School Science Lessons
Topic 10 Separation of substances, chemical and physical separation
2012-01-25 SP
Please send comments to: J.Elfick@uq.edu.au
See: Interesting websites
Table of contents
10.0.0 Separation of substances
10.1.0 Separate by adsorbing impurities
10.2.0 Separate by chromatography
10.5.0 Separate by distillation
10.6.0 Separate by fractional distillation
10.8.0 Separate by froth flotation of heavy minerals
10.9.0 Separate by recrystallization
10.10.0 Separate by reduction of metal oxides to metals, charcoal blocks
10.11.0 Separate by sedimentation and filtration
10.3.0 Separate by solubility of soluble substances from insoluble substances
10.12.0 Separate by solvent extraction
10.13.0 Separate by sublimation
10.01 Separate pure substances, linked experiments
10.4.0 Separate immiscible liquids in a mixture
10.7.0 Separate substances with different melting points
3.31.3 Tests for water with cobalt (II) chloride
10.01 Separate pure substances, linked experiments
10.01.3 Filter milk
10.01.2 Prepare copper carbonate from copper sulfate and sodium carbonate
10.01.10 Prepare alum from alum solution by crystallization
10.01.1 Separate muddy water into mud and water
3.18.0 Separate substances from mixtures:
10.01.4 Separate suspension of coloured blackboard chalk by filtration
10.01.5 Separate salt from salt water by evaporation
10.01.6 Separate ammonium chloride from its solution
10.01.7 Separate a mixture of salt and sand
10.01.8 Separate a mixture of sand and copper sulfate
10.01.9 Separate water from copper sulfate solution by distillation
10.01.11 Separate a mixture of copper carbonate and magnesium sulfate
10.01.12 Separate a mixture of methyl orange and litmus by chromatography
10.1.0 Separate by adsorbing impurities
10.1.0 Separate by adsorbing impurities
10.1.1 Absorb impurities on charcoal, test with litmus
3.33.1.2 Odour tests for ammonia
10.1.2 Clean dirty water clean with charcoal
10.1.3 Prepare white sugar from brown sugar
10.2.0 Separate by chromatography
10.2.0 Separate with chromatography
3.24 Separate pigments from green leaves with paper chromatography
3.24.1 Separate mixed inks with paper chromatography
6.5.5 Chromatography of chlorophyll pigments
10.2.1 Separate with column chromatography
10.2.2.4 Detect a forgery
10.2.2.5 Separate amino acids with paper chromatography
10.2.2.6 Separate aspirin, caffeine and paracetamol (acetaminophen) with thin layer plate chromatography
10.2.2.7 Separate food colours in coloured sweets, e.g. jelly beans, "Smarties"
10.3.0 Separate by solubility of soluble substances from insoluble substances
10.3.1 Separate a sand and salt mixture
7.7.1 Separate soluble from insoluble substances
10.4.0 Separate immiscible liquids in a mixture
3.26 Separate immiscible liquids of different density
10.4.1 Shake different liquids in water
10.5.0 Separate by distillation
10.5.0 Separate by distillation
10.5.1 Distil ink
10.5.2 Distil copper (II) sulfate solution
10.5.3 Distil sea water
10.5.4 Distil essences from leaves and flowers
10.5.5 Steam distillation to find water and fat content of food
10.5.6 Steam distillation of eucalyptus leaves, eucalyptol (1,8-cineole) oil of cloves, eugenol
10.5.7 Gases dissolved in a water sample
10.6.0 Separate by fractional distillation
10.6.0 Separate by fractional distillation
10.6.4 Catalytic cracking of kerosene
10.6.3 Distil crude oil and collect the fractions, composition of petroleum
10.6.5 Prepare gas by destructive distillation of coal
10.6.1 Separate a mixture of ethanol and water
10.7.0 Separate substances with different melting points
3.18 Separate tin from a mixture of tin and carbon (charcoal)
3.19 Separate by sublimation
3.20 Separate by distillation
3.21 Separate crude oil fractions by fractional distillation
3.22 Separate salt and sand
3.23 Solvent extraction of oil from nuts
3.24 Separate pigments from green leaves with paper chromatography
3.24.1 Separate mixed inks with paper chromatography
3.26 Separate immiscible liquids of different density
3.27 Separate solids using density differences
10.7.2 Separate iodine from a mixture of iodine and sodium chloride
10.8.0 Separate by froth flotation of heavy minerals
10.8.0 Separate heavy minerals by froth flotation
