G C S E

C H E M I S T R Y N O T E S

Topics-

1. Hazard Symbols2. Man-Made Materials3. Composite Materials

4. Gases5. Solubility

6. Kinetic Theory7. Atomic Structure

8. Elements, Compounds & Mixtures9. Bonding

10. Chemical Nomenclature11. Rusting12. Redox

13. Hard Water14. Acids & Bases

15. Electrolysis16. Energetics

17. Reactivity Series18. Reaction Rates19. Periodic Table

20. Chemical Calculations 21. Metals

22. Non-Metals23. Organic Chemistry24. Human Influences

25. Industrial Processes26. Radioactivity

1. Hazard Symbols

In any chemical catalogue or any bottle of chemical you should be warned about the potential dangers of a chemical.

Hazard Symbols are used to warn of potential dangers of a chemical. Hazard symbols are used because-

o Internationally Agreedo Easily Recognised

Flammable- Liquids which have a flash point equal to or greater than 21® and less than or equal to

55®

Toxic- Substances which present a series risk of acute or chronic poisoning by inhalation, ingestion or skin

absorption

Corrosive- Substances which destroy living tissue

Explosive- Substances which may explode under the effect of flame or heat or shock/friction

Harmful- Substances which present moderate risks to health by inhalation, ingestion or skin absorption

Irritant- Substances which are non-corrosive but are liable to cause inflammation through immediate, prolonged or

repeated contact with the skin.

Table 1: Chemical Symbols

2. Man-Made Materials

Materials can be classified as Natural or Man-Made. Materials can also be classified further into five categories-

o Metalso Ceramicso Glasso Plastics- Thermosoftening and Thermosettingo Fibres

Thermosoftening & Thermosetting Plastics

Thermosofteningo Thermosoftening plastics are flexible and can be moulded into

different shapes. This is because long chains in the polymer can- Stretch easily Soften on warming Are flexible Can be shaped on warning

Thermosettingo Thermosetting plastics are strong, rigid and once formed

do not soften or melt. o The long chain molecules are

joined by cross-links and when the chains are heated the crosslink’s stop movement.

Figure 1: Thermosoftening plastic with no bonds

Figure 2: Thermosetting plastics with bonds

Properties of Materials

Groups of Materials Examples Properties of Materials

Metals Copper, Aluminium, Iron, Lead, Zinc

Conduct Electricity, Conduct Heat, Malleable, Ductile, High Melting Point

Ceramics Pottery, Tiles Brittle, High Melting Point

Glass Soda Glass, Pyrex Brittle, High Melting Point, Transparent

Fibres Nylon Flexible, Low Melting Point

Plastics

Thermosetting- Bakelite, Melamine, Epoxy Resin

Brittle, High Melting Point, Electrical Insulators

Thermosoftening- Polythene, PVC, Polystyrene

Flexible, Can be Moulded, Low Melting Point, Electrical Insulators

Table 2: Properties of Materials & Examples

Hardness- How easy it is to scratch or dent a material. A harder material will always scratch a softer material.

Brittle- A brittle material will shatter if dropped on a hard floor. Brittle materials such as glass or ceramics cannot absorb the energy of a large collision without cracking or shattering totally.

Strength- A material which is difficult to break when a force is applied. Strength is usually associated with a stretching force.

Flexibility- A flexible material is one that is easy to bend without breaking. Flexible materials have good tensile strength and compressive strength.

In deciding suitable materials we must ask ourselves these questions-

1. Are the physical properties suitable?2. Are the chemical properties suitable?3. Is the cost of the material suitable?

Material Use PropertyIron Bridges High StrengthAluminium Saucepans Good Conductor of HeatCopper Electrical Wiring Good Conductor of ElectricityLead Roofing MalleableZinc Galvanising Iron Chemically more reactive than ironMelamine Kitchen Worktops High Heat ResistancePolythene Bottles Easy to melt and mouldTable 3: Some uses of Materials

3. Composite Materials

A Composite Material is one which combines the properties of more than one material to produce a more useful material for a particular purpose.

In a composite material, one of the materials is used as a matrix while the other acts as a filer.

Composite materials are not just synthetic but natural also. Natural Composites include bone, ivory and teeth.

The four composite materials needed are listed below-

Composite Materials present Advantages UsesReinforced Glass Glass matrix

reinforced with wire mesh

Stronger and less brittle than glass

Windows and Doors

Reinforced Concrete

Concrete matrix reinforced with steel rods

Hard like concrete with the flexibility and strength of steel

Construction industry, for buildings

Glass-reinforced plastic

Plastic matrix reinforced with glass fibre matting

Flexible like plastic. Much stronger than plastic and less brittle than glass

Boats, car bodies and canoes

Bone Calcium phosphate reinforced with protein fibres

Hard like calcium phosphate but more flexible than calcium phosphate

Skeleton

Table 4: Composite Materials and Advantages

4. Gases

Diffusion

Diffusion provides us with evidence that the particles of a gas can move and it is described as the movement of particles from a region of high concentration to a region of lower concentration.

The coloured particles diffuse quickly into the air particles and as the same time, the air particles diffuse into the coloured particles.

Diffusion in liquids is much slower as particles in a liquid move more slowly than those in gas.

Figure 3: Diffusion of Bromine and the Diffusion of Potassium Permanganate

Speed of Diffusion

The ring of white powder is closer to the HCL than the NH3. This is because the NH3 molecules are lighter (smaller) and have diffused more quickly through the air in the tube.

Effect of Temperature & Pressure

As pressure increases, at a given temperature, volume will decrease. As pressure decreases, at a given temperature, volume increases. As temperature increases, at a given pressure, volume increases. As temperature decreases, at a given pressure, volume decreases.

PV/T = Constant

P1×V 1T 1

=P2×V 2T 2

Pressure is measured in Pascals (Pa). Temperature is measured in Kelvin. To work out Kelvin, add 273 to °c

temperature. Volume is measured in Cubic Metres (m3).

5. Solubility

80 cm3 of oxygen in a gas syringe at 27°c and a pressure of 12 000 Pa. The gas was then heated to 87°c at a new pressure of 18 000 Pa. What is the volume of oxygen under the new conditions?

¿(12000×80)

300=

(18000×V 2)360

¿V 2=(12000×80×360)(300×18000)

¿V 2=64 cm3

• Solubility: the amount of a solute that can be dissolved in a certain amount of solvent.

• Solubility of a solute in a solvent – measured in:

▫ grams of solute

▫ per 100 grams of solvent

▫ at a particular temperature

• Solubility of most solid solutes increases with temperature.

▫ Solute = Solid

▫ Solvent = Liquid

▫ Solution = Mixture

Solubility Equation

Grams of Solute× 100Grams of Solvent

=x g /100 gwater

Solubility Curve

This allows us to plot a graph after working out solubility at different temperatures. The graph allows us to work out-

o The solubility at a given temperatureo The temperature at which the solution

will saturate and produce crystalso The mass of crystals which will form

when the solution is cooled to a lower temperature

6. Kinetic Theory

Table 5: The Important Properties of solids liquids and gases

Property Solids Liquids Gases

Shape Stay the Same Take the shape of the Container

Take the shape of the Container

Volume Stay the Same Stay the Same Take the volume of container

Density High Density Medium Density Low Density

Compressibility Cannot Compressed Slightly Can be compressed into smaller volumes

Changes in State

1. Melting When a solid is heated, particles gain energy causing them to vibrate

faster and faster about fixed positions. When sufficient energy is gained, the particles break away and the solid

melts. Melting is endothermic as it takes in energy to melt.

2. Boiling and Evaporation When a liquid is heated the particles gain energy and move around

faster. Before reaching boiling temperature, some of the higher energy

particles will have enough energy to overcome the attractions to escape and form a gas, evaporation.

On further heating all particles gain sufficient energy to overcome the attractive forces and the liquid boils. These are endothermic.

3. Condensation and Freezing These are exothermic reactions so give out energy. During cooling, the gas particles lose energy and are able to move

closer together until condensation takes place. When particles of a liquid are cooled, the particles move closer and

form strong attractive forces for freezing to take place.

4. Sublimation Sublimation takes place when a solid goes directly from a solid to a gas

or from a gas to a solid. Solid carbon dioxide (dry ice) and iodine crystals are examples.

7. Atomic Structure

Element: Any substance that cannot be broken down into a simpler one by a chemical reaction.

Compound: A substance formed by the chemical combination of elements.

Atom: The atom is a basic unit of matter that consists of a dense central nucleus surrounded by a cloud of negatively charged electrons.

Ion: An atom or group of atoms that has acquired an electric charge by losing or gaining one or more electrons.

Atomic Number: The number of protons in an atom of that element. Mass Number: The number of protons and neutrons in the nucleus of an

atom of that element.

Particle Relative Mass Relative Charge PositionNeutron 1 0 NucleusProton 1 -1 Nucleus

Electron 11840 -1 Shell

Structure of the first twenty elements

Element Atomic No. Mass No. No. Protons No. Electrons No. NeutronsHydrogen 1 1 1 1 0

Helium 2 4 2 2 2Lithium 3 7 3 3 4

Beryllium 4 9 4 4 5Boron 5 11 5 5 6

Carbon 6 12 6 6 6Nitrogen 7 14 7 7 7Oxygen 8 16 8 8 8Fluorine 9 19 9 9 10

Neon 10 20 10 10 10Sodium 11 23 11 11 12

Magnesium 12 24 12 12 12Aluminium 13 27 13 13 14

Silicon 14 28 14 14 14Phosphorus 15 31 15 15 16

Sulphur 16 32 16 16 16Chlorine 17 35 17 17 18

Argon 18 40 18 18 22Potassium 19 39 19 19 20

Calcium 20 40 20 20 20

Isotopes

Isotopes are the atoms of an element with different numbers of neutrons. They have the same proton number, but different mass numbers.

Isotope Protons Electrons Neutrons35 17 Cl 17 17 1837 17 Cl 17 17 20

1 1 H 1 1 02 1 H 1 1 13 1 H 1 1 2

isotope symbol

hydrogen-1

1 proton, 0 neutron, 1 electron

hydrogen-2

1 proton, 1 neutron, 1 electron

hydrogen-3

1 proton, 2 neutrons, 1 electronFigure 4: Three Isotopes of Hydrogen

8. Elements, Compounds & Mixtures

Metallic & Non-Metallic Elements

Metallic Elements Non-Metallic Elements

Good conductors of electricity Poor Conductors of electricityGood conductors of heat Poor conductors of heat

All are solids at room temp. Can be gas, liquid or solid at room temp.High Density Low Density

High melting + boiling points Low melting + boiling pointsMalleable + ductile Soft + brittle

Shiny solids Usually dull

Compounds & Mixtures

Compounds are substances which contain two or more elements chemically joined together.

A mixture can be defined as consisting of two or more substances that are usually easy to separate.

Compound MixtureIs a pure substance Two or more substancesChemical reaction occurs when a compound is formed and there is an energy change

No chemical change takes place

Composition is always the same Composition of a mixture can varyProperties are different to those of elements which make it up

Properties are same as the elements which make it up

Difficult to separate and only broken down by chemical means

Easy to separate by physical means

9. Bonding

Some atoms are very reluctant to combine with other atoms and exist in the air around us as single atoms. These are the Noble Gases and have very stable electron arrangements e.g. 2, 2, 8 and 2, 8, 8 because their outer shells are full.

All other atoms therefore, bond together to become electronically more stable, that is to become like Noble Gases in electron arrangement. Bonding produces new substances and usually involves only the 'outer shell' or 'valency' electrons and atoms can bond in two ways.

Ionic Bonding

IONIC BONDING - By one atom transferring electrons to another atom to form oppositely charged particles called ions which attract each other - the ionic bond.

An ion is an atom or group of atoms carrying an overall positive or negative charge

If a particle, as in a neutral atom, has equal numbers of protons (+) and electrons (-) the particle charge is zero i.e. no overall electric charge.

The proton/atomic number in an atom does not change BUT the number of associated electrons can!

If negative electrons are lost the excess charge from the protons produces an overall positive ion.

If negative electrons are gained there is an excess of negative charge, so a negative ion is formed.

The atom losing electrons forms a positive ion (cation) and is usually a metal. The atom gaining electrons forms a negative ion (anion) and is usually a non-metallic element. The ionic bond then consists of the attractive force between the positive and negative ions in the structure.

The ionic bonding forces act in all directions around a particular ion, it is not directional, as in the case of covalent bonding.

Covalent Bonding

COVALENT BONDING - sharing electrons to form molecules with covalent bonds, the bond is usually formed between two non-metallic elements in a molecule. The two positive nuclei (due to the positive protons in them) of both atoms are mutually attracted to the shared negative electrons between them - the covalent bond. They share the electrons in a way that gives a stable Noble Gas electron arrangement.

Metallic Bonding

Metals form giant structures in which electrons in the outer shells of the metal atoms are free to move. The metallic bond is the force of attraction between these free electrons and metal ions. Metallic bonds are strong, so metals can maintain a regular structure and usually have high melting and boiling points.

Metals are good conductors of electricity and heat, because the free electrons carry a charge or heat energy through the metal. The free electrons allow metal atoms to slide over each other, so metals are malleable and ductile.

10. Chemical Nomenclature

Names of Ionic Compounds

The name of the chemical compound tells us the elements present. For example, magnesium oxide tells us magnesium and oxygen is present.

The name of the metal is always given as the first part of the name, while the non-metal name appears as the second part of the name.

To show that it is a compound, the non-metal usually ends in –ide.

Reacting Elements Compound ProducedMagnesium + Oxygen Magnesium OxideIron + Sulphur Iron SulphideSodium + Fluorine Sodium FluorideSodium + Chlorine Sodium ChloridePotassium + Bromine Potassium BromideSodium + Iodine Sodium IodideMagnesium + Nitrogen Magnesium Nitride

Some ionic compounds end in –ate or –ite; both indicate that oxygen is present along with the metal and non-metal.

Formulae of Ionic Compounds

The whole number ratio in which the ions or atoms exist in the compound.

When writing formula use the following rules-o Write down the cation and anion present in the compound.o Because ionic compounds are neutral, the charges on the cations

and anions must cancel out.

Formulae of Ionic Compounds

The number of the formula can be worked out by considering the valences of each atom.

o Silica, SiO2: Silicon has a valency of 4, oxygen of 2. This means it takes 2 oxygen atoms to combine with 1 silicon atom.

Balancing Equations

CaCO3 → CaO + CO2

The above equation is balanced. It has the same elements on both sides and the same number of atoms of each element.

NaHCO2 → Na2CO3 +CO2 + H2O

The above equation is not balanced. It does have the same elements on both sides but not the same number of atoms of each element.

Writing Symbol Equations

All the elements that appear on the left must appear of the right. Not only must you have the same elements present on both sides, you

must also have the same number of atoms of each element. You cannot change the formula of a chemical to get the equation to

balance.

Example-

Reaction: sodium + water → sodium hydroxide + hydrogen

1. Write the correct formula: Na + H2O → NaOH + H2

2. Check the NA: 1 on the left as the NA

1 on the right in the NaOH

One on both sides- balanced

3. Check the H: 2 on left in H2O

2 on right in NaOH and 2 in H2

Na + H2O + H2O → NaOH + H2

Now there are 4 on left and 3 on right, we add another NaOH

4. Check the O: 2 on the left, 1 in each H2O

2 on the right, 1 in each NaOH- balanced

5. Recheck the Na: 1 on the left in Na

2 on right, 1 in each NaOH

We add another Na, there are now 2- balanced

6. The final equation is- 2Na + 2H2O → 2NaOH + H2

11. Rusting

Fe2O3.2H2O

Air and Water cause rust Water with no air does not cause rust. Air with no water does not cause rust. Air and Water must be present for rust to form.

Rust Prevention

There are many methods to stop rust forming, these include- Painting Oiling Greasing Tin-plating Galvanising

Sacrificial Protection

Sacrificial protection is when a more reactive metal is placed alongside iron and is corroded before rust.

This is used in ships; zinc bars placed on the iron hull react before the iron and slow down rusting.

12. Redox

Oxidation and Reduction in terms of oxygen

Oxidation is the gain of oxygen and reduction is the loss of oxygen.

Oxidation and Reduction in terms of hydrogen

Oxidation is the loss of hydrogen and so reduction is the gain of hydrogen.

Oxidising and Reducing Agents

An oxidising agent “does the oxidising” that is it supplies the oxygen or removes the hydrogen.

The oxidising agent itself is reduced; it loses oxygen and gains hydrogen.

Important Redox Reactions

Rusting: When Iron rusts it forms an oxide by gaining oxygen, the iron is oxidised. Water is also needed.

Combustion of Fuels: Combustion is the reaction with oxygen forming an oxide and releasing energy. This means that when a fuel burns an oxidation is taking place.

Extraction of Aluminium and of Iron: Aluminium and iron are found naturally as their oxides. The oxygen is removed to obtain the metal so the aluminium or iron loses oxygen and is reduced.

Manufacture of Ammonia: Ammonia is formed by the reaction of nitrogen with hydrogen; the nitrogen is gained hydrogen and is reduced.

13. Hard Water

Water that does not lather easily with soap is called hard water. If the water does lather easily it is soft water.

When soap is used with hard water, it is hard to form lather and a scum is formed.

Hard water will form lather eventually but will use more soap than a sample of soft water.

Soapless detergents will lather well with both hard and soft water because it is only soap that reacts to form scum.

Causes of Hard Water

Solution Behaviour with SoapSodium Chloride Good LatherCalcium Chloride No Lather, scum

Magnesium Chloride Poor Lather, scumPotassium Nitrate Good Lather

Calcium Nitrate Poor Lather, scumMagnesium Nitrate No Lather, scum

Sodium Sulphate Good Lather

It can be seen that only dissolved calcium or magnesium ions make water hard. The calcium or magnesium ions react with soap forming insoluble salts which are precipitated out of the mixture as scum.

Ca2+ (aq) + 2C17H35COONa (aq) → (C17H35COO)2Ca (s) + Na+ (aq)

Types of Hard Water

1. Temporary Hard Water Carbon Dioxide in the air dissolves in rain water forming the week acid,

carbonic acid.

CO2 (g) + H2O (I) → H2CO3 (aq)

When this dilute acidic solutions falls on rocks containing calcium carbonate e.g. limestone, soluble calcium hydrogencarbonate is formed. As a result there is calcium ions dissolved in water and the water is hard.

H2CO3 (aq) + CaCO3 (s) → Ca(HCO3)2 (aq)

The Calcium Hydrogencarbonate is easily decomposed on heating. The calcium carbonate produced is insoluble and is precipitated out.

Ca(HCO3)2 (aq) → CaCO3 (s) + CO2 (g) + H2O (l)

As calcium ions are removed, the hard water is softened. Calcium Carbonate is deposited on the heating vessel.

2. Permanent Hard Water Cannot be softened by boiling Carbonates are not the only calcium or magnesium containing

compounds found in rocks, gypsum, for example contains calcium sulphate.

When rain passes over these rocks, calcium and magnesium ions can dissolve in the water and make it hard.

These compounds do not decompose on heating, the ions stay in the water and it remains hard.

CaSO4 (s) + aq → Ca2+ (aq) + SO42- (aq)

Softening Hard Water

Boiling can be used but only for temporary hard water. Adding washing soda, hydrated sodium carbonate Na2CO3.10H2O,

precipitates out the calcium as its carbonate.

Na2CO3 (aq) + Ca(HCO3)2 (aq) → 2NaHCO3 (aq) + CaCO3 (s)

Using an Ion Exchanger that removes the calcium or magnesium ions and replaces them with other suitable ions.

Advantages of Hard Water

Calcium is needed for strong bones and teeth and may help to prevent heart disease. You would, however, have to drink a large amount.

Hard water is supposed to taste better but this is presumably a matter of taste. It is better for making beer also.

Less likely to dissolve heavy metals such as lead. So if the hard water is flowing through old lead pipes then there is smaller possibility of lead dissolving in the water and damaging your health.

In tanning leather the calcium or magnesium ions make the leather cure better.

Disadvantages of Hard Water

Hard water will, of course, produce lather with soap eventually but the amount of soap required makes it much more expensive.

When temporary hard water is heated in a kettle the calcium carbonate builds up on the heating element. This is known as fur.

When the hot water is in boilers and popes the deposits are known as scale or limescale. Pipes can become blocked and the hot water system is much less efficient.

Characteristics of a Hard Water Area

Hard water comes from areas with chalk or limestone. As the rain, containing the carbonic acid runs through these rocks some of the calcium carbonate is removed as the soluble calcium hydrogencarbonate.

Over many centuries this can create caves, stalagmites and stalactites. A drop of temporary hard water can lose water by evaporation and as a result the calcium hydrogencarbonate decomposes leaving a solid deposit of calcium carbonate.

Treatment of Water

The treatment of water can involve a variety of processes, depending on the origin of the water, but there are two main treatments.

1. Filtering: The water is allowed to run through sand beds to remove insoluble solid matter. There may be two different sand beds: first course to remove larger solid and after fine sand to remove smaller particles.

2. Chlorination: Microbes in water cause several diseases e.g. cholera. Chlorine is added to water in order to kill bacteria. Great care is needed in order to use enough chlorine to kill bacteria but not harm humans or animals.

Pollution

A pollutant is a chemical in a situation where it is likely to kill or harm. There are many ways in which water can be polluted.

1. Fertilisers: Used to get a better crop yield; they contain the nitrates and phosphates required for healthy growth for plants. If too much is used, it can run off the field and into the water system.

2. Detergents: Containing phosphates as brighteners also contribute to water pollution.

14. Acids & Bases

Acids: Acids contain hydrogen and when they dissolve in water they produce hydrogen ions. Acids react to form salts and the acid determines the salt.

Bases: A base reacts with an acid to form a salt and water. Metal oxides and hydroxides are bases. Alkalis are soluble bases. When an alkali dissolves in water it produces hydroxide ions.

Neutralisation: When an acid and an alkali react the hydrogen and hydroxide ions form water. Water is neutral and so this type of reaction is called neutralisation

Acid reacts with metal- metal + acid → salt + hydrogen

Acid reacts with carbonates- acid + carbonate → salt + CO2 + H2O

Further Classification

Oxides-o Metal oxides are basic and non-metal oxides are acidic. o Metal Oxide and Non-Metal Oxide-

Acid + Base → Salt + Water

15. Electrolysis

Electrolysis- the decomposition of a liquid electrolyte by a direct current of electricity.

Electrodes- graphite rods are placed in the liquid and connect to a supply of electricity. The positive pole is the anode and cathode is the negative pole.

The negative cathode attracts positive ions, cations. The positive anode is attracts negative ions, anions.

Molten Electrolysis

Electrolyte Cathode Product

Anode Product

Lead Bromide Lead Bromine

Cathode- Pb2+ (l) + 2e- → Pb (s)Anode- 2Br- (l) → Br2 (g) + 2eOverall- PbBr2 (l) → Pb (l) + Br2 (g)

Lithium Chloride Lithium Chlorine

Cathode- Li+ (l) + e- → Li (l)Anode- 2Cl- (l) → Cl2 (g) + 2e-

Overall- 2LiCl (l) → 2Li (l) + Cl2 (g)

Electrolysis in Aqueous Solutions

Electrolyte Cathode Product

Anode Product

Lead Bromide Lead BromineCathode- 2H+ (aq) + 2e- → H2 (g)Anode- 4OH- (aq) → 2H2O (l) + O2 (g)Overall- H2O (l) → H+ (aq) + OH- (aq)

Electrolysis in Industry

Extraction of Aluminium

Cathode- Al3+ + 3e- → Al Anode- 2O2- → O2 + 4e-

Oxygen reacts with carbon at this temperature forming Carbon Dioxide.o C + O2 → CO2

Refining of Copper

Cathode- Cu2+ (aq) + 2e- → Cu (s) Anode- Cu (s) → Cu2+ (aq) + 2e-

The copper ions in the electrolyte move to the cathode. They gain elections forming copper atoms that are deposited on the pure copper cathode. As a result the cathode increases in size.

At the anode the copper atoms lose electrons and become ions. The ions leave the anode and enter the electrolyte. The anode gets smaller.

Electrolysis of Brine (the chlor-alkali process)

Brine is used to produced Chlorine, Hydrogen and Sodium Hydroxide The Chloride ions are discharged at the anode- 2Cl- → Cl2 + 2e-

The hydrogen ions are discharged as the cathode- 2H+ + 2e- → H2

The remaining ions are Na+ and OH-, they form sodium hydroxide.

The products are of this process are very useful-o Chlorineo Sodium Hydroxideo Hydrogen

16. Energetics

Energy Changes in Reactions

Exothermic reactions:

In an exothermic reaction, heat energy is given out.

An energy level

diagram to show

an exothermic

reaction.

This is because the products are lower in energy than the reactants, so the excess energy from the reactants are given out as heat energy.

Examples: combustion reactions metals with an acid neutralisation (metals in water)

Endothermic reactions:

In an endothermic reaction, heat energy is taken in.

An energy level

diagram to show

an endothermic

reaction.

Heat energy given out

Heat energy taken in

This is because the products are higher in energy than the reactants, so the extra energy needs to be taken from the surroundings.

Examples: thermal decomposition of metal carbonates (products CO2 + metal oxide)

Experiments to Measure Energy Changes

1. Reactions involving solids

e.g. For neutralisation reactions, displacement reactions, dissolving, metal and acid etc.

Polystyrene cup

Reaction mixture

Thermometer

The change in temperature of the reaction is measured.

Heat energy given out / taken in (J) = mass (g) x specific heat x temperature change (c)

(1) (2) (3)

(1) of solutions – for most solutions mass = volume ( mass = density x volume – density of water = 1gcm3)

(2) 4.18 Jg-1C-1

(3) no (-xoC) just temperature change

2. Combustion reactions

e.g. Burning on alcohol

The alcohol is burnt in a spirit burner, and heat produces is used to heat up a container of water.

Conical flask

Clamp

Thermometer

Known volume of water

Spirit burner

Alcohol

The alcohol is allowed to burn for a given time. The mass of alcohol is recorded before and after burning, so that the mass of alcohol burnt is known. The change in temperature of the water is measured.

Heat energy given out / taken in (J) = mass (g) x specific heat x temperature change (c)

(1) (2) (3)

(1) of solutions – for most solutions mass = volume ( mass = density x volume – density of water = 1gcm3)

(2) 4.18 Jg-1C-1

(3) no (-xoC) just temperature change

- ΔH

+ ΔH

Enthalpy change

‘The amount of heat energy given out or taken in per mole of reagent during a reaction = ΔH’

Δ means ‘change in’

H means ‘energy’

ΔH is negative for exothermic reactions (the reactants are losing energy)

ΔH is positive for endothermic reactions

(the reactants are gaining energy)

1. Heat energy (kJ) = (mass (g) x specific heat x temperature change (oC)) ÷ 1000

2. Work out per mole

3. Give sign (+ ΔH or – ΔH)

Why do reactions give in or take in energy?

Break bonds --> energy taken in (endothermic).

New bonds formed --> exothermic

If more energy needed to break bonds than given out making more bonds – reaction is endothermic.

If less energy needed to break bonds than given out making more bonds – reaction is exothermic.

Calculating bond energies

Bond energy (KJ mol-1) = the amount of energy needed to break a particular bond

The stronger the bond, more energy needed to break it, the higher the bond energy.

Method:

E.g. Methane and chlorine

CH4 + Cl2 --> CH3Cl + HCl

Bonds that are broken: 4 x H – C

1 x Cl – Cl

Bonds that are made: 3 x C – H

1 X C – Cl

1 X H – Cl

Bond energies:

C – H = +413 kJ mol-1

Cl – Cl = + 243 kJ mol-1

C – Cl = + 346 kJ mol-1

H – Cl = + 432 kJ mol-1

Bonds that are broken:

4 x H – C

= 4 x +413

= +1652 kJ mol-1

1 x Cl – Cl

= 1 X 243

= +243 kJ mol-1

Total energy taken in = +1895 kJ mol-1

Bonds that are made:

3 x C – H

= 3 x -413

= -1239 kJ mol-1

1 x C – Cl

= 1 x -346

= -346 kJ mol-1

1 X H – Cl

= 1 x -432

= -432 kJ mol-1

Total energy given out = -2017 kJ mol-1

Add together the values for total energy taken in and total energy given out to find the overall energy change:

Overall energy change ΔH = +1895 – 2017

= -122 kJ mol-1

Because ΔH is negative, we can see that the reaction is exothermic.

17. Reactivity Series

Potassium- Poor

Sodium- Scientists

Calcium- Can

Magnesium- Make

Aluminium- A

Zinc- Zoo

Iron- In

Copper- Coleraine

Collision TheoryChemical reactions occur when particles of reactant collide with enough energy to react. This minimum energy is called the Activation Energy.Smaller object react faster because there is a greater surface  are to volume area ratio, therefore there are more collisions, and more frequently.

The rate of reaction decreases as the concentration of reactant becomes less, and more products are made.

As the temperature increases, the rate of reaction increases as the particles have more kinetic energy, therefore they collide more frequently. More particles achieve activation energy.

Factors Affecting Rates of Reaction

Temperatureo Increasing the temperature of a reaction SPEEDS it up (INCREASES

the rate of reaction)o The particles have more kinetic energy so they move about more

and collisions occur more frequently.o As there are more collisions, there are more successful collisions

so the rate of reaction increases. Concentration

o Increasing the concentration of reactant liquids in a reaction also increase the rate of reaction.

o A high concentration means more particles per cm3 so there are more collisions per second which means there are more successful collisions so the reaction speeds up.

Surface Areao Increasing the surface area of a reactant solid increases the rate of

reactions.o A powdered substance always has a larger surface area than a

block substance weighing the same amount.o The more finely divided the solid is, the more of it is exposed to

react with the other particles. Use of a Catalyst

o Use of a catalyst increases the rate of reaction

o A catalyst is a substance that speeds up a reaction but is chemically unchanged. When the reaction finishes you have the same mass of catalyst.

o A catalyst provides an alternative route for the reaction, one with lower activation energy.

19. Periodic Table

The periodic table was developed to classify elements before atomic structure was understood.

It is a powerful aid to understanding the properties and reactions of the elements.

Early Attempts to Classify the Periodic Table

Newlands, and then Mendeleev, attempted to classify the elements by arranging them in order of their atomic weights.

The list can be arranged in a table so that elements with similar properties are in columns, known as Groups.

