topic09

School Science Lessons
Topic 9 Polymers and plastics, prepare crystals, prepare ink, water of crystallization
2012-01-24 SP
Please send comments to: J.Elfick@uq.edu.au
See: Interesting websites

Table of contents
3.4.0 Polymers and plastics
3.1.0 Prepare crystals
3.2.5.0 Prepare ink, invisible ink, secret ink, sympathetic ink
3.2.0 Water of crystallization

3.1.0 Prepare crystals
7.7.14 Fractional crystallization of sea water
3.1.4 Prepare aspirin crystals
12.10.1 Prepare boric acid crystals
3.54.6 Prepare crystal clusters
4.14 Prepare crystals (Primary)
3.54 Prepare crystals from solutions
3.54.2 Prepare crystals from a melt
3.54.3 Prepare crystals with different shapes
3.54.4 Prepare crystals from a mixture of salts
3.54.01 Prepare double salt crystals
3.54.5 Prepare large crystals
3.54.1 Prepare sea water crystals
12.18.6.1 Prepare sodium thiosulfate crystals, "hypo", Na₂S₂O₃.5H₂O
3.54.7 Prepare split crystals
3.54.8 Prepare stalactite crystals
3.1.10 Prepare sucrose crystals from brown sugar
3.1.10.1 Prepare sucrose crystals from sugar cane juice
10.9.0 Separate by recrystallization

3.4.0 Polymers and plastics
2.0.0 List of polymers, plastics, and synthetic fibres
3.0.1 Polymers
3.0.2 Thermoplastic polymers
3.0.3 Thermosetting polymers
3.4.4.0 Breakdown polymers into small molecules
3.97 Breakdown polymers using heat
3.95 Breakdown starch to sugars
3.5.0.1 Describe polymers
3.102 Tests for plastics, natural fibres and synthetic fibres
3.103 Tests for polymers
3.104 Tests for plastics in known density solutions
3.4.9 Prepare Bakelite plastic, phenol / methanal polymerization
3.4.4.1 Prepare expanded polystyrene beads with propanone
3.4.6.1 Prepare formaldehyde-resorcinol resin
3.4.7 Prepare nylon polymer
3.100 Prepare plastic with milk casein
3.4.8 Prepare rayon, copper (II) sulfate with ammonia solution, "regenerated fibre", "artificial silk"
3.4.8.1 Prepare rayon, basic copper carbonate with ammonia solution
3.4.11 Prepare slime balls, "Silly putty", silicone polymer to amuse children
3.4.2.5.1 Prepare sodium polyacrylate gels, acrylic sodium salt polymer, ASAP
3.101 Prepare urea-formaldehyde resin
3.4.2.1a Push pencils through a polythene bag
3.4.1.1 Stretch rubber band

3.2.5.0 Prepare ink, invisible ink, secret ink, sympathetic ink
3.2.5.1 Alum solution, K₂SO₄Al₂(SO₄)₃.2H₂O, invisible writing ink
3.2.5.5 Ammonium iron (II) sulfate or ammonium chloride, invisible writing ink
3.2.5.3 Cane sugar, sucrose solution, invisible writing ink
3.2.5.2 Cobalt (II) chloride solution, invisible writing ink
3.2.5.10 Gold in aqua regia, invisible writing ink
3.2.5.11 Iron (II) sulfate, invisible writing ink
3.2.5.9 Milk, invisible writing ink
3.2.5.8 Phenolphthalein (uncoated laxative tablets), invisible writing ink
3.2.5.12 Prepare black ink from iron (II) sulfate and oak galls
4.19 Prepare invisible inks (Primary)
3.2.5.13 Prepare red invisible ink with phenolphthalein
12.15.1 Prepare yellow invisible ink, copper sulfate
3.2.5.6 Sodium chloride, invisible writing ink
3.2.5.4 Starch, cornstarch suspension, invisible writing ink
3.2.5.7 Vinegar, lemon juice, squeezed onion juice, invisible writing ink

3.2.0 Water of crystallization
8.4.5 Water of crystallization
3.31.1 Expose different salts to the air
3.31.2 Expose sodium carbonate decahydrate, washing soda, to the air
3.31.3 Tests for water with cobalt (II) chloride
3.2.1 Heat copper (II) sulfate-5-water crystals, test for water
3.2.2 Heat iron (II) sulfate-7-water crystals
3.2.3 Heat different crystals with water of crystallization, test for the presence of water with blue cobalt (II) chloride paper.
3.2.4 Heat magnesium sulfate-7-water crystals
3.2.6 Make fibrous plaster board with plaster of Paris
3.67 Strength of plaster of Paris

3.1.0 Crystals
Many solids are crystalline. Their particles exist in an ordered arrangement. Crystallization involves the formation of the pure solid from its solution. Many crystals contain water of crystallization, e.g. copper (II) sulfate crystals, CuSO₄.5H₂O. However, anhydrous copper (II) sulfate, CuSO₄, contains no water of crystallization.

3.1.4 Prepare aspirin crystals
See diagram 16.3.4.11: Aspirin
Dissolve an aspirin table in methylated spirit. BE CAREFUL! Filter if necessary. Heat the solution.

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. After filtering, concentrating and cooling you can obtain the white (refined) sugar crystals.
1. Put 5 to 10 g of brown sugar in a small beaker. Dissolve the sugar in 40 mL water by heating. Add 0.5 to 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.
2. Dissolve 100 g of brown sugar in 90 mL water. Add calcium hydroxide solution until the solution turns red litmus blue. Filter the solution then heat the filtrate with absorbent charcoal while it is still hot. Evaporate at reduced pressure at 50 to 65^oC. Put the syrup in a refrigerator for several days to form crystals.

