a student prepared four solutions of known $cu^{2+}$ and measured the absorbance of each solution using the same cuvette. the graph shows the data for two absorbance measurements done for each solution. which of the following identifies the most likely error that affected the absorbance recorded for the solution with $cu^{2+}approx7 imes10^{-3}m$ in the second trial?
a the cuvette was rinsed with water between measurements.
b a fingerprint was left on the side of the cuvette facing the detector.
c the absorbance was measured at a wavelength where $cu^{2+}$ has a lower molar absorptivity.
d the cuvette was not filled with the same volume of solution.

Question

a student prepared four solutions of known $cu^{2+}$ and measured the absorbance of each solution using the same cuvette. the graph shows the data for two absorbance measurements done for each solution. which of the following identifies the most likely error that affected the absorbance recorded for the solution with $cu^{2+}approx7	imes10^{-3}m$ in the second trial?
a the cuvette was rinsed with water between measurements.
b a fingerprint was left on the side of the cuvette facing the detector.
c the absorbance was measured at a wavelength where $cu^{2+}$ has a lower molar absorptivity.
d the cuvette was not filled with the same volume of solution.

Accepted Answer

# Brief Explanations:
- **Option A**: Rinsing the cuvette with water between measurements would dilute the solution, but for a single - trial deviation (the second trial for the $7\times10^{-3}M$ solution), this is not the most likely cause. If the cuvette was rinsed with water, it would affect all subsequent measurements of that solution, not just one trial.
 - **Option B**: A fingerprint on the side of the cuvette facing the detector would scatter light. According to the Beer - Lambert law $A = \epsilon lc$ (where $A$ is absorbance, $\epsilon$ is molar absorptivity, $l$ is the path length, and $c$ is concentration). Scattering of light would lead to an increase in the amount of light absorbed (or more accurately, an increase in the absorbance reading, because the detector would receive less transmitted light). A single - trial error like a fingerprint is a plausible cause.
 - **Option C**: If the absorbance was measured at a wavelength where $Cu^{2 +}$ has a lower molar absorptivity, this would affect all measurements of $Cu^{2+}$ solutions, not just one trial of a single solution.
 - **Option D**: The Beer - Lambert law is based on the assumption that the path length $l$ (related to the cuvette dimensions) is constant. The volume of the solution in the cuvette (as long as it covers the light path) does not affect the absorbance reading according to the Beer - Lambert law $A=\epsilon lc$ (where $l$ is the path length of the cuvette, not the volume of the solution in the cuvette).

# Answer:
B. A fingerprint was left on the side of the cuvette facing the detector.

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