Question 21 (15 marks) Consider the titration of 25.0 mL of 0.0100 M Sn2+ by 0.0

Question

Question 21 (15 marks) Consider the titration of 25.0 mL of 0.0100 M Sn2+ by 0.0500 M T3in 1 M HCI, using Pt and saturated calomel electrodes to find the end point. (a) Write a balanced titration reaction. (b) Write two different half reactions for the indicator electrode. (c) Write two different Nernst equations for the net cell reaction. (d) Calculate E at the following volumes of T3+: 1.00, 2.50,4.90,5.00, 5.10 and 10.00 mL Sketch the titration curve. Use the graph paper provided at the end of the exam paper. (e)

Explanation / Answer

Balanced reaction would be

Sn2+ + TI3+ -> Sn4+ + TI1+.

Half cell reactions are as follows

Sn2+-> Sn4+ + 2e- Eo= -.015 V

TI3+ + 2e-->  TI1+ Eo= 0.77V

Nernst eqn for the half cells are as follows

For Sn electrode E= -.015 - (.059/2) ln([Sn4+]/[Sn2+]

For Tl electrode E= .077 - (.059/2) ln([Tl1+]/[Tl3+])

moles of Sn = .25 millimoles

moles of Tl in different scenarios are .05 millimoles, .125millimoles, .245 millimoles, 0.25 , 0.255, .5 millimoles

for casecase 1,2,3 only Sn will be present at end point and in case 4 both have equal numbers of moles and will nuetralise each other completely.

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