Topic 1 - Chemical ReactionsChemical Reactions:

Chemical reactions always produce new substances. Special examples of forming new substances include:

effervescence - bubbling or fizzing in a liquid.precipitation - a solid forming in a liquid.

Chemical reactions can also involve a colour change. Some chemical reactions can involve a detectable energy change

like:heat and light produced by a burning candle.electrical energy from a battery.

Chemical reactions do not involve:meltingboilingevaporatingfreezingcondensingdissolving

Atoms: Everything in the universe is made of atoms. A substance in which all the atoms are of the same type is called an

element. The elements are arranged in the periodic table according to atomic

number. There are around 111 elements in total.

Compounds: A compound is formed when different elements react and join

together. Compounds containing two elements end in the letters - ide:

- copper chloride - copper and chlorine Compounds containing three or more elements including oxygen end

in the letters -ite or -ate:- nickel sulphate - nickel, sulphur and oxygen- sodium phosphite - sodium, phosphorus and oxygen

Exceptions to this rule:- hydroxides (OH)

calcium hydroxide - calcium, hydrogen and oxygen- cyanides (CN)

iron cyanide - iron, carbon and nitrogen To separate a compound into its elements, energy is needed:

iron oxide- iron can be separated from oxygen by heating with carbon.

copper chloride- copper can be separated from chlorine using electricity.

Mixtures: Mixtures are formed when substances come together without joining. These substances can be separated without using energy:

- iron and sulphur can be separated using a magnet.- chalk and water can be separated by filtration.

Dissolving

A soluble substance dissolves in a liquid. An insoluble substance does not dissolve in a liquid. A solvent is a liquid in which a substance dissolves. The solute is the substance which dissolves in the liquid (solvent). A solute can be a solid, liquid or gas. A solution is formed when a solute dissolves in a solvent. For example: Brine is made when salt is dissolved in water.

water is the solventsalt is the solutebrine is the solution

In an aqueous solution water is the solvent. A saturated solution is one that can't dissolve any more solute.

Topic 2 - Speed of Reactions

Factors affecting the speed of a reaction are:

Particle SizeThe smaller the particle size the higher the rate of the reaction.

Wood shavings burn faster than a block of wood. Coal dust is explosive, unlike coal lumps. Steel wool is flammable, a steel bar isn’t.

TemperatureThe higher the temperature the higher the rate of the reaction.

Hot car exhausts rust faster than the rest of the car body which is cooler.

Food in a fridge takes longer to go off than food at room temperature.

ConcentrationConcentration is measured in moles per litre (mol/l or M).A 2M solution is more concentrated than a 1M solution.The higher the concentration the faster the rate of the reaction.

cars rust quicker in cities where the concentration of acid rain is higher than in the country.

boats corrode slower in fresh water than in sea water which has a higher concentration of salt.

CatalystsA catalyst speeds up the rate of a reaction without being used up itself. Catalysts are unchanged at the end of the reaction and can be used again and again.

Catalytic converters in car exhausts change toxic oxides of nitrogen and carbon into harmless substances.

Biological catalysts (enzymes) are used by our bodies to break down food into substances we need to stay alive and healthy.

Nickel is used as a catalyst to speed up the manufacture of margarine from vegetable oil.

Topic 3 - Atoms and the Periodic TableElements:

can be naturally occurring or made by scientists. can be solid, liquid or gas. can be metals or non-metals.

Periodic Table:H HeLi Be B C N O F NeNa M

gAl Si P S Cl Ar

K Ca Sc Ti V Cr Mn

Fe Co Ni Cu Zn Ga Ge As Se Br Kr

Rb Sr Y Zr Nb Mo

Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe

Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At RnFr Ra Ac

is a chart which lists all the elements a row from left to right is called a period a column from top to bottom is called a group metals are on the left hand side of the zigzag line and non-metals

are on the right.

Atoms: are very small particles which make up every element each element is made from only one type of atom the nucleus is the small core at the centre of the atom the nucleus has a positive charge atoms of different elements vary in size and mass elements are arranged in the periodic table in order of increasing

atomic number elements in the same group have similar chemical properties; e.g.

