safety in is experiments -...

INTEGRATED

SCIENCE

EXPERIMENTS

IN

PHYSICAL SCIENCES SECTIONADVISORY INSPECTORATEEDUCATION DEPARTMENT1999

SAFETY

PRECAUTIONS

PREFACE

This pamphlet is a revised edition of the one published in 1995.There are some changes and additions. Aiming at promoting laboratorysafety in the teaching of Integrated Science, the pamphlet highlights thesafety precautions to be taken in experiments and activities as suggestedby the CDC Syllabus for Science (Secondary 1-3). For easy reference,the experiments and activities listed in part III of the pamphlet are in theorder as they appear in the CDC Syllabus.

Teachers are also advised to make reference to the pamphlet Safetyin Science Laboratories published by the Education Department formore information on laboratory safety.

It must, however, be emphasized that the advice and informationoffered in this pamphlet are inevitably not exhaustive and do not precludethe need for exercising care and good judgement at all times in safe-guarding against laboratory accidents.

Comments and suggestions are welcome and should be directedto the Principal Inspector, Physical Sciences Section, AdvisoryInspectorate, Education Department, Room 1208, Wu Chung House,213 Queen�s Road East, Wan Chai, Hong Kong or the e-mail [email protected].

Physical Sciences SectionAdvisory InspectorateEducation Department1999

CONTENTS

I. PROPER USE OF PROTECTIVE EQUIPMENT 1

II. SAFE USE OF GAS TAPS 2

III. SAFETY PRECAUTIONS IN EXPERIMENTS / ACTIVITIESUnit 1 Introducing Science 3Unit 2 Looking at Living Things 7Unit 3 Energy 8Unit 4 Matter as Particles 10Unit 5 Solvents and Solutions 15Unit 6 Cells and Reproduction 17Unit 7 Living Things and Air 18Unit 8 Making Use of Electricity 20Unit 9 Making Heat Flow 21Unit 10 Hydrogen, Acids and Alkalis 23Unit 11 Detecting the Environment 26Unit 12 Forces and Movement 29Unit 13 Food and Transport 31Unit 14 Materials from the Earth 35Unit 15 Electricity and Electronics 39

IV. EXPERIMENTS/ACTIVITIES NOTRECOMMENDED 42

APPENDICESA Hazard warning labels 44B Hazards in the use of naphthalene in science

experiments 45C Wormery for earthworm/snail house 46D Experiments involving animal blood, cell

and human saliva 47E Some common plants known to be poisonous 49F Handling and killing of rats for dissection 50

Page

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G Sterilization of boiled seeds for experiments onrespiration 51

H Safety precautions in handling micro-organisms 52I Safety precautions in using extra high tension

(E.H.T.) power supply 54

Page

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1

I. PROPER USE OF PROTECTIVE

EQUIPMENT

(i) Safety spectacles/ Face shield/ Safety screen

Teachers, pupils and laboratory staff, when working in thelaboratory, should wear safety spectacles in all circumstances whereverthere is any potential risk of eye injury. Safety spectacles should alwaysbe put on when heating chemicals, handling acids, alkalis and othercorrosive chemicals, working with glass apparatus under pressure, orcarrying out potentially violent or exothermic reactions. Scratched ordefective safety spectacles should be replaced without delay becausethey may affect visibility and cause strain to the eyes or fail to servetheir protective function. Dirty safety spectacles should be cleaned witha detergent or disinfectant (e.g. diluted Savlon) as appropriate.

If a teacher intends to demonstrate potentially dangerous experi-ments in front of a class of pupils, the safety screen should be used toisolate the apparatus from the pupils. The teacher should also put onproper protective equipment, such as a pair of safety spectacles or a faceshield, for his/her own protection.

(ii) Protective gloves

Teachers and laboratory staff, when handling animals and killinganimals for dissection e.g. rats, should wear leather gloves so as to avoidbeing bitten or scratched. Students should also put on surgical glovesduring dissection. When working with wormery/snail house or handlingmicrobiological experiments, disposable gloves should be worn in orderto prevent infection. Furthermore, chemical resistant gloves should beput on when handling acids, alkalis and organic solvents if necessary,whereas heat/cold resistant gloves should also be used when dealingwith furnace or hot plate in the laboratory for protection.

2

II. SAFE USE OF GAS TAPS

(1) Pressdown type gas tap

(2) Gas tap with automatic shut-off facility and a safety valve

hose clip

Schools should take safety precautions to prevent accidents dueto inappropriate use of gas taps. The main gas supply valve of thelaboratory should only be turned on when gas supply is required, and alldownstream gas taps inside the laboratory must be in the OFF positionbefore the main valve is turned on. Teachers and laboratory techniciansmust ensure that Bunsen burners are properly connected to the gas tapsbefore experiments. Schools should also properly secure all unused gastaps in order to prevent them from being mistakenly turned on by pupils.The ways to secure the common types of gas taps are given below forteachers� and laboratory technicians� reference.

The unused gas tap can besecured by fixing a hose clipunder the gas tap knob toprevent it from being turnedon mistakenly.

The unused gas tap can betied up, such as by using anylon cable tie, to prevent itfrom being turned onmistakenly.

cable tie

3

C.1 Mixing solutions

C.2 Measuring temperature, weighing and volume

Unit 1 Introducing Science

Blindfold a pupil. Placeone of his hands in hotwater and the other in icewater.

Do not use hot water above 50oC.

M i x s o l u t i o n s o fchemicals and makeobservations.

Label the containers of chemicals withhazard warning labels. Provide pupilswith short blunt-end droppers. Pupilsshould wash their hands afterperforming experiments in whichchemicals have been used.

Explain to pupils the meanings ofthe hazard warning labels. (SeeAppendix A for details.)

Teach pupils the proper way to holda reagent bottle and to get solutionfrom it. Remind pupils not to returnexcessive chemicals back to reagentbottles.

Experiments/Activities Safety Precautions

III. SAFETY PRECAUTIONS IN

EXPERIMENTS/ACTIVITIES

4

Evaporate salt solution todryness.

