Question

For 250.0 ml of a buffer solution that is 0.235 m in hcho2 and 0.275 m in kcho2 , calculate the initial ph and the final ph after adding 0.028 mol of naoh . ( ka(hcho2)=1.8×10−4 .)

Answer 1

The initial pH of the buffer solution is 1.63, and the final pH after adding NaOH is 1.94.

Step-by-step explanation:

To calculate the initial pH of the buffer solution, we need to consider the reaction of the weak acid, HCHO2, with water. The equation for this reaction is:

HCHO2 + H2O ⇄ H3O+ + CHO2-

The initial concentration of HCHO2 is 0.235 M, so the initial concentration of H3O+ is also 0.235 M.

The pH can be calculated using the equation pH = -log[H3O+]. Therefore, the initial pH is log(1/0.235) = 1.63.

To calculate the final pH after adding NaOH, we need to consider the reaction of NaOH with HCHO2. The equation for this reaction is:

HCHO2 + OH- ⇄ H2O + CHO2-

The moles of NaOH added can be calculated using the equation moles = concentration x volume. Therefore, the moles of NaOH added is 0.028 mol.

The new concentration of HCHO2 and CHO2- can be calculated by subtracting the moles of NaOH from the initial concentrations. The new concentration of HCHO2 is 0.235 M - 0.028 mol/0.250 L = 0.115 M, and the new concentration of CHO2- is 0.275 M + 0.028 mol/0.250 L = 0.387 M.

The pH of the final solution can be calculated using the new concentration of HCHO2. Therefore, the final pH is log(1/0.115) = 1.94.