Question

Calculate the pH of a buffer solution made by adding 15.0 g anhydrous sodium acetate (NaC2H3O2) to 100.0 mL of 0.200 M acetic acid. Assume there is no change in volume on adding the salt to the acid. (pKa for acetic acid is 4.74 or Ka is 1.8 x 10-5)3.

Answer 1

Answer:

pH of Buffer Solution 5.69

Explanation:

Mole of anhydrous sodium acetate = $\frac{Given mass}{Molecular mass}$

                                                           = $\frac{15}{82}$

                                                           = 0.18 mole

 100 ml of 0.2 molar acetic acid  means

= M x V

= 0.2 x 100

= 20 mmol

= 0.02 mole

Using Henderson equation to find pH of Buffer solution

pH = pKa + log$\frac{[Salt]}{[Acid]}$

     = 4.74 + log$\frac{0.18}{0.02}$

     = 4.74 + log 9

     = 5.69

So pH of the Buffer solution = 5.69