C.3 Dissolving, evaporation, filtration


As it is probably pupils� first time touse a thermometer, to play safe, pro-vide them with the alcohol type tostart with. Help pupils to develop thegood habit of returning the thermom-eter back to its casing immediatelyafter experiment and putting it in asafe place.

Teach pupils the correct way ofusing a Bunsen burner, including thatthe hand should be lower than thetop of the chimney when lighting aburner.

Pupils should wear safety spectaclesin this experiment.

Heat gently towards the end of evapo-ration to avoid splashing out of the hotsalt solution. If salt begins to �spit�from the solution, turn off the Bunsenflame.

Heating over a beaker of boilingwater can be a better alternative todirect heating.

Measure the temperatureof air, tap water, icy wa-ter , hot water and moltenwax, etc.

Do not use naphthalene to replacewax as the former produces harmfulvapour. (See Appendix B fordetails.)

If a sharper melting temperature isdesired, octadecan-1-ol may be usedto replace wax.

5


C.5 Making observations and recording results

Blow air into a stopperedbottle containing waterand make observations.

Ask pupils to handle glass tubingscarefully. Use clean rubber tubings forblowing. Warn pupils not to over-exert themselves in blowing.

Teacher should note that pupils whoare exempted from PhysicalEducation lessons for medical reasonsshould not be allowed to perform thisexperiment.

Pull two rubber suckersapart.

The experiment should be conductedin a more spacious part of thelaboratory. Ensure no glassware isnearby.

Remind pupils not to apply a suddenforce to pull the rubber suckers apart.

C.4 Using a stop-watch to measure small time intervals

Count the pulse rate/heartbeat for one minute.

If the effect of physical exercise onpulse rate/heartbeat is to be measured,teacher should note that pupils whoare exempted from Physical Educa-tion lessons for medical reasonsshould not be allowed to perform thisexperiment.

Never invite pupils to taste the saltformed.

6

Use clean rubber tubings for blowing.

As this experiment may exert exces-sive physical stress on some pupils,teachers should note that pupils whoare exempted from Physical Educa-tion lessons for medical reasonsshould not be allowed to perform thisexperiment.

Do not replace the plastic bottle by aglass one as the latter is quite heavyand may be broken easily.

Measure the volume ofone�s lungs by blowing airto displace water in aplastic bottle.

C.6 Looking at differences within one kind of organism

7

C.1 Looking at snail/earthworm

Unit 2 Looking at Living ThingsExperiments/Activities Safety Precautions

Activities involving thehandling of earthwormsor snails.

Wear disposable gloves to preventthe transmission of germs/parasitesfrom the animals to pupils.

After the experiments, all bench topsshould be washed with disinfectantsolution and all pupils involvedshould have their hands thoroughlywashed.

Keep wormery or snail house inhygienic conditions. (See AppendixC for details.)

8


C.2 Simple energy changes

Burn a magnesium ribbonand observe.

Hang a weight with anelastic band and thenallow it to oscillate.

Use a light weight for the experiment,say 20 g.

Heat the lower opening ofa tube with wire gauze init to produce sound.

Ensure that the long tube is firmlyclamped and the stand is stableenough by putting enough weights onthe base of the stand.

Take care that the tube may becomevery hot.

C.3 More examples of energy changes

Demonstrate chargingand discharging of lead-acid cell.

Ensure that the two lead plates willnot touch each other, otherwise short-circuiting results causing damage tothe low voltage power supply unit.

C. 5 Energy converters and daily applications

Use a steam engine and adynamo to convert energystored in fuel to electricalenergy.

Before experiment, ensure properfunctioning of the valve of the boiler.Excessive building up of pressure inthe boiler may lead to an explosion.

Unit 3 Energy

Pupils should wear safety spectaclesin this experiment.Warn pupils not tolook directly at the bright flame whichmay cause harm to the eyes.

9

C.6 Energy in food

Burn food samples over aBunsen burner.


Do not burn fats, as hot oil dropletsmay jet out and cause burns.

Clean the Bunsen burners after theexperiment as spillage of food tendsto block the chimney of the burners.


Some solid fuels accompanying thesteam engine may be harmful. Readinstructions and take necessaryprecautions.

If alcohol is used as the fuel, do notadd alcohol to the fuel-containingvessel while the vessel is still hot.

10


C.1 State of matter

C.2 Particle size

Make a solution with as i n g l e p o t a s s i u mmanganate(VII) crystal.

Unit 4 Matter as Particles

A r r a n g e m a t e r i a l sprovided into solids,liquids and gases.

Heat some substances(e.g. ammonium carbon-ate or copper(II) nitrate)in a test tube and note thegas produced.

Remind pupils not to touch thepotassium manganate(VII) crystalswith their bare hands. The crystal willturn the skin brown due to oxidation.

If nitrogen(IV) oxide is selected asan example of gas, remind pupils ofthe toxicity of the gas. Cover thecontainer properly and place itinside a fume cupboard.

Do not use bromine as it is morehazardous than nitrogen(IV) oxide.


Use only a small amount of thesubstances.

Ask pupils not to inhale the gasdirectly. Show pupils the correct wayof detecting the odour of a gas byusing a hand to fan the gas towardsthe nose.

Iodine vapour is harmful. If experi-ment on heating iodine is to be done,it should be performed as a teacher�sdemonstration in a well-ventilatedlaboratory or in a fume cupboard.

11

C.6 Gas pressure

Compress gas inside asyringe.

Do not provide needles for thesyringes.

S.4 Particles - more to do

Perform dilution experi-ment and taste orangejuice at different dilutions.

Pupils must not normally be allowedto eat or drink in the laboratory. Whenthese activities are essential to theirstudies, clean domestic containers anddrinking water should be used.

Polystyrene beads fallen on the floorcan be dangerous as they are veryslippery. Avoid dropping the beadsonto the floor.

C.5 A particle model

Demonstrate with a kineticmotion model.

C.3 More about particles

Demonstrate diffusionusing nitrogen(IV) oxide.


