Calculate the ph of 0.375 l of a 0.18 m acetic acid-0.29 m sodium acetate buffer after the addition of 0.0070 mol of hbr. assume that the volume remains constant.

The pH of 0.375 L of a 0.18 M acetic acid-0.29 M sodium acetate buffer after the addition of 0.0070 mol of HBr : 4.9

A buffer solution is a solution that can maintain a good pH value due to the addition of a little acid or a little base or dilution.

The buffer solution can be acidic or basic

valence according to the amount of salt anion

valence according to the amount of salt cation

a slight addition of acid (H⁺) will be balanced by the conjugate base

the addition of a small base (OH⁻) will be balanced by the weak acid

the addition of a little acid (H⁺) will be balanced weak base

the addition of a small base (OH⁻) will be balanced

Acetic acid-sodium acetate is an acid buffer solution

Reaction:

CH₃COOH + NaOH ↔ CH₃COO-Na + H₂O

mole of weak acid CH₃COOH =0.18 x 0.375=0.0675

mole of CH₃COONa =0.29 x 0.375=0.11

After addition of 0.0070 mol of HBr.

Reaction :

CH₃COONa + HBr ⇔ CH₃COOH + NaBr

0.11                 0.007        0.0675

-0.007           -0.007      +0.007

====================================

0.103                0               0.0745

assumption pKa CH₃COOH = 4,76

[salt]=[CH₃COONa] = 0.103 : 0.375 = 0.275

[acid]=[CH₃COOH] = 0.0745 : 0.375 = 0.199

We can calculate [H+] :

pH = 4.76 + 0.140 = 4.9

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pH scale

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solution has the lowest ph

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Keywords : buffer, acid, salt, pH

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