School Science Lessons
Topic 10
2024-06-01
Separate pure substances from mixtures
(topic10)
Contents
10.1.0 Separate
10.1.3 Separate by adsorbing impurities
10.2.0 Separate by chromatography
10.1.9 Separate by different methods
10.11.1 Separate by decanting
10.3.0 Separate by distillation
10.11.2 Separate by filtration
10.3.6 Separate by fractional distillation
10.5.0 Separate by froth flotation of heavy minerals
10.6.0 Separate by heating, gases dissolved in water
10.9.0 Separate by recrystallization
10.19.0 Separate by melting points, tin from a tin and carbon mixture
10.11.3 Separation by precipitation
10.11.0 Separate by sedimentation and filtration of precipitates
10.4.1 Separate by shaking different liquids in water
10.11.5 Separate by solubility, salt from salt and sand mixture
10.12.0 Separate by solvent extraction of oil from peanuts
10.21.0 Separate by sublimation, naphthalene, iodine
10.1.10 Separate alum from alum solution by crystallization
10.1.6 Separate ammonium chloride from ammonium chloride solution
10.1.4 Separate chalk from coloured blackboard chalk suspension by filtration
10.1.11 Separate copper carbonate and magnesium sulfate mixture
10.1.13 Separate dirt from dirty water with charcoal
10.3.5 Separate gases dissolved in a water sample
10.18.0 Separate iodine from a mixture of iodine and sodium chloride
10.13.2 Separate iodine from kelp
10.1.1 Separate litmus solution with charcoal
10.10.0 Separate metals by reduction of metal oxides, charcoal blocks
10.17.0 Separate miscible liquids by fractional distillation
10.16.0 Separate mud and water from muddy water
10.1.7 Separate salt and sand mixture
10.1.5 Separate salt from salt water by evaporation
10.1.8 Separate sand and copper sulfate mixture
10.13.1 Separate sodium chloride from iodine
10.1.12 Separate soluble from insoluble substances
10.8.0 Separate two solids using density differences
10.22.0 Separate two immiscible liquids of different density
10.1.2 Separate efficiency of a mixture
10.3.7 Separate water from copper sulfate solution by distillation
10.11.6 Separate with a simple centrifuge
10.11.7 Separate with paper towels
10.2.0 Separate by chromatography
10.2.1 Chromatography of chlorophyll pigments
10.2.2 Detect a forgery
10.2.3 Separate by chromatography, "colour writing"
10.2.4 Separate by chromatography, green leaf pigments
10.2.5 Separate by chromatography, mixed inks
10.2.6 Separate amino acids with paper chromatography
10.2.7 Separate aspirin, caffeine and paracetamol by thin layer plate chromatography
10.2.8 Separate food colours in coloured sweets by chromatography
10.2.9 Separate methyl orange and litmus mixture by chromatography
10.3.0 Separate by distillation
10.3.01 Separate by distillation
10.3.1 Distil copper (II) sulfate solution
10.3.2 Distil essences from leaves and flowers
10.3.3 Distil ink
10.3.4 Distil sea water
10.3.5 Separate gases dissolved in a water sample
10.3.6 Separate by fractional distillation
10.3.7 Separate water from copper sulfate solution by distillation
10.3.8 Catalytic cracking of kerosene
10.3.9 Distil crude oil and collect the fractions
10.3.10 Steam distillation of eucalyptus leaves
10.3.11 Steam distillation to measure water and fat content of food
10.11.0 Separate by sedimentation and filtration of precipitates
10.11.1 Separate by decanting
10.11.2 Separate by filtration
10.11.3 Separate by precipitation
9.1.11 Cork taint of wine, "corky" wine
Brandy
Experiments
10.11.4 Clarify muddy water by filtration and flocculation
10.11.5 Separate by solubility, salt from salt and sand mixture
10.11.6 Separate by a simple centrifuge
10.11.7 Separate with paper towels
10.1.1 Separate litmus solution with charcoal
Boil blue litmus solution.
Filter the hot solution.
The blue colour remains.
Filter the solution through charcoal.
The blue colour has gone.
Shake the charcoal in methylated spirit.
The blue colour returns.
10.1.2 Separate efficiency of a mixture
Use one of two mixtures:
1. sand, pebbles, salt and oil,
2. sand, iron filings, wood shavings and salt.
Determine the mass off each of the components before mixing them.
When the components are separated again, find the efficiency of the separation process from the recovery percentage for each component.
Analyse potential sources of any differences seen:
1. not washing the filtrate with distilled water, thus leaving a residue behind, or
2. adherence of one material to another.
Repeat the experiment, by improving the efficiency of their separation, and then comparing the recovery percentage of the first trial vs the second trial.
Evaluate the efficacy of different separation techniques, and discus different types of error.
Think about the impact of equipment error on laboratory investigations.
10.1.3 Separate by adsorbing impurities
Some forms of carbon can adsorb coloured substances and release them later in suitable solvents
For example , charcoal made from bones removes coloured impurities in the production of cane sugar crystals.
10.1.4 Separate chalk from coloured blackboard chalk suspension by filtration.
Grind a finger width of coloured blackboard chalk with a mortar and pestle and mix it with a quarter of a test-tube of water.
Filter the suspension of chalk.
Describe what you see.
The suspension of chalk is easily filtered.
Remove the filter paper from the filter funnel, open it and lay it on a flat surface and leave to dry.
Store and label the dry chalk.
10.1.5 Separate salt from salt water by evaporation
Put a finger width of sodium chloride in a half a test-tube of hot water and shake the test-tube to dissolve the salt.
When any undissolved salt has settled, pour the solution into an evaporating basin on a tripod stand.
Put on safety glasses then heat the evaporating basin until the solution boils.
Keep the solution boiling until all the water evaporates as steam and a white residue of salt remains.
However, if the salt begins to spurt out of the evaporating basin, heat very slowly.
Do not taste the salt.
Place the evaporating basin in the sun or in front of a radiator to dry the contents completely.
Store and label the dry chalk.
10.1.6 Separate ammonium chloride from ammonium chloride solution
Put a finger width of ammonium chloride in half a test-tube of hot water and shake the test-tube to dissolve the salt.
When any undissolved salt has settled, pour the solution into an evaporating basin on a tripod stand.
Put on safety glasses then heat the evaporating basin until the solution boils.
Do not heat to complete dryness.
Place the evaporating basin in the sun or in front of a radiator to dry the contents completely.
Store and label the dry ammonium chloride.
10.1.7 Separate sand and salt mixture
1. Shake salt in water in a test-tube until all the salt dissolves.
Filter the mixture.
Wash the test-tube with water and pour it into the cone of filter paper.
Dry the filter paper to recover the sand.
Heat the filtrate in an evaporating dish to recover the salt.
2. Make a mixture of salt and sand.
Mix 5 g of the sand and salt mixture with 50 mL of water.
Put about 2 mL of the mixture in an evaporating basis.
Add 5 mL water and shake until all the salt has dissolved.
Pour the contents of the tube into a filter paper in a funnel over an evaporating basin.
Wash the test-tube with water and add this to the filter paper.
The sand will remain on the filter paper and may be dried and collected.
Recover the salt by heating the mixture in an evaporating basin to drive off the water until the mixture starts to "spit".
Stop the heating and allow the moist salt to dry.
3. Mix a finger width each of sand and salt.
Put the mixture in a test-tube half full of hot water.
