Does the pH increase, decrease, remain the same of the following buffer solution

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?

Addition of 0.05 mol HCl

Addition of 0.05 mol NaOH

Addition of 0.05 mol NaCl

Addition of 0.0005 mol NaOH

Remain the same

Decrease

Increase

-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

Explanation / Answer

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

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