200 ml of 0600M propanoic acid HC3Hs02 is titrated with 0400

20.0 ml of 0.600M propanoic acid, HC3Hs02, is titrated with 0.400M sodium hydroxide, NaOH. Calculate the pH of the solution after the addition of 10.0 ml of NaOH solution pH = Check

Solution

HC3H5O2 + NaOH -----------> C3H5O2Na + H2O

millimoles of acid = 20 x 0.600 = 12.0

millimoles of NaOH added = 10.0 x 0.400 = 4.0

12 - 4.0 = 8.0 millimoles acid left

4.0 millimoles salt will form

total volume = 20 + 10 = 30.0 mL

[salt] = 4.0 / 30.0 = 0.1333 M

[acid] = 8.0 / 30.0 = 0.2667 M

pka of propionic acid = 4.87

pH = pKa + log [salt] / [acid]

pH = 4.87 + log [0.1333] / [0.2667]

pH = 4.57