid washes all the inside surfaces.
Place the pipette on a towel.
Label all glassware.
Clean and fill the burette
2. Titrant solution: Pour about 100 mL of 0.01M EDTA titrant solution into a 250 mL beaker
3. Analysis solution: Pipette 25 mL of the water sample into a conical flask and dilute it with 25 mL distilled water.
Add at least one mL of pH 10 buffer solution to the sample.
The pH should be 10, so check the pH with pH paper or a pH meter.
4. Add a 1-2 drops Eriochrome Black T indicator (or a small scoop of powder indicator formulation) to the conical flask.
The solution should now be red / pink.
5. Titration: Test 1. Immediately begin to titrate the sample two drops at a time.
Be careful to titrate slowly near the endpoint, as the colour will take about 5 seconds to develop.
Thus, add the last few drops at 3-5 second intervals.
The endpoint colour is blue.
6. Perform this procedure at least two more times, Test 2 and Test 3.
The titre volumes should be within 0.1 mL of each other.
Titre (mL)
 Test 1
 Test 2
 Test 3
Initial Volume
 -
 -
 -
Final Volume
 -
 -
 -
Titre Volume
 -
 -
 -

Express hardness as parts per million (mg per litre) of equivalent CaCO3.
If the titration required 5 mL EDTA, the calculation is as follows:
(5 mL 0.01 M EDTA / 0.025 L sample) x ( 1 mg equivalent CaCO3 / 1 mL 0.01 M EDTA) = 200 ppm CaCO3
Reference: Standard Methods for the Examination of Water and Wastewater, 20th ed., L. S. Clesceri, A. E. Greenberg, A. D. Eaton
editors, 1998, American Public Health Association.
12.5.16 Water softening using ion exchange resin
The charge on Ca2+ is greater than the charge on Na+ so the Ca2+ ions have a stronger attraction to -ve groups attached to the ion exchange resin.
Add 2 g of dry cation exchange resin to 50 mL of tap water sample.
Rotate the mixture in a flask for 10 minutes to produce soft water.
Titrate a 5.0 mL sample of the soft water with 0.0100 M Na2EDTA.
Calculate the percentage of water hardness removed by ion exchange:
[(mmol / L (Ca + Mg) tap water - mmol / L (Ca + Mg) soft water) / mmol / L (Ca + Mg) tap water] × 100
The exchange capacity is usually found on the label of the bottle of resin, expressed in milliequivalents (meq), per gram of dry resin or in milliequivalents per millilitre of resin bed.
For example for a resin of 1.7 meq / mL, 1 mL of resin can exchange about 1.7 mmol of charge (1.7 mmol of Na+ ion).
The resin is expensive so keep it for regeneration by washing it in concentrated sodium chloride solution then washing it with water.
12.5.3 Make soap suds using hard water and soft water
Put 5 mL of the soft water in test-tube
1. Put 5 mL of tap water into test-tube.
2. Put 5 mL of deionized water into test-tube.
3. Add 5 mL of 0.1% soap solution to each test-tube, insert a stopper and shake for 10 seconds.
Compare the amount and stability of the foam.
Note any insoluble calcium soap scum.
12.5.8 Prepare cup of tea
1. The traditional advice is to use freshly drawn water every time you make a cup of tea and the traditional explanation was that water that had been reboiled or boiled many times contained less oxygen, causing less tea to be extracted from the tea leaves so the tea tastes "flat".
Dissolved oxygen is supposed to make the tea taste better.
Make two cups of tea with once boiled water and many times boiled water.
Note any difference in taste and colour.
2. Aluminium kettles may cause a bad taste in tea if used without first adding water.
However, the bad taste is eliminated by boiling and discarding the contents many times to discard aluminium ions and allowing a patina of aluminium oxide to form inside the kettle to prevent loss of aluminium ions into solution.
Modern kettles may not have the same problem, but the calcium and magnesium bicarbonates, chlorides, and sulfates in tap water may affect the taste of tea.
Clean kettle "fur" with vinegar, then rinse with cold water many times.
Make two cups of tea with once boiled deionized water and once boiled tap water.
Note any difference in taste and colour.
3. Temporary hard water contains bicarbonates, which precipitate as insoluble carbonates as a white scum (kettle fur), on cooling after boiling, even after reboiling.
Such precipitates affect the taste of tea even more than the soluble bicarbonates.
Also salts in water not destabilized by boiling become more concentrated by evaporation during repeated boiling to a concentration that can affect the taste of tea.
Also, copper and iron ions can react with phenolic reducing agents in tea to produce undesirable tastes.
4. Brewing guideline for herbal tea.
(1) For hot tea, use about one gram of dried herbal tea per cup.
Follow the water and timing specification on the packet for each kind of herbal tea.
Remove the tea leaves and serve.
(2) For chilled herbal tea prepare the tea as with for hot tea and then leave to chill for eight hours.
Add flavour or garnish with any natural edible her, fruit, vegetable or flower just prior to serving.
For a room temperature brew use about two gram s per cup and triple the timing specifications.
After it reaches room temperature leave to chill for eight hours.
5. To find the best way to make black tea: Prepare cups of tea using the following:
1. distilled water,
2. deionized water,
3. temporary hard water (natural or prepared),
4. temporary hard water (natural or prepared) artificially softened with sodium bicarbonate,
5. permanent hard water (natural or prepared),
6. tap water from the cold tap,
7. tap water from the cold tap that has been reboiled many times for long periods,
8. tap water from the hot tap.
Observe the taste and colour of the tea after the same period and same concentration of infusion.
6. Rate of diffusion from tea leaves.
Add boiled water to tea leave in a teapot.
Pour out the same volume of tea into clear glasses after one, two and three minutes.
Leave to cool and observe the difference in colour in the three glasses.
12.5.10 Tea with iron (II) sulfate
Wash a small crystal of iron (II) sulfate in a test-tube with water and pour away the water to remove any surface layer of iron (III) sulfate.
Dissolve the crystal in half a test-tube of cold water and add drops of cold tea.
A violet liquid forms.
12.5.12 Tea with iron (III) salts
Add drops of cold tea to a solution of ammonium iron (III) sulfate or iron (III) chloride.
A black precipitate forms that can be the basis of most types of blue-black ink.
12.5.9 Tea with dilute sulfuric acid
Add dilute sulfuric acid or sodium hydrogen sulfate (sodium bisulfate), solution to half a test-tube of cold tea.
The liquid is cloudy, because of the precipitation from the tea.
Test the liquid a iron (III) salt solution.
No black precipitate forms as in the previous experiment.
12.5.11 Tea with limewater
Add 2 cm of limewater to an equal amount of cold tea in a test-tube and boil the mixture.
A red-brown precipitate of the calcium salt forms.