The table is called a periodic table because similar properties occur at regular intervals.

The early periodic tables were incomplete and some elements were placed in inappropriate Groups if the strict order of atomic weights was followed.

Mendeleev overcame some of the problems by leaving gaps for elements that he thought had not been discovered.

When electrons, protons and neutrons were discovered early in the 20th century, the periodic table was arranged in order of atomic (proton) numbers. When this was done, all elements were placed in appropriate groups.

The Modern Periodic Table

The modern periodic table can be seen as an arrangement of the elements in terms of their electronic structures.

Elements in the same Group have the same number of electrons in their highest occupied energy level (outer shell).

The trends in reactivity within Groups in the periodic table can be explained because the higher the energy level: the more easily electrons are lost the less easily electrons are gained.

Group 1- Alkali Metals

The elements in Group 1 of the periodic table (known as the alkali metals):

are metals with low density (the first three elements in the Group are less dense than water)

react with non-metals to form ionic compounds in which the metal ion carries a charge of +1. The compounds are white solids which dissolve in water to form colourless solutions

react with water releasing hydrogen form hydroxides which dissolve in water to give alkaline solutions.

In Group 1, the further down the group an element is:

the more reactive the element the lower its melting point and boiling point.

Group 7- Halogens

The elements in Group 7 of the periodic table (known as halogens):

have coloured vapours consist of molecules which are made up of pairs of atoms form ionic salts with metals in which the chloride, bromide or iodide ion

(halide ion) carries a charge of –1 form molecular compounds with other non-metallic elements.

In Group 7, the further down the group an element is:

the less reactive the element the higher its melting point and boiling point.

A more reactive halogen can displace a less reactive halogen from an aqueous solution of its salt.

Example:

Potassium Iodide + Chlorine = Potassium Chloride + Iodine

Transition Metals

In the periodic table between Groups 2 and 3 is a block of elements known as the transition elements. These elements are all metals.

The transition elements have similar properties and some special properties because a lower energy level (inner shell) is being filled in the atoms of the elements between Groups 2 and 3.

This is because the third energy level can hold up to 18 electrons, once two electrons have occupied the fourth level.

Compared with the elements in Group 1, transition elements:

have higher melting points (except for mercury) and higher densities are stronger and harder are much less reactive and so do not react as vigorously with Water or oxygen.

Many transition elements have ions with different charges; form coloured compounds and are useful as catalysts.

Can be found by adding together all the atomic masses of all the atoms in the formula of the element or compound.

Br2= (RAM Br) x 2 NaCl= RAM Na + RAM Cl

Moles and Number of Particles

One mole of any element or compound contains the same number of particles, which is 6 x 1023. The number of moles is found by dividing the number of particles by 6 x 1023.

moles=number of particles6 x1023

Moles and Mass

One mole of any element or compound weighs it RAM or RFM in grams and so the number of moles in a sample can be found.

moles= mass(g)RAM∨RFM

Chemical reactions can be represented by balanced chemical equations. Balanced chemical equations do much more than tell us what reacts and what is formed. The big numbers that you see in front of some formulae are called stoichiometric coefficients.

Mg + 2HCl MgCl2 + H2

Stochiometric coefficients tell us the ratio of moles that react. In the example above, they tell us how much magnesium is needed to react completely with hydrochloric acid.

mass

moles RMM

When we read out the balanced equation above, we don’t just say ‘magnesium plus hydrochloric acid goes to magnesium chloride plus hydrogen’. Instead, we should actually say ‘one mole of magnesium plus two moles of hydrochloric acid goes to one mole of magnesium chloride plus one mole of hydrogen’.

Calculating Reacting Masses

There are three steps to these calculations:

1. Work out the number of moles of reactant (moles = mass / RAM).

2. Use the balanced chemical equation to work out the number of moles of product.

3. Work out the mass of product using mass = moles x RMM.

Example One

Calculate the mass of magnesium chloride formed when 20g of magnesium reacts with hydrochloric acid: Mg + 2HCl MgCl2 + H2

moles of Mg = mass / RAM

= 20 / 24

= 0.833 mol

moles of MgCl2 = 0.833 mol because the balanced chemical equation shows a 1:1 ratio

mass of MgCl2 = 0.833 x (24 + 71)

= 79.2g

If you need to calculate the mass of reacant needed to make a given quantity of product, the method is almost identical:

Example Two

Calculate the mass of calcium carbonate needed to generate 11g of carbon dioxide according to the following balanced chemical equation: CaCO3 + H2SO4 CaSO4 + H2O + CO2

moles of CO2 = mass / RAM

= 11 / (12 + 32)

= 0.25 mol

moles of CaCO3 = 0.25 mol because the balanced chemical equation shows a 1:1 ratio

mass of CaCO3 = 0.25 x (40 + 12 + 48)

= 25g

Sometimes the question mentions that one of the reactants is in excess. For example, question 1 below says that “7.3g of hydrogen chloride reacts with excess ammonium hydroxide “. This just means that all 7.3g of hydrogen chloride reacts and none is left over.

1) Calculate the mass of ammonium chloride, NH4Cl, formed when 7.3g of hydrogen chloride reacts with excess ammonium hydroxide:

NH4OH + HCl NH4Cl + H2O

2) Calcium carbide, CaC2, reacts with water to form acetylene, C2H2 :

CaC2 + 2H2O C2H2 + Ca(OH)2

Calculate the mass of acetylene formed when 80g of calcium carbide reacts with excess water.

3) Calculate the mass of sodium oxide, Na2O, formed when 1.2g of oxygen gas reacts with excess sodium:

4Na + O2 2Na2O

4) What mass of iron is formed when one kilogram (1 000 g) of iron ore, Fe2O3, reacts with excess carbon monoxide?

Fe2O3 + 3CO 2Fe + 3CO2

5) Calculate the mass of nitric acid required to react completely with 90g of copper:

3Cu + 8HNO3 3Cu(NO3)2 + 2NO + 4H2O

6) A student needs to prepare 80g of magnesium oxide, MgO, by combustion of magnesium metal in oxygen:

Mg + H2O MgO + H2

What mass of magnesium is required?

7) What mass of copper oxide needs to be reduced to obtain 8g of copper?

CuO + H2 Cu + H2O

8) Calculate the mass of sodium hydroxide required to precipitate out 36g of iron(II) hydroxide:

FeSO4 + 2NaOH Fe(OH)2 + Na2SO4

9) What mass of water is required to react with aluminium carbide, Al4C3, in order to form 9.6g of methane gas?

Al4C3 + 12H2O 4Al(OH)3 + 3CH4

10) Calculate the mass of phosphoric acid required to generate 30g of hydrogen gas:

6Li + 2H3PO4 2Li3PO4 + 3H2

21. Metals and their Compounds

Properties of Metals

High melting and boiling points Most are hard- not easily dented or scratched Most are strong- easily support a load Most are denser than water High Lustre- Shiny Good Electrical Conductors Good Thermal Conductors Metals are ductile- drawn into wires

Answers

1. 10.7g

2. 32.5g

3. 4.65g

4. 700g

5. 236.25g

Metals are malleable- beaten into shape

Reaction of Metals with Non- Metals

1. Reaction with Cold Water- Only calcium, potassium and sodium react immediately with cold water.

The metal will move rapidly over the surface and a noise will be heard as hydrogen evolved burns.

Potassium will have a lilac flame and sodium a yellow one. A metal hydroxide is produced and it dissolves in the water to create an alkaline solution.

metal+cold water→metal hydroxide+hydrogen

2. Reaction with Steam Iron, Magnesium and zinc will react when heated with steam. The

products are the metal oxide and hydrogen.

metal+steam→metal oxide+hydrogen

3. Reaction with dilute acid Copper, iron, magnesium and zinc can be placed in dilute acid usually

hydrochloric acid. All but copper will react producing metal salt and giving off hydrogen. As before, magnesium is the most reactive, then zinc and iron is the least

reactive. Calcium, potassium and sodium have vigorous reactions.

metal+acid→metal salt+hydrogen

4. Displacement Reactions A more reactive metal will displace a less reactive metal from a solution

of its salt.

