a. Name two group 2 elements which do not impart colour to the fl… - Vidyadip

Question

a. Name two group 2 elements which do not impart colour to the flame and why?
b. Arrange $\mathrm{K}_2 \mathrm{CO}_3, \mathrm{MgCO}_3, \mathrm{CaCO}_3, \mathrm{BeCO}_3$, in increasing order of thermal stability and why?
c. Which metal hydroxide is most soluble in water in group 2 and why?
d. What is Epsom salt?
e. Why is $\mathrm{Na}_2 \mathrm{O}_2$ diamagnetic?

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Answer

a. Be and Mg do not impart colour to the flame because they have high ionisation enthalpy and do not absorb light from visible region.
b. $\mathrm{BeCO}_3<\mathrm{MgCO}_3<\mathrm{CaCO}_3<\mathrm{K}_2 \mathrm{CO}_3$ It is due to increase in ionic character and increase in lattice enthalpy.
c. $\mathrm{Ba}(\mathrm{OH})_2$ is most soluble in water because its hydration enthalpy is more than lattice enthalpy.
d. $\mathrm{MgSO}_4 \cdot 7 \mathrm{H}_2 \mathrm{O}$ is epsom salt.
e. In $\mathrm{Na}_2 \mathrm{O}_2, \mathrm{O}_2{ }^{2-}(18)$ has unpaired electron, that is why it is diamagnetic.

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