Calculate the pH of buffer solution made from 0.2M HC2H3O2 and 0.5M C2H3O2 that has acid dissociation constant for HC2H3O2 of 1.8×10-5?

Question

Calculate the pH of buffer solution made from 0.2M HC2H3O2 and 0.5M C2H3O2 that has acid dissociation constant for HC2H3O2 of 1.8×10-5​?

Answer

pH Calculation of Buffer Solution

Given:

Concentration of HC2H3O2 (acetic acid) = 0.2 M

Concentration of C2H3O2 (acetate ion) = 0.5 M

Acid dissociation constant (Ka) for HC2H3O2 = 1.8×10^-5

Buffer Solution:

A buffer solution is a solution that resists changes in pH when small amounts of acid or base are added to it. It consists of a weak acid and its conjugate base (or a weak base and its conjugate acid) in approximately equal concentrations.

In this case, the buffer solution is made from acetic acid (HC2H3O2) and acetate ion (C2H3O2).

Buffer Action:

The buffer solution works through the principle of the common ion effect. When a strong acid is added to the buffer, the acetate ion reacts with the added H+ ions to form acetic acid, thus minimizing the change in pH. Similarly, when a strong base is added, the acetic acid reacts with OH- ions to form acetate ion, preventing a significant change in pH.

pH Calculation:

To calculate the pH of the buffer solution, we need to consider the dissociation of acetic acid (HC2H3O2) and the equilibrium expression for Ka.

Step 1:

Write the balanced equation for the dissociation of acetic acid:

HC2H3O2 ⇌ H+ + C2H3O2-

Step 2:

Write the equilibrium expression for the acid dissociation constant (Ka):

Ka = [H+][C2H3O2-] / [HC2H3O2]

Step 3:

Since the concentration of HC2H3O2 and C2H3O2 are given, we can substitute these values into the equilibrium expression:

1.8×10^-5 = [H+][0.5] / [0.2]

Step 4:

Solve the equation for [H+]:

[H+] = (1.8×10^-5)(0.2) / 0.5

[H+] = 7.2×10^-6 M

Step 5:

Calculate the pH using the formula:

pH = -log[H+]

pH = -log(7.2×10^-6)

pH ≈ 5.14

Conclusion:

The pH of the buffer solution made from 0.2 M HC2H3O2 and 0.5 M C2H3O

Similar Chemistry Doubts

The dissociation constant of a substituted benzoic acid at 25C is 1.0 104. The pH of a 0.01 M solution of its sodium salt is _______. Correct answer is '8'. Can you explain this answer?

Measured freezing point depression point of a 0.1m aq. Acetic acid solution is 0.19oC. The acid dissociation constant at this concentration will be (in the multiple of 10–5): Correct answer is '4'. Can you explain this answer?

Measured freezing point depression point of a 0.1m aq. Acetic acid solution is 0.19oC. The acid dissociation constant at this concentration will be?(in the multiple 10-5) Correct answer is '4'. Can you explain this answer?

When 0.045 mole of NaOH was added to one litre of buffer solution, its pH changes from 5.72 to 5.92. Calculate buffer index (rounded up to three decimal places): Correct answer is between '0.220,0.230'. Can you explain this answer?

Top Courses for Chemistry

Suggested Free Tests

Related Content

Schools

Competitive Examinations

Quick Access Links

Technical Exams