Redox

Question 0

A redox reaction is one where

Answer 0

Both oxidation and reduction take place

Question 1

Oxidation number of an uncombined element

Answer 1

0

Question 2

Oxidation number of combined oxygen

Answer 2

-2

Unless in H2O2

Question 3

Oxidation number of combined hydrogen

Answer 3

+1

Question 4

Define oxidation number

Answer 4

A measure of the number of electrons that an atom uses to bond with atoms of another element

Question 5

Define oxidising agent

Answer 5

A reagent that oxidises another species

Question 6

Define reducing agent

Answer 6

A reagent that reduces another species

Question 7

Half reactions show…

Answer 7

Reduction or oxidation only

Question 8

Define oxidation

Answer 8

A loss of electrons, or an increase in oxidation number

Question 9

Define reduction

Answer 9

A gain of electrons, or a decrease in oxidation number

Question 10

Define standard electrode potential

Answer 10

The emf of a half cell compared with the standard hydrogen half cell, measured at 298K with solution concentrations of 1moldm^-3 and a gas pressure 1atm

Question 11

Describe a metal/metal ion half cell eg Zn/Zn2+

Answer 11

A zinc strip is placed in a solution of Zn2+ (aq) (1moldm^-3)

Question 12

Describe a standard hydrogen half cell

Answer 12

A platinum electrode, which is surrounded by a glass tube with holes in to allow bubbles of H2(g) to escape, is placed in a beaker of acid solution containing 1moldm^-3 H+(aq)
H2(g) is pumped into the glass tube from the top at 298K and 1atm

Question 13

Describe a metal ion/metal ion half cell

Answer 13

A platinum electrode is placed in a solution containing equal concentrations of Fe2+ (aq) and Fe3+ (aq)

Question 14

What does a negative electrode potential tell you about the half cell?

Answer 14

It undergoes oxidation (releases electrons) when connected to a hydrogen half cell

Question 15

What does a positive electrode tell you about a half cell?

Answer 15

The half cell undergoes reduction (accepts electrons) when connected to a hydrogen half cell

Question 16

Which half equation gets reversed when working out full equations of reactions from half equations and their electrode potentials

Answer 16

The equation with the more negative electrode potential

Question 17

What are the limitations of predictions made using standard electrode potentials?

Answer 17

Non-standard conditions alter the value of the electrode potential:
Changes in concentration
Many reactions may not take place in the aqueous state, or at room temperature
The rate of reaction may be extremely slow because of a high activation energy

Question 18

What are the 3 main types of modern-day cells and batteries?

Answer 18

Non-rechargeable cells
Rechargeable cells
Fuel cells

Question 19

A fuel cell…

Answer 19

Uses the energy from the reaction of a fuel with oxygen to create a voltage

Question 21

What half equation takes place at the negative terminal of a hydrogen-oxygen fuel cell?

Answer 21

2H2O(l) + 2e- H2(g) + 2OH-(aq)

Question 21

Scientists in the car industry are developing fuel cell vehicles fuelled by…

Answer 21

Hydrogen gas and hydrogen-rich fuels

Question 22

What are the advantages to using fuel cell vehicles?

Answer 22

Less pollution and less CO2

Greater efficiency

Question 23

What half equation takes place at the positive terminal of a hydrogen-oxygen fuel cell?

Answer 23

1/2O2(g) + H2O(l) + 2e- 2OH-(aq)

Question 24

How might hydrogen be stored in fuel cell vehicles?

Answer 24

As a liquid under pressure
Adsorbed on the surface of a solid material
Adsorbed within a solid material

Question 25

What are the limitations of hydrogen fuel cells?

Answer 25

The feasibility of storing a pressurised liquid
Current absorbers and adsorbers of hydrogen have a limited lifetime
Fuel cells use toxic chemicals in their productions
Storing and transporting hydrogen is expensive and requires a lot of energy
Current fuel cells have a limited lifetime, requiring regular replacement and disposal following high production costs

Question 27

What are the limitations of a hydrogen economy?

Answer 27

Public and politic acceptance of hydrogen as a fuel
Handling and maintenance of hydrogen systems
Initial manufacture of hydrogen, requiring energy