Question

A white salt is readily soluble in water and gives a colourless solution with pH of about $9$ . The salt would be:
(A) $N{H_4}N{O_3}$
(B) $C{H_3}COONa$
(C) $C{H_3}COON{H_4}$
(D) $CaC{O_3}$

Answer 1

There are different types of categories for the type of solution: weak acid and strong base, strong acid and weak base, weak acid and weak base. On the basis of properties of these categories we can identify the compound.

Complete step by step solution:
First of all let us understand the acid and basic nature of the compound.
Acid nature: The compound which releases hydrogen ions on hydration. For example: carboxylic acid. Carboxylic acid on hydration gives hydrogen ions. pH for the acids ranges from $0 - 7$ . Higher the pH lower will be the acidic character.
Basic nature: The compound which releases hydroxide ions on hydration. For example: alcohol. Alcohol on hydration gives hydroxide ion. pH for the acids ranges from $7 - 14$ . Higher the pH higher will be the basic character.
Here we have different types of solutions: weak acid and strong base, strong acid and weak base, weak acid and weak base. And the products formed by these solutions are: weak acid and strong base will form basic products, strong acid and weak base will form acidic products and weak acid and weak base will form may be acidic or basic products.
Now here we are given the solution with pH of about $9$ i.e. the solution is basic in nature. Hence the type will be weak acid and strong base.
The examples of weak acids are $C{H_3}COOH$ and $Ca{(OH)_2}$ and the examples of strong bases are as: $NaOH$ and ${H_2}C{O_3}$ . And the reactions are as: $C{H_3}COOH + NaOH \to C{H_3}COONa$ and $Ca{(OH)_2} + {H_2}C{O_3} \to CaC{O_3}$ . And in the question it is given that the product is soluble in water but $CaC{O_3}$ is insoluble in water. Hence the salt will be $C{H_3}COONa$ .
Hence option B is correct.

Note:
$p{K_a}$ value is defined as the value to measure the strength of the acid. It is defined as the negative logarithm of the acid dissociation constant or ${K_a}$ value. Lower value indicates the acid is more dissociable in water.