Shake the test-tube to make the salt dissolve.
Filter the mixture and collect the salt water filtrate in an evaporating basin.
Wear eye protection then heat the salt solution with a Bunsen burner.
When the salt solution starts to "spit", i.e. sends out small explosions of damp salt, turn off the Bunsen burner and leave the damp salt in the sun to dry.
Remove the filter paper from the filter funnel and open it.
Wash the sand on the filter paper with hot demineralized water.
Lay the filter paper on a flat surface and leave to dry.
Store and label the dry sand and salt.
4. Prepare a mixture of salt and sand.
Put 2 mL of the mixture in a test-tube.
Add 5 mL of water and shake until all the salt has dissolved.
Pour the contents of the tube into a filter paper in a funnel over an evaporating basin.
Wash the test-tube with water and add this to the filter paper.
The sand will remain on the filter paper and may be dried and collected.
Recover the salt from the filtrate by warming the evaporation basin to drive off the water.
10.1.8 Separate sand and copper sulfate mixture
Mix a finger width each of sand and copper sulfate crystals.
Put the mixture in a test-tube half full of hot water.
Shake the test-tube to make the copper sulfate dissolve.
Filter the mixture and collect the copper sulfate filtrate in a test-tube.
Heat the test-tube, but do not completely evaporate the solution.
When half of it has boiled away and the remaining liquid is a deeper blue colour, pour it into an evaporating basin.
Leave it on the bench until blue crystals of copper sulfate form.
Place the evaporating basin in the sun or in front of a radiator to dry the contents completely.
Store and label the dry copper sulfate crystals.
10.1.9 Separate by different methods
1. Separate a solution of calcium chloride and sodium chloride by adding a solution of sodium carbonate to precipitate calcium as insoluble calcium carbonate.
Both Cacl2 and Na2CO3 are soluble in water and dissociated completely to ions.
The calcium will precipitate in a white precipitate as CaCO3, because :
CaCl2 (aq) + Na2CO3 (aq) --> 2 NaCl (aq) + CaCO3 (s)
and NaCl is highly soluble in water.
This is a chemical separation technique.
2. Sulfide ores are roasted to oxides and then reduced to the metals.
For example, in the metallurgy of iron, iron ore is roasted in a blast furnace, and then reduced to metallic iron by carbon.
3. Noble metals like gold and silver are converted into their soluble cyanide complexes, which are later recovered after separation from insoluble impurities.
4. Organic compounds are separated by converting them in to their derivatives by adding reagents and recovered after removal of impurities.
5. Activated carbon removing colours and odours from organic compounds, e.g. butter absorbing the perfume of roses.
10.1.10 Separate alum from alum solution by crystallization
Common alum is aluminium potassium sulfate.
Add a finger width of alum to a quarter of a test-tube of hot water.
Shake the test-tube to dissolve the alum.
Keep shaking until no more alum will dissolve and some alum remains on the bottom of the test-tube.
Pour a finger width of this hot saturated solution into the evaporating basin and leave to cool for a few hours.
Note the shape of the alum crystals.
They form diamond-shaped double pyramids.
Store and label the dry alum crystals.
Repeat the experiment using magnesium sulfate instead of alum.
Store and label the dry magnesium sulfate crystals.
Repeat the experiment using sodium carbonate instead of alum.
Store and label the dry sodium carbonate crystals, washing soda.
10.1.11 Separate copper carbonate and magnesium sulfate mixture
Mix solid copper carbonate with magnesium sulfate crystals.
Put the solid chemicals on a folded piece of clean paper and mix them with a spatula.
Pour the mixture into a test-tube.
Add hot water and stir the mixture to dissolve the magnesium sulfate.
Filter the mixture to form a residue of copper carbonate on the filter paper.
Wash the residue on the filter paper and leave to dry.
Evaporate the filtrate of magnesium sulfate solution to form magnesium sulfate crystals.
Store and label the dry magnesium sulfate crystals.
10.1.12 Separate soluble from insoluble substances
Shake a mixture of sand and sodium chloride in a test-tube containing water.
Filter the mixture into an evaporating basin.
Heat the filtrate to form sodium chloride crystals.
Sodium chloride, the solute, dissolves in water, the solvent, to form a solution.
Sand is insoluble in water.
Repeat the experiment with a mixture of ammonium chloride and sulfur.
The sulfur is insoluble in water.
The ammonium chloride is soluble in water and can be recovered by filtration and evaporation of the filtrate.
10.1.13 Separate dirt from dirty water with charcoal
Make dirty water by adding to muddy water drops of: methyl orange, aqueous ammonia solution, calcium nitrate solution, barium sulfate (VI) solution.
Wash sand with tap water then deionized water.
Put washed sand on filter paper in a filter funnel.
Filter the dirty water through the sand.
Mix dirty water with powdered wood charcoal or animal charcoal.
Filter the mixture through a filter paper in a filter funnel.
Compare the sand filtrate with the charcoal filtrate.
Note the presence of clay particles, look for cloudiness.
Note the presence of methyl orange, look for colour.
Note the presence of ammonia, smell the pungent odour.
Test with moist litmus paper.
Note the presence of Ca2+.
Ammonium ethanedioate-1-water (ammonium oxalate) forms a white precipitate.
Note the presence of SO42-.
BaCl2 solution forms a white precipitate.
10.2.1 Chromatography of chlorophyll pigments
Chloroplasts derive their colour from several pigments (carotenes, xanthophylls and chlorophylls), which are present in differing amounts, the proportions varying with species.
You can separate them by paper chromatography.
1. Cut grass into small pieces and place them in a mortar.
Add sand, 40 mL methanol and 5 mL petroleum benzene and grind the mixture vigorously for two minutes with the pestle.
Pour a few mL of the bright green solution of crude chlorophyll obtained into a test-tube.
Add 1 mL of deionized water and shake well.
Leave the test-tube to stand.
Most of the pigment passes into the petroleum benzene layer that settles on top of the diluted methanol.
2. Heat the centre area of a hollow glass tube in a Bunsen burner flame while rotating the tube slowly.
When the central area is sufficiently soft, move your hands away from each other to draw out the hot glass in the middle to form a fine capillary tube.
After cooling, snap the capillary in two at the centre, thus producing two small pipettes with very finely drawn tips called Pasteur pipettes.
Use one pipette to take a sample of the petroleum benzene containing the crude chlorophyll layer settled in the upper part of the test-tube.
Apply the sample in a line 2 mm wide to a strip of chromatographic paper so that the line is parallel to and 2 cm from the narrow edges of the strip.
The coloured line should not touch the edges of the chromatographic strip.
Prepare more applications to ensure that you have put enough pigment on the paper.
Let the solution dry after each application to prevent the coloured line from spreading too widely.
Leave to dry.
3. Pour eluting solvent to a height of 2 cm into a measuring cylinder.
Fix the chromatographic strip between the two halves of the vertically cut cork and suspend it inside the cylinder.
Push the strip far enough down so that you immerse 1 cm of its lower end in the eluting solvent, but keep the line of pigment above the solvent level.
The strip must not touch the inside wall of the cylinder, otherwise, the reagent will not rise evenly.
Seal the measuring cylinder with a stopper so that the atmosphere surrounding the chromatographic strip is saturated with the vapour of the eluting solvent.
Watch the solvent rising up the chromatographic strip.
After 15 minutes, remove the strip from the cylinder, mark the height reached by the solvent with a pencil line and allow the strip to dry in air.
