Question

ASSERTION
Sodium and potassium carbonates are soluble in water but magnesium and calcium carbonate are insoluble in water.
REASON
Lattice energy of Mg and Ca carbonates is much higher than sodium and potassium carbonate.
A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion.
B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion.
C. Assertion is correct but Reason is incorrect.
D. Both Assertion and Reason are incorrect.

Answer 1

Hint: The lattice energy of a crystalline solid can be defined as the energy released when ions are combined to form a compound. It generally calculates those cohesive forces through which ions are bound. Lattice energy can be related to other practical properties like hardness, solubility and volatility.

Complete Step by step solution: Lattice energy is calculated with the help of Born-Haber cycle which is used to analyze reaction energies. This cycle is concerned with the formation of an ionic compound from the reaction of a metal with a halogen or any other non-metallic element. The lattice enthalpy can be defined as the enthalpy change involved in the formation of an ionic compound from gaseous ions and can also be stated as the energy needed to break the ionic compound into gaseous ions which is generally an endothermic process. Sodium and potassium carbonates are soluble in water but magnesium and calcium carbonates are insoluble in water because lattice energy of Mg and Ca carbonates is much higher than sodium and potassium carbonate. Because for solubility conditions lattice energy must be less than the hydration energy.

So we can say that both assertion and reason are correct and reason is the correct explanation for assertion. Hence option A is correct.

Note: Hydration energy which is also known by hydration enthalpy can be defined as the amount of energy released when one mole of ions undergoes hydration. Lattice energy is generally used in the calculation and estimations of electron relationships and fluoride relationships. It is also used in the calculation of standard enthalpies of formation and to find the strength of ionic acids.