Take care not to allow the toxic gasto escape out of the gas jars.

Ensure good ventilation or perform theexperiment inside a fume cupboard.

Do not replace nitrogen(IV) oxide bybromine as bromine is morehazardous.

12

Measure lung pressure byblowing strongly into aBourdon gauge.

Ask pupils not to over-exert them-selves in blowing.

Teacher should note that pupils whoare exempted from Physical Educa-tion lessons for medical reasonsshould not be allowed to perform thisexperiment.

Demonstration: Removeair from the Magdeburghemispheres using avacuum pump. Then try toseparate them.

Check the apparatus before theexperiment to ensure that it will notbreak apart very easily upon pulling.To avoid accidents, remind pupils thatthe apparatus will suddenly breakapart upon pulling.

The experiment should be conductedin a more spacious part of thelaboratory. Ensure no glassware isnearby.

Demonstration: Removeair directly with a vacuumpump from a metal canuntil it collapses.

Never allow pupils to stand too closeto the vacuum pump while it is turnedon.

C.7 Density

Demonstration: Add sol-ids to a jar containing lay-ers of immiscible liquids(e.g. oil, water andmercury).


Take care not to spill mercury orexpose pupils to mercury vapour,which is hazardous to health.

The jar should not be made of glasswhich is easily be broken when heavysolids are dropped into the jar .

In case of spillage or leakage, collect

13

C.8 Heating substances

Heat the bar or the bi-metallic strip in thermalexpansion experiment.

Remind pupils to handle the hotapparatus with care.

Demonstration: Raise aplastic bag by hot air fromburning alcohol.

Beware of the potential fire hazard ofthe experiment. Have fire fightingequipment ready.

Hold the cotton pad soaked in alco-hol in a metal dish but not in a watchglass.

Never use a Bunsen burner in placeof burning alcohol to lift up the plasticbag.

large drops of mercury immediatelywith a dropper. Cover remnants ofmercury with zinc dust (or a paste ofsulphur and lime), and leave for a fewhours, then collect them as chemicalwastes.

E.8 More applications of thermal expansion

Examine an aquariumheater with a thermostatand see how it works.

The heater should be operated inwater to avoid danger resulting fromover-heating of the heating wire.

Demonstrate working offire alarm using bimetallicstrip.

Remind pupils to handle the hotbimetallic strip with care.


14

C.9 Joining and separating particles

Demonstration: Heatmeta l (e .g . copperturnings, iron filings) withsulphur in test tubes.

Demonstration: Drop apiece of Dutch metal intoa jar of chlorine.

Electrolyze copper(II)chloride solution.


Make use of safety spectacles/safetyscreen.

Toxic sulphur dioxide gas will beproduced. Use small amount of thechemicals. Ensure good ventilation inthe laboratory or perform the dem-onstration in a fume cupboard.

Reaction between sulphur and ironfilings may be vigorous. Stop heatingonce glowing starts to spread throughthe tube.

Use minimum amount of copper(II)chloride to avoid large quantity ofpoisonous chlorine gas being evolved.Ensure adequate ventilation.

Carry out the experiment in a fumecupboard as fumes and heat areevolved, and chlorine is poisonous.

15

Effect of adding salt on theboiling point of water.


C.1 Finding out about water

C.3 Water purification

Filter muddy pond waterand evaporate the filtrateto dryness.

Distil the filtrate andevaporate the distillate todryness.

In distilling the filtrate, add anti-bumping stones (pumice stones orbroken porcelain) to the filtrate toavoid uneven heating which mayresult in shooting out of hot liquid.

C. 4 Dissolving

Dissolve substances (e.g.sodium hydroxide) intowater and measure thetemperature change.

Unit 5 Solvents and Solutions


Warn pupils of the corrosive natureof sodium hydroxide and ask them tohandle it with care.


Heat gently towards the end of evapo-ration to avoid splashing out of the hotliquid. Heating over a beaker ofboiling water can be a better alterna-tive to direct heating.


Neve r s t i r wa t e r w i th t hethermometer. Alert pupils not to letthe bulb of thermometer touch thebottom of the flask/beaker.

16

Test the solubility ofsulphur in water andmethylbenzene(toluene).

Find a suitable solvent fornail varnish and lacquer.


Propanone, ethyl ethanoate and�thinner� are flammable. Use minimalamount of the solvents and ensuregood ventilation.

Toluene is flammable and harmful.Use minimal amount of the solventand ensure good ventilation.

C.6 Solvents other than water

Test the solubility ofiodine in different liquids.

Warn pupils of the harmful nature ofiodine. Use minimal amount of thechemical and handle it with care.

17

Experiments/Activities

Unit 6 Cells and ReproductionSafety Precautions

C.2 Animal and plant cells

Observe animal cellsunder a microscope.

Do not use human cheek cells as thereis a potential danger of transmittingblood-borne diseases.

Use other sources of animal cells orcommercially prepared slides. (SeeAppendix D for details.)

C.4 Reproduction in plants

Examine different parts ofa flower and pollen grain.

Some pupils may be allergic to pollengrains, remind them not to handleflowers or pollen grains.

Avoid using plants known to bepoisonous.(See Appendix E fordetails.)

C.6 Mammal development

Look at dissection orprepared specimens of apregnant rat/rabbit.

If dissection is intended, ensure thatthe animal is healthy and clean.

Dissection should be done by teacheror laboratory technician.(SeeAppendix F for details.)

If specimen preserved in formalin(methanal solution) is to be used,ensure that the specimen jar is wellcovered, as methanal vapour irritatesthe respiratory system, skin and eyes.

18

Unit 7 Living Things and AirExperiments/Activities Safety Precautions

C.3 Breathed and unbreathed air

Collect breathed air andcompare its compositionwith that of unbreathed air.

Excessive rebreathing of the samesample of air is dangerous.

Pupils exempted from Physical Edu-cation lessons should not be allowedto breathe in and out of the plastic bag.

C.4 Breathing system in man

Examine a pig�s lung. Use clean and fresh lungs.

