Question

Calculate the poh of a buffer solution that contains formic acid given that the ratio of conjugate base to acid is 1:1 and the ka of formic acid is 1.77×10–4?

Answer 1

Using the Henderson-Hasselbalch equation and the given 1:1 ratio of conjugate base to acid for formic acid, the pOH is calculated to be 10.25.

Step-by-step explanation:

To calculate the pOH of a buffer solution containing formic acid with a conjugate base to acid ratio of 1:1, we use the Henderson-Hasselbalch equation. Given that the ratio of the conjugate base to acid is 1:1, the base and acid concentrations are equal, and therefore the log part of the equation is zero. The pKa can be converted to pKb using the formula pKw = pKa + pKb (where pKw is the ionic product of water, typically 14 at 25°C). Thus, the formula for calculating pOH would be:

pOH = pKw - pKa = 14 - (-log 1.77×10−4)

Once we calculate the pKa, we can subtract it from 14 to get the pOH:

pKa = -log Ka = -log 1.77×10−4 = 3.75

pOH = 14 - 3.75 = 10.25