Question

Does the pH increase, decrease, remain the same of the following buffer solution, 1.0 L of 1.0 M HA and 1.0 M A−, on addition of each of the following?

-A.B.C.

Addition of 0.05 mol HCl

Read Answer Items for Question 1

-A.B.C.

Addition of 0.05 mol NaOH

Read Answer Items for Question 1

-A.B.C.

Addition of 0.05 mol NaCl

Read Answer Items for Question 1

-A.B.C.

Addition of 0.0005 mol NaOH

A.	Remain the same
B.	Decrease
C.	Increase

Answer 1

A)

we know that

for a buffer solution

pH = pKa + log [ A- / HA]

now HCl is added

the reaction is

A- + H+ --> HA

so

the conc of HA increased and A- decreases

as result

[A-] / [HA] decreases

so

pH decreases

B)

now NaOH is added

the reaction is

HA + OH- --> A- + H20

so

the conc of A- is increased and HA decreases

as result

[A-] / [HA] increases

so

pH increases

C)

NaCl is a neutral salt

so

it does not react with HA or A-

so

the pH remains the same

D)

NaOH is added

so

the pH increases