Assignment answers

Assignment 2 Page 1

CHEM 218 ASSIGNMENT #2 – Spectrophotometry

Course: CHEM 218 Section: 51 Term: Winter 2020 Instructor: Dr. Dajana Vuckovic Due date: Moodle – 23:59 on Friday April 10, 2020 TOTAL MARKS: 45 + 5 OPTIONAL BONUS MARKS

General instructions:

 You must show full/detailed calculations to receive full marks for each calculation problem. Please upload Excel, Word, pdf or photo of handwritten calculation as appropriate for calculation questions. Please name the document with your last name_student number.

 Enter your FINAL answer in Moodle as specified. Please show your FINAL answer to correct number of significant figures. During intermediate steps, keep all digits in your calculator to avoid large rounding errors in the final answer. In other words, do not round off your answers during intermediate calculation steps.

 For non-calculation questions, you can prepare your answer in Word and then copy and paste it into appropriate text box in Moodle when you have finalized your answer.

1. The following results were obtained for a spectrophotometric titration that was carried out at 600

nm to measure Cu2+ in a water sample according to the reaction below: Cu2+ + Trien → Cu(trien)2+

A 10.00 mL sample of water was used for this titration, trien concentration was 0.0500M and the following results were obtained upon the addition of increments of titrant to the sample:

Sample volume (mL) Volume Trien (mL) Absorbance

0.00 0.00 0.002 10.00 0.00 0.005 10.00 2.00 0.181 10.00 4.00 0.306 10.00 6.00 0.402 10.00 8.00 0.416 10.00 10.00 0.375

(a) (8 marks) What was the concentration of Cu2+ in the original sample? (b) (2 marks) Explain the shape of the titration curve obtained for this analysis. What does this curve

tell you about the ability of the analyte, titrant and product to absorb light at the wavelength used for this titration?

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2. (15 marks) Given the following spectra of ciprofibrate and sulindac, in numbered bullet format

explain how you would perform the analysis of a tablet sample containing unknown amounts of ciprofibrate and sulindac. For full marks, you have to be very specific and describe all steps in detail and correct order.

http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1984-82502011000100004#fig2a

UV spectra from Photostability of drugs and drug formulations, 2nd edition, by H.H. Tonessen (p.11)

ciprofibrate

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3. (10 marks) Atomic absorption spectroscopy was used to measure zinc in an unknown urine sample. The analysis was performed by mixing aliquots of sample solution with aliquots of zinc standard solution according to the table(s) below. The zinc standard solution used in this analysis contained 1000.0 µg/mL of zinc. Two different students performed this analysis using different experimental designs. Calculate the concentration of zinc in the unknown urine sample obtained by each of the two students. Which student obtained a more accurate concentration of zinc in urine and explain your reasoning?

Student 1 experiment and results

Volume of unknown (mL)

Volume of standard added (mL)

Total volume (mL)

Absorbance

10.00 0.00 100.0 0.163 10.00 1.00 100.0 0.240 10.00 2.00 100.0 0.319 10.00 3.00 100.0 0.402 10.00 4.00 100.0 0.478

Student 2 experiment and results

Volume of unknown (mL)

Volume of standard added (mL)

Total volume (mL)

Absorbance

10.00 0.00 100.0 0.150 10.00 0.00 100.0 0.150 10.00 0.00 100.0 0.151 10.00 3.00 100.0 0.423

4. (10 marks) Analytical testing of patient samples is critically important for managing the current COVID- 19 crisis. If you successfully developed a new test to diagnose the presence of virus that causes COVID- 19,

(a) how would you ensure that your test performs well each time it is used in a laboratory? In other words, how would you apply the ideas of blanks, standards, replication and calibration that we covered in our course to this testing? How would you ensure correct results are obtained?

(b) Are there any other considerations beyond your answer in (a) that you would pay attention to when deploying this test across Canada?

(c) What are some of the main sources of error in this test? Answer this question in general terms without focusing on the specific analytical method used for the detection of the virus.

BONUS MARKS

(5 marks) for participation during online classes – asking/answering questions either in chat or on video OR completing in full three Sapling online homeworks by April 10 submission deadline.