Redox Reactions

What is a redox reaction at its simplest?

A transfer of electrons

What happens to electrons in an oxidation reaction?

Loses electrons (OiL) and becomes more positively charged, becomes an electron donor

What happens to electrons in a reduction reaction?

Gains electrons (RiG) and becomes more negatively charged, becomes an electron acceptor

What is an oxidising agent/oxidant?

Undergoes reduction and gains electrons

What is a reducing agent/reductant?

Undergoes oxidation and loses electrons

What is the oxidant/reductant in the following reaction?

2Na(s) + Cl2(g) —> 2NaCl(s)

Oxidant: Cl2(g)

Reductant: Na(s)

Oxidation number rules

Elements = 0

Monatomic ions = charge on ions

Oxygen = 2- (except peroxides (-1) and F2O (+2))

Hydrogen = +1 (except metal hydrides (-1))

Polyatomic species = charge on ion

Neutral molecule/compound total = 0

What is the oxidation number of Cl in HClO4?

H = +1, 4 x O = -8

1-8-Cl

-Cl = -7

Cl = 7

What happens when the oxidation number of an atom increases?

Oxidation

What happens when the oxidation number of an atom decreases?

Reduction

What is disproportionation?

When a substance oxidised and reduces itself in the same reaction

What is redox displacement?

One substance displaces ions of a different substance from the solution

What is the trend for halogen oxidising strength?

Decrease moving down the periodic table (F is strongest, I is weakest)

How do you know if a halogen displacement reaction will occur?

A halogen will oxidise a halogen ion (halide) lower on the list

Ie: Cl2 will oxidise Br- and I- but not F-

What does the reactivity of metals tell us?

The more reactive an element, the more it will donate e-

How do you know if a metal displacement will occur?

A metal will reduce a metal ion which is higher in the activity series

What halogen has the highest reduction potential?

F-

And the lowest?

I-

How does this trend work?

F can oxidise Cl-, Br- and I-, but not the other way around

What is a primary cell?

A cell where the spontaneous redox reactions cannot be reversed

What are secondary cells?

A cell which can be recharged by passing a current through them to revert products into reactants

What is a fuel cell?

Reactants are supplied continuously (and products removed continuously) to the electrodes