Extraction of Iron

You will mainly see iron in the form of its alloy – steel. Iron is found as an ore in its oxides – haematite Fe2O3 or magnetite Fe3O4. Iron is extracted from its ore by reduction with carbon; this is because carbon is relatively cheap.

The blast furnaceIron is extracted in a blast furnace, this is a continuous reaction, and the furnaces are only ever turned off after a few years to replace the lining. Coke, iron ore and limestone are fed into the top of the furnace and hot blasts of air at the bottom keep the furnace at around 1500 degrees Celsius.

Coke is a cheap form of carbon which is created by heating carbon in the absence of air. This reacts with oxygen and more coke to produce carbon monoxide which acts as the reducing agent.

Reactions

1. First, the coke reacts with oxygen to produce carbon dioxide:

C (s) + O2 9g) → CO2 (g)

2. Then the carbon dioxide further reacts with coke to produce carbon monoxide:

CO2 (g) + C (s) → 2CO

3. This carbon monoxide then acts as a reducing agent and reduces the haematite to carbon dioxide and iron:

Fe2O3 (s) + 3CO (g) → 2Fe (l) + 3CO2 (g)

4. The iron then forms a liquid from the high temperatures in the blast furnace. It trickles to the bottom where it is tapped off.

5. Limestone is broken down in the blast furnace:

CaCO3 (s) → CaO (s) + CO2 (g)

Because calcium oxide is a base, it reacts with silica which is an acid:

CaO (s) + SiO2 (s) → CaSiO3 (l)

The molten carbon silicate floats on top of the molten iron and it’s known as slag, this is tapped off and used in building rods.

Carbonates

Use of Metals

Magnesium is combined with other metals to form a light weight alloy which is used on air plane bodies.

Aluminum is used to make overhead cables. It can also be used to make saucepans because of a layer of oxide which forms over it.

Zinc is used to cover iron and prevent it from rusting. Zinc is alloyed with copper to form brass.

Iron, as steel, has many uses. It is used in the construction of ships, bridges, tools, car bodies and cookers. It is strong and cheap. Iron is essential in our diet because it is needed in the formation of hemoglobin.

Copper is a good conductor of electricity and does not react with water even when hot so it is used to make water pipes. Also used to make alloys for coins.

Calcium is needed in our diet to help make strong bones and teeth.

22. Non-Metals and their Compounds

Hydrogen

1. Physical Properties It is colourless and odourless, insoluble in water and less dense

that air.2. Chemical Properties

A Sample of hydrogen burns explosivelyi. Burns with a clean blue flame producing water vapour that

may condense on glass1. 2H2 + O2 → 2H2O

Hydrogen has reacts with heated copper (ll) oxidei. Black copper oxide changes to pink, condensation appears

1. CuO + H2 → Cu + H2O Hydrogen reacts with nitrogen forming ammonia in the Haber-

Bosch process1. N2 + 3H2 → 2NH3

3. Preparation of Hydrogen Hydrogen is prepared using zinc (or magnesium) and dilute

hydrochloric acid

Hydrogen is collected over water as it is insoluble in water. The reaction with magnesium is more vigorous and not

recommended for a controlled preparation of hydrogen gas.

Zn + 2HCL → ZnCl2 + H2

4. Test for Hydrogen Apply a lighted splint to the gas.

5. Uses of Hydrogen Weather Balloons Rocket Engines Clean Fuel

Carbon

Carbon exists as two distinct isotopes, Graphite and Diamond. The two forms have identical atoms but it is the way in which atoms are bonded that makes the forms different.

Diamond-

Hardest naturally occurring substance Very high melting point (3500c) Diamond-tipped tools are used for cutting glass/drilling/engraving Each carbon atom is strongly bonded to four others in a tetrahedral

arrangement The strength and number of bonds accounts for very high melting

point Does not conduct electricity

Graphite-

Only non-metal to conduct electricity Very high melting point (3600c) Layered structure that means layers can slide over each other Each carbon atom is strongly bonded to three others in a hexagon Has delocalised electrons between the layers Strong covalent bonds within layers give it a high melting point

Buckminsterfullerene (C60)-

Covalently bonded ball consisting of hexagons and pentagons

Soluble in organic solvents like toluene

Chemical Properties of Carbon

1. Carbon burns in an excess of oxygen. It burns with a dirty orange flame, forming a colourless and odourless gas.

i. C + O2 → CO2

2. Carbon monoxide is formed in a limited supply of oxygen.i. 2C + O2 → 2CO

Chemical Properties of Carbon Dioxide

1. Reaction of Carbon Dioxide with Wateri. Carbon reacts with water to form the weak acid carbonic

acid, H2CO3

ii. This is used in fizzy drinks2. Reaction of Carbon Dioxide with burning magnesium

i. A piece of burning magnesium in a gas jar of carbon dioxide1. A bright white light; a white solid is produced which is

magnesium oxide and specks of black carbona. 2Mg + CO2 → 2MgO + C

Test for Carbon Dioxide

Carbon Dioxide is bubbled through limewater and it turns milky white.

Use of Carbon Dioxide

Carbon Dioxide is used in:o Fire Extinguishers o Carbonated Drinkso Dry Ice

Nitrogen (N2)

Nitrogen is a colourless, odourless gas that is insoluble in water. It is a diatomic gas which means it consists of two atoms of the same element.

Properties of Nitrogen (N2)

1. Nitrogen and hydrogen react to form ammonia, the Haber-Bosch process.

i. Nitrogen and hydrogen are mixed 3:1ii. They are reacted at 450c, a pressure of 200 atm and with an

iron catalyst.iii. N2 + 3H2 → 2NH3

iv. The gases are then cooled to condense the ammonia.v. Unreacted nitrogen and hydrogen are recycled.

vi. The Haber-Bosch process cannot be demonstrated in the laboratory due to the high pressure and temperature used, the specialised plan required and safety of staff and students. It is also too expensive.

Uses of Nitrogen

Nitrogen is used:o As a coolant (liquid nitrogen)o In food packaging (nitrogen creates an inert atmosphere used to

keep food fresh)

Nitric Acid

Nitric acid is manufactured from ammonia. There are three main stages of production.

Nitric Acid Manufacture

Stage 1: Catalytic oxidation of ammonia

Ammonia and air are mixed and pass over platinum gauze at a temperature of 950c and at a pressure of 2 atmospheres.

The product is nitrogen monoxide, NO

Equation: 4NH3 + 5O2 → 4NO + 6H2O

Stage 2: Further oxidation of nitrogen monoxide

The gases are mixed with more air and nitrogen monoxide is converted to nitrogen dioxide.

Equation: 2NO + O2 → 2NO2

Stage 2: Formation of Nitric Acid

The gases are mixed with more air and passed up a tower of glass beads that have water flowing down.

Equation: 4NO2 + O2 + 2H2O → 2HNO3

Oxygen

Oxygen is a colourless, odourless gas that is only slightly soluble in water and is slightly denser that air.

Test for Oxygen

A glowing splint is put into oxygen and it relights.

Uses of Oxygen

Oxygen is used in:o Medicineo Weldingo Rocket Engines

Properties of Oxygen

(See revision book pg 136-137)

Sulphur

Sulphur is a brittle yellow solid Sulphur does not react with water or acid but burns with a blue flame in

air/oxygen producing the colourless but pungent gas sulphur dioxide, SO2.