10.8.1 Separate sand and lead powder by panning
10.8.2 Separate heavy minerals by froth flotation
10.9.0 Separate by recrystallization
10.9.0 Separate by recrystallization
10.9.1 Separate sodium chloride from sodium nitrate
10.10.0 Separate by reduction of metal oxides to metals, charcoal blocks
10.10.0 Separate to metals by reduction of metal oxides, ores
3.39.0 Carbon monoxide (reduce metallic oxides to the metal):  See 4.
3.41.3 Reduce metal oxides to metals with hydrogen gas
10.10.1 Reduce metal oxides to metals, red lead to lead and oxygen
3.41.4 Reduce copper oxide with natural gas, methane
3.51.2 Reduce potassium manganate (VII) with sulfur dioxide
3.51.3 Reduce iron (III) chloride with sulfur dioxide
10.10.1 Reduce metal oxides to metals, red lead to lead and oxygen
10.10.2 Reduce copper (I) oxide (copper oxide) to copper
10.10.3 Reduce red iron oxide, or rust, to iron
10.11.0 Separate by sedimentation and filtration
10.11.1 Clarify muddy water with filtration, potash alum, SIROFLOC
10.11.2 Separate with a simple centrifuge
10.12.0 Separate by solvent extraction
10.12.1 Extract oil from peanuts (groundnuts)
10.13.0 Separate by sublimation
10.13.1 Separate sodium chloride from iodine
10.13.2 Extract iodine from kelp
10.01 Separate pure substances, linked experiments
10.01.1 Separate muddy water into mud and 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. The mud particles are too large to pass through the filter paper.
10.01.2 Prepare copper carbonate from copper sulfate and sodium carbonate
Dissolve a finger width of copper sulfate in a test-tube half filled with water. Dissolve a finger width of sodium carbonate in another test-tube half filled with water. Shake each test-tube to help the chemicals dissolve. Add the two liquids by pouring one into the other. A blue-green solid substance forms, copper carbonate.
Filter the mixture from the previous experiment that contains the blue-green solid. Copper carbonate remains on the filter paper.
Pour half a test-tube of hot water onto the copper carbonate to wash away other substances. 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 copper carbonate.
10.01.3 Filter milk
Filter a quarter of a test-tube of milk. Describe what you see. All the milk passes through a filter paper. Milk is a suspension of substances in water, but the particles are very small and can pass through filter paper.
10.01.4 Separate suspension of coloured blackboard chalk 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.
10.01.5 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.
10.01.6 Separate ammonium chloride from its 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.
10.01.7 Separate a mixture of salt and sand
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.
10.01.8 Separate a mixture of sand and copper sulfate
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 and leave 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.
10.01.9 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.
10.01.10 Prepare 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.
10.01.11 Separate a mixture of copper carbonate and magnesium sulfate
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.
10.01.12 Separate a mixture of methyl orange and litmus 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.
10.1.0 Separate by adsorbing impurities
Some forms of carbon can adsorb coloured substances and release them later in suitable solvents, e.g. charcoal made from bones removes coloured impurities in the production of cane sugar crystals.
10.1.1 Absorb impurities on charcoal, test with litmus
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.
10.1.1.1 Tests for ammonia
3.33.1.2 Odour test
Put a drop of aqueous ammonia solution in a test-tube with a stopper. Shake the test-tube and warm it with the hands. Note the pungent odour of ammonia.
See diagram 1.13: Smelling test
BE CAREFUL! DO NOT INHALE GASES DIRECTLY FROM THE TEST-TUBE! Fan the gas towards the nose with the hand and sniff cautiously. If you detect no odour, move closer and try again. Add powdered wood charcoal. Shake the test-tube and smell the contents again. Filter the mixture. Heat the charcoal and note the absence of the pungent odour of ammonia.
