JSSS
Teacher Support Material
To investigate the reaction between zinc and HCl and test for
hydrogen
OC51
The apparatus being used for the preparation of hydrogen is the same as that used for oxygen and
carbon dioxide. The apparatus used in the student material is of the traditional nature. The use of
polypropylene funnels and flasks will extend the life of the apparatus. The use of a dropping
funnel, rather than a thistle funnel, allows the release of the hydrochloric acid, and hence that of
the hydrogen, to be controlled. A 50 cm3 plastic syringe could be used instead of the dropping
funnel. (Alternative gas preparation setups are included in the teacher document for OC24 and
OC27.) The water ‘trough’ used is a plastic food / ice cream container. Test tubes are used for
collecting the hydrogen. This works well for two reasons:
1. The volumes of gas required for any tests are small
2. The gas samples are collected very quickly
The test tube can be hand held over the delivery tube, doing away with the need for a beehive
shelf and clamp. A weight near the end of the delivery tube helps to keep it in place under the
water.
The funnel, flask, plastic tube, 6 test tubes and stoppers can be stored in the plastic container.
This then is a gas preparation kit. A number of them could be made up and kept together.
Safety
Warning: Hydrogen is extremely flammable. It forms an explosive mixture with air.
Flames must be kept well away from the gas preparation apparatus. The delivery tube
should be kept under the water in the basin at all times. The test for hydrogen should be
carried out well away from the gas preparation apparatus.
Teaching tips: One Bunsen burner on the teacher’s desk could be used to test the gas
ensuring that students have to move away from where they are preparing the gas.
A few drops of copper sulfate solution added to the reaction flask speeds up the production
of hydrogen.
Prior knowledge
Students would need to be familiar with the concept of density before attempting to show that
hydrogen is less dense than air.
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JSSS
Teacher Support Material
Links
Connections can be made involving H2 across the syllabus: OC34 the electrolysis of water,
OC43 the bonding in H2, OC49 the alkali metals and water, and OC52 the relative reactivities of
certain metals.
Reference can be made to
1. Hydrogen having the lowest density of any substance known (about 14 times lighter
than the same volume of air)
2. The radioactive form being used in the hydrogen bomb
3. Vegetable oils being reacted with hydrogen (hydrogenated) to make semisolid spreads
4. Hydrogen as a powerful fuel in the main engine of the orbiter in the US space shuttle
system
5. Hydrogen in fuel cells
Chemical hazard notes
Concentrated hydrochloric acid
: Very corrosive to eyes and skin, and its vapour is very
irritating to lungs. Add acid to water when diluting.
Zinc powder
: The dust is flammable. Moist zinc dust may ignite spontaneously.
Preparation of reagents
Hydrochloric acid solution (3 M) is made up as follows: in a fume cupboard, add 645 cm3 of
concentrated hydrochloric acid slowly with stirring to about 1 litre of water and make up with
deionised water to 2.5 litres in a Winchester flask. Stopper the flask, and invert the flask a
number of times to ensure thorough mixing.
Disposal of wastes
Filter the waste liquid. Add the unused zinc powder slowly in small quantities (50 g) to excess
dilute hydrochloric acid. Neutralise the filtrate and the reacted zinc solution with sodium
carbonate, dilute with excess water and flush to the foul water drain.
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