The Sblock Elements Ques 30
30. The correct order of increasing thermal stability of $\mathrm{K}_2 \mathrm{CO}_3, \mathrm{MgCO}_3, \mathrm{CaCO}_3$ and $\mathrm{BeCO}_3$ is
[2007]
(a) $\mathrm{BeCO}_3<\mathrm{MgCO}_3<\mathrm{CaCO}_3<\mathrm{K}_2 \mathrm{CO}_3$
(b) $\mathrm{MgCO}_3<\mathrm{BeCO}_3<\mathrm{CaCO}_3<\mathrm{K}_2 \mathrm{CO}_3$
(c) $\mathrm{K}_2 \mathrm{CO}_3<\mathrm{MgCO}_3<\mathrm{CaCO}_3<\mathrm{BeCO}_3$
(d) $\mathrm{BeCO}_3<\mathrm{MgCO}_3<\mathrm{K}_2 \mathrm{CO}_3<\mathrm{CaCO}_3$
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Answer:
Correct Answer: 30.(a)
Solution: (a) As the cation size increases down the group, the metal carbonates become more ionic in nature. Hence, the thermal stability increases as: $\mathrm{BeCO}_3<\mathrm{MgCO}_3<\mathrm{CaCO}_3$.
The ionic character of group 1 carbonates is more than that of group $2$ , thus they possess more thermal stability. Hence, the correct order of thermal stability: $\mathrm{BeCO}_3<\mathrm{MgCO}_3<\mathrm{CuCO}_3$ $<\mathrm{K}_2 \mathrm{CO}_3$.
BETA
