In: Chemistry
A buffer solution is 0.20 M in acetic acid and sodium acetate. Calculate the change in pH upon adding 1.0mL of 0.10 M HCL to 10mL of this solution.
[CH3COOH] = 0.2M
[CH3COONa] = 0.2M
no of moles of CH3COOH = molarity * volume in L
= 0.2*0.01 = 0.002 moles
no of moles of CH3COONa = molarity * volume in L
= 0.2*0.01 = 0.002 moles
PKa = 4.75
PH = Pka + log[CH3COONa]/[CH3COOH]
= 4.75 + log0.002/0.002
= 4.75 + 0 = 4.75
no of moles of HCL = molarity * volume in L
= 0.1*0.001 = 0.0001 moles
no of moles of CH3COOH after addition of 0.0001 moles of HCl = 0.002 + 0.0001 = 0.0021 moles
no of moles of CH3COONa after addition of 0.0001 moles of HCl = 0.002-0.0001 = 0.0019 moles
PH = Pka + log[CH3COONa]/[CH3COOH]
= 4.75 + log0.0019/0.0021
= 4.75- 0.04346 = 4.71
change in PH = final - initial
=4.71-4.75 = -0.04