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