Recipe cards update

PS57 JAT 09/07 © CLEAPSS®, The Gardiner Building, Brunel Science Park, Uxbridge UB8 3PQ

PS57 Amendments to Recipe Cards

As a result of the publication of the new edition of Hazcards in September 2007, it has been necessary to makechanges to the majority of Recipe Cards. These changes include alterations to the hazard classification of somechemicals together with updated references to specific Hazcard numbers and changes to the names of somechemicals to match those on the 2007 edition of Hazcards. The cover, contents list, how to deal with unusualrecipes and Index cards have also been revised.More-substantial changes have been made to Recipe Cards 28, 39, 45 and 59.The only Recipe Cards that have not been altered are 1, 2, 4, 15, 29, 51, 55, 63 and 64.It is recommended that all changed Recipe Cards are either downloaded from the members-only part of theCLEAPSS web site: www.cleapss.org.uk or accessed from the 2008 CLEAPSS Science Publications CD-ROMwhen it is issued. Recipe Cards dated 2007 include all changes made to cards since 1999 that have previouslybeen listed in this document, PS57. If the paper version of Recipe Cards is still consulted, all the changed cardsshould be printed to replace existing cards. Check that the card below, changed in 2001, has been corrected.

Changes made in 2001 to cards that have not been revised in 2007 include the following.Recipe Card 64. The recipe for alkaline pyrogallol solution was changed – please replace the original card.

© CLEAPSS 2007

28 Gas solutionsComment: Aqueous solutions of gases should be prepared and tested just before use. In storage, solutions become weaker.

ProceduresSolution Preparation of solution Risk assessment

Bromine water(3 methods tomake a0.02 Msolution)

1. Add 1 cm3 of bromine to 500 cm3 of water in a 1 litre beaker. Add astirrer bar and place on a magnetic stirrer to dissolve the bromine. Thiscan take some time. Dilute to 1 litre with water. Alternatively, a smallampoule (1 cm3 ) can be crushed (under 500 cm3 of water) and madeup to 1 litre. The solution must be decanted so that no glass is present.2. Dissolve 4.76 g of potassium bromide in 76 cm3 of water, add 14 cm3

of 10% (available chlorine) sodium chlorate(I) solution and 10 cm3 of2 mol dm-3 hydrochloric acid. Dilute to 1 litre with water.3. Add 1.12 g of potassium bromate(V), 12 g of potassium bromide and14 cm3 of 2 mol dm-3 hydrochloric acid into a 1 litre jug or measuringcylinder. Add water to 1 litre and pour into a bottle.Label the bottle of bromine water HARMFUL.

Bromine is very TOXIC and CORROSIVE. Usea fume cupboard. Wear goggles or a faceshield and chemical-resistant gloves.

Sodium chlorate(I) is CORROSIVE. Use afume cupboard. Wear goggles or a faceshield.(See also Hazcards 15A & B and 89.)

Chlorine water 1. Chlorine gas is bubbled into 250 cm3 water in a fume cupboard untilthe solution goes light green.2. To prepare a 1% (v/v) solution, one volume of 10% (available chlor-ine) sodium chlorate(I) solution is diluted ten times with water and onevolume of 2 mol dm-3 hydrochloric acid is added.Label the bottle of chlorine water HARMFUL. Further dilution is possiblewhich lowers the level of hazard.See Hazcard 22B for a recipe using sodium dichloroisocyanurate.

Chlorine is TOXIC. Use a fume cupboard.Wear goggles or a face shield.Sodium chlorate(I) is CORROSIVE. Use afume cupboard. Wear goggles or a faceshield.(See also Hazcards 22A & B and 89.)

Sulfur dioxidesolution

1. In a fume cupboard, SO2 is passed into 250 cm3 of water via aninverted funnel with the rim of the funnel just touching the water surface.2. In a fume cupboard, dissolve 9.5 g of sodium metabisulfite in100 cm3 of water. Add 100 cm3 of 0.5 mol dm-3 sulfuric(VI) acid andmake up to 250 cm3.Label the bottle “TOXIC sulfur dioxide will be given off”. Further dilution ispossible and recommended.See Hazcard 92 for a recipe to simulate acid rain.

