(a) Name one metal in each case Which: (i) exists as a liquid at room temperature, (ii) can be found in nature in the uncombined state (b) X and Y are 0.5 m...
Question 1 Report
(a) Name one metal in each case Which:
(i) exists as a liquid at room temperature,
(ii) can be found in nature in the uncombined state
(b) X and Y are 0.5 mol. dm\(^{-3}\) freshly prepared aqueous solutions of two salts of iron
(II) With excess sodium hydroxide solution, X gave a dirty green precipitate which was not obtained in the case of Y.
Answer Details
(a) Naming metals
- (i) Liquid at room temperature: mercury (Hg).
- (ii) Found in nature in the uncombined (native) state: gold (Au) (silver or platinum are also acceptable).
(b) The two iron(II) solutions X and Y
With excess sodium hydroxide, a genuine iron(II) salt gives a dirty green precipitate of iron(II) hydroxide: \[Fe^{2+}_{(aq)} + 2OH^-_{(aq)} \rightarrow Fe(OH)_{2(s)}\] Since X gave this dirty green precipitate, X is the true iron(II) salt (Fe2+). Y did not give the dirty green precipitate; this shows that the iron(II) in Y had been oxidized by air to iron(III), so with sodium hydroxide it gives instead a reddish-brown precipitate of iron(III) hydroxide, Fe(OH)3. Iron(II) hydroxide itself is unstable and slowly turns reddish-brown on standing as it is oxidized to iron(III) hydroxide.
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