A25.00-ml sample of propionic acid, hc3h5o2, of unknown concentration was titrated with 0.141 m koh. the equivalence point was reached when 43.76 ml of base had been added. what is the hydroxide-ion concentration at the equivalence point? ka for propionic acid is 1.3 × 10–5 at 25°c. a. 1.5 × 10-9 m b. 1.1 × 10-3 m c. 1.1 × 10-5 m d. 8.3 × 10-6 m e. 1.0 × 10-7 m

Concentration of hydroxide-ion at equivalence point =

Explanation:

1 mol of reacts with 1 mol of KOH to produce 1 mol of

At equivalence point, all gets converted to .

Moles of produced at equivalence point is equal to moles of KOH added to reach equivalence point.

So, moles of produced =

Total volume of solution at equivalence point = (25.00+43.76) mL = 68.76 mL

Concentration of at equivalence point =

produced at equivalence point is due to hydrolysis of . We have to construct an ICE table to calculate concentration of at equivalence point.

I:0.0897                               0                    0

C: -x                                     +x                   +x

E: 0.0897-x                          x                      x

species inside third bracket represent equilibrium concentrations

So,

or,

So, M =

So, concentration of hydroxide-ion at equivalence point = x M =