Question

Out of the following, the compound whose water solution has the highest pH is

• A. $NaCl$
• B. $N{a}_{2}C{O}_3$
• C. $N{H}_{4}Cl$
• D. $NaHC{O}_3$

Answer 1

The correct option is B $N{a}_{2}C{O}_3$

A. $NaCl$ is a neutral salt so $pH=7$.

$NaCl+H_{2}O\to NaOH+HCl$

B. $N{a}_{2}C{O}_3$ on dissociation in water gives strong base ($NaOH$) - weak acid ($H_{2}C{O}_3$), so its pH will be greater than 7.

$N{a}_{2}C{O}_3+2H_{2}O\to 2NaOH+H_{2}C{O}_3$

C. $N{H}_{4}Cl$ on dissociation in water gives strong acid ($HCl$) - weak base ($N{H}_{4}OH$), so its pH will be less than 7.

$N{H}_{4}Cl\to N{H}_3+HCl$

D. $NaHC{O}_3$ on dissociation in water gives strong base ($NaOH$) - weak acid ($H_{2}C{O}_3$), so its pH will be greater than 7. This dissociation, however, generates only half the amount of $NaOH$ compared to $N{a}_{2}C{O}_3$. So it will have a lower pH than $N{a}_{2}C{O}_3$.

$NaHC{O}_3+H_{2}O\to NaOH+H_{2}C{O}_3$

Hence, the correct option is B.