-the alkali metals (group 1 and 1 outer electron) -the halogens (group 7 and 7 outer electrons)-the noble gases (group 8 and 8 outer electrons [except He])

Inside the Atom: atoms are made up of smaller particles. These are:

Particle Charge Mass Positionproton 1+ 1 a.m.u nucleus

electron 1- Almost zero orbiting nucleusneutron 0 1 a.m.u. nucleus

Notes: If asked for the charge on a proton or electron in the exam always

write 1+ or 1- and not simply positive(+) or negative (-). Also, if asked about the mass of particles don’t forget the units - a.m.u

(atomic mass units). Electrons are arranged in energy levels around the nucleus.

Symbols: the atomic number and mass number of an atom can be shown as:

Exy

elementsymbol

massnumberatomicnumber

the mass number is the number of protons and the number of neutrons added together (i.e. = x)

the atomic number shows the number of protons in an atom (i.e. = y) in an atom the number of protons equals the number of electrons all atoms are neutral because the positive charge of the nucleus is

cancelled by the negative charge of the electrons the number of neutrons in an atom can be calculated by subtracting

the atomic number from the mass number (i.e. x - y = neutrons) isotopes are atoms with the same number of protons but different

numbers of neutrons the relative atomic mass is rarely a whole number as it is the

average mass of all the atoms of an element; e.g. bromine has two isotopes each has an abundance of 50%

Br79 8135 35Br&

the relative atomic mass of bromine is the average of the mass numbers, i.e. 80.

Topic 4 - How Atoms Combine

Covalent Bonding: occurs between non-metal atoms involves atoms sharing electrons

Stable Electron Arrangements:

occur when atoms have a filled outer energy level. sharing electrons allows atoms to have full outer shells; i.e. the

electron arrangement of a noble gas

Molecules: a molecule is a group of atoms held together by covalent bonds. a diatomic molecule contains two atoms joined together by a covalent

bond; i.e. HF (g), O2(g). the chemical formula of a covalent molecule shows the number of

each type of element in the molecule. the diatomic elements are: hydrogen (H2), nitrogen (N2), oxygen

(O2) and all of group 7 (i.e. F2, Cl2, Br2, I2, At2). the diatomic elements contain single bonds except for: oxygen

(double bond;i.e. O=O), and nitrogen (triple bond; i.e. N-N). the full structural formula shows the way in which the atoms are

arranged in a molecule.

OH H

HC

HH H water methane

Covalent Bond: a covalent bond is formed between two atoms when the positive

nucleus of each atom is attracted to the same shared pair of negative electrons.

covalent bonds are very strong and a lot of energy is needed to break them.

fluorine molecule showing outer electrons simplified versionTopic 5 - Fuels

Changes of State: all substances have their own melting and boiling points.

Fuels: are substances which react with oxygen (burn) to produce energy. combustion is another word for burning. an exothermic reaction releases energy (gives out heat). an endothermic reaction uses up energy (uses up heat).

Fossil Fuels:

the shapes of molecules are based on the tetrahedral arrangement of electrons.

F F F F

the main fossil fuels are coal, natural gas, and oil fossil fuels are formed from the remains of dead plants and animals coal is formed from vegetation in swamps oil is formed from marine plants and animals natural gas is formed at the same time as coal and oil fossil fuels are finite resources (will run out) the substances which make up oil and natural gas are mainly

hydrocarbons hydrocarbons are compounds made from hydrogen and carbon

only

Fractional Distillation: crude oil is a mixture of hydrocarbons as it comes from the ground different hydrocarbons have different boiling points hydrocarbons are separated from the crude oil mixture using

fractional distillation a group of hydrocarbons with similar boiling points is called a fraction

Fraction No. of C Atoms

Boiling Range Uses

Petroleum Gas 1 -4 -160 - 20 ˚C gas fuelNaphtha 5 - 10 20 - 120 ˚C petrolKerosene 11 - 12 120 - 240˚C paraffin/jet enginesGas Oils 13 - 25 240 - 350˚C dieselResidue 25+ 350˚C+ lubricants, tar

as molecular size increases;- the boiling point increases- the flammability decreases- the viscosity increases

Pollution: fossil fuels contain sulphur compounds which burn to produce

sulphur dioxide. sulphur dioxide dissolves in raindrops producing acid rain. oxides of nitrogen are produced in car engines from the igniting

spark. nitrogen oxides also dissolve in raindrops producing acid rain. in restricted oxygen, carbon monoxide is produced(a poisonous gas). carbon monoxide and nitrogen oxide levels can be reduced using

catalytic converters in car exhausts. carbon dioxide contributes to the greenhouse effect (global

warming). lead compounds in petrol are poisonous when breathed. Use

unleaded petrol.

