School Science Lessons
Chemistry
2025-10-20
Chemistry, Aa to Ac
Contents
Aluminium
AAS Atomic Absorption Spectroscopy
Abbreviations for Chemistry
Abbreviations English language
Abrin
Absolute zero, Kelvin scale
Absorption spectrum of Sodium
Abietic acid
Abscisic acid
Absinthin
Absolute alcohol
Absolute zero Kelvin scale
Abuse of volatile substances
Acacetin
Acanthicifoline
Acanthosides
Acaricides
Accumulator, Lead accumulator cell
Accuracy and errors
Acepromazine
Acerosin
4.9.1 Acephate
Acesulfame
Acetal
Acetaldehyde
Acetates, Ethanoates
Acetyl group, −COCH3, −C(=O)−CH3, Ac, ethanoyl
Acetylharpagide
Acetamide
Acetaminophen, Paracetamol
Acetamiprid, Neonicotinoid insecticide
Acetic acid, Ethanoic acid
Acetic alcohol, Prepare
Acetic anhydride, Prepare
Aceto-alcohol, Prepare
Aceto-carmine, Prepare
Aceto-orcein, Prepare
Acetoacetic acid
Acetochlor
Acetone
Acetone peroxide, TATP
Acetonitrile
Acetosyringone
Acetyl chloride
Acetyl eugenol, Eugenol acetate
Acetylcholine
Acetylides
Acetyldigoxin
Acetylene, (ethyne)
Acetylpyrrolidine
Acetylpyrroline
Acetylsalicyclic acid, Aspirin
Achillin
Acid-base indicators
Acid acid-, acids, acidic, acidify
Acid anhydrides
12.3.12 Acid dissociation constant
Acid fuchsin, Prepare
Acid rain
Acidity
Acolongifloroside K
Aconine
Aconitine
Acridine
Acriflavine
Acrilan
Acroleic acid
Acrolein
Acronidine
Acryl polymer
Acrylamide
Acrylates
Acrylic acid, "acrylics"
Acrylic glass Polymethyl methacrylate
Acrylonitrile
Actinides actinoids
Actinidine
Actinium, Ac
Actinolite, (Geology)
Activated carbon activated charcoal
Active constituent (Pesticides label)
Activity series of metals as reducing agents
Acute toxicity
Acyclic hydrocarbons
Acyl halide
Aluminium
Abbreviations
i.e. (id est) means "that is" or "in other words".
e.g. (exempli gratia) means "for example".
viz. (videlicet) means "namely" or "that is to say".
et al. (et alii) means "and others" or "and collaborators".
q.v. (quod vide) means "which to see", written after words to be looked up in the current document.
ibid. (ibidem) means "in the same place", refers to a previously listed work.
cf. (confer) means to see a given citation for comparison.
Absinthin
Absinthin, C30H40O6, a sesquiterpene lactone, a triterpenoid, anti-inflammatory agent, nervousness, convulsions
It occurs in Wormwood (Artemisia absinthium).
Artemisia absinthium, anthelmintic, flavouring Vermouth, is a bitter-tasting constituent of Absinthe.
Abietic acid
Abietic acid, C20H30O2, sylvic acid, abietate, diterpenoid, colophony rosin, Greek pitch, a monocarboxylic acid, irritant
It is a yellow resinous powder, and it is used on violin bows and ballet shoes.
It is a main component of Gums rosin.
It is used to make varnishes, soaps, plastics), most abundant compound in rosin, in Pinus.
Acepromazine
Acepromazine, C19H22N2OS, a phenothiazine, psychotropic drugs, used as a sedative and antiemetic
Alleged overuse of Acepromazine on race horses in Australia.
Acerosin
Acerosin, C18H16O8, is a trimethoxyflavone metabolite.
It occurs in Scoparia, Iva, Helianthus, Gardenia, Vitex, and in peel of mandarin orange, (Citrus reticulata).
Acesulfame
Acesulfame, C4H5NO4S is a sulfamate ester, irritant, sweetening agent, and environmental contaminant.
Food code E950, Acesulphame potassium, Acesulfame-K, Ace-K, C4H4KNO4S, synthetic chemical, artificial sweetener, Health risk
Food code E962, salt of aspartame-acesulfame, artificial sweetener, emulsifier, stabilizer, thickener and gelling agent, Health risk
19.6.3 Cola, Diet or Light contents
Acesulfame potassium, C4H4KNO4S, or Ace-K, is a zero-calorie sweetener in foods and drinks.
It occurs in combination with the sweetener disaccharide derivative Scralose, C12H19Cl3O8, in Splenda.
or in combination with the dipeptide Aspartame, C14H18N2O5, in Equal or Coke Zero.
Acesulfame K is also sold under the brand names "Sunett" and "Sweet One".
The fact that the crystal powder has a bitter aftertaste is the main reason for mixing it in sweeteners.
The mixture of sweeteners is used to create a sugar taste.
Acetaldehyde
Acetaldehyde C2H4O, CH3CHO, ethanal, colourless liquid, BP 21°C, choking vapour irritates eyes, tobacco smoke carcinogen.
16.3.2.7 Ethanal with potassium dichromate, Prepare
16.3.2.6 Ethanal with potassium manganate (VII), Prepare
Acetamide
Acetamide, CH3CONH2, C2H5NO, ethanamide, acetic acid amide, colourless crystals, mouse odour, low toxicity, skin irritation.
It is formed from condensation of acetic acid with ammonia, and it is used as solvent.
Amide RCONH2, (amine + acid), No prefix
Suffix, -oic, Suffix, -amide, e.g. acetamide = ethanamide, CH3CONH2
16.1.5.6 Amides
24.7.3 Heat energy changes solid to liquid
24.7.5 Latent heat of fusion of ice to water
Acetates
Acetates CH3COO-, Ethanoates
An acetate (ethanoate) is a salt or ester of acetic acid (ethanoic acid).
An acetate as a salt: Sodium acetate (sodium ethanoate), CH3COONa.
An acetate as an ester: Ethyl acetate, (ethyl ethanoate), CH3COO(C2H5).
If acetate is shown as OAc−, acetic acid is shown as HOAc.
Weak acids, e.g. ethanoic acid (acetic acid, CH3COOH, carbonic acid and sulfurous acid dissociate little in aqueous solution.
However, their salts, e.g. potassium acetate CH3COOK are completely dissociated into ions.
Acetic anhydride (CH3CO)2O
3.5.7 Celluloid
3.5.8 Cellulose acetate, Cellulose triacetate
12.3.9 Acids with salts
16.4.2 Ethyl acetate, Prepare
17.3.5 Ethyl acetate with sodium hydroxide, autocatalyctic hydrolysis
Acanthosides
Acanthoside B, Eleutheroside e1, C28H36O13, syringaresinol beta-D-glucoside
It occurs in (Eucommia ulmoides) bark, and in (Acanthopanax sessiliflorus) roots
Acanthoside D, Syringaresinol-di-O-glucoside, Liriodendrin, C34H46O18, beta-D-glucoside, antioxidant, anti-inflammatory
Acetic anhydride
Acetic anhydride, (CH3CO)2O, ethanoic anhydride, acetic acid anhydride, acetyl oxide, acetic oxide
Use < 25 mL or g in a fume cupboard or a well-ventilated area
Solution < 8%, Not hazardous, i.e. 8% acetic acid
It is a highly volatile liquid, irritating odour, reacts with moisture in air, corrosive to skin, strong respiratory irritant.
(CH3CO)2O + H2O --> 2 CH3COOH
acetic anhydride + water --> acetic acid
You can prepare acetate esters from alcohols by reaction with acetic anhydride.
Reactions with alcohols, oxides, permanganates, nitric acid may be hazardous to explosive. Be careful!
Acetoacetic acid
Acetoacetic acid, C4H6O3, CH3COCH2COOH, 3-oxobutanoic acid, is a fatty acid.
