Question

describe laboratory preparation of hydrogen and oxygen

Answer 1

In the laboratory, H2 is usuallyprepared by the reaction of acids on metals such as zinc with Kipp's apparatus. The electrolysis of water is a simple method of producinghydrogen. A low voltage current is run through the water, and gaseousoxygen forms at the anode while gaseous hydrogen forms at the cathode
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Answer 2

Hydrogen gas is prepared in laboratory by the action of dilute HCl upon granulated zinc.

Zn+dil⋅H2SO4⟶ZnSO4(aq)+H2↑

The granulated zinc pieces are taken in a Woulfe’s bottle and the apparatus is fitted as shown in figure. The two necks of woulfe’s bottle is tighten up with cork so that no air enters from outside. It is connected with the delivery tube to a water trough containing water. Dilute sulphuric acid is poured slowly from the thistle funnel. Some crystals of copper sulphate are added to increase the rate of reaction. The hydrogen gas thus formed is collected in a gas jar through delivery tube by the downward displacement of water.

Whereas,

Oxygen is prepared in lab generally in two ways either by the application of heat or no application of heat.
Oxygen in lab is prepared by heating the mixture of powdered potassium chlorate and manganese dioxide in the ratio 4:1 in a hard glass test tube.

Using heat:
The oxygen gas is observed in a gas jar through the downward displacement of water. The reaction involved is given below:
2KClO3−→−−−−−MnO2200−300∘C2KCl+3O2↑