Question

Aqueous solution of which salts will have a pH value less than 7.
$a\left)K_{2}HP{O}_{4}b\right)N{a}_{2}Sc\left)K{H}_{2}P{O}_{4}d\right)FeC{l}_3$

• A. a and c
• B. c and b
• C. a and d
• D. c and d

Answer 1

The correct option is D

c and d

$K_{2}HP{O}_4\to 2K^{+}+HP{O}_4^{2-}$
$HP{O}_4^{2-}$ is an amphoteric anion and is a stronger base than it is an acid, hence the solution is basic.
$N{a}_{2}S\to 2N{a}^{+}+S^{2-}$
$N{a}^{+}$ is a neutral cation (cation of a strog base NaOH)
$FeC{l}_3\to F{e}^{3+}+3Cl$ (acidic solution)
$K{H}_{2}P{O}_4\to K^{-}+H_{2}P{O}_4^{-}$
$H_{2}P{O}_4^{-}$ is a stronger acid than it is a base, hence the solution is acidic.