Answer:
pH = 12.08
Explanation:
First we calculate how many moles of each substance were added, using the given volume and concentration:
- HBr ⇒ 0.05 M * 75 mL = 3.75 mmol HBr
- KOH ⇒ 0.075 M * 74 mL = 5.55 mmol KOH
As HBr is a strong acid, it dissociates completely into H⁺ and Br⁻ species. Conversely, KOH dissociates completely into OH⁻ and K⁺ species.
As there are more OH⁻ moles than H⁺ moles (5.55 vs 3.75), we calculate how many OH⁻ moles remain after the reaction:
- 5.55 - 3.75 = 1.8 mmoles OH⁻
With that number of moles and the volume of the mixture, we calculate [OH⁻]:
- [OH⁻] = 1.8 mmol / (75 mL + 74 mL) = 0.0121 M
With [OH⁻], we calculate the pOH:
With the pOH, we calculate the pH:
