Question

Assuming complete dissociation, which of the following solutions will have $pH=13$?

• A. 2g of $NaOH$ in $500ml$ solution
• B. $100ml$ of solution of $0.05M$ $Ca(OH{)}_2$
• C. $100ml$ of solution of $0.1NCa(OH{)}_2$
• D. $4g$ of $NaOH$ in $500ml$ solution

Answer 1

Answer: (A), (B), (C)

The correct options are
A $100ml$ of solution of $0.05M$ $Ca(OH{)}_2$
B 2g of $NaOH$ in $500ml$ solution
C $100ml$ of solution of $0.1NCa(OH{)}_2$

$pH=13$ corresponds to hydrogen ion concentration of ${10}^{-13}$ moles per litre or hydroxide ion concentration of 0.1 moles per litre.

A) $2g$ ($0.05$ moles) of $NaOH$ (molecular mass $40$) in $500ml$ solution corresponds to hydroxide ions concentration of $0.1$ moles in one litre. Hence, it will have $pH=13$.

B) $100ml$ of $0.05M$ calcium hydroxides corresponds to hydroxide ion concentration of $2\times 0.05=0.1$ M. Hence, it will have $pH=13$.

C) $100ml$ of $0.1N$ calcium hydroxide corresponds to hydroxide ion concentration of $0.1M$. Hence, it will have $pH=13$.

D) $4g$ ($0.1$ moles) of $NaOH$ (molecular mass $40$) in $500ml$ solution corresponds to hydroxide ions concentration of $0.2$ moles in one litre. Hence, it will not have $pH=13$.