Seminar Assignments - Assignment #1 – Precipitation Titrations and Introduction to Electrochemistry PDF

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ASSIGNMENT #1 – Precipitation titrations and introduction to electrochemistry...

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CHEM 218 ASSIGNMENT #1 – Precipitation titrations and introduction to electrochemistry Section: 01 Term: Winter 2016 Instructor: Dr. Dajana Vuckovic Due date: 11:40 am before the beginning of the class on Feb 3, 2016 in CC-310 TOTAL POINTS: 75 TOTAL QUESTIONS: 3

General instructions:   

 1.

You must show full/detailed calculations to receive full marks for each problem. Please enter your FINAL numerical answer on Moodle before the deadline. 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. Write in pen. Use KSP values from textbook – Harris 8th or 9th edition A 25.00 mL solution containing 0.0300 M Na2C2O4 was titrated with 0.0210 M La(ClO4)3 to precipitate lanthanum oxalate: 2 La3+ + 3 C2O42-

(a) (b) (c) (d) (e) (f) (g)

(h)

(i)

La2(C2O4)3(s)

(2 points) What volume of La(ClO4)3 is required to reach the equivalence point? (3 points) Find pLa3+ when 10.00 mL of La(ClO4)3 has been added. (3 points) Find pLa3+ at equivalence point. (3 points) Find pLa3+ when 27.00 mL of La(ClO4)3 has been added. (5 points) Plot the titration curve for this titration using Excel or other spreadsheet software. (5 points) Plot the titration curve for the same titration if the concentration of the titrant is increased to 0.0700 M. What effect does this have on the shape of the titration curve? (3 points) If you plot the titration curves from (e) and (f) using number of moles of titrant added on x axis instead of volume added, how does this affect the curves observed in (e) and (f) (3 points) Another analytical chemist performed the titration of the same oxalate sample using calcium to precipitate calcium oxalate. Is this a better approach to this analysis? Why or why not? (3 points) A third analytical chemist decided to use reagent X(ClO4)3 to precipitate X2(C2O4)3(s) whose KSP value is 1 x 10-32. Is this a better approach to this analysis? Why or why not?

Assignment 1

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2. A mixture having a volume of 10.00 mL and containing 0.1000 M Ag+ and 0.04500 M Hg22+ was titrated with 0.0800 M KCN to precipitate Hg2(CN)2 and AgCN. (a) (3 marks) Explain which salt will precipitate first and why. (b) (3 marks) Calculate volume of KCN required to reach first and second equivalence points and sketch by hand the expected titration curve. (c) (3 marks) Calculate pCN- at 8.00 mL KCN added. (d) (4 marks) Calculate pCN- at 12.50 mL KCN added (e) (4 marks) Calculate pCN- at 18.00 mL KCN added. (f) (3 marks) Calculate pCN- at 23.75 mL KCN added. (g) (3 marks) Calculate pCN- at 28.00 mL KCN added. (h) (5 marks) At the first equivalence point in the above titration, will the second precipitate already start to form? Explain why or why not and show your calculation to derive the answer. (i) (2 marks) Can you propose a better titrant to perform this titration? Justify your reasoning briefly. 3. Balance the following reactions: For full marks, you must show all work including half reactions and number of electrons being transferred. (a) (6 marks) SbH3 + Cl2O

H4Sb2O7 + Cl- (acidic conditions)

(b) (7 marks) K2NaCo(NO2)6 + MnO4-

K+ + Na+ + Co3+ + NO3- + Mn2+ (acidic conditions)

(c) (2 marks) balance reaction in (b) under basic conditions

Assignment 1

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FINAL ANSWER SHEET – Please staple this sheet to the front of your assignment with your final answer shown to the correct number of significant figures. NAME: STUDENT NUMBER: FINAL MARK: Assignment 1 Answers

Marks

Total Marks

Question 1 (a)

2

Question 1 (b)

3

Question 1 (c)

3

Question 1 (d)

3

Question 1 (e) Question 1 (f) Question 1 (g) Question 1 (h) Question 1 (i)

See graph See graph and answer See graph and answer See answer See answer

5 5 3 3 3

Question 2 (a)

3

Question 2 (b)

3

Question 2 (c)

3

Question 2 (d)

4

Question 2 (e)

4

Question 2 (f)

3

Question 2 (g)

3

Question 2 (h) Question 2 (i)

See answer See answer

5 4

Question 3 (a)

6

Question 3 (b)

7

Question 3 (c)

2

Assignment 1

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