9. Redox processes

Question 1

oxidation is

Answer 1

the loss of hydrogen and electrons
the gain of oxygen

Question 2

reduction is

Answer 2

the gain of hydrogen and electrons
the loss of oxygen

Question 3

for a reaction to be a redox reaction, it must involve

Answer 3

a change in oxidation number

Question 4

oxidising agents

Answer 4

oxidise other species
get reduced

Question 5

reducing agents

Answer 5

reduce other species
get oxidised

Question 6

balancing half equations in neutral solution

Answer 6

check nb of e-

Question 7

balancing half equations in aqeous solutions

Answer 7

1. balance all atoms except H and O
2. add H2O to the side deficient in O to balance O
3. add H+ to the side deficient in H to balance H
4. add e− to the side deficient in negative charge to balance charge

Question 8

overall redox equations never contain electrons – only … have electrons

Answer 8

half- equations

Question 9

balancing redox equations for reactions in acidic / neutral solution

Answer 9

1. separate the reaction equation into oxidation and reduction half-equations
2. balance each half-equation separately
3. combine the two half-equations after multiplying by the appropriate numbers to balance the electrons in each
4. subtract any duplications on left- and right-hand sides

Question 10

the metals in the activity series are arranged in order of

Answer 10

how easily they are oxidised to form positive ions

Question 11

metals high in the activity series displace

Answer 11

those lower in the series from solutions of their salts

Question 12

BOD (biochemical oxygen demand) is defined as

Answer 12

the amount of oxygen used by the aerobic microorganisms in water to decompose the organic matter in the water over a fixed period of time (usually 5 days) at a fixed temperature (usually 20°C)

Question 13

oxidation happens at the

Answer 13

anode

Question 14

reduction happens at the

Answer 14

cathode

Question 15

in a voltaic cell, the anode is the

Answer 15

negative electrode

Question 16

in a voltaic cell, the cathode is the

Answer 16

positive electrode

Question 17

electrolysis is

Answer 17

the breaking down of a substance (in molten state or solution) by the passage of electricity through it

Question 18

differences between voltaic cell and electrolytic cell

Answer 18

Question 19

the standard cell potential is

Answer 19

EMF (voltage) produced when two half-cells are connected under standard conditions

Question 20

standard hydrogen electrode

Answer 20

hydrogen gas at 100kPa
platinum electrode of high surface area
solution of H+ ions of c 1mol/dm3

Question 21

standard electrode potential

Answer 21

EMF (voltage) of a half-cell connected to a standard hydrogen electrode, measured under standard conditions

Question 22

in general, the procedure for calculating a cell potential is

Answer 22

1. write down the half-equations
   and standard electrode potentials for the two reactions involved
2. change the sign of the more negative (less positive) standard electrode potential and add it to the other electrode potential

Question 23

a positive value for cell potential indicates

Answer 23

a spontaneous reaction

Question 24

whichever half-cell has
the more negative standard electrode potential will be the negative electrode in the cell, and the electrons will flow from this half-cell to the other one

Question 25

the more positive the standard electrode potential

Answer 25

the stronger the oxidising agent

Question 26

the more negative the standard electrode potential

Answer 26

the stronger the reducing agent

Question 27

a substance with a more positive standard electrode potential will

Answer 27

oxidise a substance with a less positive electrode potential

Question 28

a substance with a more negative standard electrode potential will

Answer 28

reduce a substance with a less negative standard electrode potential

Question 29

reactive (with very negative standard electrode potentials) metals produce

Answer 29

hydrogen when aqueous solutions of their ions are electrolysed

Question 30

unreactive metals (with positive standard electrode potentials) produce

Answer 30

the metal when aqueous solutions of their ions are electrolysed

Question 31

at low concentrations of halogen, … is produced
at high concentration, the halogen is produced

Answer 31

oxygen

Question 32

in electroplating, the object to be coated should be at the

Answer 32

cathode