Question

Which of the following is an acidic salt?
A. $N{a}_{2}S{O}_4$
B. $NaHS{O}_3$
C. $N{a}_{2}S{O}_3$
D. $K_{2}S{O}_4$

Answer 1

Hint: Consider the acids and bases that undergo neutralization reactions to form the given salts. Determine which is the acidic salt based on if any acidic protons are left unreacted during the reaction.

Complete step by step answer:
Acidic salts are considered to be the ones which have a $pH$ less than 7. This is seen due to the presence of acidic protons that are left unreacted while the neutralization reaction to form the salt occurs. We will see the reactions for each of the mentioned salts and determine which one is acidic.
- $N{a}_{2}S{O}_4$
This salt is prepared by the combination of sodium hydroxide and sulphuric acid. The reaction is as follows:
$$H_{2}S{O}_4+2NaOH\to N{a}_{2}S{O}_4+2H_{2}O$$

Here, we can see that both the hydrogen atoms in the sulphuric acid are completely replaced by the sodium ions and both the acidic protons are neutralized. So, this is a neutral salt.
- $NaHS{O}_3$
This salt is prepared by the combination of sulphurous acid and sodium hydroxide. The reaction is as follows:
$$H_{2}S{O}_3+NaOH\to NaHS{O}_3+H_{2}O$$

Here, we can see that only one out of the two acidic protons present in the sulphurous acid are replaced. Only one acidic proton is neutralized and the salt is free to donate to the other proton. Thus, this is an acidic salt.
- $N{a}_{2}S{O}_3$
This salt is prepared by the combination of sulphurous acid and sodium hydroxide. The reaction is as follows:
$$H_{2}S{O}_3+2NaOH\to N{a}_{2}S{O}_3+2H_{2}O$$

Here, we can see that both the acidic protons in the acid are replaced by the sodium ions and both the protons are completely neutralized. So, this is a neutral salt.
- $K_{2}S{O}_4$
This salt is prepared by the combination of potassium hydroxide and sulphuric acid. The reaction is as follows:
$$H_{2}S{O}_4+2KOH\to K_{2}S{O}_4+2H_{2}O$$

Here, we can see that both the acidic hydrogens in the acid are replaced by potassium and both protons are neutralized. So, this is a neutral salt.
According to these observations on the nature of all the salts given in the options, we can say that $NaHS{O}_3$ is an acidic salt.
So, the correct answer is “Option B”.

Note: Take note that you can also determine whether a salt is acidic or not by predicting the structure and bonding of the salt. Then figure out if the hydrogen atoms bonded in the molecule are acidic or not based on how easily they can be donated in the proton form.