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title: "A student determines the molar concentration of \\(\\text{Cu}^{2+}\\text{(aq)}\\) in an industrial wastewater sample using spectrophotometry. A calibration curve of absorbance versus \\([\\text{Cu}^{2+}]\\) is generated at \\(\\lambda_{\\text{max}} = 620\\text{ nm}\\) using standard solutions of \\(\\text{Cu(NO}_3\\text{)}_2\\text{(aq)}\\) dissolved in distilled water, with the spectrophotometer properly zeroed using a distilled water blank. The wastewater sample contains \\(\\text{Cu}^{2+}\\text{(aq)}\\) along with a nonreactive organic additive that also absorbs light at \\(620\\text{ nm}\\). If the student measures the absorbance of the wastewater sample directly without zeroing the spectrophotometer with a blank containing the organic additive, what is the effect on the calculated \\([\\text{Cu}^{2+}]\\) in the sample, and why?"
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url: "https://nerd-notes.com/ubq/123636/"
date_modified: "2026-09-28T12:01:52+00:00"
---

# A student determines the molar concentration of \(\text{Cu}^{2+}\text{(aq)}\) in an industrial wastewater sample using spectrophotometry. A calibration curve of absorbance versus \([\text{Cu}^{2+}]\) is generated at \(\lambda_{\text{max}} = 620\text{ nm}\) using standard solutions of \(\text{Cu(NO}_3\text{)}_2\text{(aq)}\) dissolved in distilled water, with the spectrophotometer properly zeroed using a distilled water blank. The wastewater sample contains \(\text{Cu}^{2+}\text{(aq)}\) along with a nonreactive organic additive that also absorbs light at \(620\text{ nm}\). If the student measures the absorbance of the wastewater sample directly without zeroing the spectrophotometer with a blank containing the organic additive, what is the effect on the calculated \([\text{Cu}^{2+}]\) in the sample, and why?

A student determines the molar concentration of \(\text{Cu}^{2+}\text{(aq)}\) in an industrial wastewater sample using spectrophotometry. A calibration curve of absorbance versus \([\text{Cu}^{2+}]\) is generated at \(\lambda_{\text{max}} = 620\text{ nm}\) using standard solutions of \(\text{Cu(NO}_3\text{)}_2\text{(aq)}\) dissolved in distilled water, with the spectrophotometer properly zeroed using a distilled water blank. The wastewater sample contains \(\text{Cu}^{2+}\text{(aq)}\) along with a nonreactive organic additive that also absorbs light at \(620\text{ nm}\). If the student measures the absorbance of the wastewater sample directly without zeroing the spectrophotometer with a blank containing the organic additive, what is the effect on the calculated \([\text{Cu}^{2+}]\) in the sample, and why?

- **A.** The calculated \([\text{Cu}^{2+}]\) will be less than the actual value because the organic additive decreases the effective path length of light through the cuvette.
- **B.** The calculated \([\text{Cu}^{2+}]\) will be less than the actual value because the additive scatters incoming photons toward the detector, increasing the transmitted light intensity.
- **C.** The calculated \([\text{Cu}^{2+}]\) will be greater than the actual value because the additive absorbs photons at \(620\text{ nm}\), reducing the transmitted light intensity and increasing the total measured absorbance.
- **D.** The calculated \([\text{Cu}^{2+}]\) will be greater than the actual value because the presence of the additive increases the molar absorptivity (\(\varepsilon\)) of the \(\text{Cu}^{2+}\) ions in solution.

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