Iron is a transition metal in Group 8 of the Periodic Table. Table 3.1 gives values for the stability constants, $$\(K_{\text {stab }}\)$$, of different complexes of iron. (i) $$\(\left[\mathrm{Fe}\left(\mathrm{H}_{2} \mathrm{O}\right)_{5}\left(\mathrm{H}_{2} \mathrm{PO}_{4}\right)\right]^{2+}\)$$ can form when $$\(\mathrm{H}_{3} \mathrm{PO}_{4}\)$$ reacts with $$\(\left[\mathrm{Fe}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{3+}\)$$. Write an equation for this reaction. ................................................................................................................................. (ii) Write an expression for $$\(K_{\text {stab }}\)$$ of $$\(\left[\mathrm{Fe}\left(\mathrm{H}_{2} \mathrm{O}\right)_{5} \mathrm{SCN}\right]^{2+}\)$$ and give its units. $$\[ K_{\text {stab }}= \]$$ $$\[ \text { units }= \]$$ ..................................................... (iii) Use the stability constant data in Table 3.1 to calculate the value of the equilibrium constant, $$\(K_{\mathrm{c}}\)$$, for the following equilibrium. $$\[ \left[\mathrm{Fe}\left(\mathrm{H}_{2} \mathrm{O}\right)_{5}\left(\mathrm{H}_{2} \mathrm{PO}_{4}\right)\right]^{2+}+\mathrm{SCN}^{-} \rightleftharpoons\left[\mathrm{Fe}\left(\mathrm{H}_{2} \mathrm{O}\right)_{5} \mathrm{SCN}^{2+}+\mathrm{H}_{2} \mathrm{PO}_{4}^{-}\right. \]$$ value of $$\(K_{\mathrm{c}}=\)$$ .....................................................

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