Answer
The pH of this solution is equal to $1.82$;
Work Step by Step
1000ml = 1L
30ml = 0.03 L
20ml = 0.02 L
1. Find the numbers of moles:
$C(HClO_4) * V(HClO_4) = 0.125* 0.03 = 3.75 \times 10^{-3}$ moles
$C(KOH) * V(KOH) = 0.15* 0.02 = 3 \times 10^{-3}$ moles
2. Write the acid-base reaction:
$HClO_4(aq) + KOH(aq) -- \gt KClO_4(aq) + H_2O(l)$
- Total volume: 0.03 + 0.02 = 0.05L
3. Since the base is the limiting reactant, only $ 0.003$ mol of the compounds will react.
Therefore:
Concentration (M) = $\frac{n(mol)}{Volume(L)}$
$[HClO_4] = 0.00375 - 0.003 = 7.5 \times 10^{-4}$ moles.
Concentration: $\frac{7.5 \times 10^{-4}}{ 0.05} = 0.015M$
$[KOH] = 0.003 - 0.003 = 0 $ moles
- Since : $HClO_4$ is a strong acid:
$[HClO_4] = [H_3O^+] = 0.015M$
5. Calculate the pH Value
$pH = -log[H_3O^+]$
$pH = -log( 0.015)$
$pH = 1.824$