Burning Hydrocarbons: hydrocarbons burn in plentiful oxygen to produce carbon dioxide

and water.

if carbon dioxide is present, the lime water will turn milky. This shows that the fuel contains carbon.

if water is present, cobalt chloride paper changes from blue to pink. This shows that the fuel contains hydrogen.

lime water turns cloudy

cobalt chloride paper changes from blue to

pink

To water pump

Topic 6 - Structures and Reactions of HydrocarbonsA homologous series a set of compounds with similar chemical properties which can be represented by a general formula.

Saturation: a saturated hydrocarbon contains only single carbon to carbon

bonds. an unsaturated hydrocarbon contains at least one carbon to carbon

double bond.

Alkanes: are a subset of the set of hydrocarbons all end in the letters -ane are a homologous series with general formula CnH2n+2 are used as fuels (gas and petrol), lubricants and bitumen. are saturated hydrocarbons

Prefix Number of Carbons

Alkane State

meth- 1 gaseth- 2 gas

prop- 3 gasbut- 4 gaspent- 5 liquidhex- 6 liquidhept 7 liquidoct- 8 liquid

Note:If you forget the prefixes then look at page 6 of the data booklet. The alkanes are listed in a table, in order, so you can work out the number of carbons from that.

Alkenes: are a subset of the set of hydrocarbons all end in the letters -ene are a homologous series with formula CnH2n are unsaturated hydrocarbons

Cycloalkanes: are a homologous series with general formula CnH2n are saturated hydrocarbons

Saturation Test (Bromine water): unsaturated hydrocarbons decolourise bromine water immediately. saturated hydrocarbons decolourise bromine water very slowly.

Cracking: fractional distillation yields more long chain hydrocarbons than are

useful for present day industrial purposes. cracking is an industrial method for producing smaller more useful

molecules. cracking produces a mixture of saturated and unsaturated products.

e.g.C8H18 C5H12 + C3H6

saturated saturated unsaturated

a catalyst allows the reaction to take place at a lower temperature.

Structures:

Series Alkanes Alkenes CycloalkanesMolecularFormula C3H8 C3H6 C3H6

FullStructuralFormula

C C C HH

H

H

HH

H

HC C C

HH

H

H

HH

CC C

H H

HH H

HShortenedStructuralFormula

CH3CH2CH3 CH3CH=CH2

CH2CH2 CH2

isomers are compounds with the same molecular formula but different structural formulae.

Note: Alkenes and cycloalkanes are isomers of each other, e.g. butene and cyclobutane both have formula C4H8. You can tell the difference between them using bromine solution. Butene decolourises bromine solution instantly.

Reactions of Hydrocarbons: alkenes react with hydrogen to form the corresponding alkane.

e.g.

C CH

H

H

HC CH HH

H

H

H+ H2

ethene ethane

alkenes react with brominee.g.

C CH

H

H

HC CH HH

Br

H

Br+ Br2

ethene dibromoethane

both these reactions are addition reactions.

Topic 7 - Properties of Substances

Electrical Conductivity: an electric current is a flow of charged particles. metal elements and carbon (graphite) are electrical conductors non-metal elements are non-conductors of electricity covalent compounds do not conduct electricity in any state. ionic compounds conduct when molten or in solution. ionic compounds do not conduct when solid. electrons flow through metals. ions flow through solutions or melts. electrical energy chemically changes a liquid or solution which

conducts. a d.c. supply must be used if the products are to be identified.

Formation of Ions: atoms lose or gain electrons to form the stable electron arrangement

of the nearest noble gas. metal elements lose electrons to form positive ions;

e.g.Na Na+ + e

non-metal elements gain electrons to produce negative ions; e.g.

Cl2 + 2e 2Cl-

At room temperature: covalent compounds can be solids, liquids or gases. ionic compounds are all solids.

Structures: ionic solids exist as networks/lattices of oppositely charged ions. some covalent solids are network structures. both these contain strong bonds and so have high melting points. other covalent compounds exist as molecules. the forces holding the molecules are weak and so these compounds

have low melting points.

Dissolving: some covalent substances do not dissolve in water but will dissolve in

other covalent solvents. when ionic compounds dissolve in water, the lattice breaks up

completely.

Electrolysis: an electrolyte is a liquid which conducts electricity electrolysis is the break up of a compound into its elements using

electricity positive metal ions are attracted to the negative electrodes where

they gain electrons forming atoms; e.g.

