Question

Using sodium hydroxide solution, how will you distinguish:
(a) zinc nitrate solution from calcium nitrate solution?
(b) iron (II) chloride from iron (III) chloride?
(c) lead hydroxide from magnesium hydroxide?

Answer 1

We can distinguish the below given compounds from each other with their unique reactions with sodium hydroxide solution, which are explain below.

(a)

Action of sodium hydroxide solution
Zinc nitrate solution	Calcium nitrate solution
Zinc nitrate solution on reaction with NaOH solution forms white gelatinous precipitate of zinc hydroxide, which, on further addition of excess of sodium hydroxide, forms soluble, complex sodium zincate. Zn(NO3)2 + 2 NaOH → Zn(OH)2 + 2NaNO3 Zn(OH)2 + 2 NaOH → Na2ZnO2 + 2H2O	Calcium nitrate solution on reaction with NaOH solution forms white precipitate of calcium hydroxide, which is sparingly soluble in excess of sodium hydroxide. Ca(NO3)2 + 2 NaOH → Ca(OH)2 + 2NaNO3

(b)

Action of sodium hydroxide solution
Iron (II) chloride	Iron (III) chloride
Iron (II) chloride solution on reaction with NaOH solution forms dirty green precipitate of ferrous hydroxide, which, on further addition of excess sodium hydroxide, stays insoluble. FeCl2 + 2 NaOH → Fe(OH)2 + 2NaCl	Iron (III) chloride solution on reaction with NaOH solution forms reddish brown precipitate of ferric hydroxide, which is insoluble in excess of sodium hydroxide. FeCl3 + 3 NaOH → Fe(OH)3 + 3NaCl

(c)

Action of sodium hydroxide solution
Lead hydroxide	Magnesium hydroxide
Lead hydroxide, being amphoteric in nature, reacts with sodium hydroxide solution to form colourless, soluble salt, sodium plumbite and water. Pb(OH)2 + 2 NaOH → Na2PbO2 + 2H2O	As magnesium hydroxide is a base, it will not react with sodium hydroxide solution.