Question

Which has highest pH?

• A. $CH_{3}COOK$
• B. $Na_{2}CO_{3}$
• C. $NH_{4}Cl$
• D. $NaNO_{3}$

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 $\left( NH _{4} Cl \right)$ is a salt of weak base and strong acid. So, its aqueous solution will be acidic as
$NH _{4} Cl + H _{2} O \longrightarrow \underset{\text{weakbase}}{NH _{4} OH} + \underset{\text{strong acid}}{HCl}$
So, $pH$ of $NH _{4} Cl$ is less than 7
(b) $NaNO _{3}$ (Sodium nitrate) is the salt of strong acid and strong base. So, its aqueous solution is neutral as
$NaNO _{3}+ H _{2} O \longrightarrow \underset{\text { strong base }}{NaOH} +\underset{\text { strong acid }}{ NNO _{3}}$
So, $pH$ of $NaNO _{3}$ is 7 .
(c) $CH _{3} COOK$ (Potassium acetate) is a salt of strong base and weak acid. Its aqueous solution will be basic and $pH$ value will be $>7 \approx 8.8$
$CH _{3} COOK + H _{2} O \longrightarrow \underset{\text { weak acid }}{ CH _{3} COOH }+\underset{\text { strong base }}{ KOH }$
(d) $Na _{2} CO _{3}$ (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.
$Na_2CO_3 + H_2O \longrightarrow \underset{\text{strong base}}{2NaOH} + \underset{\text{weak acid}}{H_2CO_3}$