redox

pass chem

oxidation definitions

1. gain of oxygen

2. loss of hydrogen

3. loss of electrons

4. increase in oxidation number

OIL

the general equation is: X(s) --\> X+(aq) + e-(aq)

reduction definitions

1. gain of hydrogen

2. loss of oxygen

3. gain of electrons

4. decrease in oxidation number

RIG

the general equation is: X+(aq) + e-(aq) --\> X(s)

Oxidation Number Rules

1. atoms in elemental form always \= 0

2. monoatomic ion always \= charge of ion

3. oxygen usually \= -2, except in peroxides \= -1

4. hydrogen \= +1 (non-metals) and \= -1 (metals)

5. fluorine \= -1

6. sum of OS in neutral compounds \= 0

7. sum of OS in polyatomic ions \= charge of ion

which reactions are redox and which are not redox

redox:

acid + metal

displacement reactions of halogens

not redox:

acid + alkali (neutralisation)

acid + carbonate

base + ammonium salt

What is a disproportionation reaction?

Where a single element is simultaneously oxidised and reduced at the same time to form 2 different products

answering technique: X is being oxidised and reduced at the same time to form A and B.

X is oxidised as oxidation state increased from \__ in X to \__ in A.

X is reduced as oxidation state decreased from \__ in X to \__ in B.

Definition of Oxidising Agent

Substance that oxidises another and is itself reduced in the process

Definition of Reducing Agent

Substance that reduces another and is itself oxidised in the process

oxidising agents

1. KMnO4: purple solution turns colourless

2. chlorine with halogens

w/ bromine: colourless solution turns orange

w/ iodine: colourless solution turns brown

reducing agents

1. KI: colourless solution turns brown

2: reactive metals: less reactive metal produced (displacement to form deposit --\> recall in QA the deposit colours)

3. hydrogen: reddish-brown solid (Cu) is formed (reduces CuO to Cu)

reactions of metals with water, steam, acid

water: metal hydroxide + hydrogen

steam: metal oxide + hydrogen

acid: salt + hydrogen

reactions of potassium

water: reacts very violently to form KOH and H2. H2 burns with a lilac flame

steam: - (too dangerous, will explode)

acid: explosive reaction

reactions of sodium

water: reacts violently to form NaOH & H2. H2 may catch fire and burn with a yellow flame

steam: - (too dangerous, will explode)

acid: explosive reaction

reactions of calcium

water: reacts readily to form Ca(OH)2 & H2

steam: - (too dangerous, will explode)

acid: reacts violently

reactions of magnesium

water: reacts very slowly to form Mg(OH)2 & H2

steam: reacts violently to form MgO & H2. Bright white glow produced

acid: reacts rapidly

reactions of zinc

water: -

steam: reacts readily to form ZnO + H2

acid: moderately fast

reactions of iron

water: -

steam: reacts slowly to form FeO + H2

acid: reacts slowly

reactivity series

Potassium (please)

sodium (stop)

calcium (calling)

magnesium (me)

aluminium (a)

carbon (cute)

zinc (zebra)

iron (I)

lead (like)

hydrogen (hot)

copper (cute)

silver (sexy)

gold (guys)

reduction of potassium oxide with carbon and hydrogen

carbon: not reduced

hydrogen: not reduced

reduction of sodium oxide with carbon and hydrogen

carbon: not reduced

hydrogen: not reduced

reduction of calcium oxide with carbon and hydrogen

carbon: not reduced

hydrogen: not reduced

reduction of magnesium oxide with carbon and hydrogen

carbon: not reduced

hydrogen: not reduced

reduction of aluminium oxide with carbon and hydrogen

carbon: not reduced

hydrogen: not reduced

reduction of zinc oxide with carbon and hydrogen

carbon: reduced to metal and CO

hydrogen: not reduced

reduction of iron oxide with carbon and hydrogen

carbon: reduced to form metal and CO

hydrogen: reduced to form metal and steam

reduction of lead (ii) oxide with carbon and hydrogen

carbon: reduced to form metal and CO

hydrogen: reduced into metal and steam

reduction of copper (ii) oxide with carbon and hydrogen

carbon: reduced to form metal and CO2

hydrogen: reduced into metal and steam

reduction of silver oxide with carbon and hydrogen

carbon: can be reduced via heating w/o any reducing agent

hydrogen: reduced into metal and steam

displacement reactions of metals

more reactive metals will displace less reactive metals (greater tendency to lose electrons)

the more reactive metal will become compound while the less reactive metal stays as the metal

What is rusting?

The corrosion of iron (& steel) due to the reaction of iron with air in the presence of water

forms reddish-brown substance AKA hydrated iron (iii) oxide

equation: 4Fe(s) + 3O2(g) + 2XH2O(l) --\> 2FeO3·xH2O(s)

Ways to prevent rusting

painting, electroplating or greasing, sacrificial protection, galvanising (electroplating & sacrificial protection)

sacrificial protection answering technique

A is more reactive than B. A oxidises more readily than B. A corrodes in place of B.