3.1.10.1 Prepare sugar crystals from sugar cane juice
In commercial production of cane sugar, the solution is clarified by adsorbing impurities on bone char, a type of carbon made by heating bones in the absence of air.
Add calcium hydroxide to sugar cane juice or sugar beet juice until red litmus turns blue. Leave it to stand overnight. Filter by suction. Evaporate in reduced pressure at 50 to 65^oC until it becomes a brown syrup that is so viscous that it scarcely flows. Put the syrup in a refrigerator for several days to form crystals. Use a centrifuge to separate crystals from the liquor.

3.2.1 Heat copper (II) sulfate-5-water crystals, test for water
See 3.80 Exothermic reactions give out heat energy
1. Use anhydrous copper (II) sulfate to test for the presence of water. Heat the crystals gently in a test-tube until they change from blue to white. Water vapour collects on the side of the test-tube. Cool the test-tube. Put some condensed water vapour on the white substance, anhydrous copper (II) sulfate. The copper (II) sulfate turns blue again. This is an example of a reversible change. The return of the blue colour is also a test for water. (In this direction heat enters the reaction. --->) CuSO₄.5H₂O (s) <--> CuSO₄ (s) + 5H₂O (l) (<--- In this direction heat leaves the reaction.)
2. Heat copper (II) sulfate crystals to make it lose its water of crystallization and leave anhydrous copper (II) sulfate as a white powder. The lost water appears as drops on the inner surface of the upper part of the test-tube. Test the drops for the presence of water with blue cobalt (II) chloride paper. Transfer the anhydrous copper (II) sulfate to another test-tube and add a drop of water. The blue hydrated salt forms again.

3.2.2 Heat iron (II) sulfate-7-water crystals
The water in the crystal is necessary for the shape and colour of the crystal. Put crystals in a test-tube. Heat gently and note any reaction. The crystals lose water vapour that condenses as liquid in the cool upper region of the test-tube. The crystals lose their shape and colour.
Fe₂SO₄.7H₂0 <--> FeSO₄ + 7H₂O

3.2.3 Heat crystals that have water of crystallization
Heat crystals of bluestone CuSO₄.5H₂O, borax Na₂B₄O₇.10H₂O, common salt NaCl, Epsom salts MgSO₄.7H₂O, Glauber's salts Na₂SO₄.10H₂O, green vitriol FeSO₄.7H₂O, hypo Na₂S₂O₃.5H₂O, washing soda Na₂CO₃.10H₂O, and white vitriol ZnSO₄.7H₂O. They all contain water of crystallization except common salt. Test the presence of water with blue cobalt (II) chloride paper, CoCl₂.
CoCl₂ (s) + 6H₂O (l) <--> CoCl₂.6H₂O (s)

3.2.4 Heat magnesium sulfate-7-water crystals
1. Heat 5 g of Epsom salts crystals, MgSO₄.7H₂O, in a dry test-tube over a flame. Hold the test-tube in a paper holder so that it slopes down slightly towards the open end. The water of crystallization lost forms steam to condense as water in the cooler part of the test-tube to leave anhydrous magnesium sulfate in the test-tube is a white powder.
2. Repeat the experiment with copper (II) sulfate crystals, CuSO₄.5H₂O
3. Relative molecular mass = 246.47.
Weigh the hydrated crystals, W1. Heat the crystals and weigh again. Continue heating and weighing until the weight does not change, W2.
Weight of a water of crystallization = (W1 - W2).
Number of molecules of the crystal, n = (W1 / 246.47).
Number of molecules of water in each molecule of crystal = (W1 - W2) / n = 7.

3.2.5.0 Prepare ink, invisible ink, secret ink, sympathetic ink
For over 1000 years in the Northern hemisphere ink was made from a mixture of an iron salt, e.g. iron (II) sulfate and infusion of plant galls. The galls are formed by plants in reaction to attack by gall wasps. e.g. Biorhiza, Amphibolips. The galls used were from the oak tree, Quercus, oak apple gall, oak marble gall and other nut galls, e.g. Rhus, Caesalpinia. The galls contain tannic acid (C₇₆H₅₂O₄₆, gallotannic acid). The reaction of the iron salt with tannic acid produced a grey liquid that would turn purple-black with the addition of a gum, e.g. gum acacia, gum arabic. Sometimes carbon was added to the ink. The ink would become darker and harder with exposure to the air as Fe²⁺ converted to Fe³⁺, so it was kept in tightly-sealed bottles.

3.2.5.1 Alum solution, K₂SO₄Al₂(SO₄)₃.2H₂O
1. Let the ink dry on the paper then heat the paper over a warm stove until the dry invisible letters become visible as dark carbonized areas. The alum dehydrates the cellulose in the paper by acting as a proton donor to form H₂O from the -OH groups of the cellulose.
2. The experiments below can also be done on a clean egg. After writing on the egg, wait to allow the chemical to sink in, then wash the egg leaving the secret writing chemical still on the inside of the eggshell. Then treat the egg as below.

3.2.5.2 Cobalt (II) chloride solution, invisible writing ink
See 12.6.1: Properties of cobalt salts, See 4.
Novelty weather indicators contain cobalt (II) chloride that turns blue to show that the weather is fine and turns pink to show that the weather is wet.
Dissolve crystals of cobalt (II) chloride-6-water and use for ink. Use a small paint brush or a chewed end of a match to paint the ink on the paper, then leave to dry. Dilute cobalt salt solutions are almost invisible but if you write on paper with the invisible solution, you can later see the writing by heating the paper over a flame without burning the paper or wrap the paper over a 100 watt light globe or to iron it with a hot iron, not a steam iron. The secret message appears as blue writing. When you paint the message with water, it disappears again. Some spies use a mixture of cobalt chloride and glycerine. However, if you put the paper aside, the cobalt salt absorbs water from the atmosphere and the writing becomes invisible again. So there is no chemical reaction - just a dilution or evaporation effect. Add some sodium chloride to the cobalt chloride solution to allow the writing to appear after heating then fade many times.

