Question

On graph paper, sketch the titration curve for the titration of 50.0 ml of generic 0.010 M weak base B- ( Kb = 1.2 x 10-9) with a .010 M monoprotic strong acid. On this curve, indicate and label the points that correspond to the following:

The stoichiometric (equivalence) point [calculate this pH and label on your graph.]

The region with maximum buffering

pH=14 - pKb [or equivalently you could say pOH = pKb, calculate and label this pH on your graph]

The point where pH calculation depends only on Kb equilibrium ice box [calculate and label this pH on your graph]

The point where pH calculation depends on Ka equilibrium ice box [calculate and label this pH on your graph]

The region where pH depends primarily on the amount of excess strong acid added. [determine the limiting pH value for this region]

Answer 1

a. At equivalent point, Moles of acid = moles of base

Moles = Molarity × Volume

Both have molarity 0.01 M, so at equal volume we have equilvalent point.

b. At pH = 14 - pKb = 14 -( - Log Kb) = 14 -(- Log (1.2 × 10-9) )= 14- 8.92 = 5. 079

c. At pH 5.079

d. After equilvalent point, the pH will depends on Ka.

e. At equilvalent point.

there is no H+ and B, there is only BH+ with 0.005 M.

[H+] = √( C × kw/ kb) = √( 0.005 × 10-14/1.2 × 10-9)

[H+]= 0.00020 M

pH = -log [H+]= 3.69

At pH 3.69 below, the pH will depends upon Ka.

f. The pH below 3.69, it depends amount of acid added