The questions are on the Beer-Lambert law test. Take it under real conditions before reading the mark scheme.
Quick answer: Molarity is moles of solute per litre of solution, and dilution follows M₁V₁ = M₂V₂. This mark scheme gives the model answers and the marks for the 8 questions of the AP Chemistry test on Beer-Lambert law, from molarity to choosing the wavelength, with the equivalent answers to accept.
This is the Beer-Lambert law test answers for AP Chemistry, with the marks for each answer. First sit the test without notes, then mark it here and revise with the lesson.
Marking points are given after each answer. Give credit for correct working even if the final answer has a small arithmetic slip, and accept answers within rounding. In explanations, accept equivalent wording.
Level: AP Chemistry · Curriculum: AP Chem Unit 3
Beer-Lambert law test answers: answers and marks
Question 1 Molarity (3 marks)
n = 4.00/40.00 = 0.100 mol; M = 0.100/0.2000 = 0.500 mol/L.
Marking: 1 moles, 1 volume in litres, 1 answer with unit.
Question 2 Dilution (3 marks)
V₁ = 1.20 × 250.0 / 6.00 = 50.0 mL.
Marking: 1 equation, 1 substitution, 1 answer.
Question 3 Chromatography (2 marks)
Rf = 3.2/8.0 = 0.40. It is the ratio of the distances and can be compared with reference values to identify a compound.
Marking: 1 calculation, 1 use.
Question 4 Beer-Lambert calculation (3 marks)
ε = A/(bc) = 0.375 / (1.00 × 2.5 × 10⁻⁵) = 1.5 × 10⁴ L/(mol·cm).
Marking: 1 rearrangement, 1 substitution, 1 answer with unit.
Question 5 Percentage transmittance (2 marks)
T = 10−0.699 = 0.200, i.e. 20.0 percent.
Marking: 1 method, 1 answer.
Question 6 Calibration line (3 marks)
a. 2.5 × 10⁻⁵ mol/L (0.300/0.120 × 10⁻⁵).
b. A is directly proportional to c.
c. This is beyond the highest standard and the Beer-Lambert relationship fails at high absorbance; dilute the sample.
Marking: 1 + 1 + 1.
Question 7 Separation methods (2 marks)
(i) Simple distillation. (ii) Chromatography.
Marking: 1 each.
Question 8 Choosing the wavelength (2 marks)
At λmax the absorbance changes most for a given change in concentration, so the sensitivity is greatest, and the absorbance changes least with small errors in wavelength, which makes the result more precise.
Marking: 1 sensitivity, 1 reliability.
