---
title: "A student determines the equilibrium constant, \\(K_c\\), for the reaction represented by the equation below.  \\[ \\text{Fe}^{3+}\\text{(aq)} + \\text{SCN}^-\\text{(aq)} \\rightleftharpoons \\text{FeSCN}^{2+}\\text{(aq)} \\]  The student mixes solutions containing known initial concentrations of \\(\\text{Fe}^{3+}\\text{(aq)}\\) and \\(\\text{SCN}^-\\text{(aq)}\\). After equilibrium is established, the student transfers a portion of the mixture to a cuvette and measures its absorbance with a spectrophotometer to calculate \\([\\text{FeSCN}^{2+}]_{\\text{eq}}\\). If the student fails to wipe fingerprints from the optical faces of the cuvette before placing it in the spectrophotometer, how will this error affect the calculated value of \\(K_c\\)?"
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url: "https://nerd-notes.com/ubq/120280/"
date_modified: "2026-08-23T04:04:15+00:00"
---

# A student determines the equilibrium constant, \(K_c\), for the reaction represented by the equation below.

\[ \text{Fe}^{3+}\text{(aq)} + \text{SCN}^-\text{(aq)} \rightleftharpoons \text{FeSCN}^{2+}\text{(aq)} \]

The student mixes solutions containing known initial concentrations of \(\text{Fe}^{3+}\text{(aq)}\) and \(\text{SCN}^-\text{(aq)}\). After equilibrium is established, the student transfers a portion of the mixture to a cuvette and measures its absorbance with a spectrophotometer to calculate \([\text{FeSCN}^{2+}]_{\text{eq}}\). If the student fails to wipe fingerprints from the optical faces of the cuvette before placing it in the spectrophotometer, how will this error affect the calculated value of \(K_c\)?

A student determines the equilibrium constant, \(K_c\), for the reaction represented by the equation below.

\[ \text{Fe}^{3+}\text{(aq)} + \text{SCN}^-\text{(aq)} \rightleftharpoons \text{FeSCN}^{2+}\text{(aq)} \]

The student mixes solutions containing known initial concentrations of \(\text{Fe}^{3+}\text{(aq)}\) and \(\text{SCN}^-\text{(aq)}\). After equilibrium is established, the student transfers a portion of the mixture to a cuvette and measures its absorbance with a spectrophotometer to calculate \([\text{FeSCN}^{2+}]_{\text{eq}}\). If the student fails to wipe fingerprints from the optical faces of the cuvette before placing it in the spectrophotometer, how will this error affect the calculated value of \(K_c\)?

- **A.** The calculated value of \(K_c\) will be too low because light scattering by the fingerprints causes a falsely low absorbance reading, resulting in an underestimated value of \([\text{FeSCN}^{2+}]_{\text{eq}}\).
- **B.** The calculated value of \(K_c\) will be too high because light absorption and scattering by the fingerprints cause a falsely high absorbance reading, resulting in an overestimated \([\text{FeSCN}^{2+}]_{\text{eq}}\) and underestimated equilibrium reactant concentrations.
- **C.** The calculated value of \(K_c\) will be too low because a falsely high absorbance reading causes the calculated equilibrium concentrations of \(\text{Fe}^{3+}\text{(aq)}\) and \(\text{SCN}^-\text{(aq)}\) to be overestimated.
- **D.** The calculated value of \(K_c\) will be unchanged because optical imperfections on the cuvette do not alter the chemical equilibrium established in the solution.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/120280/*