Cu2+ + 2e Cu

negative non-metal ions are attracted to the positive electrode where they give up electrons to form atoms; e.g.

2Br- Br2 + 2e

ionic liquids and solutions conduct electricity as the ions are free to move

ionic solids do not conduct as the ions cannot move covalent compounds cannot be electrolysed as there are no ions

present.

Colour of Ions:

Some ions are coloured. Examples are shown in the table below. You do not need to learn these though.

Ion Colourcopper bluenickel green

potassium colourlesssodium colourlesschloride colourless

chromate yellowpermanganat

epurple

sulphate colourless

Topic 8 - Acids and Alkalis

Dissolving Oxides:• non-metal oxides dissolve in water to produce acid solutions• metal oxides dissolve in water to produce alkaline solutions

Acid Rain:• sulphur dioxide reacts with water in the atmosphere to produce acid rain• acid rain corrodes stone buildings and kills animal and plant life.

The pH Scale:• the pH scale is a continuous range• acids have a pH of less than 7• alkalis have a pH of more than 7• pure water and neutral solutions have a pH equal to 7

Acids AlkalisFound in the Home vinegar (ethanoic

acid)lemon juice

caustic soda (sodium hydroxide)ammonia cleanertoothpaste

Found in the Laboratory

sulphuric acid (H2SO4)hydrochloric acid (HCl)nitric acid (HNO3)

sodium hydroxide (NaOH)lime water (Ca(OH)2)

Ions in Solution:• H+(aq) ions are present in an acid solution.• acidic solutions contain more H+(aq) ions than does pure water.• OH-(aq) ions are present in an alkali solution.• the concentration of ions in water is small.• alkaline solutions contain more OH-(aq) ions than does pure water.• in water and a neutral solution, the concentration of H+(aq) and OH-(aq) ions is the

same.

Adding water to:• acids decreases the concentration of H+(aq) ions and increases the pH.• alkalis decreases the concentration of the OH-(aq) ions and decreases the pH.

Topic 9 - Reaction of Acids

Neutralisation: neutralisation is the reaction of acids with neutralisers; e.g.

-reducing acidity in soil by adding lime-the use of lime to reduce acidity in lakes caused by acid rain-treatment of acid indigestion

neutralisation moves the pH of an acid up towards 7 the reaction of acids with alkalis is an example of neutralisation neutralisation moves the pH of an alkali towards 7 the reaction of H+(aq) with OH-(aq) ions to form water is an example of

neutralisation.

Bases: a base is a substance which neutralises an acid a base that dissolves in water forms an alkali

Salts:A salt is a substance in which the hydrogen ion of an acid has been replaced by a metal ion (or the ammonium ion).

Reactions of Acids:1. acid + base salt + water

HCl + NaOH NaCl + H2O

2. acid + carbonate salt + carbon dioxide + waterHNO3 + LiCO3 LiNO3 + CO2 + H2O

3. acid + metal salt + hydrogen gasH2SO4 + Mg MgSO4 + H2

Environmental Impact: acid rain reacts with limestone and chalk (in buildings and monuments) acid rain dissolves iron structures (bridges etc.)

Preparation of Salts:When preparing a soluble salt it is easier to use an insoluble carbonate or base as the neutraliser as the excess can be filtered off.

CuO(s) + H2SO4(aq) CuSO4(aq) + H2O(l)

Insoluble salts can be formed by precipitation; e.g.

Ba(OH)2(aq) + H2SO4(aq) BaSO4(s) + H2O(l)

Topic 10 - Making ElectricityBatteries:

in a battery, electricity comes from a chemical reaction electricity passing along metal wires is a flow of electrons batteries need to be replaced when the chemicals inside are used up.

some batteries are rechargeable; e.g. the lead-acid battery all batteries contain electrolytes the purpose of the electrolyte is to complete the circuit

Comparing Battery and Mains Electricity: batteries are safer and more portable mains electricity is cheaper both mains and battery electricity use up finite resources (fossil fuels

and metals)

Cells: electricity can be produced by connecting two different metals

together (with an electrolyte) to form a cell. ammonium chloride in a cell is an example of an electrolyte the voltage between different pairs of metals varies electricity can be produced in a cell by connecting two different metals

in solutions of their metal ions.e.g.