Specimens provided by abattoirs maycarry germs. Pupils should cover anywounds on their hands with water-proof dressings and wear surgicalgloves to prevent infection whenhandling the specimen.

After the experiment, all bench topsand instruments used should bewashed with disinfectant solution,whereas pupils involved should havetheir hands thoroughly washed.

C.6 Formation of starch in green plants

Test for the presence ofstarch in leaves.

Alcohol is flammable. When alcoholis used, ensure that there is no flamenearby.

Small and thin leaves should be usedfor the experiment. When using hotethanol to remove chlorophyll from

19

C.8 Respiration

Place germination seedsand sterilized boiled seedsin vacuum flasks andobserve the temperaturechanges.

the leaves, heat the alcohol by usinga beaker of very hot water. Remindpupils to handle the hot water withcare.


hot water

alcohol

leaf

The commonly used sterilized agent -mercury (II) chloride is poisonous.Handle it with care or use safersubstitutes. (See Appendix G fordetails)

20

E.5 More about electromagnet

Experiments involving theuse of low voltage d.c.power supply.

Warn pupils of the danger of short-circuiting as this may produce heat andcause burns.

To avoid any mishap in electricityexperiments, it is important for pupilsto acquire the habit of wiring a circuitaccording to a circuit diagram.Always start from the positive poleof the cell, and wire up the apparatusone after the other until the negativepole is reached. It is always good toinclude a circuit key. Before pressingon the key, the circuit should bechecked by teacher.


Making an electromagnetwith insulated wire.

Ensure insulated wire is used to avoidshort-circuiting.

Unit 8 Making Use of Electricity

C.1-5

21

C.2 Convection in liquids

C.3 Conduction in solids

Heat a paper kettlecontaining water.

Make a kettle just large enough to besupported on the tripod used.

Ask pupils to use a small flame,otherwise the paper kettle may catchfire.

Remind pupils that the paper kettlemay collapse and cause hot waterspillage.

Heat rods of differentmaterials.

Rods do not give any visible sign whenthey are hot. Remind pupils to handlethe hot rods with care.

Heat rods of differentmetals.

Remind pupils to handle the hot rodswith care.

If paper indicators are placed at theend of the rods, it will take a longertime for them to change colour. Theglass/aluminium rod may melt orsoften due to over-heating. Placingthe paper indicators midway be-tween the two ends of the rods andat equal distance from the heatsource can also achieve the aim ofthe experiment.

Unit 9 Making Heat FlowExperiments/Activities Safety Precautions

paper indicator

Bunsenburner

paper kettle

22

C.6 Applications of heat transfer

Study factors affecting therate of heat loss of hotwater.

Remind pupils to handle hot watercarefully to avoid heat burns.

Show that water is a poorconductor of heat byheating water containingice in a boiling tube.

Study how a vacuum flaskworks to prevent heattransfer.

Handle the vacuum flask with care toavoid accidental breakage of the flask.

It is always safe to prepare a woodenstand to hold the vacuum flask.

C.4 Air and water are poor conductors

Show that air is a poorconductor of heat.

Ensure that there is a hole in therubber bung for hot air to escape.

Ensure that the glass of the tube isstrong enough to stand high tempera-ture and the thermometer bulb doesnot touch the glass wall.


hole

thermometer


Point the mouth of the boiling tubeaway from anybody. Do not heat witha stationary flame.

23

Unit 10 Hydrogen, Acids and Alkalis

C.1 Electrolysis of water

Electrolyze water and testfor the gases produced.

C.2 Action of metals on water

Demonstration: Addsodium metal to water ina trough.


Warn pupils of the potential hazardsof hydrogen gas and ask them tocollect only small samples of the gasfor the �pop� sound test.

Pupils should wear safety spectaclesduring the test for hydrogen.

Sodium is a highly reactive metal andshould be handled with care.

Demonstrate the experiment behind asafety screen and ask pupils to wearsafety spectacles if necessary.

Use only a small piece of sodiummetal. Cut the metal with care. Itshould be noted that old stock ofsodium which may appear yellow dueto the formation of superoxide, isliable to explode upon friction orshock. It should not be used for prac-tical work.

Never attempt to collect the hydro-gen gas evolved.

Avoid using potassium metal as it ismore hazardous.

24

Add calcium granules towater.

C.3 Action of metals on acids

Add samples of metals todilute acids.


Ask pupils to handle calcium withforceps , and avoid skin contact whichmay result in burns.

Never add highly reactive metals suchas potassium and sodium into acidsas the reactions are extremelyvigorous.

Do not use magnesium powder as itsreaction will be very vigorousresulted from its large surface area.Use only the ribbon form. For thesame reason, use aluminium foils andzinc granules instead of their powder.

Do not use an excessive amount ofdilute acids.

Pupils should wear safety spectaclesduring the test for hydrogen.

When collecting the hydrogen gas,remind pupils to fit the tube looselywith a stopper to avoid splashing outof acid and shooting out of thestopper due to excessive pressure.

25

Evaporate the neutralizedsolution to dryness andobtain the salt produced.

E.5 Concentration and neutralization

Dissolve solid sodiumhydroxide in water andneutralize the solution byacid.

C.4 Degree of acidity & alkalinity

C.5 Neutralization

Add dilute hydrochloricacid to neutralize sodiumhydroxide solution.


When disposable syringes are used formeasuring the volume of solutions, donot provide needles for the syringes.

Find the pH value of somegiven chemicals andhousehold substances.

If lemon juice, 7-up, coke etc. areused, remind pupils that the materialsare intended for experimental useand the rule that eating and drinkingare not allowed in laboratory shouldbe strictly followed.



Warn pupils of the corrosive natureof sodium hydroxide and ask them tohandle it with care.


Remind pupils to heat gently towardsthe end of evaporation to avoidsplashing out of the hot liquid. Heat-ing over a beaker of boiling water canbe a better alternative to direct heating.

Never invite pupils to taste the saltproduced.

