SS - Electrode Potentials

Question 1

Describe how electrochemical cells can be made

Answer 1

Electrochemical cells can be made from 2 different metals dipped in salt solutions of their own ions connected by a wire (the external circuit) and a salt bridge

Question 2

Describe a salt bridge

Answer 2

Filter paper soaked in KNO₃ which connects the 2 half-cell solutions. The K⁺ and NO₃⁻ ions flow through the salt bridge and balance out the charges in the beaker

Question 3

In which way do the electrons flow through the wire between the half-cells?

Answer 3

From the most reactive metal to the least reactive metal

Question 4

How is the cell potential (emf) between 2 half-cells measured?

Answer 4

A voltmeter connected in the external circuit

Question 5

Describe how you can use a half-cell of 2 aqueous ions and give an example

Answer 5

Because neither the reactants nor the products are solids, you need something else for the electrode. It must conduct electricity and be very inert (so it wont react with anything in the half-cell). Platinum or graphite can both be used
Example: Conversion of Fe²⁺ to Fe³⁺ (or vice versa)

Question 6

Define standard electrode potential, Eᶱ

Answer 6

The standard electrode potential Eᶱ of a half-cell is the voltage measured under standard conditions when the half-cell is connected to a standard hydrogen electrode

Question 7

Which side does the standard hydrogen electrode go of a test half-cell?

Answer 7

Left

Question 8

Give the equation to find the standard electrode potential of a half-cell

Answer 8

Whole cell potential = Eᶱ(right) - Eᶱ(left)
For a hydrogen half-cell, Eᶱ(left) = 0.00V so the voltage reading will be equal to Eᶱ(right) and could be positive or negative, depending on the direction for the flow of electrons

Question 9

In an electrochemical cell, in which half-cell does oxidation occur?

Answer 9

The most negative

Question 10

In an electrochemical cell, in which half-cell does reduction occur?

Answer 10

The most positive

Question 11

Give the equation to work out the cell potential from standard electrode potentials

Answer 11

Eᶱ(cell) = Eᶱ(most positive) - Eᶱ(most negative)

Question 12

What does the standard electrode potential show about the rate of reaction?

Answer 12

Nothing

Question 13

Describe the feasibility of a reaction from its standard electrode potentials

Answer 13

If the standard electrode potential for what is being reduced is greater (more positive) than the electrode potential of what is being oxidised, then the reaction could take place

Question 14

Explain why a reaction may be feasible but doesn’t happen

Answer 14

The rate of reaction could be so slow that effectively the reaction doesn’t happen