Question

1)The compound dimethylamine is a weak base like ammonia. A solution contains 0.205 M (CH₃)₂NH₂⁺ and 0.295 M dimethylamine, (CH₃)₂NH.

The pH of this solution is  .

2)The compound ethylamine is a weak base like ammonia. A solution contains 0.461 M C₂H₅NH₃⁺ and 0.367 M ethylamine, C₂H₅NH₂.

The pH of this solution is  .

Answer 1

1) concentration of (CH3)2NH2+ = 0.205M

   Concentration of (CH3)2NH = 0.295M

Kb of Dimethyl amine = 5.9x10^-4

kb= 5.9x10^-4

-log[kb]=-log(5.9x10^-4)

Pkb= 3.23

POH= PKb + log[(CH3)2NH2+]/(CH3)2NH]

POH= 3.23+log(0.205/0.295)

POH= 3.07

PH+POH=14

PH= 14-POH

PH= 14-3.07

PH= 10.93

2)

Concentration of ( C2H5NH3+) = 0.461M

Concentration of C2H5NH2 = 0.367M

Kb of C2H5NH2 = 5.6x10^-4

-log(Kb) = -log(5.6x10^-4)

PKb= 3.25

POH= Pkb + log[ C2H5NH3+/C2H5NH2]

POH= 3.25 + log( 0.461/0.367)

POH= 3.35

PH= 14-POH

PH= 14- 3.35

PH=10.65