Question

$NaOH(aq),HCl(aq),$ and $NaCl(aq)$ concentration of each is $10^{-3}M$. Their $pH$ will be respectively :

• A. 10, 6, 2
• B. 11, 3, 7
• C. 10, 3, 7
• D. 10, 4, 7

Answer 1

Answer: (B)

Use $pH=-\log \left[H^{+}\right]$
and $pH+pOH=14$ to solve problem.
$pH$ of $10^{-3}MNaOH$
$\underset{10^{-3}M}{\mathrm{NaOH}}⟶N{a}^{+}+\underset{10^{-3}M}{O{H}^{-}}$
$pOH=-\log 10^{-3}$
$=3$
$pH+pOH=14$
$pH=14-3=11$
pH of $10^{-3}HCl$
$\underset{10^{-3}M}{\mathrm{HCl}}⟶\underset{10^{-3}M}{H^{+}}+C{l}^{-}$
$pH=-\log \left[H^{+}\right]$
$=-\log \left[10^{-3}\right]$
$=3$
if of $10^{-3}NaCl$ is $7$ (neutral)
$\because$ It is salt of strong acid and strong base.