Question

Q. A buffer solution prepared by mixing 50.00 mL of 0.200 M acetic acid and 50.00 mL of 0.200 M sodium acetate (K_{a, acetic acid} = 1.76 x 10^-5). (Hint: Calculate the pH using the Henderson-Hasselbach equation, remember to allow for the dilution effect when mixing the two solutions together.)

Answer 1

The given solutions are

i) 50mL of 0.200M Acetic acid                                                                                                                      ii) 50mL of 0.200M Sodium acetate                                                                                                          The concentration of acetic acid and sodium acetate in the mixture should be calculated. We can do this using the formula M₁V₁=M₂V₂                                                                                                                      i) new concentration of acetic acid =                                                                                   which is 0.200*50/100 = 0.100M                                                                                                               ii) Similarly new concentration of sodium acetate is 0.100M

Applying this in the henderson hasslebach equation, we get

pH = -log(1.76*10^-5) +log (0.100/0.100)

pH = pK_a = 4.75