0-3 Laboratory Safety

III. Laboratory Safety

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Topic

III.

Laboratory Safety

Reading Assignment

0.3 Integrated Chemistry Today (2nd Ed.), L.H.M Chung, Book 1A, pg 4 – 5, 227 – 231

Objectives

Laboratory Safety First Aid Treatment Disposal of Chemical

Notes

It is impossible to list all the safety precautions in every experiment. Moreover, most accidents can be avoided by exercising your common sense and observing the discipline in the laboratory. A. General safety precaution Chemical spurting out from a test tube is the most popular accident in laboratory. This happens under 3 circumstances 1.

There is too much reagent (either liquid or solid) in the test tube. 1 The maximum effective capacity of a test tube is only of its total volume. In general, the fewer a test tube 3 holds, the better it works. Only minimum amount of reagent should be used. e.g. 1 cm of height of solution. In order to mix the solution in a test tube, swirling is preferred to shaking.

2.

Excessive gas pressure is built up in the test tube. This happens if gas is evolving in a stoppered test tube. The pressure built up will force the stopper out with the gas and solution. Therefore, even if you are attempting to collect the gas, pressure inside the test tube must be released occasionally.

3.

The test tube is heated improperly. When water is heated, it turns into steam, the large steam bubble formed at the bottom of test tube will spurt the solution out. First of all, test tube is not designed to heat solution strongly. Only moderate heating with constant swirling may be applied. Shaking breaks up the large bubble and makes the heating smoother.

B. Hazard warning labels In order to keep the user informed the potential hazard of individual chemical, some hazard warning labels are put on the reagent bottles.

_____ A. Explosive E. Corrosive

_____

_____

B. Oxidizing F. Harmful

_____ C. Toxic G. Irritant

_____

_____

_____

D. Carcinogenic H. Flammable / Inflammable

For example, tetrachloromethane (a common solvent used in industry) is a toxic substance. Chemical with potential hazard will have a hazard warning label on it container to warn the user.

_____

III. Laboratory Safety

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C. Storage of hazardous chemicals The storage of a chemical is depending on the nature of the chemical. In general, all chemicals should be kept in air tight bottles away from heat and direct sunlight. However, some chemicals require special method of storage. Examples 1.

Phosphorus

Phosphorus is an element with ignition point 34 ºC. Therefore, it catches fire easily by itself in air. It must be kept under water. It should also be cut under water because the heat from the cutting will be able to ignite the phosphorus block. 2.

Bromine

Bromine is a very volatile and toxic element. It boils at 59 ºC. Before use, it is kept in a sealed glass capsule. After the capsule have been opened, it is impossible to keep the element from evaporating. Therefore, bromine is usually stored in form of a solution by employing in a solvent (e.g. tetrachloromethane). 3.

Light sensitive substances e.g. concentrated nitric acid, potassium permanganate solution, silver nitrate solution

These solutions are sensitive and decomposes readily under direct sunlight. Therefore, they are commonly kept in dark brown bottle. D. Common first aid treatments 1.

Inhalation of toxic vapour The victim should be taken to a well-ventilated area to breath some fresh air.

2.

Minor chemical burn of hand The affected area should be rinsed with running water for a few minutes.

3.

Acid spillage on eye The treatment is similar to that of chemical burn of hand. Since eye is even more dedicate than hand, it should be rinsed for a long time and it is advisable to send the victim to hospital for further treatment.

After any first aid treatment has been administrated, teacher must be notified immediately.

E. Disposal of chemical waste

No chemical waste should be disposed causally through the sewage system. 1. 2.

Glossary

All solid chemical must be put in the plastic bucket provided. Liquid waste must be disposed in the waste bottle in the fume cupboard and then the glassware should be washing at your own bench. The waste should never be run down the sink directly, this will cause pollution.

common sense discipline hazard warning labels corrosive oxidizing carcinogenic harmful

explosive irritant

flammable

toxic

III. Laboratory Safety

Past Paper Questions

93 I 3 b I

93 I 3 b i 3b In school laboratories, chemical wastes such as concentrated hydrochloric acid, methylbenzene and tetrachloromethane produced during practical work are to be stored in containers and then sent to a chemical waste treatment plant for disposal. i Explain why chemical wastes should not be poured down the sink in the laboratory. 1 causes water pollution 1 mark

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III. Laboratory Safety 90 44 B

44 If dilute hydrochloric acid gets into a student's eye during an experiment, the first thing the student should do is to A. dial 999 for help. B. wash the eye with water. C. wash the eye with dilute ammonia solution. D. wash the eye with dilute sodium hydroxide solution.

91 5 B

5

Tetrachloromethane is a common solvent in the chemistry laboratory. Which of the following hazard warning labels should be displayed on a bottle of tetrachloromethane ?

(1)

(2)

(3) A. B. C. D. 94 32 A

32 Which of the following label(s) should be placed on a bottle containing tetrachloromethane ? (1) (2) (3)

A. B. C. D. 99 38 C

(1) only (2) only (1) and (3) only (2) and (3) only

(1) only (2) only (1) and (3) only (2) and (3) only

38 Which of the following reagents is/are commonly stored in brown bottles ? (1) potassium permanganate solution (2) concentrated sulphuric acid (3) concentrated nitric acid A. (1) only B. (2) only C. (1) and (3) only D. (2) and (3) only

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