It occurs in (Phaseolus vulgaris), and in (Apium graveolense).
16.1.9 Ethyl acetoactonate
16.3.3 Keto acids
19.5.1Tests for ketones
Acetone
Acetone, CH3COCH3, 2-propanone, a dimethyl ketone, is highly flammable, irritant vapour, slightly toxic if ingested.
Use low cost, technical grade acetone, from hardware store, as solvent, and to clean glassware.
Acetone ACS reagent, 99.5%, clear colourless volatile liquid, characteristic smell, inflammable
RD 0.79 gm cm-3, BP 56.5oC, miscible with water and ether, and oils sharp sweet taste
Acetone is a curing agent for epoxy resin adhesives, surface coating, irritant.
Use acetone in a fume cupboard or use < 50 mL in a well-ventilated area.
Acetone react violently with chloroform.
Use ethyl acetate or methyl isobutyl ketone as alternative solvent to acetone.
Heat acetone on a water bath, NOTon a naked flame.
Acetone dissolves polystyrene packing pieces rapidly by dissolving the linking units.
Common names: Nail polish remover, (not Australia), e.g. "Cutex", nail paint remover and thinner
It may be sold as "pure acetone".
Junior secondary students should use acetone only as a cold solvent, and they should not heat acetone.
2.3.7 Cleaning agents, solvents
3.1.2 Boiling point of inflammable liquids
12.19.9.7 Bromination of acetone
15.4.16 Potassium dichromate as an oxidizing agent, (See: 5.)
10.12.0 Separate by solvent extraction of oil from peanuts
17.3.7 Oxidation of acetone vapour, copper catalyst
Acetonitrile
See diagram Acetonitrile
Acetonitrile, CH3CN, (acetonitrilo), cyanomethane, methyl cyanide, flammable, colourless liquid, sweet ether-like odour
It is the simplest organic nitrile and it is toxic if ingested.
Acetonitrile, Solution < 3%, Not hazardous
Acronitrile is used in C3H3N acrylics (plastics), vinyl cyanide, cyanoethylene, synthetics, paint.
Indole-3-acetonitrile C10H8N2
Acetosyringone
Acetosyringone, C10H12O4, is a phenol, irritant, non-steroidal anti-inflammatory, anti-asthmaticg, non-narcotic analgesic.
It occurs in (Justicia adhatoda), (Polyporus umbellatus), and in (Saccharomyces cerevisiae).
It occurs in (Nicotiana tabacum) root cultures, exuded from roots, to cause infection by (Agrobacterium tumefaciens).
Acetoxychavicol acetate
Acetoxychavicol acetate, C13H14O4, is a galangal acetate, an acetate ester, a phenylpropanoid, and an antineoplastic agent.
It occurs in Sweet flag, (Acorus calamus), Acoraceae, and in Snap ginger, (Alpinia calcarata), Zingiberaceae
Acetoxyeugenol acetate
Acetoxyeugenol acetate, C14H16O5, is a phenylpropanoid, a monomethoxybenzene.
It occurs in Greater galangal, (Alpinia galanga), Zingiberaceae, and in Snap ginger, (Alpinia calcarata), Zingiberaceae
Acetylbrowniine
Acetylbrowniine, C27H43NO8, 14-O-Acetylbrowniine, is an acetate ester obtained by acetylation of browniine, C25H41NO7.
Acetyl chloride
Acetyl chloride, C2H3ClO, CH3COCl, C2ClH3O, ethanoyl chloride, acyl chloride, acetic chloride, has low flash point.
It is toxic colourless, fuming liquid, pungent odour, vapour heavier than air, irritates eyes and mucous membranes, corrodes metals.
Acetylcholine
Acetylcholine C7H16NO2+, neurotransmitter, stimulates muscle, acetyl ester of choline, is a major transmitter at neuromuscular junctions.
It occurs in fruit and seed of breadfruit.
9.0, Fruit and seed, (See: 4. Acetylcholine)
Atropine C17H23NO3, alkaloid
Nicotine C10H14N2, alkaloid
Acetylharpagide
Acetylharpagide, C17H26O11, 8-O-Acetylharpagide, iridoid glucoside, ecdysteroid
Chinese medicine, anti-inflammatory, vasoconstrictor, antibacterial, antiviral, acts on smooth. muscle, inhibits, Epstein-Barr virus (EBV).
It occurs in Ajuga decumbens, and in Ajuga reptans
Acetylpyrrolidine
Acetylpyrrolidine, C6H11NO, 2-Acetylpyrrolidine
Substituted pyrrolidine, CH3COC5H4N, occurs in malt, popcorn, and beer
Acetylpyrroline
Acetylpyrroline, C6H9NO, 2-Acetyl-1-pyrroline (2AP), occurs in jasmati and basmati rice, wheat bread crust, sweet corn.
It is the white bread smell in cereals, and hot popcorn.
It occurs in screwpine, Pandanus.
Achillin
Achillin, C15H18O3, santolin, sesquiterpene lactone, a guaianolide, plant growth inhibitor
It occurs in Achillea, and in Artemisia.
Acids
7.4.1 Acids
Acid-base indicators
19.1.1 Acid-base indicators in the home
12.11.4.1 Acid-base neutralization
12.2.1 Acid-base reactions
16.1.5.7 Acid anhydrides
12.3.6 Acid dissociation constants
12.3.7 Acid dissociation constant at logarithmic scale, pKa
12.3.15 Acid dissociation constant at logarithmic scale
1.0.0 Acid fuchsin indicator, Andrade's
Acid rain
12.3.0 Acids, Chemical reactions
19.1.5 Acids in foods, Food acids
1.1 Acids, List of mineral acids
1.2 Acids, List of organic acids
Acids with other substances
Acidic oxides
Acidity
19.1.2 Acidulated water for cooking
12.3.1Amphoteric substances
3.9.0 Carbonic acid, soda water
12.3.5 Concentrated acids, with a non-metal, carbon
12.3.10 Concentrated acids, with metals, H2SO4 + Cu
12.3.12 Concentrated acids with metals, nitric acid with copper
12.3.11 Concentrated acids with a non-metals, carbon
12.4.0 Dilute acids with
12.3.5 Ionization reaction of carbonic acid
12.3.9 Nitric acid with metals
12.3.4 pH
12.3.2 Polyprotic acids
Prepare acids
12.3.1 Properties of acids
12.16.5 Reactions of sulfuric acid
19.1.17 Solid acids, solubility
12.3.3 Strong acids and weak acids
12.11.2 Tests for acid radicals in solution
12.3.17 Taste of acids, solid acids in the home
12.3.8 Taste of acids
12.11.2 Tests for acid radicals in solution
Titration
Acidity
Acidity, definition, [degree of being an acid]
18.1.0.1 Acidity and alkalinity
12.11.4.2 Acidity of vinegar and wine
19.1.1 Acidity regulators, food additives
16.1.5 Acidity test, (milk testing)
6.1.0 Soil acidity
Prepare acids
5.6.4 Prepare acid-base indicators
3.1 Prepare acid alcohol solution
11.0 Prepare acids and bases, dilution instruction
5.4.7 Prepare dilute acids
3.4.10 Prepare dilute acids and bases, (Safety)
Boric acid, Boracic acid, H3BO3
12.3.16, Hydroiodic acid, a strong acid
Hydrochloric acid, HCl
12.19.7.0, Hydrofluoric acid, HF
Nitric acid, HNO3
Nitrous acid, HNO2
Phosphoric acid, H3PO4
Acid rain
12.8.11 Acid rain and nitrogen oxides, NOx
12.6.0.1 Acid rain, SOx, from burning S or S compounds
18.6.0 Air pollution
12.19.5.0 CFCs, "Freons"
Acidic oxides
An acidic oxide is oxide of a nonmetal, e.g. carbon dioxide, or a metal in high oxidation state, e.g. CrO3.
