Question

Match the column

Column-I	Column-I I
$PhN{H}_3^{+}C{l}^{(}aq.)$	Basic
$N{a}_{2}C{O}_3(aq.)$	Acidic
$RbN{O}_3(aq.)$	Neutral
Aqueous solution of salt of weak acid and weak base	Cannot predict

• A. 2 4 1 3
• B. 1 2 3 4
• C. 3 2 1 4
• D. 2 1 3 4

Answer 1

The correct option is D 2 1 3 4

As we know, there are following four type of Salts:
1. Salts of Strong Acid and Strong Base
2. Salt of Weak Acid and Strong Base
3. Salt of Strong Acid and Weak Base
4. Salt of Weak Acid and Weak Base
To know the type of salt, just add $H_{2}O$ to all the salts to obtain the corresponding acids and bases.
In general, we should know the below common examples:
Strong Acids:$HCl,H_{2}S{O}_4,H_{3}P{O}_4,HN{O}_3$
Strong Bases:$NaOH,KOH,RbOH$
Weak Acids:$C{H}_{3}COOH,HCN,H_{2}C{O}_3$
Weak Bases:$N{H}_{4}OH,PhOH,N{H}_3,RN{H}_2,PhN{H}_2$
So, in the above question,
$PhN{H}^{3+}C{l}^{-}\left(aq\right)$ gives $HCl\left(aq\right)$ & $PhN{H}_2\left(aq\right)$. As it is a combination of Strong Acid and Weak Base, the resulting solution is Acidic.
$N{a}_{2}C{O}_3\left(aq\right)$ gives $NaOH\left(aq\right)$ & $H_{2}C{O}_3\left(aq\right)$. As it is a combination of Weak Acid and Strong Base, the resulting solution is Basic.
$RbN{O}_3\left(aq\right)$ gives $RbOH\left(aq\right)$ & $HN{O}_3\left(aq\right)$. As it is a combination of Strong Acid and Strong Base, the resulting solution is Neutral.
The nature of aqueous solution of Weak Acid and Weak Base cannot be predicted. This is because, the nature depends on the values of $K_{a}and{K}_b$ of corresponding acids and bases.