3.2.5.3 Cane sugar or milk, invisible writing ink
Use cane sugar solution, or sucrose solution in water or milk. Write on a piece of cardboard. Read the secret message by burning paper and rubbing the ash on the cardboard.

3.2.5.4 Starch, cornstarch suspension, invisible writing ink
See 1.6: Iodine Solution
Use liquid starch for ink. First test the paper with iodine solution to be sure that it does not contain starch. Read the secret message by wiping the paper with iodine solution. The writing appears dark blue on light blue paper.

3.2.5.5 Ammonium iron (II) sulfate or ammonium chloride, invisible writing ink
Use ammonium iron (II) sulfate solution or ammonium chloride solution for ink. On heating, the secret message appears as brown black or yellow brown writing.

3.2.5.6 Sodium chloride, invisible writing ink
Use a saturated solution of sodium chloride for ink. Rub the dry paper with a soft lead pencil. The secret message appears as a darker pencil mark where the pencil scrapes on the salt crystals.

3.2.5.7 Vinegar, or lemon juice, or squeezed onion juice, invisible writing ink
These juices convert paper to substances similar to cellophane with ignition temperature lower than paper. When you gently heat the paper, the parts written on turns brown. Most organic liquids will char on heating as some of the organic molecules are reduced to carbon with loss of water. Also, you can add dilute iodine solution to see white writing on a light blue background. Also, you can use red cabbage water to make the secret writing appear red.

3.2.5.8 Phenolphthalein (uncoated laxative tablets), invisible writing ink
Sprinkle sodium bicarbonate or washing soda solution on the secret writing to make it appear pink.

3.2.5.9 Milk, invisible writing ink
Use milk solution in water. Write on a piece of cardboard. Read the secret message by burning paper and rubbing the ash on the cardboard.

3.2.5.10 Gold in aqua regia, invisible writing ink
To make a very expensive invisible ink, dissolve gold in aqua regia (1 part concentrated HNO₃ + 3 parts concentrated HCl) and let dry in the shade. Wet the paper with a sponge wetted in a solution of tin in aqua regia. Purple writing appears.

3.2.5.11 Iron (II) sulfate, invisible writing ink
Using a wood spill, write on a sheet of plain paper with iron (II) sulfate solution. let the paper to dry and then heat it by holding it in front of a fire or over a flame. The writing appears yellow or brown.

3.2.5.12 Prepare black ink from iron (II) sulfate and oak galls
Make black ink from iron (II) sulfate and oak galls, the round nut-like growths found on the branches of oak trees, from which they can be collected in autumn. Crush or cut up one or two galls and boil the pieces with water in a beaker or small pan. The water extracts tannic acid from the oak galls. Strain off or filter the solution of tannic acid. Prepare a solution of iron (II) sulfate in cold water and mix it with an equal amount of the cold oak gall solution. This forms iron (II) tannate in the liquid. Write on paper with the liquid. The writing shows little colour, but when left for a day or two turns black because iron (II) tannate on exposure to air forms black iron (III) tannate, ferric tannate. Ordinary blue-black ink contains a blue dye in addition to the iron (II) tannate. The dye acts as temporary colouring matter until the black colour of the iron (III) tannate develops. Make blue-black ink by adding to the ink prepared as above a solution of log wood or methylene blue, two common dyes. If methylene blue is used, however, the ink should be stored in a dark cupboard, because light makes the colour fade. Use iron (II) sulfate if the solution is first oxidized to iron (III) sulfate by boiling it with drops of hydrogen peroxide.

3.2.5.13 Prepare red invisible ink with phenolphthalein
Write on paper with a solution of phenolphthalein. Let the paper to dry and the writing becomes invisible. Wet a cloth or sponge with weak sodium carbonate solution and smear it over the paper. The writing shows up in red letters.

3.2.6 Make fibrous plaster board with plaster of Paris
Plaster of Paris is made by heating the mineral gypsum (calcium sulfate-2-water) to remove some of its water of crystallization. This process is called calcination or calcining. Plaster of Paris is partly dehydrated gypsum 2CaSO₄.H₂O (s). Gypsum as a hemihydrate is shown as CaSO₄.½H₂O. Plaster of Paris is used for making casts, e.g. of the shape of a shell or for keeping broken bones in place.
CaSO₄.½H₂O. 2CaSO₄.2H₂O (s) <--> 2CaSO4.H₂O (s) + H₂O (l) gypsum <--> plaster of Paris + water
Mix wet Plaster of Paris with fibres. As the mixture dries, gypsum crystals form again by taking in water. The setting plaster gives out heat and expands slightly, but it does not dry because of evaporation.

3.4.1.1 Stretch rubber band
1. Stretch a thick rubber bandit quickly against your lips and note the change in temperature. Hold it stretched, allow it to cool back to room temperature. Then let it suddenly contract against your lips to its original length and note the temperature change. Polymers behave in an opposite way to metals in that rubber contracts on heating and expands on cooling.
2. Use a hair dryer to heat a stretched rubber band with a weight on the end.
3. Cool a rubber band. Stretch a wide rubber band between the index finger of your two hands. Let the rubber band touch your lips. Stretch the rubber band (not so far that it breaks!) then slowly release the tension. You can feel heat in your lips when the rubber band stretches because of friction between the rubber molecules. The stretched rubber band feels cooler when you release the tension.
4. Suspend a 100 g mass from a rubber band. Use a vertical ruler to measure the length of the suspended rubber band. Bring a heat sources. e.g. a lighted match close to the middle of the stretched rubber band. Note that the heated rubber band contracts.
5. Observe the thermal properties of rubber. Hang a 1 kg mass from four rubber bands so it touches the table. Heat with a radiant heater for 20 seconds and the mass will lift. Enclose a rubber tube in a copper cylinder and heat with a Bunsen burner. The rubber tubing contracts as it is heated. Stretch and unstretch rubber bands on the lips to feel the changes in temperature.