Acidic oxides do not react with acids.
Acidic oxides form when a nonmetal burns.
Acidic oxides are usually gases at room temperature, e.g. CO2, NO2, SO2, SO3.
Acidic oxide + base --> salt + water
CO2 (g) + NaOH (aq) --> Na2CO3 (s) + H2O (l)
Acidic anhydride is an acidic oxide which reacts with water to form a base.
CO2 + H2O --> H2CO3 (carbonic acid)
SO3 (g) + H2O --> H2SO4 (aq) (sulfuric acid)
12.13.01, Acidic oxides
12.13.6, Carbon dioxide, acidic oxides, (non-metal oxides)
12.13.7, Carbon dioxide, with barium hydroxide solution
12.13.8, Carbon dioxide, with sodium hydroxide solution
12.13.0, Reactions of oxides
Acids with other substances
12.3.4 Acids with aluminiums
12.1.18 Acids with baking soda
12.1.25 Acids with sodium carbonate
12.1.40 Acids with sodium thiosulfate
12.14.18 Acids with zinc
12.3.10 Concentrated acids with metals, nitric acid with copper
12.3.11 Concentrated acids with a non-metals, carbon
12.4.0 Dilute acids with
Acridine
Acridine, C13H9N, toxic if ingested and skin contact, give First aid if ingested: Give water, and induce vomiting
Acridine orange, C17H19N3, an aminoacridine, hydrochloride salt 'acridine orange', is used to stain cell nuclei, e.g. DNA.
See diagram Acridine, (9-Azaanthracene), (2,3-Benzoquinoline)
Acriflavine
Acriflavine, C14H14ClN3, orange-brown, dye and antiseptic
It shows green fluorescence when diluted in water.
Acroleic acid
Acroleic acid, CH2CHCO2H, C3H4O2, acrylic acid, propenoic acid, prop-2-enoic acid, Toxic
It is the simplest unsaturated carboxylic acid.
Acroleic acid, Solution < 5%, Not hazardous, Corrosive, colourless liquid with an acrid odour
It is used in polishes, paints, coatings, rug backings, adhesives, plastics, textiles, and paper.
Polyacrylic acid, cross-linked sodium salt
Polyacrylic acid, water-soluble polyelectrolyte, is used to increase building substances viscosity.
Polyacrylamide powder, superabsorbent, is used to make toy product "Instant Wet Expanding Snow".
Sodium polyacrylate, (C3H3NaO2)n, waterlock, is sold as toy product "Super Expanding Creatures".
3.1.22 Sodium polyacrylate gels, ghost crystals, Prepare
Acrolein
Acrolein, CH2CHCHO, CH2=CHCHO, C3H4O, acrylaldehyde, 2-Propenal, ethylene aldehyde, acrylic aldehyde
It is the simplest unsaturated aldehyde, colourless or yellow liquid, and a toxic chemical.
It has a horrible odour like the smell of burnt fat when glycerol breaks down into acrolein.
Acrolein test for presence of fats: Heat sample with potassium bisulfate --> acrolein released
Acrolein, Solution < 0.1%, Not hazardous, clear, yellowish liquid, sweet, pungent burnt fat smell, highly flammable
It polymerizes in the presence of light or alkali, or strong acids, and is unstable.
It occurs in cigarette smoke and vehicle exhaust, aquatic herbicide, kill algae and waterweeds, and it is used as a pesticide.
Acrylates
Acrylates, CH2=CHCOO−, prop-2-enoates, salts or esters or bases of acrylic acid
Esters of acrylic acid are commonly called acrylates, e.g. methyl acrylate, CH2=CHCOOCH3
Mixture of acrylates, acrylate polymer, is a viscous liquid, used as thickener in personal products.
Acrylonitrile
Acrylonitrile, CH2=CH-CN, flammable, low flashpoint, below 32 oC, poison, used to manufacture acrylic acid
Acryl polymer, generic name for fibres > 85% acrylonitrile units
ABS mixed polymer, acrylonitrile, butadiene, styrene, thermoset plastics:
3.7.28 Polypropenonitrile
16.7.6 Nitriles
4.3.1 Acrylonitrile-butadiene-styrene, burning test for synthetic fibres
3.4.2 Chewing gum (Tg)
Actinium Ac
Actinium Table of Elements
Actinium RSC
Actinium, Ac, (Greek actinray), refers to light causing chemical change, radioactive, no commercial use.
White radioactive metal, emits a pale blue light, forms coating of actinium oxide to prevent further chemcal reactions
Traces of isotope 227Ac are found in uranium and thorium ores.
19.1.17 Solid acids, solubility
19.1.11 pH of solid acids
19.1.16 Solid acids, add sodium carbonate
19.1.17 Solid acids, solubility
Citric acid
Tartaric acid
Boric acid
12.3.0H Properties of acids
Acids are good electrolytes, react with active metals, turn blue litmus red, and have a sour taste.
Dilute acids contain hydrogen ions in aqueous solution.
Represent the hydrogen ion, a proton, in different ways to show how it is related to the water molecules in the solution.
Show it as the hydrated hydrogen ion, [proton, H+(aq)], or as the hydronium ion [oxonium ion, H3O+(aq)]
However, for convenience, use H+(aq).
Concentrated sulfuric acid exists mainly as H2SO4 molecules.
Hydrochloric acid and nitric acid dissociate into ions even in concentrated solution.
Weak acids, e.g. ethanoic acid, acetic acid, CH3COOH carbonic acid and sulfurous acid dissociate very little in aqueous solution.
However, their salts, e.g. potassium acetate CH3COOK, are completely dissociated into ions.
Use the Bronsted-Lowry definition of acids and bases:
An acid donates a proton (H+) to another substance and a base accepts a proton from another substance.
When sulfuric acid dissociates in water it donates a proton (H+) to the water molecule.
In this reaction the water molecule acts as a base.
H2SO4 + H2O --> HSO4-+ H3O+
When ammonia dissolves in water, ammonia accepts a proton and so it is the base.
So in this reaction the water molecule acts as an acid
NH3 + H2O < --> NH4++ OH-
12.3.1 Amphoteric substances
Amphoteric substances can act as an acid or a base.
In the above reactions water is acting as a base with sulfuric acid and is acting as an acid with ammonia.
Similarly, bicarbonate ion can act as an acid to donate a proton to form the carbonate ion.
HCO3-+ H2O < --> CO32-+ H3O+
Also, bicarbonate ion can act as a base to accept a proton to form carbonic acid.
HCO3-+ H2O < --> H2CO3 + OH-
12.3.2 Polyprotic acids
Polyprotic acids can donate more than one proton, e.g. carbonic acid.
H2CO3 + H2O < --> HCO3-+ H3O+ (The first proton to be donated to a water molecule.)
HCO3-+ H2O < --> CO32-+ H3O+ (The second proton to be donated to a water molecule.)
12.3.3 Strong acids and weak acids
A strong acid completely dissociates into ions, e.g. nitric acid has almost complete dissociation, 93%.
HNO3 (aq) + H2O H3O+(aq) + NO3-(aq)
A weak acid only partly dissociates into ions, e.g. acetic acid.
CH3COOH + H2O < --> CH3COO-+ H3O+
Describing acids and bases as "strong" or "weak"only refers to their reaction with water.
It does not refer to the concentration or the number of moles in a volume.
The strong acids include:
Perchloric acid HClO4, hydrochloric acid HCl, hydrobromic acid HBr, hydroiodic acid (hydriodic acid), HI, nitric acid HNO3, and sulfuric acid H2SO4.
Any other acid is a weak acid, because it does not completely dissociate in water.
12.3.4 pH
Water can transfer a proton from one molecule to another, autionization.