26

Unit 11 Detecting the EnvironmentExperiments/Activities Safety Precautions

C.2 The eye

Dissect an ox eye andidentify the main parts ofthe eye.

Use clean and fresh ox eyes.


Before allowing pupils to carry out thedissection, teachers should demon-strate the proper dissection skills firstand remind pupils to handle the dis-secting instruments with care.


E.3 Long and short sight

Use the model eye kit todemonstrate long andshort sight and theircorrection.

Do not leave the model eye kit undersunlight, as the attached lenses mayconverge the sunlight to start a fire.

C.5 Sources of sound

Produce sound with a tun-ing fork, a taut string andthe end of a ruler.

Choose suitable type of ruler for theexperiment. Preferably the ruler canbe made to vibrate freely with a slight

27

Tap a tuning fork andplace it lightly on watersurface.

Strike the tuning forks on a rubberbung, not on any hard object like thebench top.

C.6 Transmission of sound

Demonstrate the �electricb e l l i n b e l l j a r �experiment.

Never allow pupils to stand too closeto the vacuum pump while the pumpis turned on.

C.8 Pitch

Study how the notesproduced by plucking aguitar wire change whenthe wire is tightened orloosened.

Take care not to over-tighten the wireas the wire may break and causeinjuries.

Start with the tightened position. Un-screw in the direction that only resultsin decreasing the tension of the wire.

C.9 Taste and smell

Investigate the sense oftaste by tasting differentfood substances.

Pupils should not normally be allowedto eat or drink in the laboratory.When the activities are essential to theirstudies, remind pupils of the neces-sary precautions.

Use clean domestic containers and

force. Use G-clamp if deemednecessary.

Do not use metre rule. Long rulermay give rise to accident if theceiling fans are low.


28

C.10 Touch

Study the sense of touchby putting fingers in hotand cold water.

Do not use hot water above 50oC.

Study the sense of touchby touching differentparts of the skin of ablindfolded pupil.

Avoid using pointed objects such aspins.

drinking water. Use drinking strawsto transfer solutions for tasting.


29

Unit 12 Forces and Movement


C.1 What is a force?

Pull a spring in oppositedirections.

Never allow pupils to over-extendthe spring.

Study the effect of forceby placing two ringmagnets on some polysty-rene beads in a tray.

Polystyrene beads fallen on the floorcan be dangerous as they are veryslippery. Use a deeper tray to avoidspillage.

C.2 Friction

Drop simultaneously twoidentical steel balls intotwo measuring cylinders,containing two differentliquids.

Do not use large steel balls, as theymay be heavy enough to produce animpact to break the cylinder onreaching the bottom of the cylinder.

Use transparent plastic cylinders asfar as possible.

Polystyrene beads

30

Demonstration: Fire a�water rocket� verticallyand observe the motion.

The rocket may fly off at high speedand this may become a potentialhazard to the observers.

Teachers should launch the waterrocket vertically upward in an openspace outside the laboratory. Askpupils to keep a distance away fromthe rocket.

To ensure vertical launching, a launch-ing guide can be used. It can beconstructed easily by cutting off thebottom of a large plastic soft drinkbottle (1-1.25 L capacity), andsecuring it to a rigid stand as shownin the diagram.

C.8 Action and reaction

Study action and reactionby pushing or pullingwhile sitting on a cart.

Do not allow pupils to stand or squaton the cart as they may easily losetheir balance and fall.

Remind pupils not to push or pull toohard.


launchingguide

water rocket

to pump

31

Unit 13 Food and Transport


C.3 Storing food

Study food decay causedby activities of micro-organisms.

Keep any culture of microbes incovered containers and follow thesafety precautions in handling micro-organisms. (See Appendix I fordetails.)

C.6 Tooth and tooth decay

Identify human teeth onthe jaw.

For hygienic purpose, ask pupils toclean their mouths with antisepticmouthwash first if they are allowed toobserve each other�s teeth. Instead,pupils may use a mirror to observetheir own teeth.

Bite a small piece of car-rot and chew it. Note theteeth used. Bite and tearoff a small piece of toffeefrom a toffee bar and notewhich teeth are most ef-fective for this purpose.

Pupils should not normally be allowedto eat or drink in the laboratory.When the activity is essential to theirstudies, remind pupils of the neces-sary precautions.

Cover a pig�s tooth withwax. Scratch away waxat one point and immersethe tooth into dilute acidto study tooth decay.

For hygienic purpose, use a cleanpig�s tooth.


Use forceps and never fingers to holdthe tooth for dipping into hot moltenwax and to pick up the tooth fromthe dilute acid.

32

Study acid formation bythe action of bacteria insaliva on glucose solution.

Pupils should only handle their ownsaliva, including its disposal andrinsing of equipment after use. (SeeAppendix D for details.)

C.7 Digestion and absorption

Observe a dissected rat/rabbit showing the diges-tive system.

Study digestion of starchby saliva.

Pupils should only handle their ownsaliva, including its disposal and rins-ing of equipment after use. (See Ap-pendix D for details.)

It is desirable to replace saliva bychemically prepared 5% diastasesolution to reduce the chance of trans-mitting diseases through saliva.

Observe the inner wall ofa piece of preserveds p e c i m e n o f p i g �sintestine.


If dissection is intended, use healthyand clean animals.

If specimen preserved in formalin(methanal solution) is used, ensure thatthe specimen jar is well covered, asmethanal vapour irritates the respira-tory system, skin and eyes. (See Ap-pendix F for details.)

If specimen preserved in formalin(methanal solution) is used, ensure thatthe specimen jar is well covered, asmethanal vapour irritates the respira-tory system, skin and eyes.

Rinse the tooth with water beforeobservation.

33

C.8 Transport in mammals

Take the pulse rate whenthe body is at rest and im-mediately after exercise.

Do not ask pupils who are exemptedfrom Physical Education lessons formedical reasons to perform theexperiment.

Remind pupils to stop doing theexperiment immediately if they feeluncomfortable.

C.10 Kidney and its functions

Examine a dissected freshpig�s kidney.

Use clean and fresh pig�s kidneys.