Note the different bands of colour and their pattern of distribution.
Carotene is orange yellow, xanthophyll is lemon yellow, chlorophyll a is blue green and chlorophyll b is yellow green.
Use a pencil to outline and label the different bands of colour.
Chlorophylls decompose on exposure to light, so do this experiment in the shade.
10.2.2 Detect a forgery
Write a cheque for one dollar ($1).
Use a different pen with the same colour ink to change the amount to one million dollars ($1 000 000).
Dip the edge of the cheque in chromatography solution.
The ink from the 1 behaves differently from the added zeros!
Arrest the forger!
10.2.3 Separate by chromatography, "colour writing"
Chromatography, "colour writing", is used for chemical analysis and separation.
Chromatography uses the property that some chemicals have preferential adsorption on the surface of other materials.
So chemicals absorbed at different rates can be separated.
Different substances or different components move at different speeds through a strip of wet paper, a gel, or a gas.
To separate colourless substances, spray a locating agent on the paper to colour the separated spots.
During chromatography, a mixture of different solutes, the moving phase, pass over an absorbing medium, the stationary phase.
Different solutes tend to stay longer or shorter in the moving phase.
In paper chromatography, the paper and solvent adsorbed to the paper is the stationary phase.
In thin layer chromatography, the stationary phase is a layer on a plastic or glass plate.
In column chromatography, the stationary phase substance is packed in a tube.
Experiments
1. Separate by column chromatography.
Use a piece of white chalk as a column.
Draw a line around the chalk 2 cm from the larger end with mixed ink made up of red and blue ink in equal quantity.
Turn this end upside down and let the chalk stand in a Petri dish containing water with the ink line being above the water level.
The water acts as a developing agent.
The water is drawn up the column and raises the mixed ink.
The red component of the mixed ink moves up faster than the blue component.
The component colours of the mixed ink are separated to produce two different coloured bands with red above and blue below.
2. Use a test-tube with a small hole in the bottom blocked by a plug of cotton wool.
Fill the test-tube with powdered chalk packed down lightly with a pencil.
Pour drops of an equal mixture of ink and water on top of the chalk column.
The ink mixture moves down the column producing different coloured bands.
This set of coloured bands is a chromatogram.
Each band represents a component of the ink.
10.2.4 Separate by chromatography, green leaf pigments
See diagram 3.2.24: Chromatography.
1. Collect green leaves and cut them into very small pieces.
Use a mortar and pestle to grind the leaves for five minutes with a small volume of methylated spirits and clean sand until a deep green solution forms.
Draw a fine pencil line 5 cm from the end of a 1 cm wide strip of absorbent paper (or chromatography paper).
Suspend the absorbent paper in a test-tube without touching the bottom.
Use a fine eye-dropper to put one small drop of the solution on the centre of the fine pencil line and let it dry.
When the drop is dry add more solution to the same place to make a small concentrated spot of 5 drops.
Hang the paper strip with the lower end in the methylated spirits solvent and the spot of green solution above the solvent level.
Leave the paper strip in the solvent until the methylated spirits has almost reached the top of the absorbent paper.
Capillary attraction draws up the solvent.
Mark the chromatogram on the paper to show a top orange-yellow band of xanthophyll and a lower green band of chlorophyll.
A band of carotene is visible if the solvent is toluene.
2. Repeat the experiment with other solvents, e.g. toluene, acetone (propanone).
10.2.5 Separate by chromatography, mixed inks
Prepare a mixed solvent from 6 parts of water, 3 parts of methylated spirits, and 1 part of ammonia solution.
Put 5 mL of mixed solvent in a test-tube.
Prepare mixed ink from equal quantities of red and blue ink.
Put a drop of the mixed ink near one end of a 2 cm wide paper strip.
Lower the paper strip so that its lower end is in the mixed solvent.
Use a stopper to prevent evaporation.
As the solvent moves up the paper strip, the component colours of the ink separate to form different coloured bands with red above and blue below.
Try other solvents and other inks to obtain good separation of colours.
Repeat the experiment by drawing a line with a ball pen or an ink pen near the end of the paper strip.
10.2.6 Separate amino acids with paper chromatography
See diagram 10.2.2.5: Separate amino acids by paper chromatography.
See 1.13a: Simple fume hood.
To prepare the following amino acid standards, make a 0.5% hydrochloric acid solution:
Dissolve 96 mL of concentrated hydrochloric acid (36% w / v HCl) in deionized water and make up to 2 Litres.
Use this solution to prepare standard solutions in 500 mL volumetric flasks and transfer 50 mL for storage:
Solution a1, 0.05 M Glycine: Dissolve 1.88 g of glycine in the 1.5% HCl solution and make up to 500 mL.
Solution a2, 0.05 M Tyrosine: Dissolve 4.53 g of tyrosine in the 1.5% HCl solution and make up to 500 mL.
Solution a3, 0.05 M Leucine: Dissolve 3.28 g of leucine in the 1.5% HCl solution and make up to 500 mL.
Solution a4, 0.05 M Aspartic acid: Dissolve 3.32 g of aspartic acid in the 1.5% HCl solution and make up to 500 mL.
Be careful!
Use safety glasses and nitrile chemical-resistant gloves.
Transfer 3 drops of solutions a1, a2, a3 and a4 to 4 test-tubes labelled a1, a2, a3 a4.
Transfer one of the unknown solutions c1 to c8 to a fifth test-tube labelled "unknown".
Draw a light pencil line parallel to and 1.5 cm from the bottom of a 12 × 22 cm sheet of Whatman No. 1 filter paper.
Draw 10 light crosses 2 cm apart along this line and label them a1, a2, a3, a4, and unknown.
Use a capillary tube spotter to make < 2 cm spots of solutions a1, a2, a3, a4, and unknown on the line on the filter paper.
Leave the filter paper to dry then roll into a cylinder and staple the ends together to form the edge.
Put the paper cylinder in the beaker of aqueous 2-propanol solvent, cover with aluminium foil.
Leave to allow the solvent to rise up the paper until it almost reaches the top edge.
Remove the paper cylinder and leave it upside down in the fume cupboard to dry.
Remove the staples and hang the sheet of filter paper it in a fume cupboard, fume hood.
10.2.7 Separate aspirin, caffeine and paracetamol by thin layer plate chromatography
See diagram 10.2.2.5: Separate amino acids by paper chromatography.
Chromatography plates have a layer of silica gel as adsorbent, calcium sulfate as binder and a fluorescing agent to aid location of the sample by ultraviolet illumination.
1. Prepare the following solvent mixture: butyl acetate / dichloromethane / 85% formic acid.
Mix 1200 mL of butyl acetate, 800 mL of dichloromethane, and 200 mL 85% of formic acid.
Store in Kipp's apparatus in a fume cupboard.
Label four test-tubes f1 (aspirin) f2 (caffeine) f3 (paracetamol) f4 (mixture consisting of equal volumes of aspirin, caffeine and paracetamol).
Use a capillary tube spotter to make < 2 cm spots of solutions of f1, f2 and f4 parallel to and 1.5 cm from the bottom of the chromatographic plate.
Make a similar plate with f3 and f4.
Develop the plates using the solvent mixture butyl acetate / dichloromethane / formic acid.
Leave to allow the solvent to rise up the paper until it almost reaches the top edge.
