Explain the following, giving reasons:
i) It is difficult to separate lanthanoid elements in the pure state.
ii) The transition elements form interstitial compounds.
i) It is difficult to separate lanthanoid elements in the pure state.
ii) The transition elements form interstitial compounds.
Solution
(i) All the lanthanoids show the same stable +3 state, and the lanthanoid contraction makes the Ln radii change only minutely from one element to the next — their chemical properties are therefore nearly identical, and separation requires tedious fractional methods (ion exchange).
(ii) Transition-metal lattices contain interstitial voids of just the right size for small non-metal atoms (H, C, N, B); these get trapped inside, giving non-stoichiometric interstitial compounds (e.g. TiC, FeH, VH) that are hard and high-melting.
(ii) Transition-metal lattices contain interstitial voids of just the right size for small non-metal atoms (H, C, N, B); these get trapped inside, giving non-stoichiometric interstitial compounds (e.g. TiC, FeH, VH) that are hard and high-melting.
CBSE Class 12 Board · 2002 · Foreign · Subjective