1. You cannot live without this substance. If it is absent from you for 2 minute, you may die.

2. 1. It is a colourless, odourless gas. 2. It is slightly soluble in cold water. 3. Oxygen does not burn, but is a good supporter of. combustion. A burning substance burns more vigorously. in oxygen.

3. Put a glowing splint into a gas sample. If there are lots of oxygen in the sample, the glowing splint will be relighted.

4. Put a glowing splint into a gas sample. If there are lots of oxygen in the sample, the glowing splint will be relighted.

6. Put black manganese dioxide into the flask. Hydrogen peroxide is added by means of a tap funnel. A colourless gas (I.e. oxygen) is evolved. Oxygen is collected over water.

7. The formula of hydrogen peroxide is H 2 O 2. This compound decomposes on its own, as shown in the equation below: 2H 2 O 2 (aq) -----> 2H 2 O(l) + O 2 (g)

8. The manganese dioxide speeds up the reaction, but it does not take part in the reaction above. It remains unchanged in the flask after the reaction. This kind of substance is called catalyst.

9. 1. Hydrogen: Hydrogen burns in oxygen to form water. 2H 2 + O2 O2 -----> 2H 2 O 2. Carbon: Carbon burns in plenty supply of oxygen with a sparking flame to form carbon dioxide: C + O 2 ---> CO 2 For limited supply of oxygen, carbon monoxide is formed instead of carbon dioxide. 2C+ O 2 ----> 2CO (a poisonous, colourless gas) 3. Copper: When copper is heated in oxygen, copper oxide is formed: 2Cu(s) + O 2 (g) ----> 2CuO(s)