Question

1) When a 21.3 mL sample of a 0.366 M aqueous nitrous acid solution is titrated with a 0.424 M aqueous barium hydroxidesolution, what is the pH at the midpoint in the titration?

2) A 28.0 mL sample of 0.234 M triethylamine, (C₂H₅)₃N, is titrated with 0.305 M hydrobromic acid.

At the titration midpoint, the pH is .

Use the Tables link in the References for any equilibrium constants that are required.

Answer 1

1. no of moles of HNO2 = molaity * volume in L

                                       = 0.366*0.0213

                                      = 0.00779 moles

no of moles of Ba(OH)2 = molaity * volume in L

                                         = 0.424*0.0213   = 0.009 moles

            Ba(OH)2 + HNO2 --------------> Ba(NO2)2 + H2O

    I        0.009          0.00779                    0

    C      -0.00779   -0.00779                    0.00779

    E      0.00121         0                           0.00779

PH = Pka + log[Salt]/[Acid]

at mid point PH = PKa

                  PH = 3.15 >>>.answer

2. PH = Pka

Pk of (C₂H₅)₃N is 3.2518

PH   = 3.2518