Which of the following occurs when HCl is added to a budder containing (CH 3 ) 3

Question

Which of the following occurs when HCl is added to a budder containing (CH3)3N and (CH3)3NH+?  

The concentraion of (CH3)3N will increase.

The concentraion of (CH3)3NH+ will decrease.

The concentraion of (CH3)3N will decrease.

The concentraion of (CH3)3NH+ will increase

Of the following, which is the best base to create a buffer with a pH = 8.0?

Ethylamine, Kb = 6.4 x 10-4

Aniline, Kb = 4.3 x 10-10

Hydrazine, Kb = 1.3 x 10-6

Pyridine, Kb = 1.7 x 10-9

The concentraion of (CH3)3N will increase.

The concentraion of (CH3)3NH+ will decrease.

The concentraion of (CH3)3N will decrease.

The concentraion of (CH3)3NH+ will increase

Explanation / Answer

1.

(CH3)3NH+ + H2O <----> (CH3)3N + H3O+

H3O+ can be represented by H+

Hence additino of HCl adds more H+ ions. To keep the equilibrium constant same, the backward reaction has to take place. This leads to an increase in concentration of (CH3)3NH+ .

2. Kb for the reactions

ethyl amine

C2H5NH2 + H2O C2H5NH3+ + OH-

Aniline

C6H5NH2 + H2O C6H5NH3+ + OH-

Hydrazine

N2H4 + H2O N2H5+ + OH-

Pyridines

C5H5N + H2O C5H5NH+ + OH-

Kb for the above reactions can be writtens as

Kb= [ BH+] [OH-]/ [B]

B indicates the base

pH=8

POH= 14-8=6

[OH-]= 10^(-6)

For all the bases this remins the same

since the numerator in the Kb equation remains the sane

Kb= (10-6)2/ X

whee X is the base concentration

X will be lowest when Kb is highest.

Kb is highest for Ethylaine and hence lower concentrations of ethylamine does the job for creating a buffer of pH=8

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