Question

The low solubility of $LiF$ and that of $CsI$ in water are respectively due to which of the following properties of the alkali metal ions?

• A. Higher hydration enthalpy of ${Li}^{+}$, higher lattice enthalpy of ${Cs}^{+}$
• B. Smaller hydration enthalpy of ${Li}^{+}$, higher lattice enthalpy of ${Cs}^{+}$
• C. Smaller lattice enthalpy of ${Li}^{+}$, higher hydration enthalpy of ${Cs}^{+}$
• D. Smaller hydration enthalpy of ${Li}^{+}$, smaller lattice enthalpy of ${Cs}^{+}$
• E. Higher lattice enthalpy of ${Li}^{+}$, smaller hydration enthalpy of ${Cs}^{+}$

Answer 1

The correct option is E Higher lattice enthalpy of ${Li}^{+}$, smaller hydration enthalpy of ${Cs}^{+}$

If hydration energy is greater as compare to lattice energy then the salt is soluble, and if hydration energy is lesser as compared to lattice energy, then salt is insoluble.

$LiF$ is almost insoluble due to high lattice energy. Both ions in $LiF$ are very small.

In case of $CsI$ both ions are larger in size. As a result, both the ions in $CsI$ are less hydrated therefore, its hydration energy will decrease.

Hence, it is insoluble in water.