Question

What is the correct increasing order of solubility of the following salt?
\[NaHC{{O}_{3}},\text{ }KHC{{O}_{3}},\text{ }Mg{{\left( HC{{O}_{3}} \right)}_{2}},\text{ }Ca{{\left( HC{{O}_{3}} \right)}_{2}}\]
A. $KHC{{O}_{3}}< Mg{{\left( HC{{O}_{3}} \right)}_{2}} < Ca{{\left( HC{{O}_{3}} \right)}_{2}} < NaHC{{O}_{3}}$
B. $Mg{{\left( HC{{O}_{3}} \right)}_{2}} < Ca{{\left( HC{{O}_{3}} \right)}_{2}} < NaHC{{O}_{3}} < KHC{{O}_{3}}$
C. $NaHC{{O}_{3}}<\text{ }KHC{{O}_{3}}<\text{ }Mg{{\left( HC{{O}_{3}} \right)}_{2}}<\text{ }Ca{{\left( HC{{O}_{3}} \right)}_{2}}$
D. $Ca{{\left( HC{{O}_{3}} \right)}_{2}}< NaHC{{O}_{3}}< KHC{{O}_{3}}< Mg{{\left( HC{{O}_{3}} \right)}_{2}}$

Answer 1

Hint: The solubility of the compounds is going to depend on the lattice energy of the cationic part present in it. Lattice energy of the atoms is inversely proportional to solubility of the compounds. Means if an atom has high lattice energy then the compound has less solubility.

Complete step by step solution:
- In the question it is given that we have to find the correct increasing order of solubility of the given slats.
- In the given compounds we can see clearly that all the compounds are metal bicarbonates and the anion part is bicarbonate ions.
- The cation parts in the given salts are sodium, potassium, magnesium and calcium.
- All the cationic parts belong to group IA in s-block.
- We know that as we are moving from top to bottom in the periodic table the atomic size increases.
- As the atomic size increases the lattice energy of the compounds decreases.
- As the lattice energy decreases from top to bottom in the groups the solubility of the compounds increases.
- Means the solubility of the metal carbonates increases as we are moving from top to bottom in the periodic table.
- There the increasing order of solubility of the given compounds is as follows.
\[NaHC{{O}_{3}}<\text{ }KHC{{O}_{3}}<\text{ }Mg{{\left( HC{{O}_{3}} \right)}_{2}}<\text{ }Ca{{\left( HC{{O}_{3}} \right)}_{2}}\]
So, the correct answer is “Option C”.

Note: The solubility of the metal carbonates from top to bottom across the group increases due to increases in their atomic size of metals along the groups. At the same time lattice energy of the metal carbonates decreases as we move along the groups from top to bottom.