# DBT JRF 2022 — Question 25

Exam: DBT JRF 2022 · Section: B · Topic: Biochemistry › Buffer Chemistry & pH · Difficulty: Medium

## Question

A 1 M Tris-HCl (pH 8.0) solution was diluted 10 fold. What will be the pH of the resulting solution?

## Options

- **A.** 8.0
- **B.** 7.0
- **C.** 0.08
- **D.** 0.8

## Answer

Option A

## Explanation

Buffer pH and dilution: The Henderson-Hasselbalch equation: $\text{pH} = \text{p}K_a + \log\frac{[\text{A}^-]}{[\text{HA}]}$ When a buffer is diluted: • Both the conjugate base [A−] and the weak acid [HA] are diluted by the SAME factor. • The RATIO $\frac{[\text{A}^-]}{[\text{HA}]}$ remains UNCHANGED. • Therefore, $\text{pH} = \text{p}K_a + \log(\text{same ratio})$ remains unchanged. Practical limit: Extreme dilution (very high volume) will eventually reduce buffering capacity to near zero, but the pH changes only when buffering capacity is exhausted. A 10-fold dilution of a standard buffer keeps the pH essentially constant. For 1 M Tris-HCl (pH 8.0) diluted 10-fold → 0.1 M Tris-HCl: pH remains 8.0. Answer: pH = 8.0 (Option 1).

Source: https://mypyqbuddy.com/questions/a-1-m-tris-hcl-ph-8-0-solution-6a104cd5920734408bc0c728