Question

To a 50 ml of 0.05m formic acid how much volume of 0.1m sodium formate must be added to get a buffer of ph 4

Answer 1

Let x ml of 0.10M sodium formate is added,

No. of moles in xml of 0.10M sodium formate is = 1.1*x/1000

No. of moles in 50ml xml of 0.05M formic acid is = 0.05*50/1000

Therefore, [sodium formate] / [formic acid] = (0.01*x/1000)/(0.05*50/1000)

= 0.04x

From Henderson's equation:

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

=>4 = 3.8 + log 0.04x

=> log 0.04x = 0.2

=> x = 39.6 ml