Sulfur dioxide is TOXIC. Use a fumecupboard. Wear goggles or a face shield.Sodium metabisulfite is HARMFUL. Use afume cupboard. Wear eye protection.

[See also Hazcards 92 & 97 and CLEAPSSLaboratory Handbook 13 (Gases).]

© CLEAPSS 1999

29 Gram stain – part 1Comment: The Gram staining technique is used to distinguish between two types of bacteria: Gram-positive and Gram-

negative. The following procedure will provide you with a thin film of bacteria on a microscope slide, forstaining.

Preparation of a heat-fixed smear♦ Using a clean microscope slide and, using a sterile inoculating loop, place a single drop of

water in the centre of the slide.♦ Mix in a small amount of a sample from a single bacterial colony, until the suspension is

slightly turbid.♦ Smear the suspension over the central area of the slide, to form a thin film. For liquid

cultures, use a single drop of culture fluid, spread in a similar manner.♦ Allow to dry in the air at room temperature which may take a few minutes.♦ Fix the air-dried film by passing the slide through a Bunsen burner flame. Using forceps to

hold the slide, pass it horizontally, film side up, rapidly through the hottest part of the flamejust above the blue cone. Repeat this twice more. (Excessive heating will ruin thepreparation. It is customary to check that the slide has not been overheated by touching it,after each flaming, on the back of the hand. The slide will feel hot but should not be painful!If it is, start again.)

♦ Allow to cool; the smear is now ready for staining.

© CLEAPSS 2007

38 Inorganic test reagents-2Recipes for making 100 ml of solutionA. Magenta (basic fuchsin) for sulfite ions

Dissolve 0.02 g in 100 ml of water.

! Fuchsin is HARMFUL by inhalation, in contact with skin and ifswallowed. No hazard warning is required on the solution.

B. Magneson(II) for magnesium ionsDissolve 0.001 g in 100 ml of water.

! Magneson is HARMFUL if swallowed, if inhaled and by skincontact. No hazard warning is required on the solution.

C. Potassium hexacyanoferrate(II) (0.1 M) for iron(III) ionsDissolve 4.22 g in 100 ml of water.

! See Hazcard 79. No hazard warning is required on thesolution.

D. Potassium hexacyanoferrate(III) (0.1 M) for iron(II) ionsDissolve 3.29 g in 100 ml of water.

! See Hazcard 79. No hazard warning is required on thesolution.

E. Potassium thiocyanate (0.1 M) for iron(III) ionsDissolve 1.0 g in 100 ml of water.

! Potassium thiocyanate is HARMFUL. See Hazcards 55C and95C. No hazard warning is required on the solution.

F. Sodium hexanitrocobaltate(III) (cobaltinitrite) (0.16 M) forpotassium ionsDissolve 6.8 g of the solid in water and make up to 100 ml.

! This substance is TOXIC & OXIDISING. See Hazcard 95A. It isan unstable solution with a maximum shelf-life of 3 weeks.No hazard warning is required on the solution.

G. Sodium sulfide (0.2 M) for metal ionsDissolve 5 g of the solid in water and make up to 100 ml.

! The solid is CORROSIVE (see Hazcard 51). Prepare the solu-tion in a fume cupboard, wearing gloves and eye protection.The preparation produces hydrogen sulfide gas (see Haz-card 51) which has an obnoxious smell. Label the solutionIRRITANT.

H. Thiourea for tin(II) ionsDissolve 10 g in 100 ml of water.

! Thiourea is a category 3 carcinogen (see section 7.8 of theCLEAPSS Laboratory Handbook) and HARMFUL if swallowed.

I. Uranyl(VI), zinc(II) or magnesium ethanoate for sodiumionsDissolve 10 g of uranyl(VI) ethanoate and either 30 g ofzinc(II) ethanoate or 33 g of magnesium ethanoate in 12 mlof 5 M ethanoic acid. Dilute to 100 ml, add 0.1 g of sodiumchloride, allow to stand for 24 hours, then filter.

