Electrode Potentials

Question 1

What is an electrochemical cell?

Answer 1

• Cell with 2 half cells
• Connected by a salt bridge
• With metal electrodes and solution containing that metal

Question 2

Why does a voltage form in an electrochemical cell?

Answer 2

The more negative half cell has the tendency to oxidise and release electrons

More electrons build up on that side

So a potential difference is created

Question 3

Why do you need a high resistance voltmeter?

Answer 3

Stop current flowing in the circuit

Question 4

Purpose of a salt bridge

Answer 4

Allow the flow of ions

Question 5

What are salt bridges usually made of?

Answer 5

Filter paper soaked in potassium nitrate

Question 6

Why is a wire not used as the salt bridge?

Answer 6

It would set up its own electrode system with the solutions

Question 7

What do vertical lines on a cell diagram represent?

Answer 7

Different phases

Question 8

What does a double line on a cell diagram represent?

Answer 8

Salt bridge

Question 9

How does platinum act as an electrode?

Answer 9

Provides a conducting surface for electron transfer

Question 10

Why is platinum used as an electrode?

Answer 10

Unreactive

Can conduct electricity

Question 11

How do you measure electrode potential of a cell?

Answer 11

Connect to another half cell of a known potential

Measure potential difference between 2 half cells

Question 12

What is SHE used for?

Answer 12

Comparing electrode potentials of all electrodes

Question 13

Conditions of SHE

Answer 13

1) Hydrogen gas at 100kPa

2) 1 mol dm^-3 H+ ions

3) 298K

4) Pt electrode

Question 14

What is standard electrode potential?

Answer 14

Potential difference when electrode system is connected to hydrogen electrode system and standard conditions apply

Question 15

How to calculate EMF?

Answer 15

E cell = E reduced - E oxidised

Question 16

NO PRoblem

Answer 16

More Negative half cell is Oxidised (electrons on the rhs)

More Positive half cell is Reduced (electrons on the lhs)

Question 17

What is a reducing agent?

Answer 17

The thing that gets oxidised (loses electrons)

Question 18

What is an oxidising agent?

Answer 18

The thing that gains electrons

Question 19

What are the reducing agents in an EMF table?

Answer 19

The species on the right side of the arrow

Question 20

What are the oxidising agents in and EMF table?

Answer 20

The species on left side of the arrow

Question 21

Effect of concentration on E cell

Answer 21

Increasing concentration of reactants increases E cell

Question 22

Effect of temperature on E cell

Answer 22

If forward reaction is exothermic, increased temperature decreases E cell as equilibrium shifts backwards

Question 23

What are non-rechargeable cells?

Answer 23

Reactions aren’t reversible

Question 24

What is a fuel cell?

Answer 24

One that uses energy from reaction of fuel with oxygen to create a voltage

Question 25

Hydrogen fuel cell in alkaline conditions

Answer 25

4e- + 4H2O --> 2H2 + 4OH- 4e- + 2H2O + O2 --> 4OH- Overall: 2H2 + O2 --> 2H2O

Question 26

Lithium cells half equations

Answer 26

Li+ + CoO2 + e- --> Li+[CoO2]- Li+ + e- --> Li Overall discharge reaction: Li + CoO2 --> LiCoO2

Question 27

Advantage of fuel cells

Answer 27

1) Less pollution --> less CO2 2) Greater efficiency

Question 28

Limitations of hydrogen fuel cells

Answer 28

1) Expensive 2) Hard to store and transport as its a gas 3) Flammable

Question 29

Ethanol fuel cells: reaction that occurs at the oxygen electrode

Answer 29

4e- + 4H+ + O2 --> 2H2O

Question 30

Ethanol fuel cell: reaction that occurs at the ethanol electrode

Answer 30

C2H5OH + 3H2O --> 2CO2 + 12H+ + 12e-

Question 31

Ethanol fuel cell: overall equation

Answer 31

C2H5OH + 3O2 --> 2CO2 + 3H2O

Question 32

Advantages of ethanol fuel cell

Answer 32

1) Made from renewable sources 2) Raw materials produce ethanol by fermentation 3) Less explosive 4) Easier to store