Redox And Electrode Potentials

Question 1

Define oxidising agent

Answer 1

A substance that oxidises another species but is reduced its self (electron acceptor)

Question 2

How do you balance an equation using oxidation numbers

Answer 2

Identify species whose ON change and balance to make chage in ON of both cancel out

Eg

+5
-1

Multiply species 2 by 5 to get - 5

Question 3

Manganate 7 ion

Answer 3

MnO4-

Question 4

What is a voltaic cell

Answer 4

A cell that converts chemical energy to electrical energy

Question 5

What is a half cell

Answer 5

Metal rod in ion solution

Platinum electrode in solution of ions

Question 6

Why are half cells kept apart

Answer 6

So electron flow is controlled to prevent energy loss via heat

Question 7

Describe a metal/metal half cell

Answer 7

Metal rod in 1M solution of its own ions

Question 8

How is the equilibrium of a half cell always written

Answer 8

Reduction!/ gain of electrons

Question 9

Describe an ion/ion half cell

Answer 9

Platinum rod in 1M solution of different ions

Question 10

What species makes the anode

Answer 10

More reactive metal

Loses electrons easier so oxididises easier

Question 11

Define standard electrode potential

Answer 11

Potential difference of half cell compared to standard hydrogen half cell under standard conditions

Question 12

What are standard conditions

Answer 12

100Kpa
1 moldm^-3
25°c

Question 13

What half cell will be the anode

Answer 13

The half cell with the lowest electrode potential

Loses electrons

Question 14

How do you calculate the electrode potential of the cell

Answer 14

Electrode potential of cathode – electrode potential of anode

Question 15

How do you write overall equations for cells

Answer 15

Write reduction and oxidation equations

Multiply if necessary to make electrons balance

Cancel out electrons and combine

Question 16

How can the electrode potential be used the predict the feasibility of a reaction

Answer 16

> 0 =feasible

Question 17

What are the limitations of using electrode potentials to predict feasibility

Answer 17

Gives no indication of rate of reaction

Standard conditions may not be used

Question 18

What is a storage cell

Answer 18

Two half cells joined together

Batteries you buy in shop

Question 19

What are the types of storage cells

Answer 19

Primary and secondary

Question 20

Describe a primary storage cell

Answer 20

Non-rechargeable with a non-reversible redox reaction

Low voltage and long storage uses

Question 21

Examples of primary cells

Answer 21

Smoke alarms
Wall clocks
Zinc manganate with ammonium electrolyte

Question 22

Describe secondary cells

Answer 22

Rechargeable with reversible redox reaction

Question 23

Examples of secondary cells

Answer 23

Lithium ion (laptops and mobiles)
Lead acid (car batteries)
Nickel and cadmium (radios and torches)

Question 24

How do fuel cells work

Answer 24

Energy released by fuel reacting with oxygen

Question 25

What is the main difference between fuel and storage cells

Answer 25

Fuel cells are open systems

Question 26

How are the electrodes seperated in a fuel cell

Answer 26

By a polymer exchange membrane

Question 27

What are the two types of fuel cells

Answer 27

Alkali and acid electrolyte

Question 28

What are the advantages of using methanol instead of hydrogen in a fuel cell

Answer 28

Methanol is less volatile so easier to transport

Higher hydrogen density

Methanol is already made

Methanol is made from carbon dioxide but hydrogen is made from the electrolysis of water using fossil fuels

Question 29

What ions are used to predict feasibility

Answer 29

Vanadium and manganate