Chemistry

Problem

A compound with a molar absorptivity of

2.5\times10^{4}\,\text{M}^{-1}\,\text{cm}^{-1}

is present at a concentration of

4.0\times10^{-5}\,\text{M}

. What absorbance would be recorded if the sample is measured in a 0.200 cm microcuvette? a) 1.0 b) 0.20 c) 0.087 d) 5.0

Intuitive explanation

This problem is about Beer's Law, which connects how much light a solution absorbs to three measurable quantities: the compound's inherent light-absorbing ability, how concentrated it is, and the path the light travels through. You have all three pieces of information—molar absorptivity $\varepsilon$ , concentration $c$ , and path length $b$ —so you just need to plug them into the relationship $A = \varepsilon bc$ to find absorbance. The key insight is recognizing that even a tiny path length (0.200 cm) can still produce measurable absorption if the molar absorptivity is large enough.

Intuitive explanation

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