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A Level Chemistry > Redox and Electrode Potentials > Flashcards

Redox and Electrode Potentials Flashcards

1
Q

What does the term ‘redox’ refer to?

A

Reactions involving both reduction and oxidation

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2
Q

What is oxidation

A

The process of losing electrons

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3
Q

What is reduction

A

Process of gaining electrons

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4
Q

What is the oxidising agent

A

The electron acceptor

Is itself reduced

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5
Q

What is the reducing agent

A 
Electron donor
(Is itself oxidated)
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6
Q

What is the oxidation number of an atom in an uncombined element

A

Zero

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7
Q

For groups 1,2,3 what is the oxidation number equal to

A

It’s valency

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8
Q

What is the sum of the oxidation numbers in a

a) neutral molecule?
b) compound ion

A

a) zero

b) equal to the charge of the ion

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9
Q

What is the oxidation state of hydrogen in metal hydrides?

A

-1

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10
Q

When calculating oxidation state do you include the mole number

A

NO

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11
Q

An increase in oxidation state in reduction. True or false

A

False

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12
Q

A decrease in oxidation state is reduction. True or false?

A

True

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13
Q

3 basic steps when writing an overall equation

A

Write 1/2 equations
Balance electrons
Combine equations and cancel electrons

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14
Q

When writing an overall equation which 1/2 equation is reversed?

Why?

A

The more negative one

They are string reducing agents

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15
Q

What solid is used if there isn’t one in the 1/2 equation

A

A platinum electrode

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16
Q

Why is platinum used as an electrode

A

Conducts electricity

Unreactive

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17
Q

Why is KCl not used as a salt bridge for a cell that contains Ag+ ions?

A

KCl contains Cl- ions which react with Ag+ ions to make AgCl forming a white precipitate

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18
Q

What concentration must electrode solutions have?

A

1 mol/dm3

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19
Q

In the electrochemical series which is the strongest reducing agent?

A

Product with most negative emf value

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20
Q

In an electrochemical series what is the weakest reducing agent

A

Product with most positive emf value

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21
Q

In an electrochemical series which is the strongest oxidising agent

A

The reactant with the most positive emf value

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22
Q

In an electrochemical series which is the weakest oxidising agent ?

A

The reactant with the most negative emf value

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23
Q

What are the conditions of a standard hydrogen electrode

A

HCl with concentration of 1 mol/dm3
100kPa, 298K
H2(g)
Pt(s) electrode

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24
Q

When drawing a diagram of an electrochemical cell what 5 things must be included

A

1) voltmeter
2) salt bridge
3) beaker
4) metal electrode
5) 1 mol/dm3 (ion) solution