2H2O <--> H3O++ OH-and H2O < --> H++ OH-
The product of hydrogen ion concentration, [H+] and hydroxide ion concentration, [OH-] = the constant, Kw
Kw = [H+] × [OH-] = 1.00 × 10-14
So [H+] = 10-7and [OH-] = 10-7
The hydrogen ion concentration is very small in pure water, so the concentration is describes in terms of its negative log.
pH is the negative log of the hydrogen ion concentration, pH = -log[H+], so hydrogen ion concentration, [H+] = 10-pH.
So acidic solutions have a high [H+] and low pH values.
Basic solutions have low [H+] and high pH values.
A solution that is neither acidic nor basic, a neutral solution, has [H+] = [OH-], so pH = 7.
A more acid solution has pH approaching 1.
A more basic solution has pH approaching 14.
12.3.5 Ionization reaction of carbonic acid
H2O (l) --> H+(aq) + OH-(aq)
2H+(aq) + CO32-(aq) < --> H2CO3 (aq) carbonic acid
CO2 + H2O <--> H3O++HCO3-, K1 = 4.4 × 10-7
HCO3-+ H2O <--> H3O++ CO32-, Ka = 4.7 × 10-11
12.3.6 Acid dissociation constant
Acid dissociation constant, acidity constant, acid-ionization constant
1. The acid dissociation constant, Ka, measures the strength of an acid in solution.
2. An acid, HA, dissociates into A-, conjugate base, and H+, hydrogen ion (proton).
The equilibrium equation when concentrations do not change is, HA < --> A-+ H+.
3. Dissociation refers to the break up of a molecule into smaller molecules, atoms or ions.
In a buffer solution of the salt of a weak acid with a weak acid, the dissociation of the weak acid is negligible
However, a salt may be dissociated completely into ions.
4. The dissociation constant, Ka is the equilibrium constant of a reversible dissociation including the ionization reactions of acids and bases in water.
The dissociation constant Ka = [A-] [ H+] / [HA] in mol / litre.
5. However, dissociation is usually expressed as a logarithmic constant, pKa, where pKa = -log10 (1/Ka).
It is the quotient of the equilibrium concentrations, in mol/L for ionization reactions at 25 oC.
For pKa, the larger the value the weaker the acid, so strong acids have pKa < 2, and weak acids have pKa >2, < 12.
6. Confusion happens, because both Ka and pKa are sometimes both called "acid dissociation constant"!
The acid dissociation constant, Ka of the acid HB
HB (aq) <--> H+(aq) + B-(aq)
Ka = [H+][B-] / [HB]
Ka is a measure of the degree to which an acid or base will dissociate in water.
Stronger acids have a larger Ka and a smaller pKa than weaker acids.
The greater the value of Ka, the more the formation of H+ is favoured, and the lower the pH of the solution.
12.3.7 Acid dissociation constant at logarithmic scale, pKa
pKa = -log10Ka
Strong acids have pKa value < −2.
When the pH of solution is at the value of pKa for a dissolved acid, that acid will be 50% dissociated.
Sulfuric acid, H2SO4 --> HSO4-, pKa -10
Hydroiodic acid, HI: HI (g) + H2O (l) --> H3O+(aq) + I-(aq), pKa -9
Hydrobromic acid, HBr: HBr (g) + H2O (l) --> H3O+(aq) + Br-(aq), pKa -8
Perchloric acid, HClO4: HClO4 + H2O --> H3O++ ClO4-, pKa -10
Hydrochloric acid HCl: HCl (g) + H2O (l) --> H3O+(aq) + Cl-(aq), pKa -7
Hydronium ion, H3O+: H2O + H2O < --> H3O++ OH-, pKa -1.74
Nitric acid HNO3: HNO3 + H2O --> H3O++ NO3-, pKa - 1.3
Chloric acid, HClO3, pKa -1.0: Weak acid has pKa value −2 to 12 in water.
Acetic acid, CH3COOH, pKa 4.75
12.3.8 Taste of acids
BE CAREFUL! NEVER TASTE ACIDS IN THE LABORATORY!
Do NOT taste these acids in the laboratory!
Each acid has a sour taste that is a characteristic of acids.
Lemon juice contains the white crystalline citric acid.
Vinegar contains ethanoic acid, acetic acid, CH3COOH.
Experiment
Moisten your finger with a very dilute solution of hydrochloric acid.
Rub your fingers together and then lick them.
Repeat the procedure with very dilute solutions of acetic acid and citric acid.
Do not taste any other acids, because they may damage living tissues.
Citric acid C6H8O7
9.1.6, Acetic acid, ethanoic acid, CH3COOH
12.3.9 Nitric acid with metals
Add slowly small pieces of copper, magnesium and zinc to small amounts of dilute nitric acid in separate test-tubes.
If no change is taking place, gently heat the mixture.
Repeat the procedure, 1. with concentrated nitric acid, 2. with concentrated sulfuric acid, and 3. with concentrated hydrochloric acid.
Reactions of metals with nitric acid and conc. sulfuric acid are different from reactions of metals with HCl, dilute sulfuric acid and dilute acetic acid.
Copper does not react with dilute acids or with concentrated hydrochloric acid.
Copper does react with dilute and concentrated nitric acids and with hot concentrated sulfuric acid.
However, it does not produce hydrogen gas in reaction with them.
Residual mixtures contain solutions of salts.
However, writing equations is difficult, because more than one reaction can occur between Cu, Mg, Zn and nitric acid.
When zinc reacts with nitric acid the reaction may produce nitrogen dioxide, nitric oxide, nitrous oxide, zinc nitrate and ammonium nitrate!
12.3.10 Concentrated acids with metals, nitric acid with copper
Nitric acid reacts with metals above platinum in the reactivity series, but does not form hydrogen gas.
BE CAREFUL! DO THIS EXPERIMENT IN A FUME CUPBOARD.
Pour drops of concentrated nitric acid on pieces of copper in a test-tube.
Put a stopper on the test-tube immediately, because brown nitrogen dioxide gas forms.
The nitric acid acts as an oxidizing agent and is reduced to nitrogen dioxide and water.
The reaction is exothermic.
Cu (s) + 4HNO3 (aq) --> Cu(NO3)2 (aq) + 2H2O (l) + 2NO2 (g)
12.3.11 Concentrated acids with a non-metals, carbon
DO NOT DEMONSTRATE THIS EXPERIMENT!
Hot sulfuric acid and nitric acid can react as oxidizing agents with carbon.
Carbon is oxidized to carbon dioxide and nitric acid is reduced to nitrogen dioxide and water.
C (s) + 4HNO3 (aq) --> CO2 (g) + 4NO2 (g) + 2H2O (l)
12.3.12 Acid dissociation constant
Acid dissociation constant, acidity constant, acid-ionization constant
1. The acid dissociation constant, Ka, measures the strength of an acid in solution.
2. An acid, HA, dissociates into A-, conjugate base, and H+, hydrogen ion (proton).
The equilibrium equation when concentrations do not change is, HA < --> A-+ H+.
3. Dissociation refers to the break up of a molecule into smaller molecules, atoms or ions.
In a buffer solution of the salt of a weak acid with a weak acid, the dissociation of the weak acid is negligible
However, a salt may be dissociated completely into ions.
4. The dissociation constant, Ka is the equilibrium constant of a reversible dissociation including the ionization reactions of acids and bases in water.
The dissociation constant Ka = [A-] [ H+] / [HA] in mol / litre.
5. However, dissociation is usually expressed as a logarithmic constant, pKa, where pKa = -log10 (1/Ka).
It is the quotient of the equilibrium concentrations, in mol/L for ionization reactions at 25 oC.
For pKa, the larger the value the weaker the acid, so strong acids have pKa < 2, and weak acids have pKa >2, < 12.
