(a) Account for the following (i) Ti^(3+) is coloured whereas Sc^(3+) is colourless in aqueous solution. (ii) Cr^(2+) is a strong reducing agent. (b) Write two similarities between chemistry of lanthanoids and actinoids. (c ) Complete the following ionic equation: 3MnO_4^(2-) +4H^+ to

(a) Account for the following (i) Ti^(3+) is coloured whereas Sc^(3+)

1.	(a) Account for the following (i) Ti^(3+) is coloured whereas Sc^(3+) is colourless in aqueous solution. (ii) Cr^(2+) is a strong reducing agent. (b) Write two similarities between chemistry of lanthanoids and actinoids. (c ) Complete the following ionic equation: 3MnO_4^(2-) +4H^+ to
Answer» Solution :(i) `Sc^(3+)` has no electron in the d-orbitals. There is no possibility of EXCITATION to the electron from low energy d- orbital to high energy d-orbital. There is no absorption of radiation and hence no colour. `TI^(3+)` has one electron in 3d orbital. It adsorbs radiation in excitation from lower to higher d-orbital. It is therefore coloured. (ii) `Cr^(2+)` is a strong reducing agent. That means it easily oxidised to `Cr^(3+)` in which it has a configuration `3d^3`. It is a stable electronic configuration because it is half filled in the orbitals of `t_(2g)` which are three in number. (b) Similarities between the chemistry of lanthanoids and actinoids: (i) Variations in the magnetic susceptibilities of actinoids with the number of unpaired f electrons is ROUGHLY parallel to teh corresponding results for lanthanoids. (ii) The lanthanoid and actinoid contractions have extended effects on SIZES and PROPERTIES of elements succeeding them. (c ) `3MnO_4^(2-)+4H^(+) to 2MnO_4^(-)+MnO_2+2H_2O`