Electrochemical Cells

Question 1

Redox Reaction

Answer 1

Donation of electrons from one substance (the reductant) to another (the oxidant)

Question 2

Displacement Reaction

Answer 2

A type of redox reaction between a more reactive element and a compound containing a less reactive element, resulting the in the less reactive element being displaced from the compound

Question 3

Oxidant (aka oxidising agent)

Answer 3

A substance that causes another to lose electrons

Question 4

Reductant (aka reducing agent)

Answer 4

A substance that causes another to gain electrons

Question 5

Oxidation

Answer 5

The loss of electrons from a substance. Can also be observed as a gain of oxygen, increase in oxidation number or loss of hydrogen.

Question 6

Reduction

Answer 6

The gain of electrons by a substance. Can also be observed as a loss of oxygen, decrease in oxidation number or gain of hydrogen.

Question 7

Half-equation

Answer 7

An equation describing either oxidation or reduction occurring in a redox reaction, along with the corresponding loss or gain of electrons

Question 8

Oxidation Number

Answer 8

A measure of the electron density around an atom, compared to its elemental form. Unlike charge, oxidation numbers have their sign before the value (the sign is always shown)

Question 9

Conjugant oxidant

Answer 9

A substance produced when a reductant loses electrons, containing the element that has increased in oxidation number.

Question 10

Conjugant reductant

Answer 10

A substance produced when an oxidant gains electrons, containing the element that has decreased in oxidation number.

Question 11

Electrochemical Series

Answer 11

A list or table of reduction half-equations written in order of oxidant strength. Usually shows standard electrode potential values for each reduction half-equation.

Question 12

Standard conditions (redox)

Answer 12

Both reactants and products are present for the relevant half-equation. All solutions present in 1M concentration. All gases present at 1atm pressure. All solids pure. Electrode made of the reductant if it is solid and conductive, otherwise an inert electrode such as graphite or platinum.

Question 13

Galvanic cell

Answer 13

A chemical system that produces an electrical current (DC) from a spontaneous redox reaction. Made up of two half-cells, which are two separate containers or two parts of a container that are separated by a porous barrier.

Question 14

Half-cell

Answer 14

An electrode dipped in a solution, where both oxidant and conjugate reductant are present. The electrode may be the reductant or an inert electrode.

Question 15

Anode

Answer 15

The electrode that is the site of oxidation.

Question 16

Cathode

Answer 16

The electrode that is the site of reduction

Question 17

Salt Bridge

Answer 17

A structure containing free-moving unreactive ions, that provides a connection between two half-cells. Often a piece of filter paper soaked in saturated KNO3 solution.

Question 18

Standard Electrode Potential

Answer 18

The relative strength of the oxidant under standard conditions, compared to the H+/H2 half-cell. Measured as the voltage produced when that half cell is connected as the cathode to the H+/H2 half-cell (which has a standard electrode potential of 0V)

Question 19

Standard Cell Potential

Answer 19

The voltage (potential difference) across two half-cells under standard conditions. Calculated as E(cat) - E(an), or alternatively, E(oxidant) - E(reductant).

Question 20

Standard Cell Notation

Answer 20

A written description of a galvanic cell set up under standard conditions, showing both half cells (anode on the left, cathode on the right) separated by a salt bridge (||). Electrodes are shown on either side and phase changes are also shown (|).

Question 21

Electrolytic Cell

Answer 21

A cell that uses an electric current (DC) to force a chemical reaction to occur that would otherwise not happen. Composed of two electrodes in an electrolyte that is commonly an aqueous solution or molten ionic compound.

Question 22

Electrolyte

Answer 22

A solution that conducts electricity due to ions being able to flow past each other. May be a molten ionic compound or a dissolved ionic compound.

Question 23

Electroplating

Answer 23

Using electrolysis to cover (plate) a metal item with another metal in order to improve appearance or reduce corrosion.

Question 24

Electrorefining

Answer 24

The use of electrolysis and an impure anode to plate a pure metal onto the cathode.

Question 25

Corrosion

Answer 25

The disintegration of a metal as a result of a redox chemical reaction

Question 26

Rusting

Answer 26

A specific example of corrosion involving iron.

Question 27

Sacrificial Anode

Answer 27

A more reactive metal in contact with iron, that oxidises preferentially instead of the iron.

Question 28

Storage cell

Answer 28

A galvanic cell in which the reactant chemicals are not replenished and will eventually run out.

Question 29

Oxidation number rules

Answer 29

1. Sum = overall charge.
2. Fluorine is -1 in compounds.
3. Group 1 and 2 metals are +1 and +2 respectively (in compounds)
4. H bonded to non-metals is +1, bonded to metals is -1.
5. O is -2 in compounds, except for peroxides where it is -1.
6. Group 7 are usually -1 in compounds. If >1 halogen is present, the most electronegative is -1.
7. Where no other priority exists, Group 6 NMs are usually -2, Group 15 NMs usually -3 and Group 3 metals usually +3.