Question

Consider the titration of a 81.9 mL sample of 0.172 M CH3NH2 , methylamine, with 0.2 M HBr. The Kb of methylamine is 4.4x10−4. Determine the volume (mL) of added acid required to reach the equivalence point

Answer 1

We will ignore the fact that HBr-CH3NH₂ is actually a strong-weak titration. We are only interested in the volume required for the equivalence point, not the pH at the equivalence point.

1) Chemical equation:

HBr + CH₃NH₂ ---> CH₃NH₃Br

2) HBr to CH₃NH₂ molar ratio:

1 : 1

3) Moles CH₃NH₂:

moles = MV = (0.172 mol/L) x (0.0819 L) = 0.0140868 mol

4) Determine moles of HBr used:

1 is to 1 as x is to 0.0140868 mol

x = 0.0140868 mol of HBr

5) Determine volume of HBr:

0.2 mol/L = 0.0140868 mol / x

x = 0.070434 L = 70.4 mL (to three sig figs)

volume (mL) of added acid required to reach the equivalence point = 70.4 mL

Hope this helped you!

Thank You So Much! Please Rate this answer as you wish.("Thumbs Up")