# DBT JRF 2020 — Question 41

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

## Question

How much sodium hydroxide will you weigh to prepare 0.25 L of 3 M solution?

## Options

- **A.** 30 g
- **B.** 40 Kg
- **C.** 80 g
- **D.** 40 μg

## Answer

Option A

## Explanation

Mass of NaOH needed: $m = M \times V \times M_r = 3 \text{ mol/L} \times 0.25 \text{ L} \times 40 \text{ g/mol} = 30 \text{ g}$ . MW of NaOH: Na(23) + O(16) + H(1) = 40 g/mol. Procedure: Weigh 30 g NaOH, dissolve in ~200 mL water (NaOH dissolution is exothermic — cool before making up volume), then make up to 250 mL (0.25 L) in a volumetric flask. NaOH is hygroscopic, so it should be weighed quickly to avoid absorbing atmospheric moisture.

Source: https://mypyqbuddy.com/questions/how-much-sodium-hydroxide-will-you-weigh-to-6a05a8a02adafec47029320f