Before allowing pupils to carry outthe dissection, teachers should dem-onstrate the proper dissection skills

E.7 Enzymes

Study digestion of starchby saliva.

Pupils should only handle their ownsaliva, including its disposal andrinsing of equipment after use. (SeeAppendix D for details.)

It is desirable to replace saliva bychemically prepared 5% diastasesolution to reduce the chance of trans-mitting diseases through saliva.


34

Study water transport inplants (e.g. Chinese whitecabbage seedling).

Ask pupils to take care when cuttingthe seedling with a razor blade toexpose the tissues for water transport.It is desirable to use single-edgedblades.

C.12 Absorption and transport of water in plants

Periwinkle is a poisonous plant. Useother safer alternatives such asChinese Hibiscus.

Demonstration of absorp-tion of water by the rootsof a potted woody plant.


first and remind pupils to handle thedissecting instruments with care.


35

Unit 14 Materials from the EarthExperiments/Activities Safety Precautions

C.1 Rock and soil

Illustrate the weathering ofrocks by dropping heatedgranite into cold water.

Filter some soil water andevaporate the filtrate todryness to show thepresence of minerals insoil.

Pupils should wear safety spectaclesin the experiment.

Remind pupils to heat gently towardsthe end of evaporation to avoidsplashing out of the hot liquid. Heat-ing over a beaker of boiling water canbe a better alternative to direct heating.

Study the growth ofbacterial colony/fungi onagar plate contaminatedby soil.

Keep any culture of microbes incovered containers and take thesafety precautions in handling micro-organisms. (See Appendix H fordetails.)

C.2 Building materials

M a k e m o r t a r a n dconcrete.

Pupils should wear disposable gloveswhile handling cement as it may causeirritation upon prolonged skin contact.

Test the tensile strength ofconcrete bar by addingweights to the bar untilbreakage.

Beware of dropping fragments/weights. This activity should bep e r f o r m e d a s a t e a c h e r �sdemonstration.

Use safety screen and wear safetyspectacles.

The cold water should be containedin a large metal container.

36

C.3 Getting materials from the earth�s crust

E x a m i n e m i n e r a lspecimens.

Extract a metal from itsores (sulphides andox ides ) by ca rbonreduction.

Demonstration: Use acopper wire and weightsto illustrate the ductilityof metals.

Avoid applying excessive tension tothe wire as the wire may break andcause injuries.

C.4 Coal

Perform destructive distil-lation of coal.


Asbestos is carcinogenic. Do not useasbestos specimen.


Sulphur dioxide produced from theroasting of sulphide ores is toxic. Usesmall quantities of ores. Ensure goodventilation or use the fume cupboard.

If soft drink bottle cap is used ascontainer for the reduction, remove theplastic disc inside first as it willproduce toxic fumes when burnt.


Owing to the pungent smell andharmful nature of the products, carryout the experiment in a well-venti-lated laboratory.

Ensure secure clamping of theapparatus.

37

Study burning behaviourof the fractions.


C.5 Crude oil

Perform fractional distilla-tion of crude oil.

Avoid skin contact with crude oil andits fractions as they may contain harm-ful substances. If possible, use artifi-cial crude oil which may be availablefrom some scientific suppliers.

This experiment should be carriedout in a well-ventilated laboratory.


Soak a piece of cotton wool in thecrude oil to avoid bumping. Avoidheating the soaked cotton wool witha stationary hot flame and be carefulof burns.

Ensure secure clamping of theapparatus.

Avoid collecting fractions with boilingtemperature over 300¢J¢J¢J¢J¢Jas harmfuldecomposition products may beproduced.


Use small amount of the fractionsonly.

Remind pupils not to add fuel to aburning fraction.

Ensure good ventilation as sootyfumes are produced.

38

Heat shell/coral stronglywith a Bunsen flame.

Add water to the productobtained from heatingshell/coral.

E.6 More materials from the sea

Carry out flame test onshell/coral.

Carry out flame test onsome salts and the residuefrom evaporation of seawater.


C.6 Materials from the sea

Evaporate sea water todryness.


Remind pupils to heat gently towardsthe end of evaporation to avoidsplashing of the hot liquid. Heatingover a beaker of boiling water can bea better alternative to direct heating.

Pupils should wear safety spectaclesduring the flame test.

Concentrated hydrochloric acid ishighly corrosive. Pupils should handleit with care.

Pupils should wear safety spectaclesduring the flame test.

Concentrated hydrochloric acid ishighly corrosive. Pupils should handleit with care.

Pupils should wear safety spectacles.

If soft drink bottle cap is used ascontainer for heating, remove theplastic disc inside the cap first as itwill produce toxic fumes when burnt.

Make sure that the product is cooleddown sufficiently before adding water.

Avoid direct contact with the productwhich is corrosive.

39

Unit 15 Electricity and Electronics


C.1 Electrostatics

Charge a strip of differentmaterials.

Teachers may like to charge twometal-coated plastic strips by theEHT power supply. Note that thetwo strips will stick together ifoppositely charged. Switch off theEHT power supply as soon aspossible when the strips sticktogether, as prolonged short-circuit-ing will damage the supply unit.

Experiments involvingVan de Graaff generator.

The Van de Graaff generator canproduce extremely high voltage(above 3x104 V). Generally the equip-ment is reasonably safe as the currentis at the microampere (µA) level, butsome people (e.g. those with weakhearts) are susceptible to health risk.The generator should be dischargedbefore making any alteration. Thechassis of the generator should beproperly earthed.

C.2 Pushing charges

Measure the voltages ofvarious unknown sourceswith a voltmeter.

Warn pupils not to measure themains voltage.

40

C. 5 Discharge through gas

Experiments involvingthe Extra High Tension(E.H.T.) power supply.

Check carefully that the two elec-trodes inside the discharge tube arenot in contact before the experiment.

Ensure that there are no protruding orexposed metal parts, such as thoseshown in the diagram, on the plugswhen connecting to the E.H.T.power supply.