Remove, dry, examine the plates under ultraviolet light (short wavelength, 254 nm, e.g. germicidal lamp).
Mark the position of the samples and of the solvent fronts.
Record the Rf values as in the previous experiment.
2. Repeat the experiment with ground tablets or powders of analgesics using previous plates as reference samples.
Construct a results table:
Table 10.2.2.6
Product aspirin caffeine paracetamol (phenacetin)
Codiphen yes or no yes or no yes or no (yes or no)
Veganin yes or no yes or no yes or no (yes or no)
Panadeine yes or no yes or no yes or no (yes or no)

10.2.8 Separate food colours in coloured sweets by chromatography
1. Use this method for sweets where the colour is dispersed through the sweet, e.g. jelly beans.
This method uses white thread to separate the extracted dye from the extracted sugar.
This method extracts only acid dyes.
Prepare white woollen thread: Use 1 metre of prepared wool for each colour of the jelly beans.
Boil one metre of white woollen thread for 10 minutes in 2% ammonia solution, rinse under the tap to remove fluorescing dyes, then dry.
Add 25 mL of warm water to 5 jelly beans of each colour in 5 different containers and leave to stand until they look white.
The solutions now contain dye and sugar, which can be separated by dyeing the wool.
For each colour, put a 1 metre piece of prepared white woollen thread in a 100 mL beaker and add the dye extract.
Add 3 drops of 0.1 M acetic acid.
Heat until boiling and simmer for 5 minutes.
Remove the dyed wool and wash gently under the tap until no stickiness remains.
Re-extract the dye from the wool by placing it in a beaker containing 20 mL of 2% ammonia solution and simmer for 5 minutes.
Remove the wool from the beaker.
Evaporate the extract in the beaker to dryness on a hot plate in a fume cupboard.
Ammonia will be given off.
Dissolve the dry residue, with constant stirring, in the minimum number of drops of water to maintain high concentration.
Use a capillary tube spotter to make < 2 cm spots of solutions of each colour.
Use the following solvent mixture: butanol: ethanol: 2% ammonia, in a 3: 1: 1 ratio.
2. Use this method for sweets where the colour is only on the outside layer of the sweet, e.g. "Smarties".
Wet the surface of the sweet then rub it directly on chromatography paper.
To simplify the separation, dip the paper in 1% sodium chloride solution to reduce the electrostatic attractive forces between the dye and paper molecules.
Use a capillary tube spotter to make < 2 cm spots of solutions of each colour.
Use the following solvent mixture: butanol: ethanol: 2% ammonia, in a 3: 1: 1 ratio.
10.2.9 Separate methyl orange and litmus mixture by chromatography
Mix methyl orange powder and twice as much litmus powder.
Put the powders on a folded piece of clean paper and mix them with a spatula.
Put the mixture into a test-tube, add water to the half way mark, and shake well to dissolve the powders.
Allow any excess powder to settle then pour off part of the liquid into another test-tube.
Place a filter paper on an evaporating basin.
Use an eye dropper to let drops of the liquid fall one drop at a time on the centre of the filter paper.
After a drop has spread, add another drop.
Repeat the process for four drops.
Let the liquid spread outwards.
Note whether the two substances separate.
The litmus moves through the filter paper more quickly than the methyl orange, so it forms a blue ring outside the central orange area.
The substances separate into blue and orange areas on the filter paper.
Repeat the experiment with a mixture of four drops of green food dye and six drops of pink food dye, e.g. cochineal, in half a test-tube of water.
Mix the dyes by shaking the test-tube.
Use an eye dropper to let drops of the liquid fall one drop at a time on the centre of the filter paper.
Let the liquid spread outwards.
Note whether the two substances separate.
The colours separate into a green area surrounded by a pink ring.
Repeat the experiment with only blue-black ink.
10.3.01 Separate by distillation
Distillation separates a liquid from a solution of a solid in that liquid.
In distillation, a liquid evaporates in a still and then condenses in another container as the distillate.
10.3.1 Distil copper (II) sulfate solution
Pour concentrated copper (II) sulfate solution into a distillation flask.
Add some pieces of porous pot to prevent bumping.
Stand the distillation flask on wire gauze and heat gently.
Turn on the tap water so that it flows upwards through the condenser.
Liquid condenses in the condenser and collects in the receiving flask.
Note the temperature with the bulb of the thermometer level with the sidearm.
Measure the boiling point of the distillate.
The boiling point of the distillate is less than the boiling point of the original solution.
Repeat the experiment with the distillate.
When the distillate is more pure than the original liquor, the boiling point will be less.
10.3.2 Distil essences from leaves and flowers
Eucalyptus oil contains eucalyptol, 1,8-cineole.
It has medical properties and is a disinfectant.
It decomposes at BP 176oC so you can improve the method below by passing steam over the leaves instead of boiling.
Use a distillation flask condenser and round bottom flask.
Select eucalyptus leaves with large oil glands.
Put the leaves in the flask with water.
Heat the flask gently and collect the distillate in the round bottom flask.
Note the oils floating on the water in the distillate.
Distil the oils again to make a perfume.
Repeat the experiment with other plant parts, e.g. dried cloves, camphor, laurel leaves, bay leaves, fennel, peppermint, lavender, caraway, parsley, tea tree.
10.3.3 Distil ink
1. Put ink in a boiling tube.
Add anti-bumping granules, (boiling chips).
Fit a stopper with a delivery tube to the container.
Fit a delivery tube to connect to a collecting test-tube.
Keep the collecting tube cool.
Heat the ink gently.
Do not let the ink froth or splash into the delivery tube.
Colourless liquid appears in the collecting tube.
Test the distillate for the presence of water with blue cobalt (II) chloride paper.
2. Put 10 mL ink in a flat bottom conical flask.
See diagram 3.20.1: Distil ink to form water.
Add boiling chips to prevent bumping.
Fit a stopper with a delivery tube reaching half way down a collecting test-tube or an U-tube, in a beaker of water.
Heat the ink with a Bunsen burner flame.
Drops of a colourless liquid appear in the collecting tube.
Identify the liquid as water by its action of turning white anhydrous copper (II) sulfate to blue hydrated copper (II) sulfate.
Do not allow ink to froth up or splash into the delivery tube.
10.3.4 Distil sea water
Heat a test-tube containing sea water until it boils.
Hold a second test-tube full of cold water over the mouth of the first test-tube.
Water vapour condenses on the second test-tube.
Test the distillate for the presence of water with blue cobalt (II) chloride paper.
Evaporate 4 drops of each of the sea water and the condensed water on clean watch glasses.
Compare the results.
10.3.5 Separate gases dissolved in a water sample
See diagram 3.2.25: Gas released from water.
Fill a round bottom flask to the top with tap water and insert a stopper with a delivery tube and collecting test-tube completely filled with water.
Insert the stopper while holding the whole apparatus under water.
Heat the flask with a Bunsen burner.
Bubbles of gas are released from the water and travel into the collecting test-tube.
Continue heating until the water in the flask is boiling.
You can collect about half a test-tube of gas from a litre of water, displaced from solution by heating.
10.3.6 Separate by fractional distillation
1. Put anti-bumping granules in the filter tube.
Use a dropper to put 4 mL of crude oil in the bottom of the test-tube, not on the sides.
Clamp the tube at an angle and insert the stopper with a thermometer.
Adjust the thermometer so that the bulb is opposite the side arm.
