IGCSE review

Element

Substance containing one type of atom.

Compound

Two or more different elements chemically bonded; separated only by chemical reactions.

Mixture

Two or more substances not chemically bonded; separated by physical methods.

Molecule

Two or more atoms covalently bonded.

Properties of ionic compounds

High melting and boiling points; conduct electricity when molten or dissolved but not when solid; usually soluble in water; strong electrostatic forces between ions.

Properties of covalent compounds

Simple molecules have low melting and boiling points; usually do not conduct electricity; weak forces between molecules; giant covalent structures have very high melting points.

Exothermic reaction

Releases energy; surroundings get hotter; products have less energy than reactants.

Endothermic reaction

Absorbs energy; surroundings get colder; products have more energy than reactants.

Activation energy (Ea)

Minimum energy needed for a reaction to occur.

Catalyst

Lowers activation energy by providing an alternative pathway; does not change the overall energy change.

Physical change

No new substance is formed; usually reversible.

Chemical change

A new substance is formed; usually difficult to reverse.

Collision theory

Particles must collide with enough energy to reach activation energy and with the correct orientation.

Collision theory in terms of

Number of particles per unit volume

Higher concentration means more particles per unit volume, causing more collisions and a faster reaction.

Frequency of collisions between particles

More frequent collisions give more opportunities for successful collisions, increasing reaction rate.

Kinetic energy of particles

Higher temperature gives particles more kinetic energy, causing more successful collisions and a faster reaction.

Recognizing oxidizing and reducing agent

Oxidation = loss of electrons; reduction = gain of electrons. Oxidising agent causes oxidation and is reduced. Reducing agent causes reduction and is oxidised. OIL RIG = Oxidation Is Loss, Reduction Is Gain.

Methyl orange

Red in acid; yellow in alkali.

Classify oxides either acidic or basic related to metallic and non-metallic character

Metal oxides are usually basic; non-metal oxides are usually acidic.

Preparation of soluble salts using an alkali by titration

Titrate acid and alkali to the end-point; repeat without indicator; evaporate some water; crystallise; filter; dry.

Preparation of soluble salts using excess metal

Add excess metal to acid; filter excess metal; evaporate; crystallise; filter; dry.

Preparation of soluble salts using excess insoluble base

Add excess base to acid; filter excess base; evaporate; crystallise; filter; dry.

Preparation of soluble salts using excess insoluble carbonate

Add excess carbonate to acid; produces salt + water + CO₂; filter excess; evaporate; crystallise; filter; dry.

Preparation of insoluble salts by precipitation

Mix two soluble solutions; an insoluble salt forms as a precipitate; filter, wash and dry.

Halogens at room temperature

Fluorine = pale yellow gas; chlorine = green-yellow gas; bromine = red-brown liquid; iodine = grey-black solid.

Halide ions

Fluoride, chloride, bromide and iodide ions are colourless in solution.

Properties of transition metals

High melting points and densities; strong; good conductors; form coloured compounds; have variable oxidation states; often act as catalysts.

Physical properties of metals

Usually shiny, strong, malleable, ductile, good conductors and have generally high melting points.

Physical properties of non-metals

Usually dull, brittle if solid, poor conductors and have generally lower melting points.

Alloy

Mixture containing a metal and one or more other elements; usually harder

Brass

Alloy of copper and zinc.

Stainless steel

Mainly iron, chromium and nickel; resistant to corrosion.

Condition for rusting of iron

Iron requires both water and oxygen to rust.

Barrier methods to prevent rusting

Painting, oiling, greasing, plastic coating and electroplating prevent water and

Blast furnace (extraction of iron; hematite)

Hematite is Fe₂O₃.

Production of Reducing Agent

C(s) + O2(g) -> CO2(g)
CO2(g) + C(s) -> 2CO(g)

Reduction of Iron Ore

3Fe2O3(s) + CO(g) -> 2Fe3O4(s) + CO2(g)
Fe3O4(s) + CO(g) -> 3FeO(s) + CO2(g)
FeO(s) + CO(g) -> Fe(l) + CO2(g)
Fe2O3(s) + 3C(s) -> 2Fe(l) + 3CO(g)

Slag Formation

CaCO3(s) -> CaO(s) + CO2(g)
CaO(s) + SiO2(s) -> CaSiO3(l)

Aluminium from bauxite

Aluminium is extracted from bauxite by electrolysis; aluminium oxide is dissolved in molten cryolite; Al³⁺ ions gain electrons at the cathode.

