calculate the pH of a buffer solution made by adding 100g of

calculate the pH of a buffer solution made by adding 10.0g of anhydrous sodium acetate (NaC2H3O2) to 100 ml of 0.100M acetic acid. sume there is no change in volume on adding the salt to the acid. calculate the pH change when 0.0020 moles of sodium hydroxide, NaOH is added to 100.0ml of the buffer solution i part a. asume there is no change in volume on adding the NaOH to the buffer solution

Solution

Initial Moles of CH3COOH = 100/1000 x 0.100 = 0.01 mol

Initial moles of CH3COONa = mass/molar mass = 10.0/82.034 = 0.1219 mol

Initial pH = pKa + log([CH3COONa]/[CH3COOH])

= -log Ka + log(moles of CH3COONa/moles of CH3COOH)

= -log(1.8 x 10-5) + log(0.1219/0.01)

= 5.83


Moles of NaOH added = 0.0020 mol

CH3COOH + NaOH => CH3COONa + H2O

Moles of CH3COOH = 0.01 - 0.0020 = 0.008 mol

Moles of CH3COONa = 0.1219 + 0.0020 = 0.1239 mol


Final pH = pKa + log([CH3COONa]/[CH3COOH])

= -log Ka + log(moles of CH3COONa/moles of CH3COOH)

= -log(1.8 x 10-5) + log(0.1239/0.008)

= 5.93


pH change = final pH - initial pH

= 5.93 - 5.83

= 0.10