UNIT 1 Section 9 - Electrode Potentials

Question 1

what is a half cell

Answer 1

one half of an electrochemical cells which is an electrode with its aqueous ions in solution

Question 2

what is an electrochemical cell

Answer 2

consisting of two half cells, a voltmeter, a salt bridge where one half cell undergoes oxidation and the other half cell undergoes reduction as the electrons flow from a more reactive metal to a less reactive one

Question 3

what is emf

Answer 3

the potential difference between 2 half cells

Question 4

what is the electrode potential a measurement of

Answer 4

how easily a half cell gives up electrons and oxidised

Question 5

how are the equations in the electrochemical series written

Answer 5

the reduced form is written in the forwards reaction

Question 6

what does a negative and positive electrode potential mean for electrochemical cells and what occurs because of this

Answer 6

The most negative will undergo oxidation (lose)

The most positive undergoes reduction (gain)

Question 7

what is the standard hydrogen electrode used for

Answer 7

used as a reference to measure standard electrode potential as half cells cant be measured on their own

Question 8

what are the standard conditions of a hydrogen electrode

Answer 8

• 298K temp
• 100kPa pressure
• 1 moldm-3 concentration of ions

Question 9

in the equations in the electrochemical series which side are the oxidising agents and which side are the reducing agents and is it the more or less negative

Answer 9

left oxidising agent- most positive

right is reducing agent- most negative

Question 10

how do you work out the electrode potential of a cell with the electrochemical series

Answer 10

electrode potential of the reduced half cell - electrode potential of the oxidised half cell

Question 11

outline how we do cell notation

Answer 11

R/O//OR
the lines represent different states but if they are the same state use a comma

the // represents the salt bridge

the most negative half cell goes on the left of the salt bridge

Question 12

hoe can you predict the feasibility of a reaction using standard electrode potentials

Answer 12

1. take the oxidised equation and reverse it so both equations have reduction going in the forwards direction
2. combine the equations and that is your feasible reaction
3. compare the equation of feasibility with the equation given in the question and see if they match are it is feasible
4. to check if the electrode potential of the equation in the questions is positive it is feasible

Question 13

what is a battery

Answer 13

electrochemical cell

Question 14

name a rechargeable cell and what is the strcuture of it

Answer 14

lithium ion battery

• has positice lithium colbalt oxides for the first electrode dipped in lithium ions
• negative carbon electrode like graphite dipped in
• a porous polymer membrane electrolyte

Question 15

what is the role of an electrolyte in a battery

Answer 15

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

Question 16

how do rechargeable electrons charge

Answer 16

plugging them into a supply of current and this forces the electrons to flow in the opposite way and therefore reverses the overall discharge equation

Question 17

what is different about fuel cells and batteries

Answer 17

fuel cells need a continuous external supply of chemicals rather than a ready store like batteries and the supply is external

Question 18

outline the advantages of fuel cells

Answer 18

+ more efficient
+ more energy is converted into kinetic energy and less waste on thermal energy
+ don’t need to recharge them
+ only waste product is water

Question 19

outline the disadvantages of fuel cells

Answer 19

• hydrogen is highly flammable and must be stored and transported correctly making it expensive and it has to be transported in pressurised containers
• energy is required to make the hydrogen and oxygen used and that normally comes from hydrolysis which uses fossil fuels

Question 20

how does a fuel cell work

Answer 20

1. hydrogen is fed into the cell and reacts with the OH- ions to form water and 4 e-
2. the electrons then go to the platinum electrode and are used to power something
3. oxygen is fed in on the other side and reacts with the water and 4 e- to produce OH- ions again
4. the electrons flow to the negative electrode which is also made from platinum
5. the electrolyte made from the KOH carry the OH- ions formed from the cathode to the anode
6. water is eliminated by being released into the surroundings as gas

Question 21

Where are lithium batteries often found

Answer 21

Phone tablets and power tools

Question 23

What are the half equations of the lithium ion battery cell

What is the overall equation

Answer 23

Li ——> Li+ + e-
Li+ + CoO2 + e- —> Li+[CoO2]-

Li + CoO2 ——> Li+[CoO2]-

Question 24

Why is lithium used in the lithium ions battery

Answer 24

Very low density and relatively high electrode potential