Question

Calculate the pH of each buffer prepared by the following methods: 30.0 mL of 0.15 M HCl is mixed with 0.75 g of K(CH3COO). Assume no volume change occurs after adding the solid to liquid

Answer 1

Calculate the pH of each buffer prepared by the following methods: 30.0 mL of 0.15 M HCl is mixed with 0.75 g of K(CH3COO). Assume no volume change occurs after adding the solid to liquid

initially

mmol of HCl = MV = 0.15*(30) = 4.5 mmol

mmol of acetate = mass/MW = 0.75/98.15 = 0.007641365 mol = 7.641365 mmol

now...

H+ reacts to form:

mmol of Haceatet = 4.5

mmol of acetate left = 7.641365 - 4.5 =  3.141

now

pH = pKa + log(A-/HA)

pH = 4.75 + log(3.141/4.5) = 4.59385