Question

A buret is filled with a 0.100M HCl and its used to titrate 35.0 mL of an unknown strong base. The titration requires 44.57 mL of HCl to reach the equivalence point.

The pH after adding 40 mL of HCl will be ?

The pH at the equivalence point will be?

- Please explain how you got the answer, thank you

Answer 1

millimoles of HCl = 44.57 x 0.1 = 4.457

4.457 millimoles base must be there to reach equivalent point

4.457 = 35 x M

M = 0.13 M

molarity of base = 0.13 M.

now millimoles of base present = 4.457

if 40 mL HCl added

millimoles of HCl = 4 x 0.1 = 4.0

4.457 - 4.0 = 0.457 millimoles NaOH left

[NaOH] = 0.457 / 35 +40 = 0.0061 M

pOH = - log [OH^-]

pOH = -log [0.0061]

pOH = 2.2

pH = 14 -2.2

pH= 11.8

as it is strong acid strong base reaction at equivalent point

pH = 7.0