Question

Determine the pH of each of the following solutions.

a. A solution prepared by mixing 35.0 mL of 0.300 M (CH3)2NH with 45.0 mL of 0.600 M (CH3)2NH2Br

b. A solution prepared by mixing 10.0 mL of 0.200 M C6H5NH2 with 20.0 mL of 0.150 M HCl

Answer 1

For the first part, use the pKb of that compound which is 3.23. The reaction taking place would be:

(CH₃)₂NH + H₂O --------------> (CH₃)₂NH₂⁺ + OH^-

We already have the concentrations of each ion, let's determine the pOH:

pOH = pKb + log (S/B)

pOH = 3.23 + log (0.6/0.3)

pOH = 3.53

pH = 14 - 3.53 = 10.47

For the second part, Post it in another question thread, but try to do it yourself. Just write the general equation between aniline and HCl (look for pKb or Kb of aniline). Do an ICE chart to know the concentration in equilibrium of the final product, and then, use the above equation to get the pOH, and then, the pH.

Hope this helps