10.1.2 Clean dirty water clean with charcoal
See 12.11.4.0: Group tests to identify cations
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.
10.1.3 Prepare white sugar from brown sugar
See 3.1.10: Prepare sugar crystals from brown sugar | See 11.0: Activated carbon [commercial information]
Activated carbon decolorizes and refines brown sugar solution by adsorbing coloured impurities on it. Then filter and cool to get the white (refined) sugar crystals.
Put 5-10 g of brown sugar in a small beaker. Dissolve the sugar in 40 mL water by heating. Add 0.5-1.0 g of activated carbon while constantly stirring. Filter the suspension when it is still hot to obtain a colourless solution. If the filtrate appears yellow, add a little more activated carbon, heat and filter the suspension again until the filtrate becomes colourless. By heating, concentrate the filtrate in a small beaker on a water bath until you reduce the volume of the solution to about 1 / 4. White sugar crystals separate out of the liquor after cooling it naturally.
10.2.0 Separate with chromatography
Chromatography that means "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. 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. You can separate colourless substances by spraying 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 shorted r in the moving phase. In column chromatography, the stationary phase substance is packed in a tube. 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.
10.2.1 Separate with column chromatography
1. 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.
6.5.5 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 using paper chromatography.
1. Cut grass into small pieces and place them in a mortar. Add sand, 40 mL methanol and 5 mL petroleum benzine 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 benzine 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 benzine 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.
4. Study other green parts of plants, e.g. stinging nettle leaves, and look at vegetable growth taken at different stages to find out whether the composition of the chloroplast pigments is subject to seasonal variation.
10.2.2.4 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!
10.2.2.5 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 by dissolving 96 mL of concentrated hydrochloric acid (36% w / v HCl) in deionized water and make up to 2 L. 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 a1 a2, 0.05 M tyrosine: Dissolve 4.53 g of tyrosine in the 1.5% HCl solution and make up to 500 mL.
Solution a1 a3, 0.05 M leucine: Dissolve 3.28 g of leucine in the 1.5% HCl solution and make up to 500 mL.
Solution a1 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! Do not let ninhydrin touch the skin! 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 X 22 cm sheet of Whatman No. 1 filter paper. Draw 10 light crosses 2 cm apart along this line and label them a1, a2 a 3 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, and 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. Spray the paper with a spray reagent of a 2% solution of ninhydrin in ethyl alcohol in an aerosol pack. Ninhydrin reacts with alpha-amino acids to yield coloured products. Leave the filter paper in the fume cupboard, fume hood until the spray solution is dry. Place the filter paper in an oven at 110oC until all the spots have developed. Circle the spots with a pencil before they fade. Measure from the centre of each spot to the base line. Measure the distance the solvent has travelled at each position and calculate the Rf values for each amino acid. Find the composition of the unknown by visual comparison of spot colours and by the relationships of Rf values.
10.2.2.6 Separate aspirin, caffeine and paracetamol (acetaminophen) with 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 commercial analgesics using as previous plates as reference samples. Construct a results table:
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)
10.2.2.7 Separate food colours in coloured sweets, e.g. jelly beans, "Smarties"
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 meter 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.
10.3.1 Separate a 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.
3. 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.
10.4.1 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 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.
10.5.1 Distil ink
1. Put ink in a boiling tube. Add anti-bumping granules. 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. 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.
10.5.2 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 side arm. 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.
10.5.3 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.
10.5.4 Distil essences from leaves and flowers
Eucalyptus oil contains eucalyptol, 1,8-cineole. It has medical properties and is a disinfectant. It decomposes at b.p. 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, black current, hops, tea tree.
10.5.5 Steam distillation to find 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 b.p. 85.0oC, but b.p. toluene is 110.6oC and b.p. 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) X (vapour pressure water / vapour pressure toluene)
= (18 / 92) X (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, e.g. 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
10.5.6 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. It is an effective disinfectant. The oil decomposes when boiled, b.p. 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, b.p. 164oC, from dried cloves.
10.5.7 Gases dissolved in a water sample
See diagram 3.2.25: Gas released form 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.
