---
title: "A student uses a spectrophotometer to determine the concentration of an unknown 	ext{CuSO}_4	ext{(aq)} solution. After calibrating the instrument with a blank and generating a standard curve of absorbance versus concentration at 	ext{\\lambda}_{\\text{max}} = 635\\text{ nm}, the student measures the absorbance of the unknown sample. However, the student inadvertently leaves a fingerprint smudge on the clear optical face of the cuvette in the path of the light beam. How does this error affect the calculated concentration of the unknown 	ext{CuSO}_4	ext{(aq)} solution?"
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url: "https://nerd-notes.com/ubq/121457/"
date_modified: "2026-08-23T05:04:37+00:00"
---

# A student uses a spectrophotometer to determine the concentration of an unknown 	ext{CuSO}_4	ext{(aq)} solution. After calibrating the instrument with a blank and generating a standard curve of absorbance versus concentration at 	ext{\lambda}_{\text{max}} = 635\text{ nm}, the student measures the absorbance of the unknown sample. However, the student inadvertently leaves a fingerprint smudge on the clear optical face of the cuvette in the path of the light beam. How does this error affect the calculated concentration of the unknown 	ext{CuSO}_4	ext{(aq)} solution?

A student uses a spectrophotometer to determine the concentration of an unknown 	ext{CuSO}_4	ext{(aq)} solution. After calibrating the instrument with a blank and generating a standard curve of absorbance versus concentration at 	ext{\lambda}_{\text{max}} = 635\text{ nm}, the student measures the absorbance of the unknown sample. However, the student inadvertently leaves a fingerprint smudge on the clear optical face of the cuvette in the path of the light beam. How does this error affect the calculated concentration of the unknown 	ext{CuSO}_4	ext{(aq)} solution?

- **A.** The calculated concentration will be too high, because the smudge scatters light away from the detector, resulting in an artificially high absorbance reading.
- **B.** The calculated concentration will be too high, because the residue alters the solution environment and increases the molar absorptivity (\text{\epsilon}) of the \text{Cu}^{2+}\text{(aq)} ions.
- **C.** The calculated concentration will be too low, because the smudge prevents some light from reaching the sample, decreasing the total amount of light absorbed by the \text{Cu}^{2+}\text{(aq)} ions.
- **D.** The calculated concentration will be too low, because the smudge decreases the effective path length (\text{b}) of the light traveling through the cuvette.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/121457/*