Unit 5 Redox Equilibria

Question 1

E°cell = ?

Answer 1

E°R - E°L

Question 2

On which side does reduction occur?

Answer 2

Reduction on the right

Question 3

What are the advantages of hydrogen fuel cells?

Answer 3

Clean, no greenhouse gases, produce a constant voltage provided fuel supply, hydrogen is ‘abundant’

Question 4

What are the conditions under which a standard electrode potential is measured?

Answer 4

298K, 100kPa, and the solution of ions must have a concentration of 1.00 mol dm^-3.

Question 5

Give one economic advantage, and one environmental disadvantage to the use of non-rechargeable batteries.

Answer 5

They are cheap to make.

They cannot be reused, and throwing them away wastes the energy and resources needed to manufacture them.

Question 6

Give one safety risk caused by the use of hydrogen-oxygen fuel cells.

Answer 6

Hydrogen is highly flammable.

Question 7

What three things make up the standard hydrogen electrode?

Answer 7

H2 gas being bubbled over a platinum electrode and an acid (such as H2SO4)

Question 8

How can you tell if a reaction is feasible from redox potentials (electrode potentials)?

Answer 8

More negative reaction goes to left, more positive to right. If reactants are on wrong side of “–>” then reaction isn’t feasible under standard conditions

Question 9

What does the circle mean in “E°cell”

Answer 9

Under standard conditions

Question 10

Why use a high resistance voltmeter?

Answer 10

To stop the current from flowing in the circuit

The reactions won’t be happening as a result

Question 11

What does the symbol E stand for?

Answer 11

The potential difference

Question 12

What is the salt bridge usually made from?

Answer 12

A piece of filter paper soaked in salt solution

Question 13

Why would using potassium chloride as the salt forming the salt bridge not be suitable for copper systems?

Answer 13

The chlorine would react with the copper to form complexes

Question 14

In cell diagrams, what does a solid vertical line represent?

Answer 14

The boundary between phases

Question 15

What does the double line represent in a cell diagram?

Answer 15

The salt bridge between two half cells

Question 16

What must be used if a system doesn’t include a metal that can act as an electrode?

Answer 16

A platinum electrode

Question 17

Why is a platinum electrode suitable?

Answer 17

It provides a conducting surface for electron transfer
Is unreactive
Can conduct electricity

Question 18

How is the potential of all electrodes measured?

Answer 18

By comparing their potential to that of the SHE

Question 19

What is the secondary standard?

Answer 19

A standard electrode that has been calibrated against the primary standard e.g silver chloride

Question 20

Where will the most powerful reducing agents be found?

Answer 20

At the most negative end of the series on the right (lower oxidation number)

Question 21

Where will the most powerful oxidising agents be found?

Answer 21

At the most positive end of the series on the left (higher oxidation number)

Question 22

Why will fuel cells maintain a constant voltage over time?

Answer 22

Because they are continuously supplied with hydrogen and oxygen so maintaining the concentration of reactants

Question 23

Limitations of hydrogen fuel cells

Answer 23

Expensive
Storing and transporting hydrogen is difficult
Limited lifetime and high production costs
Use of toxic chemicals in their production

Question 24

3 ways in which hydrogen can be stored in fuel cells

Answer 24

As a liquid under pressure
Adsorbed on the surface of a solid material
Absorbed within a solid material

Question 25

On which side of the cell representation is the SHE?

Answer 25

Always on the left hand side

Question 26

Why can ethanol be considered to be a carbon-neutral fuel?

Answer 26

CO2 is released by combustion which is then taken up in photosynthesis