Question

A strong monoprotic acid ionizes in water. If the [H3O+] concentration is 1.56 x 10^-4 M, what else is true?

Answer 1

Answer: The solution contains more hydronium ions than hydroxide ions.

Explanation:

pH or pOH is the measure of acidity or alkalinity of a solution.

pH is calculated by taking negative logarithm of hydronium ion concentration and pOH is calculated by taking negative logarithm of hydroxide ion concentration.

$pH=-\log [H_3O^+]$

$pOH=-log{OH^-}$

$pH+pOH=14$

Given, $[H_3O^+]=1.56\times 10^{-4}M$

$pH=-\log [1.56\times 10^{-4}]$

$pH=3.81$

$pH+pOH=14$

$pOH=14-3.81=10.19$

$10.19=-log{OH^-}$

$[{OH^-}]=6.45\times 10^{-11}M$

So $[H^+]$ > $[OH^-]$

Answer 2

I think the correct answer from the choices listed above is the second option. The other true statement would be that  the solution contains more hydronium ions than hydroxide ions. Since pH = -log[H3O+]. As pH decreases, the acidity increases. Hope this answers the question.