10.6.0 Separate by fractional distillation
See diagram 3.2.21: Fractional distillation
You can 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. Use a hard glass test-tube, or sidearm test-tube, fixed to a retort stand, a delivery tube and the five small ignition tubes. Use a 0-360oC thermometer. Put 4 mL 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 about 10 drops of distillate in the first ignition tube, then collect 10 drops of distillate successively in the other tubes. The boiling point of the remaining oil will become higher as distillation proceeds and more heat will then be required from the Bunsen burner. Arrange the fractions in order of increasing distillation temperature: 1. up to 80oC, 2. 80-120oC, 3.120-180oC, 4. 180-220oC. Observe all the different fractions: 1. The colour should change from colourless to yellow. 2. The viscosity should increase. 3. The high temperature fractions should be more difficult to ignite than the low temperature fractions. 4. 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. 5. Note the dark residue remaining in the test-tube.
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.
10.6.3 Distil crude oil and collect the fractions, composition of petroleum
In the petroleum industry, crude oil is 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 the action of silica and aluminium catalysts in a process called catalytic cracking, e.g.
C10H22 ---> C5H12 + C5H10
Lower molecular weight hydrocarbons undergo alkylation to form larger hydrocarbons with similar boiling point to gasoline, e.g.
C2H6 + C4H8 ---> C6H14
See diagram 10.6.3: Distillation
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
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!
10.6.4 Catalytic cracking of kerosene
See diagram. 10.6.4: Cracking 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 showing that unsaturated hydrocarbons are among the products of cracking the hydrocarbons in kerosene.
10.6.5 Prepare gas by destructive distillation of coal
See diagram. 10.6.5: Heat coal
When you heat a material in the absence of air, you may destroy its structure. This process is called destructive distillation. Producer gas is a mixture of carbon monoxide and nitrogen. Producer gas forms when air passes over hot coke or carbon.
2C (s) + O2 (g) + N2 ---> 2CO (g) + N2 (g)
1. Use bituminous coal because it contains mainly volatile hydrocarbons. Grind the coal with a mortar and pestle. Transfer 3-5 g of the crushed coal to the bottom of a sidearm test-tube. Insert a stopper and clamp the sidearm test-tube with its side arm downwards and its mouth inclined down. Connect the sidearm to a straight delivery tube inserted into a one-hole stopper in another sidearm test-tube. Attach a glass tube to the sidearm of the second sidearm test-tube. Heat the crushed coal in the upper test-tube with an alcohol lamp. The heated coal decomposes to produce coal tar oil that flows down into the lower test-tube. Hold a lighted match to the outlet of the glass tube to ignite volatile gas. The gas burns with a light blue flame.
2. Grind bituminous coal with a mortar and pestle and put it in a Pyrex test-tube. Fit the tube with a one hole cork carrying a glass delivery tube. Make a gas reservoir by punching two holes in the bottom of a large tin can. Insert a one-hole stopper with a short glass tube in each hole. Seal between the stopper and edge of the holes. Use rubber tubing to connect one of the short glass tubes to the delivery tube. Connect the other short tube to a medicine dropper tube and attach a screw type pinch clamp Hofmann clip to the rubber tubing. Fill the can with water and invert it in a large jar of water so that it sinks to the bottom. Heat the test-tube containing coal with a Meker burner. The coal decomposes into several substances. Gases from the decomposition leave the tube and fill the reservoir can by driving out the water. As the can fills with gas, it rises in the large jar. At first the coal gas pushes air out of the can through the second tube attached to the medicine dropper. Close the Hofmann clip and collect the gas. To test the gas, open the Hofmann clip and hold a lighted match to the end of the medicine dropper tube. The gas burns until the contents of the tin can are almost exhausted. Some volatile tar floats on the water in the can. The remaining products of the destructive distillation, e.g. coke, remain in the test-tube.
3. Prepare gas from wood. Put wood shavings or sawdust in a clamped Pyrex test-tube. Connect it to another test-tube standing in water and which has an outlet for the gas.
10.7.2 Separate iodine from a mixture of iodine and sodium chloride
See diagram 24.6.1: Heat evaporating dish
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.