3.4.2.1a Push pencils through a polythene bag
Half fill a polythene bag with water and tie it shut with one end of a long string. Suspend the bag by raising the other end of the string. Very quickly push a sharpened pencil through both polythene bag walls and enclosed water. Leave the pencil in place and push other pencils through the bag. Withdraw the pencils and the polythene bag returns to its former shape. Polythene consists of a web-like matrix of molecules such that the polythene is easily stretched and then can return to its former shape without tearing.

3.4.2.5.1 Prepare sodium polyacrylate gels, acrylic sodium salt polymer, ASAP
Order online: Expanding Spheres, super absorbent polymers
Order online: Super Slurper Polymer, hydrophilic sodium polyacrylate
Be careful! Sodium polyacrylate can irritate the eyes and nostrils.
Sodium polyacrylate, sodium prop-2-enoate, sodium poly (acrylic acid), super absorbent polymer, water lock. The monomer is polymer: [-CH₂-CHCOONa-]n.
Fibres + sodium hydroxide, then polyacrylic acid --> sodium polyacrylate, a crosslinked acrylic acid polymer sodium salt. It has a very high molecular weight, is very soluble in water and forms a linear anion polymer. Sodium polyacrylate is used as a thickening agent, in urine test kits, in baby diapers (nappies), in tampons for menstruation (but may cause toxic shock syndrome if not changed daily), as "water crystals" to store water in soils, e.g. "Aqua Crystals", as "magic instant snow powder" novelty and movie set decoration (super slurper), and as "ghost crystals" because they become invisible in water, having the same refractive index. Sodium polyacrylate can absorb 800 X its own weight of water.
1. Attach a pin to a crystal of sodium polyacrylate. Tie a string around the crystal and lower it into water. The crystal disappears but the pin remains suspended in water.
2. Dissolve some powder or gel form of sodium polyacrylate in alcohol. The solution turns a deep magenta colour until the alcohol evaporates. (Magenta is a brilliant red aniline dye derived from coal tar.)
3. The disappearing milk trick is an experiment to amuse children which uses a drinking glass with frosted sides or some decoration so that the audience cannot see into the bottom of the glass. Put about 1 teaspoon of sodium polyacrylate from a disposable nappy into the drinking glass without the audience knowing. Pour milk into the drinking glass. Attempt to pour milk out of the drinking glass. No milk comes out of the glass because it had been absorbed by the sodium polyacrylate to form a gel that sticks in the drinking glass.

3.4.4.0 Breakdown polymers into small molecules
See diagram 3.4.4: Breakdown polymers into small molecules
Put very small pieces of perspex or polystyrene in a hard glass test-tube. Connect a delivery tube to a receiving test-tube that must be cooled thoroughly with cold water because the fumes are harmful. Heat the test-tube containing the perspex gently. The polymer melts and forms vapours collected in the receiving tube. Control the heating to enable all the fumes to condense in the receiving tube. Heat breaks down the polymer to smaller molecules.

3.4.4.1 Prepare expanded polystyrene beads with propanone
Pour 50 mL of propanone into a beaker full of expanded polystyrene beads used a packing material or into a polystyrene coffee cup in a beaker. The expanded polystyrene fizzes and shrinks to form a sticky gel. The expanded polystyrene does not dissolve in the propanone but just loses the gas that had puffed it out.

3.4.6.1 Prepare formaldehyde resorcinol resin
Add 2 g of resorcinol to 5 mL of 45% formaldehyde solution in a small beaker and stir the mixture. Add drops of concentrated hydrochloric acid and stir the mixture. The mixture suddenly hardens as molecules build up into larger molecules. Take out this condensation polymer resin and wash it thoroughly.

3.4.7 Prepare nylon polymer
See diagram 16.3.4.7: Condensation polymerization to form a polyamide, Wind the polymer onto a glass rod
Nylons have a structure like a long protein. Nylons form by condensation between the amino group (-NH₂) of one molecule and the carboxylic acid group (-COOH) of another molecule. The 3 main nylon fibres are nylon 6, nylon 6,6 and nylon 6.10. Nylon 6,6 ("Bri nylon") is [-NH-(CH₂)₆-NH-CO-(CH₂)₄-CO-NH-(CH₂)₆-NH-]. Nylon 6,6 forms by condensation of hexane-1,6-diamine, (NH₂.[CH₂]₆.NH₂) and hexanedioic acid (CH₂.CH₂[COOH]₂). Nylon 6,6 is used for nylon thread, rope, toothbrush bristles, cog wheels, shirts, combs. It is thermoplastic.
Nylon6.10 is prepared by polymerization of decanedioic acid and 1.6-diaminohexane.
Chemicals
sebacoyl chloride, decanedioyl dichloride
hexane-1,6-diamine, 1,6-diaminohexane
dichloromethane, methylene chloride, methylene dichloride
hexanedioic acid, adipic acid
cyclohexane, C₆H₁₂It is best to use cyclohexane as a solvent as in the first preparation below.