6. Confusion happens, because both Ka and pKa are sometimes both called "acid dissociation constant"!
Aluminium
Contents
13.0.0 Aluminium properties
13.1.0 Aluminium compounds
13.2.0 Aluminium minerals
13.3.0 Aluminium experiments
13.4.0 Aluminium powder
Can, beer can, beverage can
35.2.11 Bauxite
13.1.0 Aluminium compounds
13.1.1 Aluminium acetate
13.1.2 Aluminium ammonium sulfate
13.1.3 Aluminium bromide
13.1.4 Aluminium carbide
13.1.5 Aluminiumchloride
13.1.6 Aluminium fluoride
13.1.7 Aluminium hydroxide
13.1.8 Aluminium nitrate
13.1.9 Aluminium oxalate
13.1.10 Aluminium oxide
13.1.11 Aluminium phosphate
13.1.12 Aluminium phosphide
13.1.13 Aluminium potassium sulfate
13.1.14 Aluminium sulfate
13.1.15 Aluminium silicate
13.1.16 Alum
13.1.17 Anti-bumping granules
13.2.0 Aluminium minerals
13.2.1 Alnico magnets
13.2.2 Bauxite
13.2.3 Cryolite
Feldspars, (Geology)
13.2.4 Kyanite
13.2.5 Stilbite
13.2.6 Zeolite
13.3.0 Aluminium experiments
13.3.1 Alumina as a catalyst in the cracking process
13.3.2 Aluminium chloride with water
13.3.3 Aluminium sulfate reactions
13.3.4 Aluminium with acids
13.3.5 Aluminium with sodium hydroxide
13.3.6 Aluminium with sulfur
13.3.7 Bauxite digestion
13.3.8 Burn aluminium in oxygen
13.3.9 Corrosion of aluminium
13.3.10 Heat aluminium foil
13.3.11 Iodine with aluminium
13.3.12 Tests for aluminium
13.3.11 Tests for aluminium compounds
13.3.12 Tests for aluminium compounds in solution
13.3.15 Thermite reaction
13.0.0 Aluminium properties
See: Aluminium, Table of the Elements
Aluminium RSC
1. Aluminium, Al (Latin alumen bitter salt, referring to alum), (US Aluminum), Aluminium ion, Al3+
In 1990, The International Union of Pure and Applied Chemistry (IUPAC) confirmed the use of the spelling "aluminium".
However, people in the US are accustomed to using the spelling "aluminum".
Aluminium is a silver, light, ductile, malleable, metal, with mechanical strength.
Aluminium compounds are abundant.
Aluminium is extracted by electrolysis from the main aluminium ore bauxite dissolved in cryolite.
Bauxite is 8% of the earth's crust so aluminium is the most abundant element in the Earth's crust.
Atomic number: 13, Relative atomic mass: 26.9815, r.d. 2.70, m.p. = 660 oC, b.p. = 2470 oC, E 173
Specific heat capacity: 900 J kg-1 K-1
Aluminium availability:
Aluminium, Al, metal filings, ion Al3+, granules (stabilized), pellets (coated) (powder 1396), Flammable powder
Aluminium is available as foil, sheet, and wire.
Aluminium foil, "Alfoil" cooking foil, 300 width × 150 m roll, "Alfoil" disposable containers, rectangular 120 mm × 175 mm, round 120 mm diameter.
Aluminium ignots, 99.7% purity
Aluminium reagent test kit, No. 1 tablets, No. 2 tablets, AAS Std, leaf, flakes, sheet, drink-can, ingot, wire
Aluminium, although toxic, is not a heavy metal.
Low cost: Aluminum kitchen foil, aluminum drink cans (beverage cans, plastic coated inside), aluminum window screen frames
Duralumin, alloy of Al + Cu + Mg
Aluminium uses
Aluminium metal is not tarnished in air, because it forms protective oxide that prevents further oxidation.
The aluminium foil used in home kitchens from grocery stores and the aluminium wire and aluminium sheeting from hardware stores are all pure aluminium.
Most reactions of aluminium are inhibited by a surface coating of aluminium oxide.
This is the reason that such an active metal as aluminium can be used widely for construction and for containers.
Alfoil disposable containers + lid, 105 mm width × 184 mm depth × 38 mm height.
Aluminium foil is used to clean pots and barbecue grill on picnics.
Rub rust from and polish chromium plating, seal used paint tins and planting pots, catch baking drips.
Aluminium is protected by layer of oxide that can be thickened if an anode in electrolytic cell, i.e. anodized then can be coloured.
It is malleable, low density, is used in "Alfoil" cooking foil, drink-cans, saucepans, duralumin (alloy of Al + Cu, Mg), aircraft bodies and struts, motor vehicle parts.
Aluminium food additive, E173 (colour: metallic) (Banned, some countries, excess unsafe)
Heated powder forms oxide.
Excess aluminium may cause short term toxicity, e.g. aluminium sulfate in drinking water, corroded cooking utensils with acidic foods, alum treatment of water.
13.1.1 Aluminium acetate
Aluminium acetate, Domeboro, C6H9AlO6, Al COOCH3)3, aluminium ethanoate, topical astringent, antiseptic agent.
13.1.2 Aluminium ammonium sulfate
Aluminium ammonium sulfate (dodecahydrate), (AlNH4(SO4)2.12H2O), ammonium alum, food additive, E523, buffer, stabilizer.
13.1.3 Aluminium bromide
Aluminium bromide, AlBrx, commonly aluminium tribromide (Al2Br6), used in Friedel–Crafts reactions for production of polystyrene.
13.1.4 Aluminium carbide
Aluminium carbide, (Al4C3), yellow-brown crystals, reacts with water to give methane.
Al4C3 + 12 H2O → 4 Al(OH)3 + 3 CH4
13.1.5 Aluminium chloride
Aluminium chloride, (AlCl3), anhydrous, covalent, Toxic if ingested, but Solution < 5%, Not hazardous
Aluminium chloride, hydrated, (AlCl3.6H2O), the anhydrous AlCl3 is covalent, for 0.1 M solution, 24 g of hydrated salt in 1 Litre water.
Aluminium chloride with water: 13.1.8
13.1.6 Aluminium fluoride
Aluminium fluoride, aluminum trifluoride, AlF3, odourless white powder, with cryolite used in production of aluminium by electrolysis.
13.1.7 Aluminium hydroxide
Aluminium hydroxide, Al(OH)3, occurs as mineral gibbsite (hydrargillite), E173 food additive, antacid, many biomedical uses.
Prepare aluminium hydroxide precipitate: 7.6.4
13.1.8 Aluminium nitrate
Aluminium nitrate, Al(NO3)3, hydrated aluminium nitrate, aluminium nitrate nonahydrate, Al(NO3)3.9H2O harmful if ingested.
Crystals are white and soluble in water. It is used in tanning, antiperspirants, to inhibit corrosion.
Aluminium nitrate with sodium hydroxide: Al(NO3)3 + 3NaOH --> Al(OH)3 + 3NaNO3.
13.1.9 Aluminium oxalate
Aluminium oxalate, C6Al2O12, strong dicarboxylic acid, occurs in many plants, produced in the human body and excreted in the urine.
13.1.10 Aluminium oxide
Aluminium oxide, (Al2O3), alumina, orundum, amphoteric oxide, almost insoluble in water (used for leaching minerals).
lung irritation, toxic if inhaled, alumina (porcelain), amphoteric, corundum (hardness 9, abrasive, sand paper, in red ruby, in blue sapphire).
Diamantine, emery powder (abrasive), corroded aluminium (bauxite, hydrated aluminium oxides, (Al2O3.nH2O + laterite).
Alumina hydrate for craft, alumina has amorphous or crystalline state in corundum and bauxite powder used for thin-layer chromatography plates.
Low cost purchase from pottery supplies store
Amphoteric oxides react with both acids and bases, e.g. (Al2O3), PbO, SnO, ZnO.
Their hydroxides are also amphoteric.
Alumina polishing powder
13.1.11 Aluminium phosphate
Aluminium phosphate, AlO4P, berlinite mineral. used in cake mixes and baking powders, and as an antacid and adsorbent of toxoids.
