Question

On the same graph, sketch the pH titration curves for the titration of 91) a 0.1 M strong monoprotic a cid (e.g. HCL) with a NaOH and (2) a weak 0.1 M monoprotic acid (e.g. HCOOH) with the same strong base. Identify how the two curves differ with respect to each of the following and explain why:

a) Initial pH

b) The pH in the region between the start of the titration and the equivalence point

c) The pH at the equivalence point

d)The volume of base required to reach the equivalence point

e) The pH beyond the equivalence point

Answer 1

Description for Strong Acid - Strong Base

1) initial pH = -log(H+) or pH = -log(Initial concentratino of Acid)

2) pH here will vary depending on the total moles of acid and total volume

moles of acid = decreases as base increases

volume = increases as volume increases

Therefore, concnetration of acid drops, [H+] drops and pH increases

3)

equivalence point pH = 7

4) volume required to reach equivalence point

M1*V1 = M2*V2

V2 = (M1/M2)*V1

5) pH beyond this point is given by how many OH ions are in exces. Ph will be basic

For a weak acid - strong base

1) intial pH is given by

Ka = [H+][A-]/[HA]

solving for H+

2) the region between initial and equivalence point

is given by henderson haselbach equation

pH = pKa + log(A-/HA)

3) the pH in the equivalence point is hydrolisis!

Kw = ka*kb

Kb = [A-][OH-]/[HA]

solve for [OH-] and find pOH, then pH

d) volume required to reach equivalence point

M1*V1 = M2*V2

V2 = (M1/M1)*V1

e) te pH beyond equivalence point

always consider the buffer

pOH = pKb + log(HA/A-)

eventually pOH will be calculated as pOH = -log(OH-)

Then pH = 14-pOH