A student has 100 mL of 0.400 M CuSO_4 (aq) and is asked to make 100. mL of 0.15
ID: 526111 • Letter: A
Question
A student has 100 mL of 0.400 M CuSO_4 (aq) and is asked to make 100. mL of 0.150 M CuSO_4 (aq) for a spectrophotometry experiment. The following laboratory equipment is available for preparing the solution: centigram balance, weighing paper, funnel, 10 mL beaker, 150 mL beaker, 50 mL graduated cylinder, 100 mL volumetric flask, 50 mL buret, and distilled water. (a) Calculate the volume of 0.400 M CuSO_4 (aq) required for the preparation. (b) Briefly describe the essential steps to most accurately prepare the 0.150 M CuSO_4 (aq) from the 0.400 M CuSO_4 (aq) using the equipment listed above. The student plans to conduct a spectrophotometric analysis to determine the concentration of Cu^2+ (aq) in a solution. The solution has a small amount of Co(NO_3)_2 (aq) present as a contaminant. The student is given the diagram below, which shows the absorbance curves for aqueous solutions of Co^2+ (aq) and Cu^2+ (aq). (c) The spectrophotometer available to the student has a wavelength range of 400 nm to 700 nm. What wavelength should the student use to minimize the interference from the presence of the Co^2+ (aq) ions?Explanation / Answer
a) Available solution = 0.400 M CuSO4
Desired solution = 100 ml 0.150 M CuSO4
So, M1 = 0.400 M
V1 = volume of 0.400 M solution required
M2 = 0.150 M
V2 = 100 ml
Using formula,
M1V1 = M2V2
0.400*V1 = 0.150*100
V1 = 37.5 ml
Volume of 0.400 M CuSO4 required = 37.5 ml
b) From the given apparatus, fill burette using funnel with 0.400 M CuSO4, and take out 37.5 ml of the solution in 100 ml volumetric flask. Then add distilled water to it till the mark in volumetric flask.
c) As peak of Co2+ lies at 500 nm and 850 for that of Cu2+. To minimize interference due to Co2+, select the range from 600 to 850 nm in the spectrophotometer. This will not show peak of Cu2+. Entire peak will be due to Cu2+ only.
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