13.1.12 Aluminium phosphide
Aluminium phosphide, AlP, fumigant, grey-yellow crystalline solid, phosphideis used to destroy pests in grain silos.
It has a strong smell like garlic or rotten fish and should be tranported in the open on the back of a vehicle.
It reacts with water to give very toxic phosphine gas.
AlP + 3 H2O -->Al(OH)3 + PH3
13.1.13 Aluminium potassium sulfate
Aluminium potassium sulfate, potassium aluminium sulfate, alum, aluminium potash, potash alum, Harmful
Potassium aluminium sulfate, aluminium potassium sulfate, alum, potash, potash alum
Potassium alum, "alum", potash alum, potassium aluminium sulfate, Al2(SO4)3.K2(SO4).24H2O, K2SO4.Al2(SO4)3.24H2O, KAl(SO4)212(H2O)
Kalinite, Aluminium potassium sulfate
Aluminium potassium sulfate-12-water Aluminium potassium sulfate-12-water, aluminium potassium sulfate hydrated
Al2(SO4)3.K2(SO4).24H2O or AlK(SO4)2.12H2O or KAl(SO4)2.12H2O
Aluminium potassium sulfate-12-water, potash alum, "alum", aluminium potash
Alum, potassium alum, "common alum", potash alum, hydrated potassium aluminium sulfate, hydrated aluminium potassium sulfate
Aluminium potassium sulfate 12-hydrate, kalinite, a double sulfate of aluminium, the "alum" sold at grocery shops
Aluminium potassium sulfate is very astringent and is used for purifying water.
13.1.14 Aluminium sulfate
Aluminium sulfate, Al2(SO4)3, hydrated aluminium sulfate Al2(SO4)3.18H2O, (NOT "alum"!)
Aluminium sulfate Al2(SO4)3 xH2O, aluminium sulfate hydrate, cake alum, Harmful to eyes, Harmful if ingested
Aluminium sulfate octadecahydrate Al2(SO4)3.18H2O, wrongly called "alum", E520, foam agent in fire extinguishers, water filter powder.
It is used as a flocculation agent, food additive E520, modifier, precipitator in sewage treatment, mordant, paper sizing.
For 0.l M solution, use 66 g of hydrated salt in 1 L water.
Aluminium sulfate reactions: 12.3.3
Aluminium sulfate with clay suspensions: 7.6.3
13.1.15 Aluminium silicate
Aluminium silicate, Al2SiO5, fibrous material, mineral andalusite Al2O3·SiO2
13.1.16 Alum
The original "alum" was the hydrated double salt of aluminium and potassium with colourless octahedral crystals and an astringent taste.
It was used for mordants before dyeing cloth.
Later the term "alum" was used to describe similar double sulfates where other elements, or radicals replaced aluminium or potassium.
So an "alum" is a hydrated aluminium potassium sulfate and related minerals.
Some plants with astringent roots are called "alum roots".
Aluminium ions form alums that are complex hydrated metal sulfates that contain 12 or 24 H2O.
"Alum" often refers to potassium alum, potash alum, potassium aluminium sulfate, aluminium potassium sulfate
KAl(SO4)2·12H2O, AlK(SO4)2.12 H2O, KAl(SO4)2, AlK(SO4)2, K2SO4.Al2(SO4)3.24H2O, AlKO8S2.
Soda alum, Na2SO4.Al2(SO4)3.24H2O
Potassium alum, "common alum", potash alum, hydrated potassium aluminium sulfate, aluminium potassium sulfate 12-hydrate.
Kalinite, a double sulfate of aluminium, the "alum" sold at grocery shops.
Aluminium potassium sulfate is very astringent and is used for purifying water.
Al2(SO4)3.K2(SO4).24H2O or AlK(SO4)2.12H2O or KAl(SO4)2.12H2O
Aluminium potassium sulfate is a buffer and firming agent, E522.
Other alums:
Ammonium alum, Aluminium ammonium sulfate dodecahydrate, AlNH4(SO4)2.12 H2O, AlH28NO20S2, NH4Al(SO4)2.12H2O, Tschermignite
Sodium alum, Soda alum, Sodium aluminum sulfate dodecahydrate, AlNa(SO4)2· nH2O (n = 0 or 12), AlH24NaO20S2, Na2SO4.Al2(SO4)3.24H2O
Chrome alum KCr(SO4)2·12H2O, CrK(SO4)2.12H2O, K2SO4.Cr2(SO4)3.24H2O, chromium (III) potassium sulfate, potassium chromium sulfate
It is used for for tanning, mordant, photography, purple or violet-red octahedral crystals.
Industrial alum (papermaker's alum) Al2(SO4)3·nH2O
Tschermignite, NH4Al(SO4)2.12H2O, ammonium alum
13.1.17 Anti-bumping granules, boiling chips, alumina
Anti-bumping granules, boiling chips (- ceramic, silicon carbide, fused alumina)
Boiling chips, fused alumina or flower pot bits, prevent large bubbles of gas forming that could cause explosive emissions from a beaker containing heated solution.
Sudden formation of a large amount of vapour from the bottom of a heated vessel of liquid, rather than the usual controlled boiling causes explosions.
So boiling chips (anti-bumping granules) are added to chemical reactions to keep the bubbles small and aid steady boiling.
Hydrocarbons with longer chains have higher boiling points than with branched chains, because of more van der Waals intermolecular bonds between molecules.
13.2.1 Alnico magnets
Alnico magnets, ferromagnetic alloy, contains Al 8-12%, Ni 15-26%, Co 5-24% + in some forms Cu 6%, Ti 1%.
It is used at 500 oC to 800 oC to make strong permanent magnets for electric motors, refrigerator doors and radio speakers.
13.2.2 Bauxite
Bauxite, Al2O3 x2H2O, (hydrated aluminium oxide, Al2O3), is a residual sedimentary mineral.
It contains alumina and other oxides of aluminium in the amorphous or crystalline state.
So it is more a rock-like mixture than a mineral.
Bauxite is a mixture of iron and aluminium hydroxides and oxides.
It is usually formed by weathering in tropical regions.
It is the most important ore for production of aluminium.
Bauxite has non-metallic lustre, white streak, no good cleavage, can be scratched by the finger nail, white to brown grey colour, uneven fracture, specific gravity 2.0-2.5.
13.2.3 Cryolite
Cryolite, sodium aluminium fluoride, Na3AlF6, has colourless to white to yellow colour, and sometimes purple to black colour.
It has Mohs scale of hardness 2.5-3, white streak, greasy to glassy lustre, no cleavage, uneven fracture and specific gravity 2.95-3.0.
The refractive index is 1.34. so the specimen almost disappears in water.
It is a colourless rare mineral used as a flux in electrolytic production of aluminium from bauxite, and is manufactured synthetically.
Note the disappearance in water, no salty taste and density of the specimen.
13.2.4 Kyanite
Kyanite, Al2(O, SiO4), disthene, munkrudite, cyanite, rhaeticite (white grey kyanite), (Greek kyanos blue), is an aluminosilicate mineral.
Mohs scale of hardness 4-5 and 6.5-7 depending on the direction of the cleavage planes, colourless streak, vitreous lustre.
Found in aluminium-rich metamorphic pegmatites and sedimentary rock.
Used in refractory and ceramic products, electrical insulators, abrasives, gemstones.
Elongated, columnar crystals.
Anisotropic, i.e. two different harnesses on perpendicular axes.
13.2.5 Stilbite
Stilbite is a member of the zeolite group, lamellar zeolite, hydrated sodium calcium aluminium silicate, Ca(Al2Si7O18).6H2O.
Stilbite, hydrated sodium calcium aluminium silicate, has more than one chemical formula, e.g. Na2CaK2Al2Si7O18.7H2O, or
NaCa2Al5Si13O3614H2O, has white to pink to yellow colour, Mohs scale of hardness 3.5-4, white streak, glassy to pearly lustre,
good cleavage in one direction, specific gravity 4.56.
