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title: "A student uses a spectrophotometer to determine the molar concentration of \\(\\text{Cu}^{2+}\\text{(aq)}\\) in an unknown solution. The student first prepares five standard solutions of known concentration and constructs an accurate linear calibration plot of absorbance versus concentration at \\(\\lambda_{\\text{max}} = 635 \\text{ nm}\\). The spectrophotometer is calibrated such that absorbance is defined as \\(A = -\\log_{10}(I/I_0)\\), where \\(I_0\\) is the light intensity transmitted through a blank sample of distilled water and \\(I\\) is the light intensity transmitted through the sample. Which of the following procedural errors would result in an experimental absorbance reading for the unknown solution that leads to an underestimate of its concentration?"
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url: "https://nerd-notes.com/ubq/121393/"
date_modified: "2026-08-23T05:02:03+00:00"
---

# A student uses a spectrophotometer to determine the molar concentration of \(\text{Cu}^{2+}\text{(aq)}\) in an unknown solution. The student first prepares five standard solutions of known concentration and constructs an accurate linear calibration plot of absorbance versus concentration at \(\lambda_{\text{max}} = 635 \text{ nm}\). The spectrophotometer is calibrated such that absorbance is defined as \(A = -\log_{10}(I/I_0)\), where \(I_0\) is the light intensity transmitted through a blank sample of distilled water and \(I\) is the light intensity transmitted through the sample. Which of the following procedural errors would result in an experimental absorbance reading for the unknown solution that leads to an underestimate of its concentration?

A student uses a spectrophotometer to determine the molar concentration of \(\text{Cu}^{2+}\text{(aq)}\) in an unknown solution. The student first prepares five standard solutions of known concentration and constructs an accurate linear calibration plot of absorbance versus concentration at \(\lambda_{\text{max}} = 635 \text{ nm}\). The spectrophotometer is calibrated such that absorbance is defined as \(A = -\log_{10}(I/I_0)\), where \(I_0\) is the light intensity transmitted through a blank sample of distilled water and \(I\) is the light intensity transmitted through the sample. Which of the following procedural errors would result in an experimental absorbance reading for the unknown solution that leads to an underestimate of its concentration?

- **A.** Leaving fingerprint smudges on the optical path of the cuvette when measuring the distilled water blank, and then thoroughly cleaning the cuvette before measuring the unknown solution
- **B.** Leaving fingerprint smudges on the optical path of the cuvette when measuring the unknown solution, after properly zeroing the instrument with a clean blank cuvette
- **C.** Rinsing the cuvette twice with the unknown \(\text{Cu}^{2+}\text{(aq)}\) solution before filling it and recording the absorbance
- **D.** Filling the cuvette to a liquid level slightly above the designated minimum fill line when measuring the unknown solution

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/121393/*