Attach a delivery tube made of clear PVC tubing and clamp the collection test-tube in place.
Gently heat the bottom of the test-tube containing the oil.
BE CAREFUL! USE AN ELECTRIC HEATER.
DO NOT USE A BUNSEN BURNER!
Use collection test-tube 1 to collect the fraction that comes over below 70oC.
Use collection test-tube 2 for the fraction that distils in the range 70o-120oC.
Use collection test-tube 3 for the range 120o-170oC.
Use collection test-tube 4 for the range 170o-220oC.
Pour the contents of each fraction on a watch glass.
The ease of flow of the sample into the test-tube is a measure of the viscosity.
Note the relationship of viscosity to collection temperature.
Note the colour of each oil fraction.
Try to ignite each fraction with a small tuft of cotton wool held in tongs. BE CAREFUL!.
See diagram 10.6.3.2: Petroleum fractions
2. Use eye protection and disposable plastic gloves.
Put glass wool into the bottom of a hard glass boiling tube.
Be careful! Do not touch glass wool with your fingers.
Drop 3 mL of petroleum onto the glass wool.
Do this very carefully so that all the drops hit the glass wool and none hit the sides of the test-tube.
3. Heat the boiling tube gently with a small Bunsen burner flame while moving it from side to side.
Collect the distillate between room temperature and 100oC in a receiving test-tube sitting in ice and water in a beaker.
Put a stopper on the receiving test-tube and label it: Fraction 1.
Repeat the procedure by heating the hard glass test-tube more strongly to Fraction 2 boiling between 100oC and 150oC, Fraction 3 boiling between 150oC and 200oC, and Fraction 4 boiling between 200oC and 250oC.
Turn off the Bunsen burner and leave the apparatus to cool.
4. Test the four petroleum fractions.
* Compare the colour of similar volume fractions.
* Compare the viscosity of similar volume fractions by tilting the test-tubes down through the same angle.
* Compare flammability by placing a watch glass on a heat-resistant mat, adding 5 drops of a petroleum fraction and igniting the fraction with a glowing splint.
After igniting the fractionm, do not add more of the fraction to the watchglass.
If the fraction does not ignite, use a cotton wool bud as a wick to absorb the fraction and try to light the soaked cotton wool, .
Record how easily the fraction ignites, the colour of the flame and how much soot (carbon) is in the flame.
5. Compare the properties of the fractions and how the properties change with temperature range of the fractions.
10.3.7 Separate water from copper sulfate solution by distillation
See diagram 10.01.9: Distillation.
Insert one end of a bent glass tube through a one-hole stopper.
Be careful! Attach rubber tubing to the other end of the bent glass tube.
Wet the bent glass tube before sliding on the rubber tubing.
Attach the one-hole stopper to a test-tube a quarter filled with copper sulfate solution.
Heat the solution, using a test-tube holder.
Keep the test-tube moving about over the flame so that the liquid does not suddenly boil and shoot up into the test-tube.
Do not look down the test-tube to see what is happening!
Heat until the liquid is slightly boiling and let it simmer for five minutes.
Do not boil the solution dry.
Collect a small quantity of water in a second test tube by the condensation of the steam.
Do not taste the water collected.
The top of the flame should then be a few centimetres below the bottom of the test-tube, which can be raised and lowered.
Repeat the experiment using ink instead of copper sulfate solution.
10.3.8 Catalytic cracking of kerosene
See diagram 10.6.4: Catalytic cracking of kerosene.
Pour 5 mL of kerosene (paraffin oil) into a Pyrex test-tube.
Put a loose plug of steel wool in the middle of the tube to act as a catalyst.
Attach the test-tube to a stand so that separate burners can heat the oil and the steel wool.
Insert a one-hole stopper with a short tube into the test-tube.
To collect the gases over water, attach the short tube to a delivery tube leading to a container of water.
Heat the oil and not the steel wool.
Collecting the gaseous distillate.
The distillate does not decolorize bromine water or dilute potassium permanganate, because it does not contain unsaturated hydrocarbons.
Preheat the steel wool and then heat the oil.
The vapours from the oil pass over the steel wool that acts as a catalyst.
The distillate decolorizes bromine or dilute potassium permanganate solution, so unsaturated hydrocarbons are in the products of cracking the hydrocarbons in kerosene.
10.3.9 Distil crude oil and collect the fractions
Crude oil can be heated to about 400oC, so that the vapours rise through a tall fractionation column where different fractions are drawn off.
Higher boiling fractions can be converted to lower boiling point fractions by use of silica and aluminium catalysts in a process called catalytic cracking,
For example: C10H22 --> C5H12 + C5H10
Lower molecular weight hydrocarbons undergo alkylation, (adding or substituting an alkyl group) to form larger hydrocarbons with similar boiling point to gasoline
For example:. C2H6 + C4H8 --> C6H14
In the alkylation of benzene, Friedel-Crafts reaction, benzene reacts with chloromethane to substitute a CH3 group for H and form methyl benzene (toluene).
The reaction does no stop there.
C6H6 + CH3Cl --> C6H5CH3 + HCl
benzene + methyl chloride --> methyl benzene + hydrochloric acid
See diagram 10.6.3: Distillation.
Combustion of gasoline
2C8H18 (l) + 25O2 (g) --> 16CO2 (g) + 18H2O (g)
Table 10.6.3 Petroleum fractions
Boiling temperature Fraction Name of fraction
20oC to 60oC 1 Petroleum ether (benzene)
60oC to 100oC 2 Light naphtha
100oC to 205oC 3 Gasoline range
205oC to 275oC 4 Kerosene range
275oC to 325oC 5 Higher temperature fractions

10.3.10 Steam distillation of eucalyptus leaves
Eucalyptol (1,8-cineole), oil of cloves, eugenol
1. The oil from eucalyptus leaves contains eucalyptol (1,8-cineole).
It is useful in cough drops and medicated soaps and it is an effective disinfectant.
The oil decomposes when boiled, BP 176oC, so use a steam distillation apparatus where the temperature of the oil never exceeds 100oC and the oil is not destroyed.
The amount of oil carried over with the steam depends the volatility of the oil.
2. Repeat the experiment to produce oil of cloves, eugenol, BP 164oC, from dried cloves.
10.3.11 Steam distillation to measure water and fat content of food
See diagram 10.5.5: Steam distillation apparatus.
| See 1.13a: Simple fume hood.
An azeotropic mixture has a boiling point that does not change when vapour is removed by evaporation.
The boiling point may be higher or lower than any of the components of the mixture, e.g. A toluene / water mixture has BP. 85.0oC.
However, BP. toluene is 110.6oC and BP. water is 100.0oC.
Steam distillation is used to separate volatile from non-volatile components and the reduction in boiling point reduces thermal decomposition.
For the toluene-water system, below 85oC the two liquid phases coexist.
At 85oC the sum of the vapour pressures of water and toluene = one atmosphere, and boiling starts.
In a mixture of toluene and water, boiling occurs at 85oC and both water and toluene are in the vapour that condenses to form two layers.
The bottom layer of water has 0.06% toluene dissolved in it.
The top layer of toluene has 0.05% water dissolved in it.
The relative volumes are 18% water and 82% toluene.
The excess toluene flows back into the flask and distils back over with more water.
At 85oC, vapour pressure of water = 57.7 kPa and vapour pressure of toluene = 50.6 kPa.
