Answer:
8.54
Explanation:
At equivalence point :
42.2 X 0.052 = Vol. NaOH X 0.0372
Vol of NaOH = 2.1944/0.0372 = 58.99 ml
So volume of NaOH recquired to reach equivalence point = 58.99 ml
Number of miliimoles of CH3COOH = molarity X volume in ml = 42.2 X 0.052 = 2.1944 millimoles
Number of millimoles of NaOH = 58.99 X 0.0372 = 2.1944
Now CH₃COOH and NaOH reacts to give CH₃COONa according to the reaction :
CH₃COOH + NaOH ------> CH₃COONa + H₂O
1 mole of CH₃COOH reacts with 1 mole of NaOH to give 1 mole of CH₃COONa
So 2.1944 millimoles of CH₃COOH will react with 2.1944 millimoles of NaOH to give 2.1944 millimoles of CH₃COONa
So all the acid (CH₃COOH) and base (NaOH) has been converted into salt (CH₃COONa) so there is no acid or base left.
Now molarity of CH₃COONa = number of millimoles of CH₃COONa/total volume in ml = 2.1944/(58.99 + 42.2) = 2.1944/101.19 = 0.02169 M
So using the hydrolysis equation :
pH = 1/2 [ pKw + pKa + log c ]
Ka for acetic acid = 1.75 X 10⁻⁵
so pKa = -log (1.75 X 10⁻⁵) = 4.74
Kw = 10⁻¹⁴
so pKw = -log 10⁻¹⁴ = 14
c = 0.02169
so log c = log 0.02169 = -1.66
putting the values....
pH = 1/2 [14 + 4.74 - 1.66 ]
pH = 1/2 [ 17.08] = 8.54
