Question

Carbonates which are soluble in water are:
A) Sodium carbonate
B) Potassium carbonate
C) Both A and B
D) None of these

Answer 1

Hint:In the options,it is visible that question is from s-block elements.The carbonates of the alkali metal are generally soluble in water because of their polar nature. Their hydration enthalpy increases down the group in general .

Complete solution:
 A carbonate is a salt of carbonic acid. They are derived either from carbonic acid or carbon dioxide . In carbonates , a carbon atom is attached to three oxygen atoms . The chemical formula of the compound is $CO_3^{2 - }$ .
The carbonates that are given to us are sodium carbonate and potassium carbonate . Sodium carbonate is generally prepared with the very well known Solvay Process. Both of the carbonates are highly alkaline in nature. The solubility of any compound depends on its hydration enthalpy . Let us talk about each one of them one by one.
Sodium Carbonate made from positive sodium ions bonded to negative carbonate ions are polar in nature. The polarity of water molecules enables it to dissolve this compound . The positive part of water molecules attracts the negative carbonate ions and the negative part of water attracts the positive sodium ions. Hence , it becomes soluble in water.
Potassium Carbonate is made from carbonate ions and potassium ions . This molecule belongs to the same group as sodium carbonate . It is soluble in water because of its polarity.

Hence, the correct option is (C).


Note: Any substance is only soluble in water if the energy released by the formation of a new bond is more than the existing energy between the bonds . We can say if the hydration enthalpy is more than the lattice enthalpy of the compound , it will be soluble else it will not be.