Solution 1. Dissolve 1.5 g of sebacoyl chloride in 50 mL cyclohexane, i.e. 15 mol per litre.
Solution 2. Dissolve 2.2 g of hexane-1,6-diamine in 50 mL of deionized water, i.e. 1.4 mol per litre.
Pour 5 mL Solution 2. into a beaker. Pour 5 mL of Solution 1. on top of Solution 2. using a glass rod so that the two solutions do not mix. A grey film of nylon forms at the interface of the two solutions.

Solution 1. Dissolve 2.0 mL of sebacoyl chloride in 50 mL of n-hexane (hexane).
Solution 2. Dissolve 3 g of hexane-1,6-diamine and 1 g of sodium hydroxide in 50 mL of deionized water.
Add phenolphthalein to make it more visible. Slowly pour Solution 1. as a second layer on Solution 2. Use forceps to grasp the polymer film that forms at the interface of the two solutions. Pull it gently from the centre of the beaker. Wind it round a glass stirrer or a cotton reel. Wash it thoroughly in 50% ethanol then in water until moist red litmus paper does not turn blue.

Solution 1. Add 2 g of sebacoyl chloride to 20 mL of dichloromethane. Add phenolphthalein to make it more visible.
Solution 2. Add 2 g of hexane-1,6-diamine to 20 mL of 1 M NaOH solution.
Slowly pour Solution 2. into the Solution 1. Do not mix the solutions. Grab the film of polymer between the two solutions with forceps. Wind the polymer onto a glass rod. Wash the nylon thread in water.

3.4.8 Prepare rayon, copper (II) sulfate with ammonia solution, "regenerated fibre", "artificial silk"
BE CAREFUL! Concentrated ammonia gives off choking fumes that badly stink your eyes. Do this experiment in a fume cupboard.
In commercial manufacture, cellulose filaments pass through solutions that then coagulate them or cellulose ethanoate (cellulose acetate) ethyl cellulose or cellulose nitrate is dissolved in a solvent. Rayon contains about 270 glucose units per molecule, but cotton contains 2 000 to 10 000 units per molecule. The solutions are forced through fine nozzles to form rayon or acetate rayon fibre. Commercial production of rayon uses treat cellulose from wood pulp with sodium hydroxide and carbon disulfide to produce xanthate that is squeezed to produce threads or cellophane.
Dissolve finely shredded paper in a saturated solution of copper (II) sulfate in concentrated ammonia solution. Put the solution in a plastic syringe and squirt into 1 M sulfuric acid. A blue thread forms that slowly runs white. The acid solution slowly turns blue.

3.4.8.1 Prepare rayon, basic copper carbonate with ammonia solution
Add 10 g of basic copper carbonate to 100 mL of 880 ammonia solution. Stir then pour the blue solution containing tetraamminecopper (II) ions into a second beaker. Slowly add 1.5 shredded cotton wool or filter paper or newspaper and stir for up to an hour until the solution becomes a gel, called viscose. Put viscose into a hypodermic syringe and inject it under 500 mL of 1 mol per litre sulfuric acid. The extruded blue fibre turns white as the as the acid neutralizes the tetraamminecopper (II) solution.

3.4.9 Prepare Bakelite plastic, phenol / methanal polymerization 1
See diagram 16.3.4.9: Phenol-methanal condensation polymerization
Bakelite is a trade name for phenol-formaldehyde resins, or phenolics. It is strong, takes a polish, is a good electrical insulator and is resistant to water, alcohol, and acids, and is used for light bulb holders, electrical fittings and saucepan handles. Phenolic resins are used in varnishes and lacquers. Phenols, hydroxybenzenes, are aromatic compounds with the hydroxyl group attached to the benzene nucleus. They react as alcohols and as weak acids to from salts. Phenol (carbolic acid, C₆H₅O₁₀) is used to make Nylon, phenolic resins and epoxy resins. It is a strong disinfectant. As it is a weak acid, it can ionize polymer: C₆H₅OH --> C₆H₅O^- + H⁺.
The phenol group C₆H₅^-is the organic group in benzene, C₆H₆. Resorcinol [1,3-dihydroxybenzene, C₆H₄(OH)₂] is a dihydric phenol used with formaldehyde (methanal, HCHO) to make cold setting adhesives, also used to make plasticizers, resins and fluorescein dyes.
Bakelite is named after its inventor, L. H. Baekeland, for the resin made from the reaction of phenol and formaldehyde. It may be produced in transparent, clear coloured masses. When powdered and mixed with various filling materials it may be moulded under heat and pressure.
BE CAREFUL! Teacher demonstration only! Do the experiment in a fume cupboard. Use safety glasses and nitrile chemical-resistant gloves.
1. Make a mould in Plasticine by pushing an object into it, e.g. a key. Put resorcinol in a beaker and add the formalin solution. Stir the solution until it is clear. Add 1 mL of dilute hydrochloric acid while stirring and then quickly pour the mixture into the mould. Leave the plastic to harden for a day or two. Remove plastic from mould and wash with water.

2. Add 30 mL concentrated sulfuric acid to 30 mL water. Be careful! Pour slowly and keep stirring! Then leave to cool to room temperature. Pour 25 mL of formalin into a disposable container and add 55 mL of glacial ethanoic acid (glacial acetic acid). Add 20 g of phenol (C₆H₅OH) and stir with a disposable glass stirring rod until the phenol dissolved. Add 60 mL dilute sulfuric acid (diluted above) and keep stirring. The mixture turns pale yellow then opaque pink, especially around the stirring rod. Heat is given off. Discard the milky liquid then take out the pink polymer, Bakelite, and heat it with a Bunsen burner flame. The polymer chars but does not melt because it is a thermosetting plastic. Discard the disposable container and the stirring rod.

