Activity 3.8 NCERT Class 10 Science, Metals and Non-metals

Activity 3.8 NCERT Class 10 Science, Chapter 3 Metals and Non-metals

Brief procedure:

Activity 3.8 asks us to react oxides of metal and non-metals with water and check if it is acidic or basic in nature.

Observation:

We get metal oxide by burning the metal in the presence of oxygen. Metal oxide reacts with water to give a base. It turns the red litmus paper blue.

Similarly, the burning of non-metal produces its oxide. The solution of oxides of non-metal with water turns the blue litmus paper into the red.

Explanation: 

Magnesium

Magnesium burns in air to form its oxide. See activity 1.1.

2Mg(s) + O₂(g) ———–> 2MgO(s)

Magnesium oxide reacts with water and forms Magnesium Hydroxide.

MgO(S) + H2O(l) ———–> Mg(OH)₂ (aq)

Magnesium hydroxide is a strong base. It makes the solution alkaline. So, the PH paper turns blue.

Application:

Many antacid syrups contain metal oxides like magnesium oxide and aluminium oxides. These metal oxides form respective metal hydroxide in the stomach and neutralises the acidity.

Sulphur:

Sulphur is a reactive non-metal; it burns to produce its oxide.

S(s) +O₂(g) ————-> SO₂(g)

Sulphur dioxide dissolves in water and forms sulphurous acid.

SO₂(g) + H₂O(l) ———–> H₂SO₃ (aq)

Sulphurous acid is a weak acid. Its 0.1N solution gives the PH of 1.5 which turns the blue litmus red.

Next: Burn test and flame colour of various metals, Activity 3.9.

See also: Comparison of properties of non-metals with metals, Activity 3.7.