Electrochemistry

Question 1

What is the purpose of the salt bridge?

Answer 1

To connect the two cells and to allow the ions to flow back towards the negative electrode

Question 2

Which electrode is the positive electrode?

Answer 2

The cathode where reduction occurs.

Question 3

Which electrode is the negative electrode?

Answer 3

The anode where oxidation occurs.

Question 4

How to set up a cell diagram?

Answer 4

The lowest charges go on the outside

Question 5

Why does the voltmeter have high resistance?

Answer 5

It has a very high resistance to stop a current flowing through the circuit to maximise the EMF produced.

Question 6

What does a single line mean in a cell diagram?

Answer 6

Phase boundary

Question 7

What does a double line in a cell diagram mean?

Answer 7

Salt bridge

Question 8

What must you remember when drawing a cell diagram?

Answer 8

All the state symbols

Question 9

Why is platinum used in an electrochemical cell?

Answer 9

It is very unreactive and can conduct electricity.

Question 10

How do you separate species which are in the same phase in a cell diagram?

Answer 10

Use a comma

Question 11

What is meant by the term ‘electrochemical series’?

Answer 11

List of electrode potentials in numerical order

Question 12

What are the conditions for the hydrogen half cell potential to be 0?

Answer 12

100kpa 1mol 298K

Question 13

Why would the actual EMF of a cell be different to the calculated one?

Answer 13

Not under standard conditions

Question 14

Why should a hydrogen fuel cell be used instead of an internal combustion engine?

Answer 14

More of the potential energy is released from a fuel cell rather than an internal combustion engine.

Question 15

Why should a hydrogen fuel cell be used instead of an internal combustion engine?

Answer 15

More of the potential energy is released from a fuel cell rather than an internal combustion engine.

Question 16

Why would an electrode be rubbed with sandpaper prior to use?

Answer 16

To remove the oxide layer

Question 17

What is a reducing agent?

Answer 17

An electron donor.

Question 18

What is an oxidising agent?

Answer 18

An electron acceptor

Question 19

Why cant some cells be recharged?

Answer 19

The reaction is not reversible

Question 20

If it asks for the discharge equation what equation is it?

Answer 20

Just the normal oxidation then reduction

Question 21

If it asks for a charging reaction what is the final equation

Answer 21

The one that normally gets oxidised is reduced and the one that normally gets reduced is oxidised

Question 22

Why is the standard electrode potential for a hydrogen electrode 0?

Answer 22

By definiton

Question 23

What salt solution should the salt bridge be dipped in and why?

Answer 23

Potassium nitrate and it should not react with either the electrodes or electrode solutions

Question 24

If the system does not have a solid conducting surface, why should a platinum electrode be used?

Answer 24

unreactive and can conduct electricity

Question 25

What is the standard electrode potential for strong reducing agents?

Answer 25

Most negative as they are being oxidised so losing electrons

Question 26

What is the standard electrode potential for strong oxidising agents?

Answer 26

Most positive as they are being reduced so gaining electrons

Question 27

What happens if you increase the concentration of the reactants?

Answer 27

The Ecell value will increase

Question 28

What happens if you decrease the concentration of the reactants?

Answer 28

The Ecell value will decrease

Question 29

How will temperature effect the value of Ecell?

Answer 29

If the temperature is increased then the value of Ecell will decrease the value of Ecell.

Question 30

What is a fuel cell?

Answer 30

A fuel cell is a cell which uses energy from the reaction of a fuel with oxygen to create a voltage.

Question 31

Why does a fuel cell maintain a constant voltage over a period of time?

Answer 31

The concentrations of the reactants and the products doesn't change as they are constantly being replenished.

Question 32

Why are high temperatures and high pressures used in fuel cells?

Answer 32

High temperature is needed because at standard conditions the Ecell value is too small, even though the forward reaction is exothermic. Therefore a high pressure is used as there are less moles of gaseous species on the right hand side so equilibrium shifts to the right.

Question 33

What are the advantages of hydrogen fuel cells?

Answer 33

Less pollution from CO2 Hydrogen is readily available good efficiency

Question 34

What are the disadvantages of fuel cells?

Answer 34

expensive storing and transporting hydrogen could be dangerous toxic chemicals are used in their production

Question 35

What components are needed for a standard hydrogen cell?

Answer 35

1 molar HCl hydrogen 100kPa platinum electrode

Question 36

Why will the EMF of a cell reach zero?

Answer 36

The concentrations of the reactants and products are equal or the reactants have been used up.

Question 37

How could recharging a cell lead to increased CO2 in the atmosphere?

Answer 37

power plant energy could come from burning fossil fuels