Siyapath
Sign up

Lesson: Chapter 16 — Changes of Matter

16.5. Hydrogen and oxygen 8 of 8

Making and testing oxygen

Oxygen is made by decomposition reactions — the very type we met in section 16.1.

Four reactions

01. Heating potassium permanganate

2KMnO4 → K2MnO4 + MnO2 + O2

02. Heating potassium nitrate

2KNO3 → 2KNO2 + O2

03. Decomposing hydrogen peroxide

2H2O2 → 2H2O + O2

04. Heating potassium chlorate

2KClO3 → 2KCl + 3O2

Figure to be added

Figure 16.4 — preparing oxygen gas in the laboratory; the stand, the boiling tube, the potassium permanganate crystals, the rubber bung, the delivery tube, the gas jar, the trough and the beehive shelf.

You will see that the method of collecting the O2 here is again the downward displacement of water.

Activity 16.9

Set up the apparatus shown in figure 16.4 and collect oxygen (O2) gas into several test tubes. Obtain a dry splint and set one end of it alight. Once it is glowing, blow the flame out. Now take a tube of collected oxygen out of the water and, the moment its mouth is opened, insert the glowing splint into it.

(Carry out this activity with your science teacher.)

The observation

The glowing splint is seen to burst back into flame and burn brightly. By this observation oxygen gas can be identified.

The uses of oxygen gas

  • It is needed by every living thing for respiration.
  • What reacts when something burns in air is the oxygen — so it is needed for combustion.
  • It is used in diving and in space travel.
  • It provides the oxy-acetylene flame used for welding metals.
  • It is used as a raw material in industries such as the manufacture of sulphuric acid and nitric acid.