Oxidation and Reduction

Oxidation is electron loss – OIL; it is an increase in oxidation number

Reduction is electron gain – RIG; it is a decrease in oxidation number

An oxidizing agent accepts electrons.

A reducing agent donates electrons.

A Redox Reaction is when oxidation and reduction take place at the same time.

Rules for determining oxidation number

1. Pure elements have an oxidation number of 0

2. Ions have the oxidation number of the ion

3. Combined oxygen usually has an oxidation number of (-2)

4. Combined hydrogen usually has an oxidation number of (+1)

5. For polyatomic ions or molecules, the sum of the oxidation numbers equals the charge on the whole ion or molecule.

Example: Deduce the oxidation number of each element in H₂SO₄.

Rule 3: Oxidation number of one O atom is -2, total is -8

Rule 4: Oxidation number of one H atom is +1, total is +2

Rule 5: Total oxidation number for the molecule is 0

(+2) + S + (-8) = 0

S = +6

Redox Equations

Example: The reaction between hydrochloric acid and magnesium

Overall Equation: 2HCl(aq) + Mg(s)  MgCl₂(aq) + H₂(g)

Half Equations: 2H⁺(aq) + 2e^-  H₂(g)

Mg(s)  Mg²⁺(aq) + 2e^-

*Quantitative Chemistry*

Atomic number = number of protons = number of electrons in an atom

Mass number = number of protons + number of neutrons

Isotopes: atoms of the same element with the same number of protons, but different number of neutrons.

Relative Atomic Mass, A_r = The average mass of all the isotopes of an element, in relation to the mass of carbon-12 (taken as 12 exactly).

Avogadro’s constant = number of particles in one mole of a substance = 6.02 x 10²³

Moles = mass(g) ÷ M_r (molecular mass)

Moles = concentration(old m^-3) x volume (dm³)

Under standard conditions (0°C and 101.3 kPa), 1 mole of gas = 22.4 dm³

Empirical Formula = the simplest ratio of each type of atom in a compound

Empirical Formula Calculations:

• Percentage of each element

• Divide by relative atomic mass

• Find the ratio (divide by the smallest number)

• Simplify to obtain the closest whole-number ratio

• Write the empirical formula

Molecular Formula: determine this by dividing the molecular mass, M_r by the empirical formula mass.

*Organic Chemistry*

Features of a homologous series

• The same functional group

• The same general formula

• Similar chemical properties

• A trend/pattern in physical properties

• Each successive member varies by a CH₂ group

Isomers: have the same molecular formula, but different structural formula

Homologous Family	General Formula	Functional Group	Example
Alkanes	CnH2n+2	C – C (saturated)	CH3CH2CH3 Propane
Alkenes	CnH2n	C=C (unsaturated)	CH3CH=CHCH2CH3 Pent-2-ene
Haloalkanes		C – X (X = F, Cl, Br, I)	CH3CH(Br)CH(Br)CH3 2,3-dibromobutane
Alcohols		O – H	CH3CH2OH Ethanol
Acids		COOH	CH3CH2CH2CH2COOH Pentanoic acid

Polymerisation: when two or more monomers (small units) are reacted together to form a polymer (a large molecule, of repeating smaller units).

Example: ethene molecules add together to form poly(ethene)

This method is frequently used to produce plastics. Many monomers, are alkenes produced from the cracking of crude oil, a non-renewable energy resource.