A student prepares five aqueous CuSO4 standard solutions by dilution from a 0.500 M stock and measures their absorbance at 635 nm in a 1.00 cm cuvette. The blank is distilled water. Concentrations and absorbances are: 0.050 M (A=0.105), 0.100 M (A=0.210), 0.200 M (A=0.420), 0.300 M (A=0.630), 0.400 M (A=0.840). An unknown CuSO4 solution gives A=0.525 in the same cuvette.
The student forgets to wipe fingerprints off the cuvette before reading the unknown. How does this affect the calculated unknown concentration?
- A
Reported concentration is too low because path length decreases
- Bcheck_circle
Reported concentration is too high because measured A is artificially increased
- C
Reported concentration is too low because A is decreased
- D
No effect since the calibration curve compensates
Explanation
Fingerprints scatter and absorb light, raising the apparent absorbance. Since c = A/(epsilon*b), a higher A gives a higher reported concentration.