Question

Calculate the pH during the titration of 30.00 mL of 0.1000 M CH₃COOH(aq) with 0.1000 M KOH(aq) after 10 mL of the base have been added. K_a of acetic acid = 1.8 x 10^-5.

Answer 1

Ch3COOH is a weak acid. If KOH is added to it, a buffer systen will be generated. pH of this buffer can be calculated by using Hinderson hasselbalch equation.

pH = pKa + log[salt/acid]

[salt] = amount of base added = 10 mL 0.1M

number of moles of KOH added = 0.1 *10mL/1000mL = 0.001 moles

total volume = 30m+ 10 mL = 40 mL

Molarity of the salt = 0.001*1000/40 = 0.025 M

Moles of acid present = 0.1*30mL/1000mL =0.003 moles

Moles of acid that has reacted with KOH = 0.001. remaing moles of acid = 0.003-0.001 = 0.002 moles

Molarity of acid = 0.002 * 1000mL/40 = 0.05 M

Ka = 1.8 *10^-5 = 4.74

pH = pKa + log [salt/acis]

pH = 4.74 + log [0.025/0.05] = 4.44

ph of the solution = 4.44