3.4.11 Prepare slime balls, "Silly putty", silicone polymer to amuse children
Order online: Slime Kit, Non-Newtonian liquid, pre-dissolved PVA
Order online: Silly Putty, Non-Newtonian liquid and dilatant compound
Slime flows like a liquid under normal conditions but bounces on impact. Commercial slime is a water soluble polymer sold by chemical supply firms or novelty firms to amuse children. The long molecules which comprise slime can slide over and around one another and cover the entire bench if left unguarded. They can also form temporary cross-linking bonds which affect the viscosity of the slime. Polymers are very large molecules made by linked monomers. Polymer molecules can cross link with weak and strong chemical bonds. A strand of PVA, molecular weight 78, 000, may contain 1800 monomer units.
Test the slime by 1. slowly poking it with your finger, 2. quickly poking it with your finger, 3. slowly pulling it apart, 4. quickly pulling it apart, 5. roll it into a ball and note whether it keeps its shape, 6. roll it into a ball and note whether it bounces when dropped on the bench.
1. Prepare glue slime with 50 mL of 4% poly(vinyl alcohol) (PVA) or use pre-dissolved PVA, and 10 mL of 4% borax solution.
2. Add 1 mL of 4% borax solution to the 50 mL of 4% poly(vinyl alcohol). With each successive addition of 1 mL of 4% borax solution, observe any changes when you stir the gel slowly, stir the gel rapidly, pour the gel into another container, roll the gel in the hands to form a ball of gel, leave the ball of gel to stand, pull on a ball of gel.
2. Dissolve 2 tablespoons of borax in half a cup of warm water with a spoon. Add a drop of food colouring. Pour some PVA glue into a bowl. Put an equal amount of the coloured water into the bowl and mix.
3. Add 7g of powdered or crystalline PVA to 100 mL of water on a hot plate with a magnetic stirrer. The PVA may take hours to dissolve. Add 10 mL of borax solution to 25 mL of the PVA solution. Observe the formation of the gel.
4. Add 10 mL of 4% borax solution to 40 mL of PVA wood glue solution. Observe the formation of the gel.
5. Dissolve a small water soluble laundry bag in 1 litre of hot water. Add 10 mL of borax solution to 40 mL of the PVA solution. Observe the formation of the gel.
6. The "viscosity builder" grade vegetable guar gum is used as a colloid stabilizer in foods, e.g. salad, dressing and ice cream. Slime is a non-Newtonian fluid. Dissolve 1 g of "viscosity builder" grade vegetable guar gum in 20 mL of water. Boil 60 mL of water and add the 20 mL suspension of guar gum while stirring. Dissolve 0.75 g of borax in 20 mL of water and add to the still warm solution while stirring. Leave to cool as a green gum and store in a closed container to prevent drying.
7. At the boiling point of water, poly(vinyl acetate) PVA, breaks down to give a lower molecular mass polymer. Dissolve 3% solution of poly(vinyl acetate) in boiling water then cool rapidly. Add 10 mL of saturated borax solution and food colouring, then stir slowly.
8. Pour 15 mL of borax solution into a plastic bag, e.g. Ziploc bag. Add 3 drops of food colouring. Add 60 mL of 50 % white glue mixture (polyvinyl acetate and polyvinyl alcohol). Close the plastic bag and kneed it for about 10 minutes until the colour is uniform. Turn the plastic bag inside out to remove the gloop polymer, called GlueP, a semi-solid plastic material with different properties to the ingredients.
9. Funny worms, magic octopus polymer: Thermoplastic polymers may be treated to form substances to amuse children. They may be plasticized and "tackified" so that when thrown against a clean wall they stick to the wall and fall slowly, so appearing to crawl down the wall.

3.5.0.1 Polymers, describe polymers
Collect, examine and describe different addition polymers, e.g. nylons, polyurethanes (urea-formaldehyde) polyesters (Terylene, fibre glass) and epoxy resins.

3.100 Prepare plastic with milk casein
Casein is a phosphoprotein thermoplastic polymer that may be used to make insulators, buttons, handles, adhesives and artist's priming paint. You can make casein from the reactions of skimmed milk with ethanoic acid (acetic acid).
1. Add 1 mL of glacial acetic acid to 10 mL of water. Heat 200 mL of skimmed milk to 50^oC then maintain the temperature. Do not let the solution boil. Add drops of the acetic acid solution or vinegar to the warmed milk while stirring. Leave to stand until the liquid becomes clear and white-yellow lumps of casein curd separates. Remove the heat and leave to cool. Use gloves to remove the lumps of casein, wash them under the tap, and squeeze them together until dry and the resulting one lump becomes rubbery.
2. Mould it into shapes and then expose it to the air for 2 days. Leave the dried casein in 40% formaldehyde solution (formalin) to harden. Polish the hard casein plastic with sandpaper.
3. Add of ammonia solution to prepare glue.
Calcium caseinate + 2H⁺ ---> casein + Ca²⁺

3.101 Prepare urea-formaldehyde resin
See diagram 1.13a: Simple fume hood
Do not use hydrochloric acid as a catalyst for these preparations because the carcinogenic bis(chloromethyl) ether may form.
1. Add 30 mL of vinegar to 50 mL of warm skimmed milk while stirring. Observe lumps of casein forming. Separate the lumps with a strainer and mix them with 30 mL of warm water. Add 90 mL of sodium bicarbonate. Sir the mixture and force it through a sieve. After leaving to stand overnight, the mixture can be used as an adhesive.
1. Mix 10 g of urea with 20 cc of 40% formaldehyde (formalin) solution in a plastic container that you can throw away. Add 1 cc concentrated sulfuric acid by drops and stir. Be careful! The solution becomes cloudy and a white powder deposits in the plastic container because of the formation of the resin. The solution becomes hot.
2. Make a Plasticine (modelling clay) mould lined with aluminium foil. Put fibres from a broom in the mould. Mix urea with twice its weight of formalin and pour it into the mould. Add drops of dilute sulfuric acid. Heat in a fume cupboard, fume hood until the solution becomes cloudy because of the formation of the hard resin.
3. Hold some hard resin with tongs in a Bunsen burner flame. The resin chars but does not burn showing that it is a thermosetting plastic
A condensation polymerization forms with the elimination of water:
(NH₂).CO.(NH₂)+ CH₂O ---> NH-CO-NH-CH₂ + H₂O
urea + formaldehyde ---> urea-formaldehyde + water
4. Concentrated solutions of formaldehyde very slowly form a white precipitate of paraformaldehyde.