V

salt bridge

magnesiummetal

Mg2+ (aq) ions

lead metal

Pb2+ (aq) ions

electron flow

halfcell

halfcell

electrons flow from the higher metal to the lower one; i.e. from magnesium to lead

the movement of ions in the “ion bridge” is to provide ions to complete the circuit.

the greater the distance between the metals in the electrochemical series, the higher the voltage.

electricity can be produced in a cell when at least one of the half cells does not involve a metal; e.g. carbon electrode in I-(aq) ions

V

salt bridge

zinc metal

Zn2+ (aq) ions

carbon rod

Iodine (I 2)solution

electron flow

The Electrochemical Series:

places metals in order of their willingness to give up electrons is shown on page 7 of the data booklet the reactions of metals with acids can establish the position of

hydrogen in the electrochemical series

Displacement Reactions: are reactions which occur when a metal higher up in the

electrochemical series is added to a solution containing ions of a metal lower down in the series; e.g. magnesium metal added to copper ions-

-the higher magnesium metal will form ions in solution-the lower copper ions will form copper metal and come out of

solution the electrochemical series can be used to predict whether or not a

displacement reaction will occur; i.e. the metal being added must be higher than the ions in solution for displacement to occur.

Oxidation: is a loss of electrons by a reactant in any reaction a metal element reacting to form a compound is an example of

oxidation

Reduction: is a gain of electrons by a reactant in any reaction a compound reacting to form a metal is an example of reduction

Redox Reactions: in a redox reaction, oxidation and reduction occur at the same time.

Topic 11 - MetalsProperties of metals:

strength - iron is used to build bridges etc. malleability - this means metals can be rolled and shaped. electrical conductivity - metals conduct electricity when solid or

liquid. Copper is used in electrical cables. conduction of heat - metals are used in cooking pots and quickly

conduct heat to food. density - aluminium has a low density and is used in aircraft.

Reasons for Recycling: some metals will soon run out it is cheaper to recycle aluminium than extract it from its ore.

Reactivity of Metals: metals can be arranged in order of reactivity

Name Symbolpotassium Ksodium Nalithium Licalcium Camagnesium

Mg

aluminium Alzinc Zniron Fetin Snlead Pbcopper Cumercury Hgsilver Aggold Au

all metals above silver combine with oxygen when heated

metal + oxygen metal oxide

metals above aluminium react with water to produce the metal hydroxide and hydrogen

metal + water metal hydroxide + hydrogen gas

metals above copper react with dilute acid to produce a salt and hydrogen

metal + acid metal salt + hydrogen gas

Metal Ores: ores are naturally occurring compounds of metals the less reactive metals are found uncombined in the Earth’s crust more reactive metals have to be extracted from ores

Extraction from Ores: the extraction of a metal from its ore is an example of reduction the less reactive metals were the first to be discovered as they were

found uncombined metals below copper can be extracted by heat alone

metal oxide metal + oxygen gas

metals below aluminium can be extracted by heating with carbon

metal oxide + carbon metal + carbon dioxide

metals above zinc need other methods as they are so reactive.

Extraction of Iron: iron is produced from iron ore in a blast furnace the two key reactions which take place in the blast furnace are:

- production of carbon monoxide2C + O2 2CO

- reduction of iron oxideFe2O3 + 3CO 2Fe + 3CO2

Alloys: an alloy is a mixture of metals or of metals with non-metals

e.g. brass, solder, stainless steel.Topic 12 - Corrosion

Corrosion: corrosion is a chemical reaction which involves the surface of a metal

changing from an element to a compound corrosion is an example of oxidation the corrosion of iron is known as rusting

Rusting of Iron: water, oxygen and an electrolyte (salt or dissolved CO2), are

required for rusting when iron rusts, the iron atoms lose two electrons to form Fe2+ ions

the Fe2+ ions can be further oxidised to Fe3+ ions the electrons lost by the iron during rusting are accepted by the water

and oxygen to form hydroxide ions salt spread on roads increases the rate of corrosion on car bodywork the salt acts as an electrolyte

Test for Rusting: ferroxyl indicator turns blue in the presence of Fe2+ ions ferroxyl indicator turns pink in the presence of OH- ions this can be used to show the extent of the rusting process

Protecting Iron from Rusting: iron does not rust when attached to the negative terminal of a battery electrons flowing from the battery to the iron prevent rusting

Iron/carbon cell:

Physical Protection: a surface barrier to air (oxygen) and water can provide physical

protection against corrosion; e.g.paintinggreasingcoating with plasticgalvanising - metal objects are dipped into molten zinc. This provides a tough coating for the metal.electroplating - silver, chromium and other metals can be deposited on the surface of a metal. The metal to be plated is used as the negative electrode and placed in a solution of ions of the plating metale.g. tin-plating - steel is used as the negative electrode and passed through a solution containing tin ions.

