Dr. S.N. DHAWAN, Dr. S.C.KHETERPAL and, P.N.KAPIL Solutions for Chapter: s-Block Elements (Alkali and Alkaline Earth Metals), Exercise 4: Competition Focus

${\mathrm{RbO}}_2 \mathrm{is}$

Magnesium burns in the atmosphere of the following gases ?

Out of $\mathrm{Li}, \mathrm{Na}, \mathrm{K}, \mathrm{Rb}, \mathrm{Cs}$, how many of them directly form superoxides on heating with dioxygen?

How many of the following $\mathrm{s}$-block elements do not give characteristic colours in the flame test:

$\mathrm{Li}, \mathrm{Be}, \mathrm{Ca}, \mathrm{Ba}, \mathrm{Sr}, \mathrm{Mg}, \mathrm{Na}, \mathrm{K}, \mathrm{Cs}$

How many of the following compounds is/are amphoteric in character?

$\mathrm{CsOH}, \mathrm{LiOH}, \mathrm{Ca}(\mathrm{OH}{)}_2, \mathrm{Be}(\mathrm{OH}{)}_2, \mathrm{Mg}(\mathrm{OH}{)}_2, \mathrm{Ba}(\mathrm{OH}{)}_2, \mathrm{Sr}(\mathrm{OH}{)}_2, \mathrm{KOH}, \mathrm{NaOH}$

How many of the following metals when heated in an atmosphere of ${\mathrm{N}}_2$ form nitrides.

$\mathrm{Li}, \mathrm{Na}, \mathrm{K}, \mathrm{Rb}, \mathrm{Cs}, \mathrm{Mg}, \mathrm{Ca}, \mathrm{Sr}, \mathrm{Ba}$

How many of the following metal sulphates dissolve in water?

${\mathrm{SrSO}}_4, {\mathrm{K}}_2{\mathrm{SO}}_4, {\mathrm{BeSO}}_4, {\mathrm{Li}}_2{\mathrm{SO}}_4, {\mathrm{MgSO}}_4, {\mathrm{BaSO}}_4, {\mathrm{Na}}_2{\mathrm{SO}}_4. {\mathrm{CaSO}}_4, {\mathrm{Rb}}_2{\mathrm{SO}}_4$

The enthalpy of formation of hypothetical $\mathrm{CaCl}\left(\mathrm{s}\right)$ is theoretically found to be $-188 \mathrm{kJ} {\mathrm{mol}}^{-1}$ and ${∆}_{\mathrm{f}}{\mathrm{H}}^{°}$ for ${\mathrm{CaCl}}_2\left(\mathrm{s}\right)$ is $-795 \mathrm{kJ} {\mathrm{mol}}^{-1}$. Calculate ${∆}_{\mathrm{f}}{\mathrm{H}}^{°}$(in $\mathrm{kJ} {\mathrm{mol}}^{-1}$) for the disproportionation reaction.

 $2\mathrm{CaCl} \left(\mathrm{s}\right)\stackrel{ }{\to } {\mathrm{CaCl}}_2 \left(\mathrm{s}\right)+\mathrm{Ca}\left(\mathrm{s}\right)$