CHEM 10054 Mohawk Valley Community College Chemistry Worksheet
CHEM 10054Midterm Test- Part B
Total Marks- 25
% 𝑆𝑝𝑖𝑘𝑒 𝑅𝑒𝑐𝑜𝑣𝑒𝑟𝑦 =
𝐶𝑠𝑝𝑖𝑘𝑒 − 𝐶𝑜𝑟𝑔𝑖𝑛𝑎𝑙
[𝑢𝑛𝑘𝑛𝑜𝑤𝑛] = | | × 2
𝑚 = 𝑠𝑙𝑜𝑝𝑒 =
A = -log(
B = intercept
Answer all of the questions below. Part marks will be given where appropriate. Your final
answer should have the correct number of significant figures unless noted otherwise.
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1. Copper sulphate pentahydrate CuSO4.5H2O is a blue solution that can be analyzed using
AA Spectroscopy. A set of standards is run and the best fit line for the calibration curve
is found to be A=0.624(%w/v) + 0.071
A 15.00mL aliquot of an unknown sample containing CuSO4.5H2O was diluted to a final
volume of 200.0mL. Analysis of the sample at a wavelength of 520nm in a 1.00cm
cuvette was found to have a %T = 22.4
Calculate the concentration of CuSO4.5H2O (%w/v) in the unknown sample. (3 marks)
2. A sample is to be analyzed for it’s caffeine content using HPLC.
A 1.00mL aliquot was transferred into a 100.0mL volumetric flask and was found to have
a peak area of 0.229min.
A second 1.00mL aliquot was spiked with 0.500mL of a 84.3ppm Caffeine standard and
diluted to a final volume of 100.0mL. Analysis of this sample gave a peak area of 0.463.
Calculate the ppm caffeine in the sample. (3 marks)
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3. A solution containing 8.89 ppm of NaMnO4 (MM = 141.925 g/mol) has a %T = 26.2 in a
2.00 cm cuvette at 520 nm. Calculate the absorptivity of NaMnO4. (2 marks)
a. Calculate the molar absorptivity of NaMnO4 . Give your answer to the nearest
whole number. (2 marks)
4. An AE calibration curve for tumeric was fitted to an equation:
I = 0.821 × [tumeric ppm]
In a 25.00 mL volumetric flask, 3.00 mL of an unknown sample was diluted to the mark;
the intensity (I) for this sample was measured to be I = 0.132.
To a second 25.00 mL volumetric flask, 3.00 mL of an unknown sample and 1.00 mL of a
15.0 ppm tumeric standard were added and diluted to the mark; the intensity (I) for this
sample was measured to be I = 0.921.
a. Calculate the %spike recovery for the tumeric analysis. (3 marks)
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b. Are your analysis results valid based on your spike recovery? (1 mark)
5. Vitamin A (MM 286.45 g/mol) can be analyzed using an electrochemical technique by a
multipoint standard addition.
A 6.00mL aliquot of a carrot juice sample was added to each of six 100.00mL volumetric
flasks. To each flask varying amounts of a 111.5ppm Vitamin A standard was added.
Each flask was analyzed and a plot of signal (mA) versus Cadded (ppm Vitamin A) was
created giving a best fit line of y = 4.9177x + 0.333.
Calculate the ppm of Vitamin A in the carrot juice sample. (3 marks)
6. Calculate the mass(g) required to prepare 200.0mL of a 200.0ppm Cl- (MM 35.45 g/mol)
solution from solid CaCl2 (MM 120.98 g/mol). (3 marks)
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a. A 25.00mL aliquot of the 200.0ppm Cl- stock solution was diluted to 500.0mL.
What is the molarity (Cl-) of the prepared working solution? (2 marks)
b. You need to prepare 100.00mL of a 15.5 ppm Cl standard solution from the
above Cl stock solution (200.0 ppm). You have a 25mL buret, a 50mL volumetric
flask and the stock solution. How would you prepare the solution? (3 marks)
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