Question

The compound whose aqueous solution has highest pH is:
A. $$NaCl$$
B. $N{H}_{4}Cl$
C. $C{H}_{3}COONH{}_4$
D. $N{a}_{2}C{O}_3$

Answer 1

Hint: The strength of pH of any salt is judged by checking whether the substance is a salt of strong acid and strong base or weak acid and weak base. The other two possibilities for a salt are strong acid and weak base or weak acid and strong base.

Complete step by step answer:
If we want to check the pH strength of any salt without going deep into its practical details, we can simply take the salt and put it into water. As soon as the salt is dropped in the water, it starts dissociating to form corresponding ions. In the case of the above mentioned salts, the ions formed will be:
$$\begin{gathered} NaCl\to N{a}^{+}+C{l}^{-} \\ N{H}_{4}Cl\to N{H}_4^{+}+C{l}^{-} \\ C{H}_{3}COON{H}_4\to N{H}_4^{+}+C{H}_{3}CO{O}^{-} \\ N{a}_{2}C{O}_3\to 2N{a}^{+}+C{O}_3^{2-} \end{gathered}$$
Among these salts, when we take NaCl and dissolve it in water, we have:
$2NaCl+H_{2}O\to 2HCl+2NaOH$
As we can see, it is a salt of strong acid and strong base and has complete dissociation in water, it is the salt with highest pH. It’s pH will be equal to 7.
Hence, the correct option is A. $$NaCl$$ .

Note:
The strong acid/weak base salt will give more $H^{+}$ ions in an aqueous solution, it will be comparatively of lower pH value than the salt of weak acid/strong base.