How to prepare hydrogen in the lab.
Aim: To prepare hydrogen in the laboratory
Apparatus: Flat bottomed flask, thistle funnel, delivery tube, trough full of tap water, bee hive shelf and gas jar
Materials: Dilute hydrochloric acid and granulated magnesium.
1. The apparatus was arranged in the same way as for the preparation of oxygen.
2. Some magnesium was put in the flat bottomed flask.
3. Dilute hydrochloric acid was poured over the granulated magnesium in the flat bottomed flask and observations were made.
4. Some granulated magnesium was put in a test tube together with a little hydrochloric acid.
5. The mouth of the test tube was closed with a finger and when the gas evolved was felt pushing, hydrogen was tested using a lighted match.
Hydrogen is a colourless, odourless gas and because of this its presence could only be shown by carrying out a specific test. However since the test for hydrogen is quite dangerous a small sample of the gas was prepared in a test tube and then the test done on the small sample to avoid accidents. When a lighted match was put close to the mouth of the test tube the latter burned out with a pop.
Hydrogen was collected by displacement of water. This type of collection could be used as hydrogen is insoluble in water. If a sample of dry hydrogen was required the gas would have had to be passed through a drying agent before collection. Then the gas could have either been collected in a gas syringe or by upward delivery as the gas is lighter than air. Then the set up of the apparatus would have been as follows:
During this experiment, the following reaction occurred:
Mg(s) + 2HCl(aq) MgCl2(aq) + H2(g)
This is a displacement reaction as magnesium displaced hydrogen from hydrochloric acid. This reaction could take place as Mg+2 is higher than H+ in the electrochemical series.
This is the ionic equation of the reaction:
Mg(s) + 2H+(aq) Mg2+(aq) + H2(g)
These are the half-equations of the reaction:
2H+ + 2e- H2
Mg - 2e- Mg+2