1. 1 Instrumental Analysis Amperometry and its applications Tutorial 8

2. Learning Outcomes 1.Define amperometric technique of analysis. 2.To solve problems on amperometric titrations. 3. Apply calculations on different non potentiometric analytical techniques. 2 By the end of the tutorial, students should be able to:

3. 3 Amperometry is the electroanalytical technique in which: the potential of the working electrode is adjusted at a fixed value on the plateau of i-E curve where the current does not change when E is changed, and the only change that happens in current is function of concentration. Amperometry is a measure of limiting current at a fixed applied potential as a function of concentration -0.2-0.4-0.6-0.8-1.2-1.4 i (  A) E vs SCE residual current (i r ) i l limiting current plateau i d = i l - i r

4. 4 Amperometric titrations Amperometry can be used to estimate the equivalence point of titrations, provided at least one of the participants or products of the reaction involved is oxidized or reduced at a microelectrode. In this case, the current (at constant applied potential) is measured as a function of the volume of titrant added.

5. 5 reactant reacts at electrode VTVT i EP C A 0 Titrant reacts at electrode VTVT i EP C T 0 Both reactant and titrant react VTVT i EP Predict the shape of the amperometric titration curve if the product is the only electroactive species ?

6. 6 Exercise 1 (self study) Suppose we wish to electrolyze I - to I 3 - in a 0.10 M KI solution containing 3.0x10 -5 M I 3 - at pH 10.00 with P H 2 fixed at 1.00 bar. 3I - + 2H 2 O  I 3 - + H 2 (g) + 2OH - a)Find the cell potential if no current is flowing. b)Suppose that electrolysis increases  I 3 -  to 3.0x10 -4 M, but other concentrations are unaffected. If the cell resistance is 2.0 , the current is 63 mA, the cathode overpotential is 0.382 V and the anode overpotential is 0.025 V, what voltage is needed to drive the reaction? Answer: a) –1.081 V b) –1.644 V Hint: Cathode : 2H 2 O + 2e -  H 2 (g ) + 2OH  E o = – 0.828 V Anode : I 3 – + 2e –  3I  E o = 0.535 V

7. Answer a)When no current is flowing: E cell = E cathode - E anode E cathode= -0.828 – 0.05916/2 log E cathode= -0.828 - 0.05916/2 log E cathode= -0.828+ 0.23664 = - 0.59136 V E anode = 0.535 - 0.05916/2 log E anode = 0.535- 0.02958 x log 33.3333 = 0.4899 V E cell = -0.59136- 0.4899 = -1.08 V

8. b) E cell = E cathode - E anode – IR- Overpotentials E cathode did not change = - 0.59136 E anode = 0.535 - 0.05916/2 log E anode = 0.535 - 0.05916/2 log E anode = 0.535- 0.02958 x log 3.3333 = 0.5195 V E cell = -0.5916-0.5195- (2)(63x10 -3 )- (0.382+0.025)= -1.644

9. 9 Try to solve Exercise 17-B and problems 17-1, 17-2, 17-4, 17-8 17- 11, 17-12, 17-13, 17-19(Harris text book, p400-403) Try to solve Exercise 17-B and problems 17-1, 17-2, 17-4, 17-8 17- 11, 17-12, 17-13, 17-19 (Harris text book, p400-403) reacted with the 8-hydroxyquinoline (HOC 9 H 6 N) that was released when the indium(III) compound was dissolved: HOC 9 H 6 N + 2Br 2 HOC 9 H 4 NBr 2 + 2HBr A heated buffer solution containing indium(III), In 3+, was treated with an excess of 8-hydroxyquinoline (HOC 9 H 6 N) to precipitate quantitatively an insoluble indium(III) compound, according to the following reaction: In 3+ + 3HOC 9 H 6 N In(OC 9 H 6 N) 3 (s) + 3H + After the precipitate was separated and washed, it was dissolved in dilute hydrochloric acid solution (which caused the above reaction to proceed in the right-to-left direction). Then an excess of bromide ion (Br – ) was added, and the solution was transferred to an electrochemical cell equipped with a platinum generator anode and a platinum auxiliary cathode. Elemental bromine (Br 2 ), which was electrogenerated by oxidation of bromide ion, 2Br – Br 2 + 2e – An end point was reached after a titration time of 186.6 seconds at a constant current of 125.3 mA. Calculate the mass of In 3+ in milligrams in the original sample solution. Faraday constant (F) = 96,500 coulombs/mol e -. Atomic mass of In = 114.8) (Answer: 2.318 mg of In 3+ ) Exercise 2 (SELF STUDY)

10. No. of moles of In 3+ reacting = It/nf I = 125.3 x10 -3 A t= 186.6 sec The question is n?? Follow each equation and you will see: 1 mole In ≡ 3 moles HOC 9 H 6 N ≡ 6 moles of Br 2 ≡ 12 moles of electrons n= 12 No. of moles of In 3+ reacting = 125.3 x10 -3 x 186.6 / 12 x 96500 = 2.019 x 10 -5 moles Wt of In = no. of moles x atomic mass = 2.019 x 10 -5 x 114.8 = 2.317 x 10 -3 gms

11. Assignment 2; weight 5 % Each group of 5 students from the same tutorial group are required to do a literature review on ONE electrochemical analysis method for a drug as assigned in the table in the next slide. Each group should submit a report including at least 5 of those points on the assigned drug: 1- Abstract. 2- Introduction. 3- Principle of analysis. 4- Instrument used. 5- Diagram of instrument used. 6- Methods and materials. 5- Advantages or limitation of the method used. 6- Results in the form of graphs or tables. 7- Uses of the drug under analysis. Students can search for literature using http://www.ekb.eg/; please create an account as a student using your GUC mail, Egyptian Knowledge Bank has free publications of the most important international publishers.http://www.ekb.eg/ All references should be cited in your report. Students are required to deliver hard copies of the reference/references used. In case you can not find an access to an article, kindly contact your TA for help. Plagiarism leads to ZERO; EVERY WORD IN THE REPORT SHOULD BE IN YOUR OWN ; NOT COPIED FROM THE REFERENCE USED. Deadline : 21-04-2016

12. DrugTutorial no. Sulfadiazine Tablets1 Cefixime tablets2 Nitrofurantoin Capsules3 Propranolol Tablets4 Atenolol Tablets5 Carbamazepine tablets6 Nifedipine7 Ciclopirox olamine8 Diclofenac9 Verapamil10 N-acetyl-L-cysteine11 Pentoxifylline12 Drug/ Tutorial Assignment

13. DrugTutorial no. Rosiglitazone13 Secnidazole14 Dopamine15 5-Fluorouracil16 Clotrimazole17 metoclopramide hydrochloride18 cisapride19 phenobarbital20

14. Quiz 2 Quiz 2 will take place on 14-04-2016 at 4:00 PM and will include lectures 6, 7 and 8 + tutorials 6,7. No make up is offered for the quiz Please respect locations of your groups.

15. HallDate / TimeGroups H3Thursday, 14-4-2016, 4:00-4:30 1-4 H5 6-9 H12 10-13 H13 14-17 H14 18-20 Location and time