! See Hazcard 105. Wear eye protection, gloves and a labor-atory coat. Avoid raising dust. Label the solution VERY TOXICand RADIOACTIVE.

© CLEAPSS 2007

39 Iodine solutionComment: Iodine is only sparingly soluble in water (0.3 g l-1) and it is usual to dissolve it in potassium iodide solution

(KI) or organic solvents such as ethanol. A 0.01 M solution is suitable as a starch test reagent.Formula I2 Molar mass: 253.80 g mol-1

!Hazards

Control measures

Iodine is HARMFUL by inhalation and in contact with the skin. See Hazcard 54. The organic solventsused are also hazardous and the relevant Hazcard should be consulted.Wear eye protection and gloves when weighing. The room should be well ventilated.

Mass of solids (g) to be usedVolume (ml) of solution requiredConcentration

requiredHazard warning

label 100 250 10000.01 M - Ten-fold dilution of the 0.1 M solution0.05 M - 1.5 g of KI + 1.27 g of I2 5 g of KI + 3.17 g of I2 20 g of KI + 12.69 g of I20.1 M - 3.0 g of KI + 2.54 g of I2 10 g of KI + 6.35 g of I2 40 g of KI + 25.38 g of I2

Procedure♦ Measure out the indicated quantity of potassium iodide (KI) into an appropriate beaker.♦ Moisten the potassium iodide with a few drops of water.♦ Measure out the indicated quantity of iodine and add it to the moistened potassium iodide.♦ Add a small volume of water and stir. When no more iodine appears to dissolve, add some more

water and stir. Keep repeating this procedure until all the iodine has dissolved.♦ Pour the solution into a measuring cylinder and dilute to the final volume. Make sure there are no

bits of iodine remaining. If there are, return the solution to the beaker and leave it on a magneticstirrer for several minutes.

♦ Add the solution to a labelled bottle and mix well.

‘Tincture of iodine’♦ Dissolve 2.5 g potassium iodide and 2.5 g iodine in 100 ml of ethanol. Label this solution HIGHLY

FLAMMABLE & HARMFUL.

© CLEAPSS 2007

44 Nitric(V) acidComment: The strength of commercial concentrated solution is about 70% (w/v) and has a specific gravity of 1.42. Old

stock may be weaker in strength than freshly-bought solutions. It should be stored in dark bottles. Whenexposed to light, the solution goes brown and TOXIC nitrogen dioxide gas is produced (see Hazcard 68).

Formula: HNO3 Molar mass: 63.01 g mol-1

!Hazards

Control measures

Nitric(V) acid is CORROSIVE and OXIDISING. If in contact with the skin, this becomes yellow and layers ofskin peel off. See Hazcard 67.Wear suitable eye protection (a face shield is preferable) and gloves. Use a fume cupboard if necess-ary.

Volume of 70% (w/v) nitric(V) acid (ml) to be usedVolume (ml) of solution requiredConcentration

requiredHazard

warning label 500 1000 25000.01 M - Ten-fold dilution of the 0.1 M solution0.1 M IRRITANT Ten-fold dilution of the 1 M solution 160.4 M IRRITANT 12 25 621 M CORROSIVE 31 62 1555 M CORROSIVE 155 310 775

Procedure♦ Measure out the indicated volume of concentrated nitric(V) acid in a measuring cylinder.♦ Add the liquid to about two thirds of the final volume of water in a beaker.♦ Stir the solution. (Heat will be given out and the solution will become warm.)♦ Pour the solution into an appropriate measuring cylinder and dilute to the final volume.♦ Pour the solution into a labelled bottle and mix well. Add a hazard warning if appropriate.

Comment: Also available from suppliers is 95-100% (fuming) nitric(V) acid, which is even more hazardous as it is unstable. If therehappens to be any old stock still present in the school, then it is better to dilute it as soon as possible.

© CLEAPSS 2007

45 Nylon rope experimentComment: Although used in the past, tetrachloromethane (carbon tetrachloride) (see Hazcard 100) and 1,1,1-trichloroethane

(see Hazcard 103), if available, should no longer be chosen as the solvent. An alternative solvent is cyclohexane.Hexanedioyl chloride (adipoyl chloride) may be used but is more unstable in storage, so it is normally better to buydecanedioyl (sebacoyl) chloride.

