1. Do you know which one is the lightest element on the earth?

2. 1. Hydrogen is a colourless, odourless gas. 2. It is less dense than air 3. Pure hydrogen burns quickly in air with a pale blue flame. 4. If hydrogen is mixed with air or oxygen, it will explode on. ignition.

3. Preparation of hydrogen by the action of dilute acids on metals. E.g. dilute sulphuric acid and zinc. Zn(s) + H 2 SO 4 (aq) ---> ZnSO 4 (aq) + H 2 (g)

4. Put some pieces of zinc in a flask and add dilute sulphuric acid by means of a tap funnel. Bubbles of colourless gas are given off. The colourless gas (i.e. hydrogen) is collected over water (by displacement of water). Zinc sulphate formed is soluble in water. It dissolves in water to form a colourless solution.

5. 1. Set up the apparatus as shown.Discard the first jar of gas coming out from the reaction flask. 2. Take a test-tube of hydrogen. Hold a lighted splint near the top. Quickly take off the stopper and light the hydrogen. 3. Take the stopper off a test-tube of hydrogen. Count ten. Light the hydrogen with a lighted splint. Procedure

6. Pure hydrogen burns ________________________________ in air. Hydrogen mixed with air burns with ________________. quietly with a pale blue flame. a ‘pop’ sound