Chemistry

Chemistry

Problem

A white solid A reacts with dilute H2SO4\text{H}_2\text{SO}_4 to produce a colourless gas B and a colourless solution C. The reaction between B and acidified dichromate yields a green solution and a slightly coloured precipitate D. The substance D, when burnt in air, gives a gas E which reacts with B to yield D and a colourless liquid. Anhydrous copper sulphate turns blue with this colourless liquid. The addition of aqueous NH3\text{NH}_3 or NaOH\text{NaOH} to C produces a precipitate that dissolves in an excess of the reagent to form a clear solution. Which of the following reactions are relevant to the action of NH3\text{NH}_3 or NaOH\text{NaOH} solution on C? a. Zn(OH)2+4NH3⟶[Zn(NH3)4]2++2OH−\text{Zn}(\text{OH})_2 + 4\text{NH}_3 \longrightarrow [\text{Zn}(\text{NH}_3)_4]^{2+} + 2\text{OH}^- b. Zn(OH)2+2OH−⟶[Zn(OH)4]2−\text{Zn}(\text{OH})_2 + 2\text{OH}^- \longrightarrow [\text{Zn}(\text{OH})_4]^{2-} c. Pb(OH)2+4NH3⟶[Pb(NH3)4]2++2OH−\text{Pb}(\text{OH})_2 + 4\text{NH}_3 \longrightarrow [\text{Pb}(\text{NH}_3)_4]^{2+} + 2\text{OH}^- d. Pb(OH)2+2OH−⟶[Pb(OH)4]2−\text{Pb}(\text{OH})_2 + 2\text{OH}^- \longrightarrow [\text{Pb}(\text{OH})_4]^{2-}

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