Question

Equal amount of $NaOH$ solution is added to aqueous solutions of ferric sulphate and ferrous sulphate taken in two different test tubes. Precipitates of two different colours can be seen in these test tubes.
(a) Which compounds are responsible for different colours?
(b) Write the subs shell electronic configuration of ferric ion.
(Hint: atomic number of iron -26)
(c) Why do iron form compounds with two different valencies?

Answer 1

(a) Transition metal compounds are responsible for different colours.
(b) $1s^{2}2s^{2}2p^{6}3s^{2}3d^5$
(c) The energy difference between the s-subshell of the outermost shell and the d-subshell of the penultimate shell in d- block elements such as iron is very small. So, during compound formation, electrons may be transferred or shared from both these subshells. Hence, iron can show variable valencies.