10.8.0 Separate heavy minerals with froth flotation
This method is often used in mineral mining to separate crushed ores from other rock materials. 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.
10.8.1 Separate sand from lead powder 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.
10.8.2 Separate heavy minerals by froth flotation
This method is used to separate crushed ores from other rock materials in mineral mining.
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.
10.9.0 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 recrystallization 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
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 deposits.
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. Do not reduce oxides of toxic metals such as mercury, lead, cadmium, nickel, arsenic or antimony because students may inhale fine particles.
10.10.1 Reduce metal oxides to metals, red lead to lead and oxygen
See diagram 10.10.1: Red lead to lead and oxygen | See 3.6.8: Lead toxicity
1. Use a crucible lid to heat red or orange-coloured red lead (red lead oxide), molecular formula Pb3O4, (2PbO.PbO2), lead tetroxide (triplumbic tetroxide, minium). If you heat red lead in a glass test-tube, the lead compounds in red lead may combine with the lead in the glass causing the glass to crack and spill its hot contents. The red lead melts at 500oC, then decomposes to the yellow solid lead (II) oxide (lead monoxide, lithage) and oxygen gas, Test the gas evolved with a glowing splint. Put some yellow residue in a cavity in a charcoal block. Heat the metal oxide strongly with a blowpipe. The residue is the element lead. You have extracted oxygen and lead from red lead.
2Pb3O4 (s) --> 6PbO (s) + O2 (g)
Lead tetroxide forms insoluble iron (II) plumbate and iron (III) plumbate with iron and iron oxides so it is used in anti-corrosive lead paints, especially rust-proof primer paints. However, lead tetroxide is soluble in dilute hydrochloric acid so it can dissolve in the hydrochloric acid in the stomach and act as a lead poison. It is not soluble in water so it can be used as lead glass. It is used to make lead cell accumulators, car batteries.
10.10.2 Reduce copper (I) oxide (copper oxide) to copper
See diagram 10.10.2: Copper oxide to copper
Most school science laboratories are not equipped to show the reactions that occur in a blast furnace.
Heat copper (I) oxide on a charcoal block until brown colours are observed in the residue. Cool the bead formed then grind it with a mortar and pestle and examine with a magnifier. Compare the reaction of dilute nitric acid with the ground residue and with copper filings. The residue might be copper. Repeat the procedure using red iron oxide. Test the ground up residue with a magnet. You have thus extracted copper from copper oxide and iron from iron oxide by their reaction with carbon.
10.10.3 Reduce red iron oxide, or rust, to iron
In a blast furnace, there are 3 reactions when iron ore is smelted, i.e. melted and reduced.
3Fe2O3 (s) + CO (g) ---> 2Fe3O4 + CO2 (g)
Fe3O4 (s) + CO (g) ---> 3FeO (s) + CO2 (g)
FeO (s) + CO (g) ---> Fe (l) + CO2 (g)
Also, water gas forms.
H2O (l) + C (s) + energy ---> CO (g) + H2 (g) (water gas)
10.11.1 Clarify muddy water with filtration
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 use 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 important in water treatment  and swimming pool management to separate out visible sediments, and other materials and to treat colloids to remove them.
10.11.2 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.
10.12.1 Extract oil from peanuts (groundnuts)
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 tetrachloromethane can be used as the solvents.
1. Put ground nuts (peanuts) or pieces of chopped coconut into a mortar. Add 20 mL of acetone or methylated spirit. Grind the nuts in the solvent as finely as possible. Pour off the liquid into a test-tube and filter into an evaporating basin. Warm the evaporating basin for 10 minutes. 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.
2. Put groundnuts (peanuts) or chopped coconut into a mortar. Add the solvent methylated spirit. Grind the nuts as finely as possible for two minutes with the solvent. Pour off the liquid into a test-tube.
Filter the liquid. 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.
10.13.1 Separate sodium chloride from iodine
See diagram 3.2.19: Heat evaporating dish
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 Extract iodine from kelp
See diagram 13.15.3: Iodine extraction
Iodine is one of the microelements 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 commercial 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 30 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.