Question

Sodium carbonate is a basic salt because it is salt derived from:
(A) strong acid and strong base
(B) strong acid and weak base
(C) weak acid and strong base
(D) weak acid and weak base

Answer 1

Hint: Try dissociating the given salt and acidify the anion and add alkali to cation to get the components which reacted to form the salt. Accordingly classify them as strong or weak acid or base depending on their ability to dissociate.

Complete answer:
- Let’s have a look at the salt given in the question and write its molecular formula.
- Sodium carbonate has the molecular formula, $N{a_2}C{O_3}$
- Sodium carbonate, $N{a_2}C{O_3}$ dissociates in water to form sodium ions, $N{a^ + }$ and carbonate ions, $CO_{3}^{2-}$.
- Sodium ion is an electrophile so would readily react with hydroxyl ions to form sodium hydroxide, NaOH.
- Carbonate ion is a nucleophile so it would easily react with protons to form carbonic acid, ${{H}_{2}}C{{O}_{3}}$.
- Therefore, the acid-base reaction taking place to form sodium carbonate is given as,
\[{{H}_{2}}C{{O}_{3}}+2NaOH\to N{{a}_{2}}C{{O}_{3}}+2{{H}_{2}}O\]
- Now, we know that sodium hydroxide is a strong base and carbonic acid is a weak acid.
- Therefore, sodium carbonate is a basic salt because it is a salt derived from a weak acid and strong base.

Therefore, the correct answer is option (C) weak acid and strong base.

Note:
Remember acid-base reactions are also called neutralization reactions. Salts are products of neutralization reactions. Whenever you get such a question, break the salt and find its ions and then go backwards to find acid and base.