Question 7
What do you observe when:
(a) Iron nail is kept in copper sulphate solution for sometime?
(b) Phenolphthalein is added to sodium hydroxide solution?
(c) Blue litmus paper is dipped in dilute hydrochloric acid?
(d) Lead nitrate is heated?
(e) Magnesium ribbon is burnt in oxygen?
(f) Ammonia is brought in contact with hydrogen chloride gas?
(a) When iron nail is kept in a blue coloured copper sulphate solution for sometime, a reddish brown coating is seen on the iron nail and the colour of the solution changes gradually from blue to light green. The reason for this observation is that iron being more reactive than copper, displaces copper from the solution and copper is deposited on the iron nail.
Fe + CuSO4 (aq) ⟶ FeSO4 + Cu
(b) When a few drops of phenolphthalein is added to sodium hydroxide solution, it turns pink indicating that sodium hydroxide solution is basic in nature.
(c) Blue litmus paper changes into red colour when dipped in dilute hydrochloric acid confirming its acidic nature.
(d) When solid lead nitrate is heated strongly, it decomposes to produce light yellow solid lead monoxide, reddish brown nitrogen dioxide gas and colourless oxygen gas.
2Pb(NO3)2 2PbO + 4NO2 (g) + O2 (g)
(e) When magnesium ribbon is burnt in oxygen gas, it burns with a dazzling white light and produces a white powder of magnesium oxide.
2Mg + O2 ⟶ 2MgO
(f) When ammonia is brought in contact with hydrogen chloride gas, dense white fumes of ammonium chloride are produced.
NH3 + HCl ⟶ NH4Cl