!Hazards

Control measures

The acid chlorides and hexane-1,6-diamine are CORROSIVE (see Hazcards 3B & 41) and cyclohexaneis HIGHLY FLAMMABLE and HARMFUL (see Hazcard 45B).Wear eye protection. Wear disposable nitrile gloves when pulling out the nylon thread. The roomshould be well ventilated and there must be no sources of ignition.

Procedure using cyclohexane as the solvent♦ Dissolve 2.2 g of hexane-1,6-diamine in 50 cm3 of distilled water in a beaker (label it ‘A’).

♦ Dissolve 1.5 g of decanedioyl chloride or hexanedioyl chloride in 50 cm3 of cyclohexane inanother beaker (label it ‘B’) and add HIGHLY FLAMMABLE & HARMFUL warning signs.

♦ Carefully pour the solution from beaker B onto solution A down a glass rod. The two liquidphases do not mix; resist any attempt to stir the mixture at all.

♦ Use forceps to pull out the nylon formed at the interface of the two solutions.

© CLEAPSS 2007

59 SlimeComment: The material formed is a gel. It is thought that borate ions react with hydroxyl groups in the polymer of vinyl alcohol to

form cross links with the elimination of water. These cross links probably involve hydrogen bonds which continually formand break under flow. The ‘sliminess’ of the gel can be adjusted by altering the amount of sodium borate used. Viscositychanges can be detected by timing the passage of a ball bearing through the ‘slime’ in a measuring cylinder. If acid isadded to the ‘slime’, the gel collapses to give a free-flowing solution. Although the slime can be stored in a labelled sealedbag and placed in a refrigerator, it can develop mould if kept for long periods. Disposal: Add enough 1 M sulfuric(VI)acid just to allow the solution to be free-flowing, dilute and pour down a foul-water drain.Different sources of polyvinyl alcohol vary in their average molar mass; some are about 115 000 g mol-1, while others aremuch less at around 17 000 g mol-1 (and less expensive). PVA wood glue is cheaper still and contains polyvinyl acetateand alcohol but the formulations from suppliers vary considerably.

!Hazards

Control measures

None of the reagents are particularly hazardous, although sodium tetraborate solutions are alkalineand may irritate the skin. There is a lot of vigorous stirring of hot liquids.Wear eye protection. Hot water from a kettle may be useful to start with.

ProcedureUsing polyvinyl alcohol (PVA):

♦ Pour about 100 ml of water (no hotter than 90 °C) into a 400 ml beaker, add 4 g of high-mass (8 g of low-mass)polyvinyl alcohol, stirring rapidly. Add food colouring and/or fluorescent dye, eg, fluorescein, for added(disgusting) effect. (Solution A.)

♦ Heat to 90 °C (but do not boil) and keep stirring as required until the polymer dissolves. Allow the solution tocool. All of this may take some time!

♦ If a high-mass PVA was used to make solution A, dissolve 0.80 g of sodium tetraborate-10-water (0.42 g ofanhydrous sodium tetraborate) in 20 ml of water. If a low-mass PVA was used, dissolve 1.6 g of sodiumtetraborate-10-water (0.84 g of anhydrous sodium tetraborate) in 20 ml of water. (Solution B.)

♦ Add solution B to A with vigorous stirring. Let the gel form before removing and washing it with water.

Using PVA glue:♦ Dilute it to about 25%; there is no need to heat it but mix it well with water. Add sodium tetraborate as

prepared above for use with low-mass PVA. Change the concentration of PVA glue to alter the ‘slime’ quality.

© CLEAPSS 2007

60 Soap and bubble solutionsComment: Soap solutions can be titrated against tap water in a stoppered bottle until a froth, stable for 15 seconds, is

obtained. The strength of the soap solution and/or volume of water involved in the titration will depend on thehardness of the local tap water. Both solutions should be tested before being presented to a class so that minoradjustments can be made.

