# DBT JRF 2020 — Question 42

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

## Question

A student made 0.15 M solution of copper sulphate. The absorbance of the solution was found to be 0.3 when using a cuvette with a path length of 1 cm. Copper sulphate solution made by a second student gave an absorbance of 0.45 using the same cuvette at the same wavelength. What is the concentration of the copper sulphate solution made by the second student?

## Options

- **A.** 0.425 M
- **B.** 0.225 M
- **C.** 0.325 M
- **D.** 0.125 M

## Answer

Option B

## Explanation

Beer-Lambert Law: $A = \varepsilon c l$ , where $A$ = absorbance, $\varepsilon$ = molar absorptivity (constant for a given solute at a given wavelength), $c$ = concentration, $l$ = path length. Since $\varepsilon$ and $l$ are the same for both solutions (same wavelength and cuvette): $\dfrac{A_1}{c_1} = \dfrac{A_2}{c_2}$ , so $c_2 = c_1 \times \dfrac{A_2}{A_1} = 0.15 \times \dfrac{0.45}{0.30} = 0.15 \times 1.5 = 0.225 \text{ M}$ .

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