CL 23- electrode potentials

Question 1

standard electrode potential

definition

Answer 1

the e.m.f. of a half cell compared with a standard hydrogen half cell, measured at 298K, with solution concentrations of 1moldm^-3 and a gas pressure of 100kPa.

Question 2

E value of good reducing agent

explanation

Answer 2

more negative e value, equilibrium shifts to left, equation flipped, new reactant more likely to oxidise

Question 3

reducing agent

definition

Answer 3

electron donor

Question 4

electrochemical series orders

location of agents

Answer 4

good reducing agents at top right, good oxidising agents at bottom left

Question 5

which reactions will be feasible?

Answer 5

any reactions with a positive E cell

Question 6

limitations of feasibility theory (2)

common exam question

Answer 6

1) the reactions may be feasible but in reality don’t ‘go’ due to high activation energy.
2) actual conditions may be very different to the standard conditions used to measure E values.

Question 7

steps when change in conc present

increase in Zn 2+, e.g.

Answer 7

1) write half equation as seen on electrochemical series (NOT overall equation)
2) use Le Chatelier’s principle to see the effect on equilibrium

Question 8

manganate half equation

Answer 8

MnO₄⁻/ Mn²⁺

Question 9

dichromate Cr half equation

Answer 9

Cr₂O₇²⁻/ Cr³⁺

Question 10

iodine half equation

Answer 10

I₂/I⁻
easily reversed

Question 11

iron half equation

Answer 11

Fe²⁺/ Fe³⁺
easily reversed

Question 12

hydrogen peroxide half equation

Answer 12

H₂O₂ –> O₂
acidic conditions

Question 13

thiosulfate half equation

Answer 13

S₂O₃²⁻/ S₄O₆²⁻

Question 14

Cu/I half equation (bleach titration)

Answer 14

2Cu²⁺₍ₐ₎ + 4I⁻₍ₐ₎ –> 2CuI₍ₛ₎ + I₂₍ₐ₎