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25
What hints will a question on redox give if there is more than one set of oxidation/ reduction reactions occurring?
It will mention an ‘excess’ of a reagent or ask for the ‘final oxidation/ reduction product’
26
What is emf
Electromotive force: the potential difference across the two electrodes
27
The emf of a cell=
E0 (reduction) - E0 (oxidation)
28
Generally which side electrode is negative? | Does this one show reduction or oxidation?
Left | Oxidation
29
Generally, the half cell showing reduction is the ____ electrode
Right (positive)
30
What does a positive emf value mean?
The reaction is feasible | A negative value means it is not feasible
31
The more positive a emf value the _____ feasible the reaction
More
32
What is the template for the “use the data from the table...” questions?
E0 __ /___ > E0 ___ / ___ | Therefore _____ is reduced to _____ and _____ is oxidised to ____
33
What does a single line in a conventional cell diagram represent?
A phase boundary | It separates substances in different states
34
What is used in a conventional cell diagram to separate cell components in the same phase
A comma
35
What does a double line represent in a conventional cell diagram?
The salt bridge
36
What is the species on the left side of the cell diagram? | Which electrode is this?
The species being oxidised | The negative electrode
37
The species on the right hand side of a cell diagram is reduced. True or false
True
38
What are not included in a cell diagram?
H+, H20, and e-
39
What must be added to a cell diagram if there is no solid in the 1/2 equation to act as an electrode?
Pt(s)
40
What is a generic layout of a cell diagram
Reactant | Product || Reactant | Product
41
When are H+ and H20 sometimes includes in a cell diagram
If they are the species that are changing oxidation states
42
When measuring the emf of a 1/2 cell, on what appears on the left side of the conventional cell diagram
The standard hydrogen electrode
43
How does changing concentration affect the emf value
Causing the equilibrium to shift in the oxidation direction (creating electrons) will make the emf more negative as it has a greater potential to release electrons Causing the equilibrium to shift in the reduction direction (losing electrons) will make the value more positive as it now has a greater potential to accept electrons
44
How does changing the emf of a 1/2 equation affect the emf of the cell
Emf (cell)= emf (reduction) - emf (oxidation) So if the reduction value becomes more positive the cell’s emf value becomes more positive. If the oxidation value becomes more positive the emf of the cell becomes more negative
45
Why is the Zn/Cu cell non-rechargeable
The Zn electrode starts to run out so the reaction can’t be reversed The solutions also make it impractical for transport
46
In a Zinc/ Carbon cell, what is the positive and negative electrode
The zinc is the negative electrode and acts as a case and has a paste electrolyte solution Carbon acts as positive electrode and is located as a rod down the centre of the canister. It behaves like the Pt(s) in the hydrogen cell
47
Why does a cell leak after along time
Zn oxidised to Zn2+, causing the case to wear away
48
Name one essential property of the non-reactive porous separater
Allows movement of electrons
49
How do rechargeable batteries work?
The current (electrons) can be forced back in the opposite direction by an applied current
50
How do you apply a current to a rechargeable battery
Plugging it in
51
What happens to the 1/2 equations when a cell is recharged
They are reversed | The more negative equation is the reduction reaction
52
How are rechargeable batteries designed differently
The electrodes do not decompose or wear down as quickly They are also small, light, and portable
53
What does the hydrogen fuel cell consist of
Two platinum electrodes separated by a special polymer electrolyte which will allow ions to pass through it
54
What are the two 1/2 equations in acidic conditions for the hydrogen fuel cell
H2(g) —> 2H+(aq) + 2e- 4H+(aq) + O2(g) + 4e- —> 2H2O(l)
55
What are the two 1/2 equations for the hydrogen fuel cell in alkaline conditions
H2(g) + 2OH- —> 2H2O(aq) + 2e- 2H2O(aq) + O2(g) + 4e- —> 4OH-(l)
56
What is the motor in a hydrogen fuel cell powered by
The movement of electrons
57
When does a fuel cell need to recharge
Never
58
Why does a fuel cell not need recharging
There is a continuous supply of fuel therefore the concentrations remain the same
59
What are the conditions inside a fuel cell
Acidic
60
What are the advantages of using a hydrogen fuel cell
Very efficient compared to internal combustion engines Generates electricity directly so minimal wasted energy compared to internal combustion engines
61
What are the disadvantages of a hydrogen fuel cell
Hydrogen is flammable Hydrogen can only be made on a large scale from fossil fuels or electrolysis of water. Both release CO2
62
What is the advantage of a fuel cell over a rechargeable battery
Fuel cell doesn’t need to be recharged
63
How does the emf vs time graph look for a rechargeable battery
Steel negative gradient immediately before quickly levelling out. Curves downwards towards the end
64
What does the emf vs time graph for a fuel cell look like
Straight horizontal line as concentration remains constant
65
Use the hydrogen fuel cell 1/2 equations to explain how an electric current can be generated
H2 electrode produces e- | O2 electrode accepts e-
66
What is a salt bridge
Filter paper soaked in SATURATED solution of KNO3
67
Acid/ base reaction in absence of water
Acid + base —-> salt
68
Reaction of Mg and steam
MgO
69
How can you identify the positive electrode in an electrochemical cell
When the cell is set up, if the reading on the voltmeter is positive then the metal connected to the positive terminal on the voltmeter is the positive electrode If the reading is negative then the metal connected to the negative terminal is the positive electrode
70
Explain why a piece of wire is not used instead of a salt bridge
No current would flow between half cells using a wire so electrode potential could not be measured
71
Function of a salt bridge
Allows flow of electrons to complete the electrical circuit whilst keeping solutions separate

A Level Chemistry (11 decks)

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