Question

Give a chemical test to distinguish between the following pair of compounds

Ferrous nitrate and lead nitrate solution

Answer 1

Reagent	Ferrous nitrate solution	Lead nitrate solution
NaOH solution is added	Ferrous nitrate react with sodium hydroxide, a dirty green precipitate is formed. $\mathrm{Fe}{\left({\mathrm{NO}}_3\right)}_2\left(\mathrm{aq}\right)+2\mathrm{NaOH}\left(\mathrm{aq}\right)\to \underset{\mathrm{a}\mathrm{dirty}\mathrm{green}\mathrm{precipitate}}{\mathrm{Fe}{\left(\mathrm{OH}\right)}_2\left(\mathrm{s}\right)}+2{\mathrm{NaNO}}_3\left(\mathrm{aq}\right)$ This precipitate indicates the formation of ferric hydroxide.	When lead nitrate react with sodium hydroxide, a white precipitate is formed $\mathrm{Pb}{\left({\mathrm{NO}}_3\right)}_2\left(\mathrm{aq}\right)+2\mathrm{NaOH}\left(\mathrm{aq}\right)\to \underset{\mathrm{white}\mathrm{precipitate}}{\mathrm{Pb}{\left(\mathrm{OH}\right)}_2\left(\mathrm{s}\right)}+2{\mathrm{NaNO}}_3\left(\mathrm{aq}\right)$ This precipitate indicates the formation of lead hydroxide
When excess reagent is added	It is not soluble in excess reagent. It turns to reddish brown precipitate slowly due to the oxidation and form Fe (OH)3 $4\mathrm{Fe}{\left(\mathrm{OH}\right)}_2\left(\mathrm{s}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)+2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\to 4\mathrm{Fe}{\left(\mathrm{OH}\right)}_3\left(\mathrm{s}\right)$	Pb (OH)2 is an amphoteric oxide. They dissolve in aqueous NaOH and soluble salt of sodium is formed. Pb (OH)2(s) + NaOH(aq) $\to$Na2 PbO2(aq)+2H2O(l)