Weight of water = (molar mass water / molar mass toluene) × (vapour pressure water / vapour pressure toluene) = (18 / 92) × (57.7 / 50.6) = 0.223 = 20%.
Be careful! Do experiment in a fume cupboard, fume hood, because toluene vapour is harmful.
You can substitute less harmful cyclohexane for toluene.
However, it is less efficient, carrying over only 8.5% water.
Use the apparatus to find the amount of water and fat in food
For example: minced meat for hamburgers 13% fat and 67% water, minced meat for sausages 26% fat and 47% water.
1. Water content
Distil 20 g minced meat or chopped cheese with 80 mL of toluene until no more water distils over at 110.6oC.
Weigh the bottom layer of water.
2. Fat content
Pour the remaining toluene from the flask into a pre-weighed beaker.
Add more toluene to the food in the flask and shake the flask vigorously to extract all the fat.
Add this toluene to the beaker.
Evaporate all the toluene under a fume cupboard, fume hood using a water bath and vacuum pump to leave the fat in the beaker that can be weighed.
10.4.1 Separate by shaking different liquids in water
See diagram 3.2.26: Shake different liquids in water
Add to separate test-tubes containing 10 mL of water, 1 mL of the following: methylated spirit, glycerol (glycerine, propane-1,2,3-triol) kerosene (paraffin oil).
Shake each test-tube.
Methylated spirit and glycerol dissolve in water.
The solution of kerosene in water becomes cloudy, because of the formation of an emulsion.
Mix pairs of substances and note whether a solution forms:
| sodium chloride and kerosene | olive oil and water | gasoline (petrol) and water | gasoline and olive oil | gasoline and kerosene | ethanol and copper|
(II) sulfate-5-water crystals, kerosene and petroleum jelly.
Pour each mixture into a separating funnel.
Try to recover the original liquids.
10.5.0 Separate by froth flotation of heavy minerals
This method is often used in mineral mining to separate crushed ores from other rock materials.
1. Mix crushed ores or a mixture of sand and powdered metal with water.
Add an oil such as kerosene.
Blow air through the mixture to form froth.
The metal-containing mineral particles or powdered metal particles become covered with the oil, because of attraction of the oil for them.
The particles stick to the air bubbles that floating on the surface along with the rising froth.
The water wets the gangue particles or sand particles and they sink to the bottom, separating the mineral or metal from the mixture.
2. Mix crushed lead sulfide (galena) or fine iron filings or zinc dust or red lead oxide with dry garden soil in a measuring cylinder.
Add water and kerosene (paraffin oil).
Close the end of the measuring cylinder with the hand shake vigorously for two minutes then leave it to stand.
The fine metal particles have been separated from the soil by the froth of kerosene.
10.6.0 Separate by heating, gases dissolved in water
See diagram 3.25: Gases dissolved in a water sample.
The higher the temperature of a solutions, the less a gas dissolves, if it does not react with the solvent.
1. Stand a container of water in sunlight.
Bubbles of air appear.
The taste of boiled water is different from the taste of tap water, because boiled water has lost its dissolved oxygen.
Note the temperature of a sample of water.
Boil the water until no more bubbles appear.
Collect the gases from the water in an inverted measuring cylinder.
2. Fill a round bottom flask to the top with tap water and insert a stopper with a delivery tube and collecting test-tube completely filled with water.
Insert the stopper while holding the whole apparatus under water.
Heat the flask with a Bunsen burner.
Bubbles of gas are released from the water and travel into the collecting test-tube.
Continue heating until the water in the flask is boiling.
Collect about half a test-tube of gas from a litre of water, displaced from solution by heating.
10.6.1 Separate a mixture of ethanol and water
See diagram 10.6.1: Fractionation.
Use a mixture of methylated spirit and water.
When you heat the mixture gently, the ethanol, boiling point 78oC, will boil first and condense first.
Use of a fractionation column allows water to condense on it and drip back.
When all the alcohol has evaporated, the temperature rises suddenly and the remaining water will evaporate.
10.8.0 Separate two solids using density differences
In industry, a separator concentrating machine shakes mixed ores to separate the different ores.
Beach sand often consists of quartz particles mixed with heavier particles, e.g. ilmenite or zircon.
Shake a mixture of sand and iron oxide to make them separate into different layers.
10.8.1 Separate sand and lead powder mixture by panning
This method is used to "pan" for gold.
Gold miners use "panning" to separate the more dense alluvial gold from the less dense "washings".
They use a rusty metal dish so that the gold shows up against the colour of rust.
Note this type of separation on sea beaches.
Incoming waves carry a mixture of materials up on to the beach.
The slower back flow carries back the lighter materials, but leaves the heavier materials.
This process can naturally concentrate minerals to form "mineral sands" with high concentrations of minerals with high molecular weights.
Put a mixture of sand and lead powder in a shallow tin pan with water.
Separate the sand from the lead by swirling the material in circles while holding the pan at an angle to the horizontal.
Strand the lead powder in the higher part of the pan.
10.9.0 Separate by recrystallization
Crystallization involves the formation of a pure solid from its solution.
Make a saturated solution of the material in a hot solvent and let the hot solution cool.
When the impurity is present in large amounts, the liquid becomes saturated with both materials and does not separate them.
10.9.1 Separate a mixture of sodium chloride and sodium nitrate
Dissolve sodium chloride in 20 mL of water at 70oC, until the solution is saturated.
Add sodium nitrate until no more dissolves.
Boil the solution filter and cool.
Sodium nitrate is much more soluble than sodium chloride in hot water, so, on cooling, more sodium nitrate than sodium chloride crystallizes out as the solution cools.
The crystals can dissolve again and cool again.
Each time this is done the sodium nitrate becomes more pure.
10.10.0 Separate to metals by reduction of metal oxides, charcoal blocks.
1. Ores are deposits of compounds that contain metals.
Ores occur naturally in the ground.
Metals or minerals are extracted from ores by different processes leaving behind the waste material gangue (called "gang").
Leaching extracts minerals by dissolving in a chemical, e.g. sulfuric acid or sodium hydroxide.
Groundwater may be contaminated by chemicals leached from mine tailings or refuse.
2. Use charcoal blocks to demonstrate reduction reactions.
Ensure that students have any long hair confined before blowing air through a blowpipe onto a Bunsen burner flame.
Use a clean flexible tube attached to the blow pipe to avoid having to lean close to the Bunsen burner and blocks.
Ensure that blow pipes are washed between student use to prevent transfer of diseases.
3. Do not reduce oxides of toxic metals such as mercury, lead, cadmium, nickel, arsenic or antimony, because students may inhale fine particles.
10.11.1 Separate by decanting
See 2.12: Decanting.
Decant, pour off liquid and not disturb underlying sediment.
Decanting separates the precipitate by inclining the test-tube or other container so that the level of the liquid rises above the level of the lip of the container so that it can be poured off the precipitate.
Formerly, wine was decanted before drinking into a container called a decanter to separate organic particles formed during the maturation of ine, e.g. tartaric acid.
Another reason for decanting wine was to expose wine to the air to release favourable odours.
Shaking the wine to allow more access to air may result in unfavourable oxidation products.
Nowadays, there is less need or no need to decant wine before drinking it, because of the use of the Stelvin capsule and modern methods of filtration.
The "damp cardboard" taste of corky wine is caused usually by 2,4,6-Trichloroanisole, Cl3C6H2OCH3, (2,4,6-TCA) mould.