Uses of Sulphur

Sulphur is used in:o Vulcanising of Rubbero Fungicide

Properties of Sulphur Dioxide

Sulphur Dioxide reacts with water to form the weak acid sulphurous acid.

SO2 + H2O → H2SO3

Sulphur dioxide in the atmosphere reacts with rain water to form acid rain.

Acid Rain has three main effects-o Corrodes limestoneo Defoliates treeso Pollutes lakes and rivers

Acid Rain can be prevented by-o Removing sulphur from fuel sourceso Using renewable energyo Using cars fitted with catalytic converterso Burning less fossil fuels

Properties of Dilute Sulphuric Acid

1. Reaction of concentrated sulphuric acid with sodium chloride.a. Bubbles of gas; fumes; heat released

i. NaCl + H2SO4 → NaHSO4 + HClb. This reaction is used to prepare hydrogen chloride gas in the

laboratory. It is the first and only reaction where you will meet the hydrogen sulphate ion.

2. Reaction of concentrated sulphuric acid with sugar.a. Concentrated sulphuric acid dehydrates sugar to form carbon

which is a black solid and water which is released as water vapour.b. The sugar swells and rises in the container. The reaction is not

immediate. Heat is released and there is a distinct caramel smell and a pungent odour. A black solid remains.

i. Sugar → Carbon + Water3. Reaction of Concentrated sulphuric acid with hydrated copper (ll)

sulphate.a. The blue solid changes to white. The concentrated sulphuric acid

again behaves as a dehydrating agent, removing the water of crystallisation to form the white solid anhydrous copper (ll) sulphate.

4. Reaction of concentrated sulphuric acid with alcohols and organic acids forming esters.

a. The formation of the ester ethyl Ethanoate is promoted using concentrated sulphuric acid, again as a dehydrating again. Concentrated sulphuric acid acts most often as a dehydrating agent removing water.

Hydrochloric Acid

Hydrochloric acid is a typical mineral acid and undergoes typical reactions with metals, metal oxides, metal hydroxides and metal carbonates.

Almost all chlorides are soluble in water and so the salts produced are in solution.

A metal ion in a compound that will not dissolve in water can be made to dissolve by reaction with a dilute acid, such as hydrochloric acid or nitric acid.

Properties of Hydrochloric Acid

1. Reaction of hydrochloric acid with metals.a. Most metals react with dilute hydrochloric acid to give the

corresponding chloride and hydrogen gas.b. Bubbles of gas produced; heat released; metal disappears;

colourless solution formedi. Mg + 2HCl → MgCl2 + H2

2. Reaction of hydrochloric acid with metal oxides and hydroxides a. Metal oxides and hydroxides react with dilute hydrochloric acid,

producing the corresponding chloride and water.b. Solid disappears; heat released; the colour of the solution formed

depends on the metal ions present, for example a solution of copper chloride is blue but most are colourless solutions.

i. CaO + 2HCl → CaCl2 + H2O3. Reactions of Hydrochloric acid with Metal carbonates.

a. All metal carbonates react with dilute hydrochloric acid, producing the corresponding chloride, carbon dioxide and water.

b. Solid disappears; bubbles of gas produced; heat released; the colour of the solution formed depends on the metal ion.

i. CaCO3 + 2HCl → CaCl2 + CO2 + H2O

23. Organic Chemistry

Origin of Oil

Crude oil is formed from organic material of the remains of plant and animal organisms that lived millions of years ago. These remains form sediments e.g. at the bottom of seas, and become buried under layers of sedimentary rock. They decay, without air (oxygen), under the action of heat and pressure to form crude oil over millions of years.

It is a non-renewable and finite (limited reserves) energy resource because it takes millions of years to form and we burn it faster than it has is formed!

Coal, peat and natural gas are the other principal non-renewable fossil fuels formed from the remains of plants or animals.

Fractional Distillation of Oil

Fractional Distillation is carried out in a fractioning column.

The crude oil enters at the bottom as a hot, gaseous mixture.

The fractioning column has bubble caps that allow gases to move upwards.

The temperature decreases up the column.

As the gases move up the column, hydrocarbons condense when the temperature of the column is the same as their boiling point.

See Table on next page for Fractioning of Oil

Combustion of Hydrocarbons

Combustion: is the reaction of a fuel with oxygen, producing oxides and releasing heat.

Complete Combustion: is a fuel burning in a plentiful supply of oxygen/air, producing carbon dioxide and water and releasing heat.

Incomplete Combustion: is a fuel burning in a limited supply of oxygen/air and producing carbon monoxide and water and releasing heat.

Homologous Series

A homologous series is a family of organic molecules that have the same general formula; show similar chemical properties and show a graduation in their physical properties and differ by a CH2 unit.

There are two hydrocarbon homologous series, called the alkanes and alkenes. Alkanes are unreactive hydrocarbons and Alkenes are more reactive hydrocarbons.

Saturation and Unsaturation

Alkenes have on C=C double bond per molecule – they are unsaturated. Alkanes have no C=C double bond per molecule- they are saturated.

Testing for double bonds/saturation

o Add the substance to bromine water.

o For an unsaturated substance/any alkene: colour changes from a red-brown to colourless

o For a saturated substance/any alkane: colour remains red-brown

Alkenes and Alkanes

Figure 5: The first four Alkanes

Figure 6: The first two Alkenes

Addition Polymerisation

Polymerisation is the process of creating a long molecule from a small molecule which forms the repeating unit in the polymer.

A polymer is a long molecule formed by bonding together small molecules into a chain.

Addition polymerisation is the process of adding molecules together to form a polymer. The long molecule is called the polymer.

The simple molecule from which a polymer is formed is called the monomer.

The monomer has a double bond between the two carbon atoms.

The monomer is an alkene.

The polymer is shown as the monomer with only a single bond in a square bracket.

n molecules of monomer must be at the beginning of the equation.

The polymer structure has n after it to show that the polymer repeats n times.

Common Addition Polymers

Polythene-

Uses: plastic bags and bottles

Poly Vinyl Chloride-

Uses: vinyl records, door and window frames, clothing

Disposal of Polymers

There are two methods of disposal for polymers-o Landfillo Incineration

There are environmental problems associated with each method of disposal-

o Landfill wastes lando Incineration produces polluting gases which are released into the

atmosphere Polymers are increasingly being recycled and biodegradable polymers

have been developed and are now in use.

Reactions of Ethene

Combustion of Ethene-

o Ethene burns with an orange flame, releasing heat. C2H4 + 3O2 → 2CO2 + 2H2O

Ethene reacts with steam, producing ethanol-o C2H4 + H2O → C2H5OH

Ethanol

C2H5OH

Reactions of Ethanol

Combustion of Ethanol-o Burns with a clean blue flame, heat is released.

C2H5OH (l) + 3O2 (g) → 2CO2 (g) + 3H2O (g)

Making Ethanol

Ethanol can be produced by the fermentation of sugars. Sugar solution is mixed with yeast in warm conditions in the absence of oxygen. The reaction produces carbon dioxide and ethanol.

o Sugar → ethanol + carbon dioxide

Ethanol can be made by reacting ethene with steam.o C2H4 + H2O → C2H5OH

Use of Ethanol

Ethanol is used for-o In alcoholic drinkso As a solvent

Ethanoic Acid

CH3COOH

Ethanoic acid is also called acetic acid. A dilute solution of Ethanoic acid is vinegar.

