Question

Which has highest pH?

• A. $C{H}_{3}COOK$
• B. $N{a}_{2}C{O}_3$
• C. $N{H}_{4}Cl$
• D. $NaN{O}_3$

Answer 1

Answer: (B)

$pH=\log \frac{1}{\left[H^{+}\right]}$
$pH$ is inversely proportional to hydrogen ion concentration. As concentration of $H^{+}$decreases pH increases and vice versa.
(a) Ammonium chloride $\left(N{H}_{4}Cl\right)$ is a salt of weak base and strong acid. So, its aqueous solution will be acidic as
$N{H}_{4}Cl+H_{2}O⟶\underset{\text{weakbase}}{N{H}_{4}OH}+\underset{\text{strong acid}}{\mathrm{HCl}}$
So, $pH$ of $N{H}_{4}Cl$ is less than 7
(b) $NaN{O}_3$ (Sodium nitrate) is the salt of strong acid and strong base. So, its aqueous solution is neutral as
$NaN{O}_3+H_{2}O⟶\underset{\text{ strong base }}{\mathrm{NaOH}}+\underset{\text{ strong acid }}{NN{O}_3}$
So, $pH$ of $NaN{O}_3$ is 7 .
(c) $C{H}_{3}COOK$ (Potassium acetate) is a salt of strong base and weak acid. Its aqueous solution will be basic and $pH$ value will be $>7\approx 8.8$
$C{H}_{3}COOK+H_{2}O⟶\underset{\text{ weak acid }}{C{H}_{3}COOH}+\underset{\text{ strong base }}{\mathrm{KOH}}$
(d) $N{a}_{2}C{O}_3$ (Sodium carbonate) is a salt of strong base and weak acid. Its aqueous solution is also basic and its $pH$ value will be more than 10.
$N{a}_{2}C{O}_3+H_{2}O⟶\underset{\text{strong base}}{2NaOH}+\underset{\text{weak acid}}{H_{2}C{O}_3}$