electrochemical cells

Question 1

What is a half cell?

Answer 1

half an electrochemical cell, made up of an electrode (platinum or using the metal itself) in a solution containing aqueous ions

Question 2

What makes up an electrochemical cell?

Answer 2

2 half cells
salt bridge
voltmeter
wire

Question 3

What does the salt bridge contain?

Answer 3

KNO3/NaNO3

Question 4

What is the role of the salt bridge?

Answer 4

allows the transfer of ions/charge

Question 5

What is the electrode potential of a cell?

Answer 5

a value that tells us how easily the half cell is to be oxidised

Question 6

What will the most negative half cell undergo?

Answer 6

oxidation

Question 7

What will the most positive half cell undergo?

Answer 7

reduction

Question 8

whats SHE

Answer 8

Standard Hydrogen Electrode
used as a reference for electrode potential values

Question 9

What is the set up of the SHE?

Answer 9

Pt electrode
1mol dm3 H+ ions in solution
298K
100kPa

Question 10

What are the standard conditions for electrochemical cells?

Answer 10

100kPa
298K
1 mol dm-3 ions

Question 11

What is the function of the porous separator in a chemical cell (battery)?

Answer 11

salt bridge - allows transfer of ions

Question 12

What happens to the chemical reaction when a cell is recharged?

Answer 12

it is reversed

Question 13

Why are some chemical cells non-rechargeable?

Answer 13

reaction cannot be reversed
reaction produces a gas

Question 14

Why does the metal case of some chemical cells break down over time?

Answer 14

the metallic case is a reactant and gets used up

Question 15

What happens to cell emf over time?

Answer 15

decreases as reactants get used up

Question 16

Which half cell is on the left?

Answer 16

half cell with most - electrode potential

Question 17

What is the equation showing the positive electrode in a lithium ion cell?

Answer 17

Li+(aq) + CoO2(s) + e- –> Li+CoO2- (aq)

Question 18

What is the equation showing the negative electrode in a lithium ion cell?

Answer 18

Li(s) –> Li+(aq) + e-

Question 19

What is the standard cell representation for a lithium ion cell?

Answer 19

Fe / Li+ / Li // Li+ / CoO2 / Li+CoO2- / Fe

Question 20

What is the discharge equation for a lithium ion cell?

Answer 20

Li (s) + CoO2 (s) –> Li+CoO2- (aq)

Question 21

What metals make up a Daniell cell?

Answer 21

Zn and Cu

Question 22

How is cell emf calculated from electrode potentials?

Answer 22

right - left

Question 23

What is an electrochemical series?

Answer 23

list of electrode potentials in numerical order

Question 24

What is one property a salt bridge MUST have?

Answer 24

must not react with the electrolyte/ions in solution

Question 25

Why would a salt bridge containing a carbonate ion not be suitable for use (when H+ is present)?

Answer 25

carbonate ions will react with acid

Question 26

What are 2 advantages of using Hydrogen Fuel Cells compared to using hydrogen in combustion?

Answer 26

HFCs: - less energy wasted as thermal energy - reaction happens at low temperatures

Question 27

What are the half equations for a hydrogen-oxygen fuel cell operating in alkaline conditions? Use these half equations to explain how an electric current can be generated

Answer 27

O2 + 2H2O + 4e- ⎯→ 4OH- H2 + 2OH- ⎯→ 2H2O + 2e- Oxygen electrode gains electrons (is reduced), hydrogen electrode loses electrons (is oxidised)

Question 28

Why does a hydrogen fuel cell does not need to be recharged?

Answer 28

emf is constant (given that supply of reactants is constant)

Question 29

What is one major hazard associated with the use of a hydrogen–oxygen fuel cell in a vehicle?

Answer 29

hydrogen is flammable/ explosive

Question 30

What would happen to the cell emf if the surface area of the electrodes was increased?

Answer 30

no change / nothing

Question 31

What are the advantages of using hydrogen fuel cells?

Answer 31

-constant emf as long as reactant supply is constant -works at room temperature so low thermal energy loss (compared to burning hydrogen) -produces H2O as by-product, no greenhouse emissions or other pollutants such as NOx, SO2 (be specific)

Question 32

What are the disadvantages of using hydrogen fuel cells?

Answer 32

-little hydrogen infrastructure in place (petrol stations) -production of H2 currently energy intensive (produces greenhouse gases in power stations) -storage of hydrogen is difficult and dangerous (explosive gas)

Question 33

what do you do to most negative half cell

Answer 33

flip equation

Question 34

wheres oxidising agents in table

Answer 34

left hand side

Question 35

wheres reducing agent in table

Answer 35

right hand side

Question 36

strongest oxidising agent and weakest reducing agent

Answer 36

most + sep

Question 37

weakest oxidising agent and strongest reducing agent

Answer 37

most - sep

Question 38

e cell equation

Answer 38

reduced - oxidised positive - negative right-left

Question 39

when is pt electrode used

Answer 39

2 non metal half cells used