It is produced by Trichoderma and Fusarium strains of fungi in contact with chlorine used to bleach corks, from the bark of the cork tree, Quercus suber, Fagaceae.
The waiters in high class restaurants will smell the cork before first pouring the newly-opened wine to detect any unpleasant odours.
The taint taste of 2,4,6-TCA may also cause the "Rio" defect in South American coffee and affect beer, sake and fish and prawns.
The wine cork is being replaced by screw-top caps to seal wine bottles, e.g. the Stelvin capsule, "Stelvin Lux", that seals the bottle.
The Stelvin capsule is popular in only a few countres, i.e. Australia.
However, itt allows a very small amount of air to touch the surface of the wine to allow maturation.
Although the screw-top capsule prevents "corkiness", the taste of the wine may still be affected by excess exposure to the air if the cork is loose.
Excessive oxidation of wine may cause unpleasant odour and bad tastes Corked wines are usually stored horizontally to keep the cork moist and prevent cork shrinkage.
10.11.2 Separate by filtration
See diagram 2.14: Fold filter paper.
Filtration uses filter papers for chemical precipitates and sand for sewage precipitates.
Filtration allows the liquid to pass through the filter and restrain the solid particles on the filter.
Use coffee filters to strain cooking oil, line plant pots, apply polish, cover microwave bowls, protect packed glassware, clean mirrors.
Use paper towels to make filters, strain fat from soup.
10.11.3 Separate by precipitation
See diagram 9.154: Limewater test for carbon dioxide in the breath.
Calcium hydroxide precipitates as a milky precipitate when breathing into limewater.
To precipitate is to cause a substance to be deposited in solid from a solution, so a precipitate is a solid substance separated from a solution.
The precipitate can be separated from the solution by decanting or by filtration.
10.11.4 Clarify muddy water by filtration and flocculation
1. Shake muddy water in a measuring cylinder and let it stand.
The larger particles separate first and the smaller and the lighter particles remain longer in suspension.
Decant the liquid containing the suspended particles and filter through filter paper.
Slowly heat the larger particle to dryness and leave the filter paper in the sun to dry.
Feel the larger particles and the smaller particles collected by the filter paper.
2. Shake muddy water in a measuring cylinder and let it stand.
Divide the suspension into two measuring cylinders.
Add 5 cc flocculating agent potash alum, Al2(SO4)3.K2(SO4).24H2O, [also shown as KAl(SO4)2.12H2O] to one of the measuring cylinders.
The treated water begins to clarify as the colloid particles begin to clump together, flocculate, and settle to the bottom.
Another flocculating agent used to clarify muddy water is SIROFLOC.
Muddy water contains soil held as a colloid.
During flocculation, charged ions gather around particles with opposite charge.
When colloids suspended in a solvent are no longer suspended in a solvent, they fall down to form a loose woolly mass, a flocculent.
Flocculation is used in water treatment and swimming pool management to separate out visible sediments, and treat colloids to remove them.
10.11.5 Separate by solubility, salt from salt and sand mixture
Prepare a mixture of salt and sand.
Put 2 mL of the mixture in a test-tube.
Add 5 mL of water and shake until all the salt has dissolved.
Pour the contents of the tube into a filter paper in a funnel over an evaporating basin.
Wash the test-tube with water and add this to the filter paper.
The sand will remain on the filter paper and may be dried and collected.
Recover the salt from the filtrate by warming the evaporation basinto drive off the water.
10.11.6 Separate with a simple centrifuge
Centrifuges rotate containers of liquids to separate suspended materials with different densities.
Centrifuges separate different components of human blood or milk and to clarify solutions.
The spin drier in washing machines is a type of centrifuge that throws out the liquid by the "centrifugal force" of the rotation.
Pour some muddy water into two test-tubes.
Put one test-tube into a sling and whirl it rapidly around the head.
Leave both test-tubes to stand and compare their contents.
The particles in the whirled test-tube precipitate faster.
Repeat the experiment with milk in the test-tube.
No precipitation forms.
However, a high speed separator can rotate at great speed and separate the fat from the milk to form the cream that rises to the surface.
10.11.7 Separate with paper towels
Use paper towels to remove candle wax from carpet with warmed iron over it, absorb excess oil from a sewing machine by stitching on it,
To absorb moisture as vegetable bin liner, strain fat from soup, prevent wet book pages from wrinkling, wipe desilked ear of corn for shucking,
To prevent stored iron pots from rusting, sprout seeds wrapped in Saran wrap before plantin, make coffee filters,.
10.12.0 Separate by solvent extraction of oil from peanuts
The solubility of oil in organic solvents may provide an access to extraction of oil from nuts.
Solubility may also be used to remove oil stains on clothes.
Alcohol, gasoline, dichloromethane and trichloroethane can be used as the solvents.
Experiments
1. Put ground nuts (peanuts) or pieces of chopped coconut into a mortar.
Add 20 mL of acetone or methylated spirit solvent.
Grind the nuts in the solvent as finely as possible for two minutes with the solvent.
Pour off the liquid into a test-tube and filter into an evaporating basin.
Warm the evaporating basin for 10 minutes.
BE CAREFUL! DO NOT HEAT THE MIXTURE DIRECTLY WITH A FLAME!
Leave the mixture in the sun or put it on top of a beaker of hot water.
Wait until the solvent evaporates leaving the oil extracted from the nuts.
The solvent evaporates leaving the oil extracted from the nuts.
2. Grind 5 g of peeled peanuts in a mortar with a pestle as finely as possible, and then transfer the ground peanuts to a beaker.
Add 15 mL of gasoline.
After stirring thoroughly, filter the resultant liquid and pour the filtrate into an evaporating dish.
Place the dish in the sun or put it on the top of a beaker containing hot water.
BE CAREFUL! DO NOT HEAT THE FILTRATE DIRECTLY WITH A FLAME!
The gasoline evaporates leaving the oil extracted from the peanuts.
10.13.1 Separate sodium chloride from iodine
See diagram 24.6.1: Heat evaporating basin.
1. Separate iodine from a mixture of crystals of iodine and sodium chloride.
Mix crushed iodine crystals with sodium chloride crystals.
Heat the mixture in an evaporating dish with a glass funnel placed on top of it.
The iodine sublimes on the cooler sides of the funnel.
2. Repeat with ammonium chloride and sodium chloride crystals.
10.13.2 Separate iodine from kelp
See diagram 13.15.3: Iodine extraction.
Iodine is one of the micro elements necessary for the human body.
Sea water contains about 0.000005% of iodine that can be absorbed and concentrated by some marine living beings.
There are 1000-4000 mg of iodine existing as iodides in kelp of per thousand grams.
Burning kelp gathers the iodides in ashes.
Decoct the ashes in water, acidify the resultant iodide solution and then evaporate it to dryness.
The follow up oxidation with potassium dichromate produces iodine, which is then separated by sublimation.
K2Cr2O7 + 6KI + 7H2SO4 --> 4K2SO4 + Cr2(SO4)3 + 3I2 + 7H2O
Weigh and cut 40 g of dried kelp into small pieces and put them in an iron vessel.
Burn the kelp chips with an electric heater in a fume cupboard until all the chips are completely turned into ash.
Transfer the ashes to a beaker, add 40 mL of deionized water, heat and boil the suspension, and add more water to make the filtrate 10 mL after filtering.