Ensure that there is a large current-limiting-resistor in series with thepositive terminal.

Always connect the negative terminalto the earth terminal unless otherwiseinstructed. (See Appendix I fordetails.)

E.3 Transmitting electrical energy

Experiment involving thepower transmission linemodel.

Demonstrate with the power transmis-sion line model, which uses lowvoltage.


protrudingor exposedmetal parts

41

Experiments involvingthe use of Extra HighTension (E.H.T.) powersupply.

Ensure that there is a large current-limiting-resistor in series with thepositive terminal.

Always connect the negative terminalto the earth terminal unless otherwiseinstructed. (See Appendix I fordetails.)

Experiments involvingthe use of cathode rayoscilloscope (C.R.O.).

Do not use the C.R.O. to measurethe mains voltage.

C.6 Current through a vacuum


42

IV. EXPERIMENTS/ACTIVITIES NOT

RECOMMENDED

The following experiments which are sometimes suggested in somescience publications, are considered unsafe. Teachers are advised not todemonstrate these experiments or arrange pupils to perform them onsafety ground.

Unit 3 Energy

Wrap a match head in aluminum foiland heat the wrapped head in aBunsen flame.

Heat food powder in an enclosedcan.

Unit 7 Living things and air

Find out the percentage volume ofoxygen in air by burning phosphorus.

C.3 Heating effect Wind an electric wire round the ther-mometer bulb and measure the tem-perature rise when electricity passingthrough the wire.

Unit 8 Making use of electricity

C.3 More examples of energy change

C.6 Energy in food

C.2 Gases in the air

Unit Experiments/Activities

43

Blow a soap bubble using hydrogenand put a burning splint close to it.

Unit 15 Electricity and electronics

C.1 Electrostatics Touch the dome of the Van de Graaffgenerator after it has been charged.

Unit 10 Hydrogen, acids and alkalis

C.2 Action of metals on water

Put the sodium metal on a filter paperand let the latter float on water.

Unit Experiments/Activities

45

Appendix B

1. Naphthalene (mothball) had sometimes been used in scienceexperiments in melting point determination in Secondary 1 IntegratedScience. However, it is known that some 4.5% of local born male babiessuffer from G6PD (glucose-6-phosphate dehydrogenase) deficiencywhich would last for life and that people with such deficiency whenexposed to naphthalene may suffer from haemolysis (destruction of bloodcells). In addition, naphthalene is harmful by inhalation, ingestion and skincontact. Science teachers are advised to note the hazardous nature ofnaphthalene and not to use it in any science experiments.

2. Wax, octadecan-1-ol or stearic acid should be used in meltingpoint determination.

3. Schools are advised to request parents to report G6PD deficiencyand any acute diseases suffered by their children so that precautions canbe taken where appropriate.

Hazards in the use of naphthalene in scienceexperiments

46

Wormery for earthworm/snail house

Appendix C

1. Wear disposable gloves when working with the wormery/snailhouse.

2. Keep wormery/snail house in hygienic condition. Clean the wormery/snail house regularly with disinfectants. The types of disinfectantsrecommended for cleaning include:

Reference:

Precautions Against Biological Hazards (pp.50-51), Imperial Collegeof Science and Technology, London, 1974

Iodophores�Wescodyne��Mikroklene�

Solution containing 150ppm available iodine

Non-irritant(a)

Ampholytes�Tego MHG��Miranol�

1% solution Virtually none(b)

Disinfectant Working Strength Toxicity

Note:

Phenolic solutions and their derivatives such as �Lysol� and �Sudol�are not recommended as they are toxic and irritating.

47

Experiments involving animal blood, cells andhuman saliva

Appendix D

1. Teachers are reminded that taking human blood and cell samples(such as cheek cells) for practical work should not be performed, as thismay carry a risk of transmitting blood borne diseases such as AIDS(Acquired Immune Deficiency Syndrome) and Viral Hepatitis B.

2. Experiments on observation of animal cells have high educationalvalue. The animal cells required for such activities could be obtained fromsources OTHER THAN HUMAN BODY, e.g. bull�s eye corneal cells.

Preparation:

Slides of bull�s eye corneal cells can be prepared by pressing amicroscope slide gently against the cornea of a bull�s eye (fresh orrefrigerated). The cells can be stained with a drop of methylene blueand covered with a cover slip in the normal way. At least 10 prepara-tions can be made from one eyeball.

(For details, please see: Lewis, JCE & Chester, MF, �BullocksCorneal Cells: An Alternative to Human Cheek Cells�, SchoolScience Review, Mar 1989, Vol 70, No 252.)

Alternatively, by using a scalpel (beware of cuts), the cells can bescraped off from the surface of the cornea of a bull�s eye which hasbeen soaked in water over-night. The tissue can be mounted in a dropof water or dye such as methylene blue for observation under amicroscope.

3. For hygienic purpose, it is highly recommended for schools to usechemicals (e.g. diastase) to replace human saliva during experiments,wherever possible. For experiments that involve human saliva, teachersshould instruct pupils to work only with their own body fluids.

48

References:

(1) Guidelines on the Prevention of Blood-borne Diseases inSchools, Department of Health and Education Department, 1994.

(2) Prevention of Hepatitis B Virus Infection in Newborn Babies,Hepatitis B Vaccination Clinic and Central Health Education Unit,1997.

4. When performing the experiments related to animal blood, cellsand human salvia, teachers should instruct pupils to wear disposableplastic/vinyl gloves for protection and hygienic reasons.

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Appendix F

Handling and killing of rats for dissection

1. Living rats may bite or scratch people handling them. Leather glovesfor handling of animals should therefore be worn when working withthem.

2. All living rats for dissection must be obtained from a licensed dealer(Please refer to School Science Newsletter Issue No.45 published bythe Education Department for a list of licensed rat traders in HongKong.) and wild rats should not be used.

3. Under no circumstances should pupils be allowed to handle livingrats. Killing of rats should only be carried out by teachers or laboratorytechnicians. It should be done in a swift and humane way with carbondioxide or chloroform (trichloromethane) in the absence of pupils. Aschloroform is harmful, the killing chamber should be exposed after useeither in fume cupboard or in the open air.

