Spectroscopy (College Board AP® Chemistry)

Exam Questions

20 mins8 questions
1a1 mark

A student is given the task of determining the molar concentration of a CuSO4  solution using two different procedures, precipitation and spectrophotometry.

For the precipitation experiment, the student adds 20.0 mL of 0.200 M Ba(NO3)2 to 50.0 mL of the CuSO4(aq).

The reaction goes to completion, and a white precipitate forms. The student filters the precipitate and dries it overnight. The data are given in the following table.

Mass of dry filter paper

0.764 g

Volume of CuSO4(aq)

50.0 mL

Volume of 0.200 M Ba(NO3)2

20.0 mL

Mass of filter paper and dried precipitate

1.136 g

Write a balanced net ionic equation for the precipitation reaction.

1b2 marks

Calculate the number of moles of precipitate formed.

1c1 mark

Calculate the molarity of the original CuSO4  solution.

1d1 mark

For the spectrophotometry experiment, the student first makes a standard curve. The student uses a 0.1000 M solution of CuSO4(aq) to make three more solutions of known concentration (0.0500 M , 0.0300 M , and 0.0100 M ) in 50.00 mL volumetric flasks.

Calculate the volume of 0.1000 M CuSO4(aq) needed to make 50.00 mL of 0.0500 M CuSO4(aq).

1e2 marks

Briefly describe the procedure the student should follow to make 50.00 mL of 0.0500 M CuSO4(aq) using 0.1000 M CuSO4(aq),a 50.00 mL volumetric flask, and other standard laboratory equipment. Assume that all appropriate safety precautions will be taken.

1f1 mark

The standard curve is given below.

q3f-june-2021---ap-chemistry

The absorbance of the CuSO4 solution of unknown concentration is 0.219. Determine the molarity of the solution.

1g2 marks

A second student performs the same experiment. There are a few drops of water in the cuvette before the second student adds the CuSO4(aq) solution of unknown concentration. Will this result ina CuSO4(aq) concentration for the unknown that is greater than, less than, or equal to the concentration determined in part (f) ? Justify your answer.

Did this page help you?

2a1 mark

A student wants to determine the concentration of permanganate, MnO4(aq), in a solution. The student plans to use colorimetric analysis because solutions containing MnO4(aq) have a purple color.

q6-june-2022-ap-chemistry

To determine the optimum wavelength for an experiment that measures the concentration of MnO4(aq), the student takes a sample of the solution and measures the amount of light absorbed by the sample over a range of wavelengths. The data are plotted in the graph shown. Identify the optimum wavelength that the student should use for the experimental procedure.

2b2 marks

The student uses a stock solution of 2.40 × 10−3 M  KMnO4(aq) to prepare the standard solutions of MnO4(aq) that are needed to construct a calibration curve.

q6b-june-2022---ap-chemistry

i) The student uses a 100.0 mL graduated cylinder to measure a certain volume of KMnO4(aq) stock solution, as shown in the diagram given. What volume should the student record?

ii) Calculate the volume, in mL, of 2.40 × 10−3 M  KMnO4(aq) that is required to produce 100.0 mL of a standard 1.68 × 10−3 M  MnO4(aq) solution.

2c1 mark

The student designs the following procedure to produce a calibration curve.

Step 1: Prepare several standard solutions that have known MnO4(aq) concentrations by dilution of the stock solution.

Step 2: Rinse the cuvette with distilled water.

Step 3: Rinse the cuvette with the standard solution and fill the cuvette with the standard solution. Step 4: Measure the absorbance of the standard solution with the colorimeter.

Step 5: Repeat steps 2-4 for each of the standard solutions.

The data are plotted in the calibration curve shown. One of the data points (indicated with an arrow) on the calibration curve is below the line of best fit.

q6bii-june-2022---ap-chemistry

Assuming that all lab equipment is functioning properly, identify which one of the procedural steps the student could have executed incorrectly that would explain why the marked data point is below the line of best fit. Justify your answer.

Did this page help you?