Add drop by drop dilute sulfuric acid (2 mol / L) to the filtrate until its value of pH becomes neutral.
Put the neutralized filtrate in an evaporating dish, evaporate it by heating to dryness.
The residues are parched and ground and uniformly mixed with 2 g of potassium dichromate.
Transfer the mixture to a dry tall beaker.
Stand a flask containing cold water on the mouth of the beaker.
On heating the beaker to sublimate the produced iodine, iodine vapour condenses on the cooler sides of the flask.
Stop heating when there is no violet red iodine vapour appearing any more.
Collect the obtained iodine crystals.
10.16.0 Separate mud and water from muddy water
Mix mud and water in a test-tube half full of water by shaking.
Put the test-tube in the test-tube rack.
This mixture of mud and water is a suspension, because the particles of mud are floating or suspended in the water, but not dissolved in it.
Place a filter funnel in another test-tube and insert a filter paper in the filter funnel.
Pour clean water into the filter paper to make it stick to the funnel.
Shake the suspension and pour it down a glass rod into the filter funnel.
The liquid that passes through the filter paper and collects in the test-tube is the filtrate.
Note whether the liquid is still muddy.
Describe what is left on the filter paper.
The filtrate should be clear water.
Mud is left on the filter paper, because the mud particles are too large to pass through the filter paper.
10.17.0 Separate miscible liquids by fractional distillation
See diagram 3.2.21: Fractional distillation.
Separate miscible liquids by fractional distillation if each liquid has a different boiling point.
The greater the difference in boiling points the easier to separate the miscible mixtures into pure substances.
A fractionation column is a long tube attached to the still containing intersections.
Some vapour condenses on the intersections.
The refluxing mixture of vapours and condensates in the column allows separation of different "fractions", i.e. liquids with different boiling points.
Distilling petroleum or mixtures of petroleum products may be too dangerous for most school science classes.
Use crude oil or a substitute for crude oil by used car oil, paraffin, thin lubricating oil, diesel oil and petroleum jelly.
1. Use crude oil or a substitute for crude oil, e.g. a mixture of used car oil, paraffin, thin lubricating oil, diesel oil and petroleum jelly.
Use a hard glass test-tube, or sidearm test-tube, fixed to a retort stand, a delivery tube and five small ignition tubes.
Use a 0o to 360oC thermometer.
Put 4 mL of crude oil in the test-tube.
Add boiling chips to prevent bumping.
Set up five small ignition tubes to collect the fractions.
Heat the oil very gently. Collect 10 drops of distillate in the first ignition tube, then collect 10 drops of distillate successively in the other ignition tubes.
The boiling point of the remaining oil will become higher as distillation proceeds and oil will then require more heat from the Bunsen burner.
2. Arrange the fractions in order of increasing distillation temperature:
* up to 80oC,
* 80oC to 120oC,
* 120oC to 180oC,
* 180oC to 220oC.
3. Examine the different fractions:
* The colour should change from colourless to yellow.
* The viscosity should increase.
* The high temperature fractions should be more difficult to ignite than the low temperature fractions.
* The high temperature fractions should burn with more soot in the flame than low temperature fractions.
* Burn the fractions in bottle tops with the cork removed and note the dark residue remaining in the test-tubes.
10.18.0 Separate iodine from a mixture of iodine and sodium chloride
See diagram 24.6.1: Heat evaporating basin.
Add iodine to sodium chloride in an evaporating dish.
Place the evaporating dish on a simple tripod stand.
Invert a large glass funnel then cover it on the evaporating dish.
Heat the evaporating dish with an alcohol burner.
Observe the iodine appearing on the taper side of the funnel and the colour of the remains at the evaporating dish.
Collect the iodine on the side of the funnel then put it into a small bottle.
10.19.0 Separate by melting points, tin from a tin and carbon mixture
Get tin bits by cutting a tin welding rod to pieces.
(66% of a tin welding rod is tin and the rest is lead.).
Do not use a "tin can", "beverage can", because it is mostly iron with a thin layer of tin on its surface!
Experiments
1. Make a mixture of tin (tin filings or small cut pieces of tin) (melting point 232oC), and carbon (crushed charcoal),
(melting point 3, 730oC.)
Mix the tin bits and charcoal bits uniformly.
Heat the mixture in a crucible.
Stir with a splint until the tin melts and forms a liquid below the charcoal.
Pour the tin onto a plaster of Paris mould or other heat-proof surface.
While pouring, hold back the charcoal in the crucible with a wood splint.
Use melting point and melting point behaviour to identify a substance and decide if it is pure.
Tin solder melts at 250oC.
Carbon melts at 3, 700oC.
2. Mix solder filings with powdered charcoal.
Heat the mixture in a crucible.
Stir with a splint until the solder melts and forms a liquid below the charcoal.
Pour the liquid into a container by holding back the charcoal in the crucible.
10.21.0 Separate by sublimation, naphthalene, iodine
Sublimation is the transition of a substance directly from the solid to the gas state without passing through the liquid state.
Naphthalene is made of non-polar molecules held together by van der Waals forces.
Solid naphthalene sublimes at standard atmospheric temperature at about 80°C.
Naphthalene vapours will solidify on cool surfaces form needle-like crystals.
Iodine produces fumes on gentle heating
However, it is not "true sublimation", because liquid iodine can form at atmospheric pressure if the temperature at just above the melting point.
10.22.0 Separate two immiscible liquids of different density
See diagram 3.26: Separation tube.
Separate two immiscible liquids of different density, e.g. kerosene(paraffin oil) and water.
Use a separating funnel or make a separating funnel with a piece of wide plastic tubing fitted with a one-hole stopper and rubber tubing with a clip.
Shake the mixture thoroughly in a closed container then run it into the separating funnel.
Wait until a clear boundary appears between the two liquids and then run off the more dense layer into a container below.
9.1.11 Cork taint of wine, "corky" wine
The "damp cardboard" taste of corky wine is caused usually by 2,4,6-Trichloroanisole, Cl3C6H2OCH3, (2,4,6-TCA) mould.
It is produced by Trichoderma and Fusarium strains of fungi in contact with chlorine used to bleach corks, from the bark of the cork tree, Quercus suber, Fagaceae.
The waiters in high class restaurants will smell the cork before first pouring the newly-opened wine to detect any unpleasant odours.
The taint taste of 2,4,6-TCA may also cause the "Rio" defect in South American coffee and affect beer, sake and fish and prawns.
The wine cork is being replaced by screw-top caps to seal wine bottles, e.g. the Stelvin capsule, "Stelvin Lux", that seals the bottle.
The Stelvin capsule is popular in only a few countres, i.e. Australia.
However, it allows a very small amount of air to touch the surface of the wine to allow maturation.
Although the screw-top capsule prevents "corkiness", the taste of the wine may still be affected by excess exposure to the air if the cork is loose.
Excessive oxidation of wine may cause unpleasant odour and bad tastes.
Corked wines are usually stored horizontally to keep the cork moist and prevent cork shrinkage.
Brandy
However, fortified wines, e.g. sherry and port, have brandy, a strong spirit distilled from wine, added before fermentation is complete, leaving some residual sugar in the wine, because the remaining yeast is killed by the extra alcohol from the added brandy.
The alcohol content may rise from 10 -13% in wine to 16-20% in port.
However, Madeira fortified wine is said to taste better if it is slightly oxidized, so it traditionally stored upright to avoid any corky taste, yet allow some oxidation.