Electrochemical Cells

Question 1

What is a half cell?

Answer 1

One half of an electrochemical cell which can be constructed of a metal dipped in its ions or a platinum electrode with 2 aqueous ions

Question 2

What is an electrochemical cell made up of?

Answer 2

• 2 half cells
• Wire
• Voltmeter
• Salt Bridge

Question 3

Why is the process described as a redox reaction?

Answer 3

process and the other is undergoing an oxidation process

Question 4

In the diagram, what is being oxidised, state the observation and the equation?

Answer 4

Zinc half cell shows loss of electrons as zinc loses electrons easier than copper (Oxidation)
Zn ↔ Zn2+ + 2e-
Observation – Zinc electrode will become thinner as more Zn2+ is produced to make electrons

Question 5

In the diagram, what is being reduced, state the observation and the equation?

Answer 5

Copper half cell accepts the electrons produced by zinc (Reduction)
Cu2+ + 2e- ↔ Cu
Observation – Copper electrode will get thicker as Cu2+ ions receive the electrons and turn into copper.

Question 6

What form are equations written it?

Answer 6

Reduction form

Question 7

What does Electrode potential (Eꝋ) shows and what are the units?

Answer 7

How easily the half cell gives up electrons (oxidised) and is measured in Volts

Question 8

Why is a Standard Hydrogen Electrode (SHE) used?

Answer 8

Because Electrode potentials can’t be measured on their own but we can measure against a reference cell called a SHE as the Eꝋ = 0.00V and also used for reaction feasibilty

Question 9

What are the standard conditions?

Answer 9

• Temperature = 298K
• Pressure = 100kPa
• Concentrations of ions = 1 mol dm-3

Question 10

Explain the Electrochemical Series

Answer 10

• Agents on the left hand side of the equation are more easily reduced as they have an increasing tendency to gain electrons
• Agents on the right hand side of the equation are more easily oxidised as they have an increased tendency to lose electrons

Question 11

What is the formula to calculate the Standard Cell Potential (Eꝋcell)?

Answer 11

Eꝋcell = Eꝋreduced - Eꝋoxidised

Question 12

What is cell notation?

Answer 12

It is the standard way of representing cells in chemistry

Question 13

What is the standard cell notation representation?

Answer 13

Reduced Form | Oxidised Form || Oxidised Form | Reduced Form

Question 14

What decides what goes on the left and right hand side of the double line?

Answer 14

The most negative half cell potential goes to the left of the double line

Question 15

What does the single line represent?

Answer 15

Shows a physical state change

Question 16

What does the double line represent?

Answer 16

It shows a Salt Bridge

Question 17

When do we use a platinum electrode?

Answer 17

When using 2 non metals

Question 18

How can you tell if a reaction is feasible?

Answer 18

A reaction is feasible if the Eꝋcell value is positive using the equation

Question 19

What are Batteries?

Answer 19

They are electrochemical cells that come in 2 forms:
• Rechargeable
• Non-rechargeable

Question 20

What is an electrolytes function?

Answer 20

It acts as a conductive pathway for ions to move from one electrode to another

Question 21

Explain the comparison when deciding to use non – rechargeable and rechargeable?

Answer 21

Non – rechargeable batteries tend to be cheaper than rechargeable batteries, however, rechargeable batteries are reversible and last longer which means they are cheaper in the long term

Question 22

What is an example of rechargeable batteries?

Answer 22

Lithium ion batteries

Question 23

What is an example of non – rechargeable batteries?

Answer 23

Zinc carbon batteries

Question 24

Explain how the Zinc Carbon electrochemical cell is setup?

Answer 24

It has a Zinc positive electrode and a mixture of manganese dioxide + carbon for a negative electrode.

Question 25

Which electrolyte is sued for zinc carbon batteries?

Answer 25

Ammonium Chloride

Question 26

What are the 2 half equations for Zinc Carbon batteries?

Answer 26

• Zn –> Zn2+ + 2e-

* 2MnO2 + 2NH4+ + 2e- –> Mn2O3 + 2NH3 + H2O

Question 27

Explain how the Lithium electrochemical cell is setup

Answer 27

A lithium cell (one type) is made from Lithium cobalt oxide (LiCoO2) electrode and a graphite electrode

Question 28

Which electrolyte is used for lithium cells?

Answer 28

Lithium Salt

Question 29

What are the 2 half equations for lithium cells?

Answer 29

• Li + CoO2 + e- ↔ Li[CoO2]-

* Li ↔ Li+ + e-

Question 30

How do you recharge batteries?

Answer 30

Current supplied forcing electrons in opposite direction around circuit and reverse reaction and this is possible as none of the substances escape or used up

Question 31

Explain how a fuel cell works (Alkaline hydrogen – oxygen fuel cell)

Answer 31

1) Hydrogen is fed in here. It reacts with OH- ions in solution in (9) but reaction is:
H2 + 2OH-  2H2O + 2e-
2) Electrons produced in step 1 travel through Platinum electrode
3) This is the flow of electrons to power circuit
4) Oxygen is fed in here. It reacts with water and 4 electrons from step 1 to make OH- ions: O2 + 2H2O + 4e-  4OH-
5) Electrons flow to negative electrode which is made from platinum
6) Electrolyte made from KOH solution. It carries OH- from cathode to anode
7) Electrons flow from positive electrode which is made from platinum
8) Product from step 1 (H2O) is released to surroundings
9) OH- ions produced from step 4 carried towards anode via electrolyte

Question 32

State 3 advantages of Fuel cells

Answer 32

• Fuel cells are more efficient as more energy is converted to kinetic energy
• Doesn’t need to be recharged; just use supply of H2 + O2
• Only waste product is water

Question 33

State 3 disadvantages of Fuel cells

Answer 33

• Hydrogen is highly flammable so must be stored correctly
• Expensive to transport and store H2 as it’s in pressurised containers
• Energy is required to make H2 + O2. Fossil fuels used to pass water through electrolysis which contributes to CO2 emissions