Electrochemical Cells

Question 1

What is the definition of electrochemical series

Answer 1

A list of electrode potentials in order

Question 2

What will be the E° of the weakest and strongest reducing agent

Answer 2

Weakest - Most positive E°
Strongest - most negative E°

Question 3

How do you calculate EMF of a cell

Answer 3

Most +ve - most -ve

Question 4

How do you maintain the EMF of a fuel cell when in use

Answer 4

Keep the concentrations of reactants constant

Question 5

State the substances and conditions needed in a standard hydrogen electrode

Answer 5

• H2 gas and 100kPa
• 1 mol dm^-3 and HCl
• Pt electrode and temperature of 298K

Question 6

Explain how a salt bridge provides an electrical connection

Answer 6

Free moving Ions can move through it to maintain charge balance

Question 7

Why is a high resistance voltmeter used

Answer 7

To stop the current from flowing in the circuit so you can measure the maximum possible potential difference

Question 8

What will be the E° of the weakest and strongest oxidising agent

Answer 8

Weakest - Most negative E°
Strongest - most positive E°

Question 9

On which sides of a half equation are the oxidising and reducing agents

Answer 9

Left - oxidising agents
Right - reducing agents

Question 10

What’s the advantages of fuel cells

Answer 10

• greater efficiency
• less pollution and less CO2

Question 11

What’s the drawbacks of fuel cells

Answer 11

• expensive
• limited lifetime
• hydrogen flammable so hard to store and transport
• toxic chemical in their production

Question 12

What’s advantages to ethanol fuel cells compared to hydrogen

Answer 12

• can be made from renewable sources in a carbon neutral way
• less explosive and easier to store

Question 13

Which half cell will be oxidised and reduced

Answer 13

More -ve half cell - is oxidised
More +ve half cell - is reduced

Question 14

Why is a platinum electrode used

Answer 14

• it is unreactive
• it conducts electricity
  It provides a surface for electron transfer

Question 15

How does changing concentration of a reactant effect the EMF of a cell

Answer 15

Increased conc - increases EMF
Decreased conc - decreases EMF

Question 16

Which half equation is always backwards when combining

Answer 16

Oxidation (the one with the more -ve emf)

Question 17

How does the equilibrium shifting left effect EMF

Answer 17

EMF will decrease

Question 18

What does electrode potential suggest about feasibility of a reaction

Answer 18

If EMF is +ve then reaction is feasible

Question 19

If the electrode potential of something is greater than the other what does it mean for oxidation

Answer 19

If its EMF is greater then it CAN oxidise the other thing
If it’s EMF is not greater then it CANNOT oxidise the other

Question 20

Why might the calculated EMF value differ from the commercial

Answer 20

Non standard conditions

Question 21

What could be a reason why EMF decreases to 0

Answer 21

The concentration of ions becomes equal

Question 22

What is the salt bridge made out of

Answer 22

KNO3 because all it’s salts are soluble so won’t form a precipitate with any ions in the half cells

Question 23

Why might the emf of two of the SAME complex ions in a table be different

Answer 23

Different ligands

Question 24

How would you write an equation for the reaction taking place in the cell while it is being recharged?

Answer 24

Combine the two half equations as normal and then reverse the whole equation

Question 25

Why does a fuel cell not need to be recharged?

Answer 25

• there is a constant supply of the reactants/hydrogen fed in

Question 26

How can you use half equations to explain how an electric current can be generated?

Answer 26

• name the thing getting oxidised and say that it produces electrons
• name thing getting reduced and say that it accepts electrons