Redox + Electrode Potentials

Question 1

reduction

Answer 1

Gain of electrons or decrease in oxidation number

Question 2

Oxidation

Answer 2

Loss of electrons or increase in oxidation number

Question 3

oxidising agent

Answer 3

(Contains species that’s being reduced)

A reagent that oxidises (takes electrons from) another species

Oxidising agent GAINS ELECTRONS

Question 4

Reducing agent

Answer 4

(Contains species that’s being oxidised)

A reagent that reduces (gives electrons to) another species

A reducing agent LOSES ELECTRONS

Question 5

What is oxidation number of an uncombined element

Answer 5

0

Question 6

What is oxidation number of combined H

Answer 6

+1

Question 7

What is oxidation number of combined O

Answer 7

-2

Question 8

What is oxidation number of an ion of an element equal to

Answer 8

It’s ionic charge

E.g. Ca^2+ = +2

Question 9

What is oxidation number of H in metal hydrides

Answer 9

-1

E.g. NaH , CaH2

Question 10

What is oxidation number of O in peroxides

Answer 10

-1

E.g. H2O2

Question 11

What is oxidation number of O bonded to F

Answer 11

+2

E.g. F2O

Question 12

Entropy

Answer 12

The quantitative measure of the degree of disorder in a system (S)

UNITS JK^-1mol^-1

Question 13

The entropy change can be calculated by

Answer 13

sum of product entropies- sum of reactant entropies

Question 14

What are standard conditions

Answer 14

Temperature of 298K, pressure of 100kPa and all solutions have concentrations of 1moldm^3

Question 15

When a metal is in contact with a solution of its ions…

Answer 15

An equilibrium is established where electrons accumulate on surface and the metal develops a NEGATIVE CHARGE

Question 16

the more reactive a metal, the more likely it is to _____ electrons

Answer 16

The more reactive a metal the more likely it is to LOSE electrons

Question 17

What is a half cell

Answer 17

A metal in contact with an aqueous solution of its ions

Question 18

What is an electrochemical cell (aka voltaic cell)

Answer 18

when 2 half cells are connected together

• high resistance voltmeter
• salt bridge of KNO3

Question 19

Why must 2 half cells be kept apart?

Answer 19

If allowed to mix, electrons would flow in an uncontrolled way and heat energy would be released rather than electrical energy

Question 20

metal/ metal ion half cells

Answer 20

Metal rod dipped in solution of its aqueous metal ions

E.g. Zn2+(aq) / Zn(s)

Question 21

ion/ion half cells

Answer 21

Contains ions of the same element in different oxidation states (there’s no solid) A INERT PLATINUM ELECTRODE MUST BE USED

E.g. Fe2+(aq),Fe3+(aq)/ Pt(s)

Question 22

the electrode with the more reactive metal _____ electrons and is ______ this is the ______ electrode

Answer 22

The electrode with the more reactive metal LOSES ELECTRONS and is OXIDISED this is the NEGATIVE electrode

Question 23

the electrode with the less reactive metal _____ electrons and is ______ this is the ______ electrode

Answer 23

The electrode with the less reactive metal GAINS ELECTRONS and is REDUCED this is the POSITIVE ELECTRODE

Question 24

standard electrode potential

Answer 24

of a half cell is the emf of the half cell where a standard hydrogen electrode is used as the reference electrode and is carried out under standard conditions (298K, 100kPa, 1moldm^-3)

Question 25

To compare electrode potentials of half cells they’re compared to the _______

Answer 25

To compare electrode potentials of half cells they’re compared to the STANDARD HYDROGEN ELECTRODE

Question 26

The more negative standard electrode potential value undergoes _______

Answer 26

The more negative standard electrode potential value undergoes OXIDATION

Question 27

The more positive standard electrode potential value undergoes _______

Answer 27

The more positive standard electrode potential value undergoes REDUCTION

Question 28

How to calculate STANDARD CELL POTENTIAL from standard electrode potentials

Answer 28

E cell = E(+ve electrode) - E(-ve electrode)

Reduced-oxidised

E.g. E cell= +0.34 - (-0.76)= 1.10V

Question 29

Cell potential

Answer 29

Potential difference between 2 half cells

Question 30

If G is _______ the reaction is feasible

Answer 30

If G is NEGATIVE (below or equal to 0) reaction is feasible

Question 31

Negative electrode is called

Answer 31

CATHODE

Question 32

Positive electrode is called

Answer 32

ANODE

Question 33

Anion

Answer 33

Negatively charged ion

Question 34

Cation

Answer 34

Positively charged ion