Reactivity 3.2

Question 1

Oxidation

Answer 1

An increase in oxidation state

Question 2

Reduction

Answer 2

A decrease in oxidation state

Question 3

Disproportionation

Answer 3

When the same element is oxidised and reduced simultaneously during the same reaction

Question 4

LEO says GER

Answer 4

Loss of electrons is oxidation
Gain of electrons is reduction

Question 5

Oxidising agent

Answer 5

Substance that is easily reduced

Question 6

Reducing agent

Answer 6

Substance that is easily oxidised

Question 7

How does the activity series work

Answer 7

Metals higher in the series can displace ions of metals lower in the series

Question 8

Numonic for reactivity series

Answer 8

Please (potassium)
Stop (sodium)
Calling (calcium)
Me (magnesium)
A (aluminium)
Careless (carbon)
Zebra (zinc)
Instead (iron)
Try (tin)
Learning (lead)
How (hydrogen)
Copper
Saves (silver)
Gold

Question 9

Potassium manganate redox equation

Answer 9

MnO4 - + 8H+ 5e -> Mn2+ + 4H2O

Question 10

Sodium thiosulfate solution redox equation

Answer 10

2S2O3 2- -> S4O6 2- + 2e

Question 11

Radio when the Winkler method (BOD) is used

Answer 11

1 mol of dissolved oxygen to 4 mol of thiosulfate ions (S2O3 2-)

Question 12

How do voltaic cells produce energy?

Answer 12

Electrons transferred during a redox reaction produce energy in the form of electricity

Question 13

What type of reaction occurs in a voltaic cell?

Answer 13

Spontaneous exothermic redox reaction

Question 14

The higher the metal is in the reactivity series, what is it likely to do in a voltaic cell?

Answer 14

Lose electrons and be the negative anode

Question 15

What happens to the anode in a voltaic cell?

Answer 15

It is oxidsed and loses electrons which flow to the anode

Question 16

What happens to the cathode in a voltaic cell

Answer 16

It is reduced and gains electrons.

Question 17

What does the salt bridge do?

Answer 17

Allows the flow of ions between the solutions to mantain neutrality

Question 18

How can you draw a cell diagram?

Answer 18

Single line is boundary between phases, double line is salt bridge. Written as anode metal, anode ion, cathode ion, cathode metal

Question 19

Battery

Answer 19

Portable electrochemical cell (voltaic or galvanic) which convert chemical energy to electrical energy

Question 20

Primary cell

Answer 20

Can only be used once as the electrochemical redox reaction cannot be reversed

Question 21

Secondary cell

Answer 21

Can be recharged as the redox reactions involved can be reversed using electricity.

Question 22

Fuel cells

Answer 22

Reactants are continually added as the redox reaction takes place. Gives a continuous supply of electricity. Don’t need an external source of electricity as they are recharging and non-polluting.

Question 23

How is voltage worked out?

Answer 23

Difference between the electrical potentials of the two half cells. Depends on nature of materials used.

Question 24

Lead acid battery (anode Pb and cathode PbO2) anode reaction

Answer 24

Pb + HSO4 -> PbSO4 + H + 2e

Question 25

Lead acid battery (anode Pb and cathode PbO2) cathode reaction

Answer 25

PbO2 + HSO4 +3H + 2e -> PbSO4 + 2H2O

Question 26

Overall lead acid battery reaction

Answer 26

Pb + Pb)2 + 2H2SO4 -> 2PbSO4 + 2H2O

Question 27

What is the disadvantage of a lead acid battery reaction?

Answer 27

They are heavy and both lead and sulfric acid are polluting

Question 28

Electrolytic cell

Answer 28

Energy is provided externally in the form of electricity to prompt a non-spontaneous reaction. Electrolyte allows passage of electricity and ions that are free to move.

Question 29

Where is the anode in voltaic and electrolytic cells?

Answer 29

Anode is the negative electrode in voltaic cells and the positive electrode in electrolytic cells

Question 30

Why must electrodes be molten?

Answer 30

In solid state, salts do not conduct electricity as ions are in a lattice. In the molten state, they conduct through the movement of ions.

Question 31

Advantages and disadvantages of primary cells

Answer 31

Advantages - low cost, light, long life, high energy density Disadvantages - single use, wasteeful

Question 32

Advantages and disadvantages of secondary cells

Answer 32

Advantages - reusable, high power density, can be used at low temps Disadvantages - poor charge retention and safety issues

Question 33

Advantages and disadvantages of fuel cells

Answer 33

Advantages - energy efficient, environmentally friendly Disadvantages - expensive, H gas is difficult to store and needs a continuous supply of reactants