Calculating the expected pH of the buffer solution: Given that the pK a for Acet

Question

Calculating the expected pH of the buffer solution:

Given that the pKa for Acetic Acid is 4.77, calculate the expected pH of the buffer solutions using the Henderson-Hasselbalch equation and the concentrations of Acetic Acid(74ML OF 0.1M) and Na Acetate(1.1g), 26 ml water added to the 250 ml Erlenmeyer flask:

pH = pKa + log { [base] / [acid] }

      = ?

Hints:

moles of base = mass of NaC2H3O2 / GMW of NaC2H3O2

(GMW acetic acid 60.052, GMW sodium acetate 82.034)

moles of acid = volume of C2H4O2 in liters x molarity of C2H4O2

Explanation / Answer

number of moles of acetic acid = (molarity)*(volume of solution in L)
= 0.1*0.074
= 0.0074 mole
number of mole NaAcetate = (given mass)/(GMW)
= 1.1/82.034
= 0.0134 mole

final volume is same for both
so,
ratio of number of mole = ratio of molarity
use,
pH = pKa + log([base]/[acid])
= 4.77 + log(0.0134/0.0074)
= 4.77 + log1.81
= 4.77 + 0.258
= 5.028

Answer : 5.028

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