Note how thin crystals stick together like a sheaf of wheat, lustre and density of the specimen.
13.2.6 Zeolite
Zeolite (T5O10, T10O20 chains), e.g. tetrapropylammonium (TPA) ZSM-5, clinoptilolite
Zeolite, e.g. tetrapropylammonium (TPA)ZSM-5, is a group of natural or synthetic hydrated aluminium silicates, appear to boil when heated in a blowpipe.
They retain pores or channels in their crystal structure, easily gain or lose water, and have a high ion exchange capacity.
Zeolites are used in detergents as water softeners, and as catalysts for reforming petroleum products.
Sodium aluminosilicates, e.g. albite (NaAlSi3O8), jadeite (NaAlSi2O6), "Zeolite A", synthetic laundry detergent, Na12Al12Si12O48. 27H2O
13.3.1 Alumina as a catalyst in the cracking process
See diagram 12.1.10 : Alumina as a catalyst
Large quantities of alumina, aluminium (III) oxide, are used in the cracking processes in oil refineries.
One of the products, ethylene gas, C2H2, is used in the petrochemical industry to produce polyethylene and other polymers.
Activate alumina is very porous and is used as a filter for water treatment, an adsorption desiccant and a catalyst for natural gas and oil refining processes.
Experiment
Use a fume hood for this experiment.
Hot paraffin oil and ethylene gas are flammable.
Set up the apparatus as in diagram 12.1.10.
See diagram 12.1.10 : Alumina as a catalyst.
Put 5 cm of paraffin oil and boiling chips in the boiling tube.
Clamp it at a shallow angle, then put 0.5 g of alumina powder half way down the boiling tube, then replace the stopper.
Hheat the alumina strongly with a Bunsen burner, then heat the alumina and paraffin oil alternately until the paraffin oil boils and its vapour passes over the alumina.
Let the first few bubbles of gas escape under the fume hood, then collect two test-tubes of gas.
Fix stoppers on the test-tubes.
Immediately after collecting the two test-tubes of gas, turn off the Bunsen burner and remove the delivery tube and stopper from under the boiling tube.
This action prevents water "sucking back" into the boiling tube as it cools.
13.3.2 Aluminium chloride with water
Be careful! Demonstrate this reaction only to senior students.
Place < 5 g of aluminium chloride in a beaker in a fume cupboard and add water drop-by-drop.
The material will hiss, crackle and release clouds of hydrogen chloride and fine particles.
Anhydrous aluminium chloride, AlCl3, reacts violently with water to form the hydrated salt by hydrolysis, and a solution of hydrochloric acid + HCl gas.
Formation of an acid solution is more like a non-metal than a metal, which reflects the position of aluminium to the right of magnesium in the periodic table.
Fine aerosol particles may also be generated.
Both the hydrogen chloride gas and the fine particles are extremely irritant to the lungs.
Aluminium chloride should only be used in a fume cupboard and only in small amounts.
Do not mix aluminium chloride with alkaline materials, e.g. sodium hydroxide, because a violent reaction may occur.
Aluminium chloride is exceedingly hygroscopic so keep it in a tightly-sealed plastic container.
Purchase the material only in small amounts, e.g. 100 g.
Aluminium bromide, AlBr3, has dangerous properties similar to anhydrous aluminium chloride.
AlCl3 (s) + 3H2O (l) --> Al(OH)3 (s) + 3H+ (aq) + 3Cl- (aq)
13.3.3 Aluminium sulfate reactions
1. Add ammonia solution, NH3 (aq) ("ammonium hydroxide") to aluminium sulfate solution.
Note the white precipitate of aluminium hydroxide that is insoluble in excess ammonia solution.
Al3+ + 3OH- --> Al(OH)3 (s)
2. Add drops of sodium hydroxide to aluminium sulfate solution.
Note the white precipitate that dissolves in excess sodium hydroxide to form sodium aluminate.
Aluminium hydroxide is amphoteric.
Al(OH)3 + OH- --> AlO2- + 2H2O
3. Add blue litmus solution to aluminium sulfate solution.
The blue litmus turns red.
Add sodium carbonate solution and note the production of carbon dioxide.
Aluminium salts in solution can act as acids, because of hydrolysis.
Al3+ + 3H2O --> Al(OH)3 + 3H +
4. Pass hydrogen sulfide through aluminium sulfate solution to produce the hydroxide, not the sulfide.
5. Mix aluminium sulfate with twice its volume of anhydrous sodium carbonate and heat it on a charcoal block.
Note the white infusible mass.
Add cobalt nitrate solution and heat again.
A bright blue solid forms.
13.3.4 Aluminium with acids
The reaction is very slow to start because ot the coating of aluminium oxide on aluminium.
After the acid has broken through the aluminium oxide, the reaction is fast, very fast if using powdered aluminium.
Dissolve aluminium in heated dilute hydrochloric acid and note that hydrogen gas forms.
2Al + 6H + --> 2A13+ + 3H2 (g).
2Al + 3H2SO4 --> Al2(SO4)3 + 3H2 Hot concentrated sulfuric acid will attack aluminium with the production of sulfur dioxide.
Dilute or concentrated nitric acid acts only very slowly on aluminium, because of passivation.
13.3.5 Aluminium with sodium hydroxide
Use aluminium cooking foil or aluminium pie pans.
Use caustic soda drain cleaner from a hardware shop.
Wear safety goggles, gloves, lab coat.
Keep away any matches, sparks, flames.
If exploding hydrogen, wear ear protection.
Be careful! Hydrogen gas forms from the very rapid reaction.
1. Use a dropper to put drops of concentrated sodium hydroxide solution onto a sheet of aluminium foil or aluminium powder in a test-tube.
2. Add 5 g coarse aluminium powder to 20 ml of 40 % sodium hydroxide solution in a test-tube.
Quickly place the test-tube in the bottom of a tall glass beaker before the violent react occurs.
The coarse aluminium powder has a surface layer of aluminium oxide, which is first dissolved by the sodium hydroxide before the main reaction .
The aluminium completely dissolves and the water acts here too as an acid.
(The aluminate ion in an anhydrous compound is shown as (AlO2-), and in the hydrated form is shown as Al(OH)4-.
2Al (s) + 2NaOH (aq) + 2H2O (l) --> 2NaAlO2 (aq) + 3H2 (g) + energy.
2Al + 2OH- + 2H2O --> 2AlO2- + 3H2 (g)
2Al (s) + 2NaOH (aq) + 6H2O --> 2Na+ (aq) + 2Al(OH)4-+ 3H2 (g)
The aluminium reacts with water to form the amphoteric aluminium hydroxide, Al(OH)3, which later goes in solution to produce aluminates, (Al(OH)4)-.
2Al + 6H2O --> 2Al(OH)3 + 3H2
Al(OH)3 + NaOH --> Na+ + Al(OH)4-
Al2O3 + 2NaOH + 3H2O --> 2Na+ + 2Al(OH)4-
It is sold as "drain cleaners", e.g. Drano, contains sodium hydroxide crystals and pieces of aluminium, which react when put in a wet clogged drain.
The reaction is very hot as the sodium hydroxide reacts with fats to form soaps.
The hydrogen evolved applies pressure to move the pieces of aluminium to whirl around and cut the blockage.
3. Stand a clear glass bottle in a container of water.
Do not use a plastic drink bottle!
Add water to the bottle to 1/3 volume and add water to the container so the water levels in the bottle and container are the same.
Add a small measured amount of caustic soda to the bottle.
Pick up the bottle, dissolve the caustic soda by swirling the bottle, then replace the bottle in the container.
Roll a sheet of aluminium foil into a tube to fit through the mouth of the bottle.
Attach a balloon to the mouth of the bottle so that it fills with hydrogen gas.