3.102 Tests for plastics, natural fibres and synthetic fibres
1.0 Transparency and feel
2.0 Density
3.0 Thermal behaviour
4.0 Flammability, burning tests for plastics
4.1 Procedures for testing
4.2 Tests for natural fabrics
4.3 Tests for synthetic fibres
5.0 Fracture type
6.0 Solubility
7.0 Heat conductivity
This experiment is based on: Selinger, Ben, 1991, "Chemistry in the market place", Harcourt Brace Jovanovich Publishers, ISBN 0 7295 0334 8, Experiment 13.13.

1.0 Transparency and feel
Note whether the plastic is glass clear, translucent, opaque. However, plastics are usually coloured during manufacture.
Clean the surface of the test strips of any grease and feel them between the first finger and thumb. Only polyethylene and polytetrafluorethylene have a waxy feel. Feel the test polymer. Only polyethylene and polytetrafluorethylene have a waxy feel. Before the test, clean the surface to remove grease or plasticizers.

2.0 Density
Density test polymer: Polyethylene, polypropylene, styrene- butadiene and some types of nitrile will float after you wet it thoroughly push it below the surface of water then release. You cannot test foam plastics in this test. Wet test strips of the following plastics and then push them down below the surface of water + a drop of detergent in a beaker. Do not use foam plastics. Some plastics contain additives that affect the density. The PE strip floats because its density is 0.9 g cm³. Slowly add sodium chloride to the water so that it all dissolves. As the density of the water increases the test pieces star to move up towards the surface of the water. Note the order the test pieces move up. The PE test strip moved up first so label it 1. then label the others
Test strips and order of moving up
Phenolic, PF, 5.
Polyester, UP, 6.
Polyethene, PE, polyethylene, 1.
Polymethyl methacrylate, PMMA, 3.
Polystyrene, PS, 2.
Polyvinyl chloride, PVC, 4.

3.0 Thermal behaviour
Put test strips of thermoplastics in hot water and compare their softness.

4.0 Flammability, burning tests for plastics
4.1 Procedures for testing
1. Copper wire test
BE CAREFUL! Hold small samples with tongs in a fume cupboard or well ventilated place.
Hold the burner at an angle at an angle. Stick a copper wire in a cork. Heat the wire with a Bunsen burner until any yellow, green or red colour disappears. Press the end hot wire into the plastic sample, then put the end with molten plastic on it back in the flame. Observe the colour in the flame, usually yellow, easy or difficult to ignite, melting, residue, fumes and odour. Remove the burning plastic from the flame and note whether it still burns. A green colour indicates that the plastic contains a halogen, e.g. chlorine in poly(vinyl chloride) (PVC) or poly(vinylidene chloride) (PVDC). Cyanide, e.g. from Orlon, may give a positive result. Before repeating the test with another plastic, again heat the copper wire until the green colour disappears.

2. The laboratory must be well-ventilated. Put on protective glasses. Place a Bunsen burner next to a sink with some water in it. Light the Bunsen burner. Use tongs to hold a test piece of plastic in the outer part of the Bunsen burner flame. When the test piece catches fire move it over the sink to allow molten drops of plastic to fall into it. Blow out the flame on the test piece. Use your hand to gently fan the the smoke towards you nose and note the smell.

3. Gently heat 0.1 g of plastic on a clean spoon over a small colourless Bunsen burner flame until it fumes without ignition. Remove the spoon from the flame then test the fumes with moist litmus paper. Note the smell of the burning plastic. Move the spoon to the hottest part of the Bunsen burner flame.
Note the following:
1. Whether the material burns, and if so, how easily.
2. The nature and colour of any flame, a very sooty flame generally indicates an aromatic polymer.
3. Whether the plastic continues to burn after removal from the flame.
4. The nature of any residue.

4. Hold each of the materials in a test-tube holder over a tin lid or dish, try burning each with the spirit burner flame. Note how easily or otherwise they burn, whether they leave much ash or char, and whether any easily recognized smell is formed.

5. Identify plastics and other materials with hot needle tests.

4.2 Tests for natural fabrics
List the natural and synthetic fabrics found in the home.
Silk: Heat a small piece of real silk in a dry test-tube, and hold at the mouth of the test-tube a moist piece of red litmus paper. The litmus paper turns blue, caused by ammonia. Animal fibres, e.g. silk, contain nitrogen compounds. When heated they form ammonia. Silk bums readily, with an orange-yellow flame. A black bead of ash is formed and a smell of burning hair.
Wool: Heat a small piece of wool in a dry test-tube, and hold at the mouth of the test-tube a moist piece of red litmus paper. The litmus paper turns blue, caused by ammonia. Animal fibres, e.g. wool, contain nitrogen compounds. When heated they form ammonia. Wool burns slowly, appearing to melt together. It chars, and gives a smell of singed hair.
Cotton: Heat a small piece of cotton in a dry test-tube, and hold at the mouth of the test-tube a moist piece of blue litmus paper. The litmus paper turns red, caused by ammonia. Cotton is of plant origin so does not contain nitrogen compounds and does not produce ammonia. You can make a piece of litmus paper blue by pouring a few drops of limewater on it and washing it in water. Cotton and burns easily, leaving only grey ash.
Linen: It is not of animal origin, does not contain nitrogen compounds, so does not form ammonia.
Distinguish wool from cotton: Place a finger width of sodium hydroxide solution in a test-tube and add a strand of wool. Heat the solution. Describe what you see. Repeat the experiment with cotton and see if the same thing happens. The wool dissolves, the cotton does not dissolve. Cotton is of plant or vegetable origin, does not contain nitrogen compounds, so does not form ammonia. Cotton forms acid vapours when heated.