4. After killing, check that the animals are dead and immerse them indilute disinfectant before handling them over to pupils for dissection.

5. It should be noted that rats should not be reared in schools for usein dissections.

6. If a pupil is bitten by a rat, the case should be reported to theteacher-in-charge at once. Basic first-aid treatment should be given tothe wounded pupil, who should then be sent immediately to hospital/clinic for medical treatment. The animal in question should be isolated forsubsequent diagnosis purpose.

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Appendix G

Sterilization of boiled seedsfor experiments on respiration

Mercury(II) chloride is a commonly used reagent for the steriliza-tion of boiled seeds for respiration experiments. Since it is corrosive tothe mucous membrane and poisonous to human bodies, teachers areadvised to replace it with safer alternatives, such as 1-2% formalin solu-tion or dilute sodium hypochlorite solution (commercial bleach).

(a) Sterilization with 1-2% formalin (methanal solution)

Prepare a 1-2% solution of formalin by diluting one part of 40%formalin with 39 parts of water. Soak the boiled seeds in the solu-tion for 5 minutes. Rinse the seeds twice with cold water beforeuse.

Note: Methanal vapour is irritating to the respiratory tract, eyesand nose. Skin contact may give rise to dermatitis. Handle it insidea fume cupboard and wear rubber gloves.

(b) Sterilization with dilute sodium hypochlorite solution

Dilute commercial bleach (containing sodium hypochlorite) with 4times its own volume of water. Soak the boiled seeds in the solu-tion for 15 minutes. Rinse 2-3 times with water before use.

Note: Although being the least hazardous of the 3 sterilizing agents,prolonged skin contact with dilute sodium hypochlorite solutioncauses irritation. Avoid inhalation of its vapour as this may pro-duce bronchial irritation.

Reference:(1) MERCK Index(2) Experimental Work in Biology (p.252), Combined edition,

Teacher�s book, D.G.Mackean.(3) Modern Certificate Biology Experimental Workbook (pp.

87-88), Mary Soltay, Longman.(4) Class Experiments in Biology (p.39), Teacher�s book, C.

J. Worsley, P.C.G. Worsley, D.G. Mackean.

52

1. Cultures of micro-organisms may be contaminated by pathogenswhich may arise from mutation or from wild sources. All micro-organ-isms should therefore be treated as potentially hazardous and be handledwith care.

2. Pathogenic micro-organisms may gain access into the human bodyif fingers with wound touch the culture or the aerosols above the cultureare inhaled or contaminated food is ingested.

3. Students who are unable to appreciate the importance of safetyprecautions in microbiological experiments should never be allowed toperform them. If class discipline cannot be relied on, the teacher shouldabandon individual experiments in favour of teacher demonstrations.

4. All hand-to-mouth operations should be strictly forbidden duringmicrobiological experiment. Pipette fillers should be used to transfer liq-uid cultures. Teachers, technicians and students should wash hands thor-oughly with soap and warm water after practical microbiological work.Paper towels are to be preferred to roller or other communal towels,which themselves may harbour large populations of micro-organisms.

5. All cuts on body surface should be covered with waterproof dress-ings before starting microbiological experiments.

6. Avoid production of aerosols during sterilization of inoculating loopby flame-heating. Always immerse the loop in 70% alcohol beforeflaming.

7. Never isolate micro-organisms from potentially dangerous sourcessuch as polluted water, human mucus, pus and faeces.

8. Do not incubate culture of micro-organisms at 37oC because thispractice tends to select organisms adapted to human body temperature.Most of the saprophytic micro-organisms used in school microbiologygrow well at normal room temperature.

Safety precautions in handlingmicro-organisms

Appendix H

53

9. Cultures of micro-organisms for class inspections should be keptin sealed containers to prevent contamination and infection. Self-adhe-sive tapes should be used to seal petri-dishes containing micro-organisms.

10. If the petri-dishes containing cultures of micro-organisms must beopened for inspection, the teacher or laboratory technician should kill themicro-organisms by adding a few drops of methanal solution (formalin)to a piece of filter paper and leave it in the lid for at least one hour priorto class inspection.

11. Unwanted cultures should be destroyed by autoclaving or immer-sing in disinfectant solutions (e.g. hypochlorite/�Chloros�, or formalin) forseveral hours before disposal.

12. All apparatus contaminated with micro-organisms should beautoclaved or immersed in disinfectant solutions for several hours beforecleaning or disposal.

13. The bench and floor should be washed with disinfectant solutionsimmediately after each practical microbiology class. Areas contaminatedwith bacteria due to spillage or accidental breakage of the containershould be covered with �Chloros� and left for 15 minutes before cleaning.

54

1. As the E.H.T. power supply is plugged into the mains, it ispossible to produce a current higher than that usually produced by theVan de Graaff generator. It is therefore essential to ensure that there isa large current-limiting-resistor in series with the positive terminal, fittedinto the power supply. Always connect the negative terminal to the earthterminal unless otherwise instructed.

2. Users should always switch off the E.H.T. power supply beforemaking adjustments to the circuit. A 5000 V shock is unpleasant thoughit is unlikely to be fatal as the large internal resistance of the power supply

limits the current to a very small value.

Safety precautions in usingextra high tension (E.H.T.) power supply

Appendix I

not immediately dropto zero

The power supply, however, will not besafe even after being switched off; thereis likely to be a large smoothing capaci-tor inside it, which will remain chargedfor a short time. The capacitor willdischarge through the voltmeter in thepower supply, so watch the reading asit falls to a safe value before makingadjustments to the circuit.

3. Any experimentation requiring the use of high voltage would besafer if the floor is covered with effective insulating materials. Nobodyshould be allowed to work alone in a room when using high voltage.Terminals should be protected and naked wire should never be used.Suitable screen or barrier for protection against electric shock should beprovided whenever necessary. All high voltage equipment should alwaysbe kept clean.

safety in is experiments -...

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