Write equations to represent the following observations. (a) A quantity of \(\mathrm{CuCl}_{2}(\mathrm{s})\) is dissolved in concentrated HCl(aq) and produces a yellow solution. The solution is diluted to twice its volume with water and assumes a green color. On dilution to ten times its original volume, the solution becomes pale blue. (b) When chromium metal is dissolved in \(\mathrm{HCl}(\mathrm{aq}), \mathrm{a}\) blue solution is produced that quickly turns green. Later the green solution becomes blue-green and then violet.

The chemical equations representing the reactions are: \n(a) \n1. \( \mathrm{CuCl}_{2}(\mathrm{s}) + 2\mathrm{HCl}(\mathrm{aq}) \rightleftharpoons [CuCl4]^{2-}(\mathrm{aq}) + 2H^+(\mathrm{aq}) \)\n2. \([CuCl4]^{2-}(aq) \rightleftharpoons Cu^{2+}(aq) + 4Cl^-(aq)\) and \(Cu^{2+}(aq) + 4H2O(l) \rightarrow [Cu(H2O)4]^{2+}(aq)\) \n(b) \n1. \(\mathrm{Cr(s)}+ 2\mathrm{HCl(aq)} \rightarrow \mathrm{CrCl2(aq)} + \mathrm{H2(g)}\)\n2. \(\mathrm{Cr^{2+}(s)}+ \mathrm{6H2O(l)} \rightarrow [\mathrm{Cr(H2O)6}]^{2+}(aq)\)\n3. \([\mathrm{Cr(H2O)6}]^{2+}(aq) + 2 \mathrm{H2O(l)} \leftrightarrow [\mathrm{Cr(H2O)4(OH)2}]^{+}(aq) + 4 \mathrm{H2O(l)}\) and \n4. \([\mathrm{Cr(H2O)4(OH)2}]^{+}(aq) \rightarrow [\mathrm{Cr(H2O)3(OH)3]\)