Question

2. One molecule of an 'ic' acid of a non-metal having 5 electrons in valence shell reacts with a molecule of base to form a salt X. The base corresponds to the metal with one electron in valence shell. If the salt so formed can react with the same base in 1:2 ratio, predict the formula of the salt X.

• A. K₂SO₄
• B. Na₂HPO₄
• C. KH₂PO₄
• D. Na₃PO₄

Answer 1

The correct option is C

KH₂PO₄

Explanation:

(C) KH₂PO₄

• Phosphorus is a non-metal with 5 valence electrons, and 'ic' acid of Phosphorus is phosphoric acid (H₃PO₄).
• Those metal having one electron in its valence shell form MOH
• Let assume the metal to be K that forms KOH. The chemical reaction between KOH and phosphoric acid is as follows:

$\underset{\mathrm{Potassium}\mathrm{hydroxide}}{\mathrm{KOH}}+\underset{\mathrm{Phosphoric}\mathrm{acid}}{{\mathrm{H}}_3{\mathrm{PO}}_4}\to \underset{\mathrm{Potassium}\mathrm{dihydrogen}\mathrm{phosphate}}{{\mathrm{KH}}_2{\mathrm{PO}}_4}+\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}}$

• If the salt react with base in the ratio 1:2 the reaction occurs is as follows:

$\underset{\mathrm{Potassium}\mathrm{di}\mathrm{hydrogen}\mathrm{sulphate}}{{\mathrm{KH}}_2{\mathrm{PO}}_4}+\underset{\mathrm{potassium}\mathrm{hydroxide}}{2\mathrm{KOH}}\to \underset{\mathrm{Tri}\mathrm{potassium}\mathrm{phosphate}}{{\mathrm{K}}_3{\mathrm{PO}}_4}+\underset{\mathrm{Water}}{2{\mathrm{H}}_2\mathrm{O}}$

• Thus, Salt ‘X’ is KH₂PO₄

Hence, option (C) is the correct answer.