Attach a balloon clip and let the balloon float up in the air.
If the balloon does not float up in the air, because it is not full enough, wait until the bottle has cooled and repeat with more caustic soda and aluminium foil.
If the balloon does not float up in the air and feels heavy, the reaction has been too vigorous so some water has condensed in the balloon.
So wait until the bottle has cooled and repeat the experiment with>less caustic soda and aluminium foil.
13.3.6 Aluminium with sulfur
Mix dry aluminium powder with twice its volume of sulfur powder.
Put into a test-tube only enough to cover the bottom of the test-tube.
Be careful! Larger quantities may explode! Set up a safety screen.
Clamp the test-tube vertically and heat with a Bunsen burner.
Note the vigorous action where aluminium sulfide is synthesized.
Leave to cool, then add drops of water.
Hydrogen sulfide forms, because of the hydrolysis of the aluminium sulfide.
2Al + 3S --> Al2S3
Al2S3+ 6 H2O --> 2Al(OH)3 (s) + 3H2S (g)
13.3.7 Bauxite digestion
Wear safety gloves and safety spectacles.
Weigh 10 g of ground, dried bauxite and transfer to a reflux flask.
Add 100 mL of 20% sodium hydroxide solution and boil under reflux for 1-2 hours.
Leave to cool, then transfer the solution and residue to a 200 mL volumetric flask.
To make sure all the contents of the reflux are transferred, use demineralized water.
Leave to cool, then make up to volume with demineralized water.
When the muddy residue has settled overnight, remove a 10 mL aliquot to a 250 mL beaker and dilute to 100 mL with demineralized water.
Heat the mixture until it boils, then make acid with 1: 1 HCl using methyl red indicator.
Add 2 g of ammonium chloride, then add 1: 1 ammonium hydroxide until the yellow end point is reached.
Boil the mixture to coagulate the precipitate, then filter it while still hot and wash the precipitate on the filter paper with hot water.
Leave the precipitate and filter paper overnight to dry to a slightly damp consistency.
Transfer the precipitate to a weighed crucible, e.g. porcelain, silica or platinum.
Dry the precipitate on the edge of a hot plate.
Do not allow any material to be lost by spitting.
Transfer the crucible and contents to a muffle furnace and ignite to a constant weight at 1, 0000 oC to 1, 200 oC.
Leave the crucible and contents to cool in a desiccator, then weigh them.
Calculate the percentage of alumina in the the bauxite: (weight of crucible and residue - weight of crucible) × 20 × 100 / weight of the sample.
If the "mud" is left with the solution it contributes to less than 1% of the total volume, an almost insignificant error.
The alumina content can also be determined volumetrically with EDTA.
13.3.8 Burn aluminium in oxygen
Sprinkle aluminium powder onto a Bunsen burner flame or heat aluminium powder in a crucible, then lower it into a gas jar of oxygen.
The aluminium burns brightly to form the white powder magnesium oxide.
4Al (s) + 3O2 (g) --> 2Al2O3 (s)
aluminium + oxygen --> aluminium oxide
Aluminium oxide is an amphoteric oxide that does not dissolve in water.
Stored aluminium is always coated with aluminium oxide, which protects it from most chemical reactions.
So aluminium can be used for many purposes where an unreacted metal is needed.
13.3.9 Corrosion of aluminium
Put a piece of aluminium foil in water.
Put a copper coin on the foil and leave it for some days. A simple aluminium /copper cell forms and a small electric current can be detected with an ammeter.
The aluminium foil has holes where the coin lies on it.
The water appears cloudy, because of the fine particles of aluminium released during corrosion.
13.3.10 Heat aluminium foil
Heat aluminium foil to form aluminium oxide
Aluminium foil (al-foil, alu-foil, "Reynolds wrap'), has thickness usually < 0.2 mm.
It is shiny on one side and matte on the other side, caused by the rolling process of manufacture.
Heat a piece of aluminium cooking foil or a "silver" milk bottle top.
Describe what happens to the aluminium foil.
You may not see any changes, because aluminium does not change colour when heated.
The melting point is 655 oC to 660 oC.
When white hot, it slowly forms a coating of aluminium oxide, alumina.
Do not heat aluminium powder.
If not pure, it may explode.
4Al (s) +3O2 (g) --> 2Al2O3 (s)
aluminium + oxygen --> aluminium oxide.
13.3.11 Iodine with aluminium
Use < 5 g total material of iodine to react with aluminium powder in a fume cupboard.
However, be aware that a cloud of unreacted iodine vapour may be released.
Fine particles of aluminium react violently with iodine, especially after a drop of water has been added.
A large amount of unreacted iodine is liberated as purple vapour into the air.
This reaction should only be done with < 5 g of materials and in a fume cupboard or outdoors.
Mix the ingredients in a small ceramic mortar and pestle.
All observers must wear eye protection.
13.3.12 Tests for aluminium
1. Heat charcoal with fusion mixture, note heated metal appearance.
Aluminium produces a white residue.
Add drops of cobalt nitrate solution and heat again to form a blue mass, but this is also caused by fusible phosphates, arsenates, borates and silicates.
2. Test aluminium
Test aluminium after dipping it in concentrated hydrochloric acid then press it on absorbent paper to remove the layer of aluminium oxide.
The voltage reading will start at a low value then increase as remaining aluminium oxide dissolves.
Record the maximum value.
13.3.13 Tests for aluminium compounds
Put two drops of red cobalt chloride solution on to a piece of filter paper.
Add two drops of aluminium sulfate solution.
Dry the paper by holding it over a flame and then ignite it over a saucer.
The ash is blue.
This is a test for all aluminium compounds in solution.
13.3.14 Tests for aluminium compounds in solution
Put 2 drops of cobalt chloride solution (red) on a piece of filter paper.
The drop 2 drops of aluminium sulfite solution of the filter paper.
Hold the filter paper over a small flame, then ignite it over a saucer.
A blue ash indicates aluminium compounds.
13.3.15 Thermite reaction
Be careful! The thermite reaction is a hazardous experiment.
Mix aluminium powder or aluminium turnings with iron oxide and ignite the mixture with a burning magnesium ribbon.
Do the experiment in the open with observers at least ten metres away.
Do not use > 25 g of the reaction mixture.
Make the reaction mixture in a cut down aluminium beverage can, suspended above a bucket or trough of sand to contain the molten iron formed.
The mixture may be difficult to ignite, but burns with white heat, producing molten iron that can be tapped from the bottom of the container.
Be careful! Burning magnesium ribbon held close to the eyes may cause eye damage.
The mixture may react violently if the aluminium particles are too fine.
Any trace of moisture in the reactants or container may cause violent evolution of steam and ejection of the white hot contents.
2Al + Fe2O3 --> 2Fe + Al2O3
8Al + 3Fe3O4 --> 9Fe + 4Al2O3
Thermit welding is used to weld iron rails together.
2Al + 3FeO -->3Fe + Al2O3
2Al + Fe2O3 --> 2Fe + Al2O3
The ends of the rails are encased in thermit putty to hold the molten products of the reaction.
The putty consists of silica sand, bentonite, carboxymethyl cellulose and water.
13.4.0 Aluminium powder
Aluminium powder is not safe for school use, so it is not supplied as powder.
So to avoid explosive reactions, do not grind aluminium metal to powder.
Finely divided aluminium particles (powder or fine turnings) burn in air with an intense white flame if ignited.
A significant amount of ultraviolet radiation is emitted, and the flame should not be watched with the naked eye.
Unoxidized aluminium powder reacts vigorously with both concentrated acids or alkalis to yield hydrogen gas, which is explosive when mixed with air.
The reaction may occur with such vigour that the aluminium particles and acid or alkali may be ejected from the container.
Aluminium metal reacts violently with halogens (chlorine, bromine, iodine).
The reaction of aluminium with liquid bromine is hazardous and should not be attempted.