Presence of water test

• Anhydrous copper(II) sulfate: Add a few drops of the liquid to a white powder sample of CuSO₄. If the solid turns from white to bright blue, water is present, forming hydrated copper(II) sulfate (CuSO₄ ⋅ 5H₂O). [1, 2]

• Anhydrous cobalt(II) chloride: Use cobalt chloride paper impregnated with CoCl₂. In the presence of water, the paper changes from blue to pink (CoCl₂ ⋅ 6H₂O). [1, 2]

Treatment of domestic water supply

Filtration removes insoluble particles; chlorination kills microorganisms.

Composition of air

About 78% nitrogen, 21% oxygen, 0.9% argon and 0.04% carbon dioxide.

Carbon dioxide from complete combustion of carbon-containing fuels

Complete combustion produces carbon dioxide and water.

Carbon monoxide and particulates from incomplete combustion of carbon-containing fuels

Incomplete combustion can produce carbon monoxide and water and sometimes soot (C)

Methane from decomposition of vegetation and digestion in animals

Methane is produced by anaerobic decomposition and digestion; methane is a greenhouse gas.

Oxides of nitrogen from car engines

High temperatures in car engines cause nitrogen and oxygen to react, forming nitrogen oxides.

Sulfur dioxide from combustion of fossil fuels containing sulfur compounds

Burning sulfur-containing fossil fuels produces sulfur dioxide.

Fuel (containing S) + O2 -> CO2 + H2O + SO2

Effect of carbon dioxide

Higher CO₂ levels increase global warming, contributing to climate change.

Effect of carbon monoxide

Toxic gas that reduces the blood's ability to carry oxygen.

Effect of particulates

Increase the risk of respiratory problems and cancer.

Effect of methane

Higher methane levels increase global warming, contributing to climate change.

Effect of oxides of nitrogen

Cause acid rain and respiratory problems.

Effect of sulfur dioxide

Causes acid rain.

Homologous series

Family of compounds with the same functional group and general formula;

• Same General Formula: E.g.,

  C𝑛

  H2𝑛+2

  for alkanes.

• Similar Chemical Properties: Due to having the same functional group.

• Gradual Physical Trends: Boiling and melting points increase regularly as molecular mass increases.

• Common Preparation: They can be synthesized using similar chemical methods.

Fossil fuels

Coal, natural gas and petroleum; non-renewable fuels.

Methane as the main constituent of natural gas

Natural gas is mainly methane (CH₄); used for heating and cooking.

Petroleum

Mixture of hydrocarbons separated by fractional distillation.

Refinery gas fraction

Contains small molecules with low boiling points; used for heating and cooking.

Gasoline

petrol fraction

Naphtha fraction

Used as a chemical feedstock.

Diesel oil

gas oil fraction

Bitumen fraction

Contains large molecules with high boiling points; used for making roads.

Fractional distillation: decreasing chain length

As fraction size decreases, hydrocarbon chain length decreases.

Fractional distillation: lower boiling points

Shorter hydrocarbon chains have weaker intermolecular forces and lower boiling points.

Test for saturated and unsaturated hydrocarbons

Add aqueous bromine. Unsaturated hydrocarbons decolourise bromine water from orange

Cracking

Breaks large alkane molecules into smaller molecules using high temperature and a catalyst; produces smaller alkanes and alkenes.

Properties of alkenes with bromine

Alkenes react with bromine in an addition reaction; bromine water is decolourised.

Properties of alkenes with hydrogen

Alkenes react with hydrogen in the presence of a nickel catalyst to form alkanes; C₂H₄ + H₂ → C₂H₆.

Properties of alkenes with steam

Alkenes react with steam in the presence of an acid catalyst to form alcohols; C₂H₄ + H₂O → C₂H₅OH.