# DBT JRF 2020 — Question 32

Exam: DBT JRF 2020 · Section: A · Topic: Biochemistry · Difficulty: Medium

## Question

A buffer contains 10% glucose, 20 mM Tris, and 50 mM HCl. For making 1 litre of buffer from the following stock solutions – 50% glucose, 1 M Tris, and 1 M HCl, the correct combination of volume of each of the stock solutions will be

## Options

- **A.** 200 ml, 20 ml, 50 ml
- **B.** 200 ml, 50 ml, 20 ml
- **C.** 50 ml, 100 ml, 10 ml
- **D.** 50 ml, 50 ml, 50 ml

## Answer

Option A

## Explanation

Using the dilution formula $C_1V_1 = C_2V_2$ for each component to prepare 1 L of buffer: Glucose: $C_1=50\%$ , $C_2=10\%$ , $V_2=1000 \text{ mL}$ → $V_1 = \dfrac{10 \times 1000}{50} = 200 \text{ mL}$ . Tris: $C_1=1 \text{ M}$ , $C_2=20 \text{ mM}=0.02 \text{ M}$ , $V_2=1000 \text{ mL}$ → $V_1 = \dfrac{0.02 \times 1000}{1} = 20 \text{ mL}$ . HCl: $C_1=1 \text{ M}$ , $C_2=50 \text{ mM}=0.05 \text{ M}$ , $V_2=1000 \text{ mL}$ → $V_1 = \dfrac{0.05 \times 1000}{1} = 50 \text{ mL}$ . Answer: 200 mL glucose + 20 mL Tris + 50 mL HCl, made up to 1 L with water.

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