!Hazards

Control measures

Some of the solutions are made up in ethanol which is HIGHLY FLAMMABLE & HARMFUL (see Hazcard40A). Propane-1,2,3-triol is LOW HAZARD (see Hazcard 37).Do not heat soap solutions made up in ethanol with a naked flame. Use a hot plate or surround thebeaker with hot water.

Procedure to make a soap solution suitable for titration♦ Dissolve 5 g of soap flakes (eg, Lux) in 500 ml of ethanol by stirring the suspension on a hot

plate. This may take some time.♦ After cooling, pour the solution into a 1 litre volumetric flask and dilute to 1000 ml with

pure water. Mix the solution well.♦ The titration with tap water to obtain a permanent froth should be rehearsed so that

adjustments to the volume of tap water or concentration of the soap solution can be made.Bubble mixture1

♦ Mix together by volume, 10 parts liquid detergent, 85 parts pure water and 5 parts propane-1,2,3-triol (glycerol).

1 From the Salters’ Chemistry Handbook. Contact The Salters’ Chemistry Club, Salters’ Hall, Fore St, London EC2Y 5DE.

Tel: 020 7628 5962; Fax: 020 7638 3679.

© CLEAPSS 1999

63 Sodium chloride

Formula: NaCl Molar mass: 58.44 g mol-1

Mass (g) of solid to be usedVolume (ml) of solution requiredConcentration

requiredHazard

warning label 100 250 10000.01 M - Ten-fold dilution of 0.1 M solution0.1 M - Ten-fold dilution of 1 M solution 5.841 M - 5.84 14.61 58.44

Saturated (20°C) - >37 >93 >370

Procedure♦ Measure out the indicated quantity of sodium chloride.♦ Add the solid to about two thirds of the final volume of water in a beaker.♦ Stir to dissolve. Warm it if necessary.♦ Pour the solution into an appropriate measuring cylinder and dilute to the final volume.♦ Pour the solution into an appropriate labelled bottle and mix well.

© CLEAPSS 2001

64 Sodium hydrogencarbonateFormula: NaHCO3 Molar mass: 84.01 g mol-1

Mass (g) of solid to be usedVolume (ml) of solution requiredConcentration

requiredHazard

warning label 100 250 10000.01 M - Ten-fold dilution of the 0.1 M solution0.1M - Ten-fold dilution of 1 M solution 8.401 M - 8.40 21.00 84.01

Saturated (20°C) - 9.6 >24.0 >96

Procedure♦ Measure out the indicated quantity of sodium hydrogencarbonate.♦ Add the solid to about two thirds of the final volume of pure water.♦ Stir to dissolve. Do not warm the solution.♦ Pour the solution into an appropriate measuring cylinder and dilute to the final volume.♦ Pour the solution into an appropriate labelled bottle and mix well.

Alkaline pyrogallol solution for absorbing / removing oxygen gasComment: Benzene–1,2,3-triol (pyrogallol) is HARMFUL (see Hazcard 12). Wear eye protection when preparing the solution. This

safer procedure replaces sodium hydroxide. However, the rate of absorption of oxygen by the alkaline solution producedusing sodium hydrogencarbonate may be too slow for some gas analysis activities in which air samples are exposed to thebenzene–1,2,3-triol for only a short time. In such circumstances, there is no alternative to the use of sodium hydroxide.The procedure described below limits the absorption of oxygen from the air. For some activities, eg, the removal of oxygenfrom the air around seeds in studies of germination, it is inappropriate. For such studies, first add the benzene–1,2,3-triolcrystals to the flask, tube etc and then the sodium hydrogencarbonate solution. Add the seeds and stopper the container.

♦ Prepare a saturated solution of sodium hydrogencarbonate using freshly-boiled pure water.♦ Place a wide-bore glass tube into the water and then pour liquid paraffin on the water’s surface.♦ Add a few crystals of benzene–1,2,3-triol (pyrogallol) down the glass tube and then slowly withdraw it. (1 g of

benzene-1,2,3-triol is capable of absorbing 190 cm3 of oxygen.)