Electrode potentials

Question 1

Redox reactions can be divided into 2 half reactions. What are they and tell me about the loss/gain of electrons?

Answer 1

Oxidation: Losses electrons

Reduction: gains electrons

Question 2

Whats does the redox potential describe ?

What does it allow us to then calculate?

Answer 2

The ability of a molecule to gains electrons (and therefore be reduced)

This allows us to quantify the ability of one molecule to oxidise/reduce another molecule

Question 3

Whats a reference electrode?

Answer 3

an electrode which has a stable and well-known electrode potential

Question 4

Whats an oxidising agent? give an example

Answer 4

Something that removes electrons from another substance e.g. NAD+

Question 5

Whats a reducing agent? give an example

Answer 5

something that adds electrons to another substance e.g. NADH

Question 6

For a spontaneous reaction to occur, what must ∆G be?

Answer 6

negative

Question 7

Apart from gibbs free energy equation, what can ∆G also equal, what do the symbols stand for?

Answer 7

∆G= -nFE

∆G= free energy

n= the number of electorns involved

F= faradays constant (96485 Cmol^-1)

E= the differenc ein the redox potential of the couples (the half reactions) (V) or the cell potential under standard conditions

Question 8

Whats does Cmol^-1 also equal?

Answer 8

V

Question 9

What are the conventions when writing redox equations?

Answer 9

• always write half reactions as reductions
• write the most positive (V) as the forward reaction
• if you invert the reaction, the sign of the half reaction changes
• if you have to balance, the voltages never change duing multiplications
• the sum of the voltages after these operations is used to decided the overall ‘E’ of the reactions

Question 10

what has to be balanced in half reactions, the electrons or the charges?

Answer 10

the electrons

Question 11

What does the Nernst equation relate?

Answer 11

potential and concentration

Question 12

What is the Nernst equation, and what does each symbol stand for?

Answer 12

n= number of electrons

T= temperature

F= Faradays constant

lnQ= accounts for change in concentration

Q= reaction quotient

R= gas constant

E= potentials

Question 13

What are the 2 ways that the nernst equation can be written, by rearranging due to log laws.

Answer 13

Question 14

worked example for the nernst equation

Answer 14

Question 15

What should the units for the nernst eqaution be?

Answer 15

V and everything else should cancel out

Question 16

When the system is in equilibrium, what does Q equal?

Answer 16

Q=K when the system is in equilibrium

Question 17

Whats the nernst eqaution when Q can = K?

Answer 17

Question 18

What is pH directly related to in a solution?

Answer 18

the concentration of H⁺

Question 19

whats the equation for how PH relates to H+?

Answer 19

pH= -log₁₀[H+]

Question 20

under standard conditions what does pH =?

Answer 20

pH=0

therefore;

-log₁₀[H+]=0

Question 21

Look at CHEM lecture 15 for PH calculations

Question 22

Whats the equation for generalising the effect of pH?

Answer 22

Question 23

The ratio of H+ to electrons, determines how much E will be effected by changes in pH, quanitfy this

Answer 23