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title: "A student uses a spectrophotometer to determine the concentration of an unknown \\(\\text{CuSO}_4\\text{(aq)}\\) solution. The student first constructs a calibration curve by measuring the absorbance of several standard solutions of known concentration at \\(\\lambda = 635\\text{ nm}\\), establishing a direct relationship between absorbance and concentration. Before measuring the unknown \\(\\text{CuSO}_4\\text{(aq)}\\) solution, the student rinses the cuvette with distilled water but does not dry the interior or rinse it with the unknown solution, leaving several drops of distilled water inside the cuvette. Which of the following best explains how this error affects the measured absorbance and the calculated concentration of the unknown \\(\\text{CuSO}_4\\text{(aq)}\\) solution?"
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url: "https://nerd-notes.com/ubq/119646/"
date_modified: "2026-08-21T08:11:54+00:00"
---

# A student uses a spectrophotometer to determine the concentration of an unknown \(\text{CuSO}_4\text{(aq)}\) solution. The student first constructs a calibration curve by measuring the absorbance of several standard solutions of known concentration at \(\lambda = 635\text{ nm}\), establishing a direct relationship between absorbance and concentration. Before measuring the unknown \(\text{CuSO}_4\text{(aq)}\) solution, the student rinses the cuvette with distilled water but does not dry the interior or rinse it with the unknown solution, leaving several drops of distilled water inside the cuvette. Which of the following best explains how this error affects the measured absorbance and the calculated concentration of the unknown \(\text{CuSO}_4\text{(aq)}\) solution?

A student uses a spectrophotometer to determine the concentration of an unknown \(\text{CuSO}_4\text{(aq)}\) solution. The student first constructs a calibration curve by measuring the absorbance of several standard solutions of known concentration at \(\lambda = 635\text{ nm}\), establishing a direct relationship between absorbance and concentration. Before measuring the unknown \(\text{CuSO}_4\text{(aq)}\) solution, the student rinses the cuvette with distilled water but does not dry the interior or rinse it with the unknown solution, leaving several drops of distilled water inside the cuvette. Which of the following best explains how this error affects the measured absorbance and the calculated concentration of the unknown \(\text{CuSO}_4\text{(aq)}\) solution?

- **A.** The measured absorbance is too high, and the calculated concentration is too high, because the water droplets scatter incident light away from the detector.
- **B.** The measured absorbance is too low, and the calculated concentration is too low, because the residual water dilutes the solution in the cuvette, reducing the concentration of absorbing species in the light path.
- **C.** The measured absorbance is too low, but the calculated concentration is too high, because a lower measured absorbance indicates less transmitted light through the cuvette.
- **D.** The measured absorbance and the calculated concentration are both unaffected, because the molar absorptivity and the path length of the cuvette remain constant.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/119646/*