Reactions of Ethanoic Acid

1. Reaction of Ethanoic acid with a metala. Bubbles of has produced, heat released, metal disappears,

colourless solution formed.b. Ethanoic Acid + metal → Metal Ethanoate + hydrogen

i. 2CH3COOH + Mg → (CH3COO)2Mg + H2

2. Reaction of Ethanoic acid with a metal oxidea. Heat released, solid disappears, colourless solution formedb. Ethanoic Acid + Metal Oxide → Metal Ethanoate + Water

i. 2CH3COOH + CaO → (CH3COO)2Ca + H2O

Uses of Ethanoic Acid

Ethanoic Acid is used as:o A preservativeo Flavouring

Esterification

An ester is a compound formed between a carboxylic acid and an alcohol.

o CH3COOH + C2H5OH → CH3COOC2H5 + H2Oo Ethanoic Acid + Ethanol → Ethyl Ethanoate + Water

Ethyl Ethanoate

CH3COOC2H5

Uses of Ethyl Ethanoate

Ethyl Ethanoate is used as:o Flavouring in Foodso Solvent

Preparation of Ethyl Ethanoate

Mix equal amounts of Ethanoic acid and ethanol in a boiling tube. Then add a few drops of concentrated sulphuric acid and warm gently.

Preparation of Organic Compounds

The first four alkanes are colourless gases. The first two alkenes are colourless gases. All the polymers are white solids. Coloured dyes can be added to them

to make coloured plastics. Ethanol is a colourless liquid with an alcohol like odour. Ethanoic acid is a colourless liquid with vinegar like odour. Ethanol and Ethanoic acid mix with water. Ethyl Ethanoate is a colourless liquid with a fruity/solvent smell. Ethyl Ethanoate does not mix with water. The high the carbon content, the sootier and more orange it’s flame

when it burns. The lower the carbon content, the less sooty and more clean and blue its

flame when it burns. Ethanol burns with a cleaner, blue flame than the alkanes or alkenes.

THIS SECTION AND PROPERTIES MUST BE KNOWN FOR QUESTIONS INVOLVING UNKNOWN ORGANIC COMPOUNDS. A SAMPLE OF PROPERTIES WILL BE GIVEN AND THE COMPOUND MUST BE WORKED OUT USING THE

COMPOUNDS.

24. Human Influences

Pollution

The effect of human activity can result in chemical being found where they cause harm, such chemicals are called pollutants.

As more has been learned about pollution, efforts have been made to deal with problems.

Once sewage went straight into the local river or sea, but now it is dealt with by sewage works.

The Clean Air Act that allowed local authorities to set up smokeless zones has greatly reduced air pollution.

Oceans, seas and rivers that are polluted in one country affect many others. A factory in Basle, Switzerland had a fire, when it was being out pollutants were washed into the river Rhine. The pollution was carried down the river causing problems as it passed through France, Germany, and The Netherlands.

The air is international and acid rain is an international problem. The sulphur dioxide may be produced in one country and carried away by the wind. Lakes in Scandinavia have been badly affected by acid rain formed in Britain.

Greenhouse gases are also another matter for international concern. Governments meet at summits to discuss the environment and the harm we are causing it. Unfortunately getting them all to agree about what has to be done seems to be impossible.

25. Industrial Processes

Limestone Quarrying

Limestone has many uses and is a very important raw material for industry.

Limestone in an abundant raw material and as it is relatively easily obtained it is fairly cheap. The business of quarrying provides jobs at the quarry and transportation.

Unfortunately, quarries destroy natural habitats and the traffic associated with them contributes to noise and dust pollution, as does blasting.

If a new quarry is to be dug consideration must be given to the balance between the demands and care for the environment.

Peat Cutting

Peat has been used as a fuel for centuries. In Ireland families has rights to remove the turf from certain, usually quite small, strip of local peat bogs.

Once industry became involved, the removal of peat from the bog speeded up and is now used as a fuel and for treating soil and making gardening composts.

Peat bogs are very special habitats and many of the plants found in them are not found anywhere else. Large-scale peat cutting was destroying these habitats too rapidly. Concern about the loss of peat bogs prompted many gardeners to stop using peat-bases products.

Lignite Mining

Lignite, a brown soft coal, can be found around Lough Neagh. The Crumlin area was estimated to have reserves of about 200 million tonnes that could be obtained by open cast mining.

During the energy crisis of the 60’s interest was shown in these reserves. Three possibly commercial seams were identified and they could have been very important for Northern Ireland.

It was suggested that the lignite could be extracted and burned to provide 40 per cent of the electricity needs for the country.

This would have been of economic value, as we would have needed to import less oil.

The project in opening and running the mine would have provided employment; the forecast was for about 400 new jobs.

The lignite found in Northern Ireland is low in sulphur and would result in relatively low atmospheric pollution when it was burnt.

There were many factors against the project. Not only would the mining destroy the natural habitat of local wildlife, it could also be unsightly. The area has a thriving fishing industry and productive agriculture land.

It included five listed buildings and thought it would interrupt water supplies.

In the end it was shelved but who knows what may happen in the future.

Solution Mining

Common salt, sodium chloride, is a very important raw material for the chemical industry. Most of our salt comes from Cheshire, England and is brought to the surface by solution mining.

Water is pumped down into the rock and the salt dissolves leaving behind the rock. The salt solution, brine, is pumped to the surface.

This method has a much less detrimental effect on the environment than other forms of mining.

Unfortunately, solution mining weakens the rock and can result in subsidence.

26. Radioactivity

Alpha Beta GammaSymbol

Contains 2 protons and 2 neutrons

1 electron – from the nucleus

An electromagnetic wave

Emitted when

4 particles are emitted from the nucleus (this is the same as a helium nucleus)

A neutron changes into a proton and emits a very fast electron

The nucleus vibrates (in an electric and magnetic field)

Relative charge

+2 -1 0

Ionising ability

high medium Low

Relative mass

4 1/2000 (very low) 0

Stopped by paper 0.5cm Aluminium A few cm of lead or a few metres of concrete.(they exist with a range of energies so a few may be stopped by Aluminium etc)

Effect in electric field

Bend towards – plate (opposites attract)

Bend towards + plate (opposites attract)

Go straight through (as they are uncharged)

Range in air

4cm A few metres Infinite (are not stopped by air)

Effect in magnetic field

Change direction in field (opposite direction to alpha)

Change direction in field (opposite direction to alpha)

Unaffected by magnetic field, go straight through.

Uses Smoke alarms – a small source of alpha particle set up a very short distance from a detector. The alpha particles ionise the air and this makes a current that completes a circuit. If smoke particles get I the way, the circuit is broken and sets off an alarm.

Not generally used. To detect thickness of Aluminium sheets on a production line. An emitter and detector are place on opposite side of the sheet. If a normal amount of gamma is detected. If the sheet is too thick then fewer gammas is detected, if the sheet is too thin then more gamma is detected and the machine is adjusted accordingly.

Can be used as a tracer either in the body or in water pipes etc. A small amount of gamma source is introduced into the vessels and a gamma detector is placed over them. If a normal level of gamma is detected then the vessels are free flowing. If very high level is detected then there is a blockage or leak at that point. If little or no radiation is detected then this must be after the blockage.Carbon dating and Uranium dating – see half life.

Most dangerous…

When inside the body as they are highly ionising and most dangerous of the 3, but are not very dangerous outside the body as they cannot go through the skin

Fairly dangerous inside and outside the body as they can go through a few layers of skin and can ionise cells causing damage.

Dangerous both outside and inside the body. Most dangerous of the 3 outside the body as they can penetrate through the body and ionise cell deep inside the body. Mot as dangerous as alpha or beta inside the body as it is less ionising.

Half-Life

As a radioactive isotope decays the activity of the sample decreases. The half-life of an isotope is the time taken for the activity to fall by half.

Each isotope has a specific and constant half-life.

Changes in the Nucleus

Alpha Decay: The two protons and two neutrons that make up an alpha particle leave the nucleus together as a helium ion.

Beta Decay: The electron that is the beta particle is formed in the nucleus. A neutron changes into a proton, which stays in the nucleus and an electron which is emitted.

Figure 7: Alpha particle emitted from Radon Figure 8: Beta Decay