4.3 Tests for synthetic fibres
Acrylonitrile-butadiene-styrene: yellow flame with blue base, smoky, burns after removing flame, styrene smell
Casein, milk casein: easy to ignite, yellow flame, does not burn after removing flame, burnt milk smell
Celluloid, cellulose acetate: easy to ignite, yellow flame, burns after removing flame, acidic fumes, acetic acid smell
Cellulose acetate, (cellulose ethanoate), easy to ignite, yellow flame, burns after removing flame, acidic fumes, acetic acid smell
Epoxy resin: easy to ignite, orange yellow smoky flame, burns after removing flame, acrid smell
Ethyl cellulose: when ignited forms drips on ignition, blue-yellow flame with a green base, burns after removing flame, burning wood smell
Polyamide, nylon: easy to ignite and forms a clear melt, blue flame with a yellow tip, does not burn after removing flame, burnt vegetation smell
Melamine-formaldehyde: very difficult to ignite and forms alkaline fumes, pale yellow flame with light blue-green edge, formaldehyde and fish-like smell
Nylon 6 and 6.6: Melts and burns in the flame, smoke with white fishy odour like celery, yellow melted falling drops. Stops burning when removed from flame with small bead on the end that can be stretched into a fine thread. Residue is a hard round bead.
Note how nylon behaves when heated in the test-tube. It first melts to a brown liquid, and ammonia is evolved. It does not burn easily. Nylon is a synthetic (man-made) fibre that gives ammonia when heated. However, the way it melts distinguishes it from animal fibres.
Phenolics, phenol formaldehyde resin: difficult to ignite and burn, yellow flame, does not burn after removing flame, phenolic / formaldehyde smell
Polyacrylonitrile: easy to ignite, yellow flame, burns after removing flame, cyanide / burnt wood smell
Polycarbonate: at first difficult to ignite, yellow smoky flame, burns after removing flame, phenolic smell
Polyester: Melts and burns with black smoke that has a faintly sweet and oily sooty odour like sealing wax, and melted falling drops. When removed from flame it stops burning with a black bead on the end that can be stretched into a fine thread. Polyester is a condensation polymer of polyhydric alcohol and polybasic acid, linear polyester is "Terylene", unsaturated polyesters are used in in fibre-glass.
Polyethylene: easy to ignite and forms a clear melt, yellow flame with a blue base, burns after removing flame, burning candle wax smell
In flame it shrinks, curls and melts and continues to burn slowly with smell like paraffin wax, when removed from the flame leaving a residue like paraffin wax. The hot melted substance cannot be stretched
Polymethyl methacrylate: easy to ignite, yellow flame with a blue base, yes
Polypropylene: Shrinks and burns in flame with smoke that smells like burning asphalt. and continues to burn rapidly when removed from the flame leaving a brown-yellow residue. The hot melted substance can be stretched into a fine thread.
Polystyrene: easy to ignite, blue-yellow smoky flame, burns after removing flame, styrene smell
Polytetrafluoroethene: difficult to ignite then chars slowly, yellow flame, does not burn after removing flame, acidic fumes, no smell
Polythene
Polyurethane: easy to ignite, yellow flame with a blue base, burns after removing flame, acrid smell
Polyvinyl acetate: easy to ignite and forms a black residue, yellow smoky flame, burns after removing flame
Polyvinyl chloride: easy to ignite, yellow flame with a green base, does not burn after removing flame, acidic fumes, acrid smell
Rayon: Heat a small piece of rayon in a dry test-tube, and hold at the mouth of the test-tube a moist piece of blue litmus paper. The litmus paper turns red, caused by ammonia. Rayon is of plant origin so does not contain nitrogen, so does not form ammonia. Rayon forms acid vapours when heated. Rayon burns easily, leaving only grey ash.
Urea-formaldehyde: very difficult to ignite, yellow flame with blue-green edge, does not burn after removing flame, alkaline / formaldehyde / fish smell

3.103 Tests for polymers
Need to specify: 1. repeat units, 2. molecular mass distribution (MMD), 3. chains, 4. fillers. Identification methods include infra-red, ultraviolet and nuclear magnetic resonance spectroscopy, also swelling tests for thermosets. Sometimes the polymer can be degraded to soluble products and these be identified.

3.104 Tests for plastics in known density solutions
See 3.6.1: Polymer density
Test about 200 cm³ of the following plastics in solutions of known density:
PET, PVC, PS, HDPE, LDPE, PP EPS
For example PS sample should float in solution 5. but sink in solution 1.

Solution	Density	Composition of 1000 cm³ solution
1.	0.79	Pure ethanol (IMS)
2.	0.91	471 g (596 cm³) ethanol in 439 cm³ deionized water
3.	0.94	354 g (448 cm³) ethanol in 586 cm³ deionized water
4.	1.00	Deionized water
5.	1.15	184 g K₂CO₃ in 965 cm³ deionized water
6.	1.38	513 g K₂CO₃ in 866 cm³ deionized water