Question

Which of the following alkaline earth metal nitrate does not crystalline with water of crystallization?

• A. $\mathrm{Ca}{\left({\mathrm{NO}}_3\right)}_2$
• B. $\mathrm{Mg}{\left({\mathrm{NO}}_3\right)}_2$
• C. $\mathrm{Sr}{\left({\mathrm{NO}}_3\right)}_2$
• D. $\mathrm{Ba}{\left({\mathrm{NO}}_3\right)}_2$

Answer 1

The correct option is D

$\mathrm{Ba}{\left({\mathrm{NO}}_3\right)}_2$

The explanation for the correct answer

(D) $\mathrm{Ba}{\left({\mathrm{NO}}_3\right)}_2$

1. The water of crystallization depends upon the power of polarization of a cation.
2. The polarisation power is less when a cation has a large size and thus does not have water for crystallization.
3. ${\mathrm{Ba}}^{2+}$is larger and has less polarization power and hence does not have water of crystallization.

The explanation for the incorrect answers

(A)$\mathrm{Ca}{\left({\mathrm{NO}}_3\right)}_2$

1. ${\mathrm{Ca}}^{2+}$is smaller in size and thus has high polarization power.
2. So, it has water of crystallization.

(B)$\mathrm{Mg}{\left({\mathrm{NO}}_3\right)}_2$

1. ${\mathrm{Mg}}^{2+}$is smaller in size and thus has high polarisation power.
2. So, it has water of crystallisation.

(B)$\mathrm{Sr}{\left({\mathrm{NO}}_3\right)}_2$

1. ${\mathrm{Sr}}^{2+}$is larger cation but smaller than ${\mathrm{Ba}}^{2+}$.
2. So it has high polarisation power ${\mathrm{Ba}}^{2+}$.
3. Thus, it has water of crystallization.

$\mathrm{Ba}{\left({\mathrm{NO}}_3\right)}_2$is the alkaline earth metal Nitrate does not crystalline with water of crystallization. Hence, option (D) is correct.