Sacrificial Protection: metals can be sacrificially protected by connecting them to another

metal the sacrificial metal must be higher in the electrochemical series the sacrificial metal loses electrons to the protected metal

iron nail

carbon rod

ferroxyl indicator

AA

preventing it from corrodinge.g. magnesium metal attached to an underground steel pipe prevents the pipe from corroding.

As well as providing physical protection, galvanising also provides sacrificial protection to iron as zinc is higher than iron in the electrochemical series.

Topic 13 - Plastics and Synthetic Fibres most plastics and synthetic fibres are made from oil synthetic is another word for man-made

Properties of Plastics: flexibility - plastic food wrappers need to be flexible waterproof - drinks bottles can be made of plastic light - makes plastic items cheap to transport durable - car bumpers are made of plastic electrical insulators - plugs are made of plastic

Advantages and Disadvantages:

Advantages Disadvantages

Natural materials:biodegradable, expensive,are made from

renewable resourcesdon’t last long

Synthetic materials:

long-lasting, non-biodegradable,cheap made from oil,

burn giving off toxic fumes,

Environmental Impact: biodegradable plastics can be broken down by micro-organisms

into simpler substances. most plastics are not biodegradable they build up in the environment and do not go away

Burning Plastics: some plastics burn or smoulder to give off toxic fumes the toxic gas given off when burning or smouldering is related to the

elements present in the plastic

e.g. Plastic Elements

PresentToxic Gas

polyethene C, H CO gaspolyvinylchloride C, H, Cl HCl & CO gaspolyurethane C, H, N, O HCN & CO gas

Types of Plastic: a thermoplastic plastic is one which can be melted or reshaped a thermosetting plastic is one which cannot be melted or reshaped thermosetting plastics are tough and heat proof thermosetting plastics are used as plugs, sockets, worktops and pot

handles.

Polymers: a polymer is a molecule made up of many repeating units polymers are made from many small molecules which join together these small molecules are called monomers the process of monomers joining together to form a polymer is called

polymerisation

Polymerisation: small unsaturated molecules join together by the opening of the

carbon to carbon double bond the small unsaturated molecules add together to form a polymer this is known as addition polymerisation the making of polyalkenes (e.g. polyethene, polyvinylchloride etc)

are an example of addition polymerisation

Plastics and Fibres: plastics are examples of polymers many plastics are made from small unsaturated molecules produced

by cracking; e.g. polyethene, polypropene the making of plastics is an example of polymerisation fibres, both natural and synthetic, are examples of polymers the name of the polymer is determined by adding the prefix poly- to

the name of the monomer

Polymerisation of Ethene:

Draw the monomer in the shape of an H with the double bond as the cross bar (this step will most likely have been done for you).CCHHHH CCHH

HH Line up 3 of them next to each other replacing the double bond

with a single bond: CCHHHH CCHH

HH CCHHHH

Draw single bonds between the molecules and one on each end:

CCHHHH CCHH

HH CCHHHH

Polyethene

Repeating Unit:

The repeating unit is the smallest part of a polymer chain which can be drawn without repeating the sequence of atoms.

e.g. polychloroethene (polyvinylchloride)

CCClHHH CCClH

HH CCClHHH

The structure is made of many thousands of CCClHHH

units joined together

This is the repeating unit.

Topic 14 - Fertilisers the increasing population has led to a need for more efficient food

production

Growing Plants: growing plants require nutrients, including compounds of nitrogen,

potassium and phosphorus different crops need fertilisers containing different proportions of

nitrogen, phosphorus and potassium

Natural Fertilisers: nitrifying bacteria in root nodules of some plants can convert

atmospheric nitrogen into nitrogen compounds examples of plants which can do this are beans, peas and clover these plants increase the fertility of the soil bacterial methods of fixing nitrogen are cheaper than chemical

methods

Fertilisers: fertilisers are substances which restore the essential elements for

plant growth in the soil artificial fertilisers can have an adverse effect on the environment by:

- making river more acidic- causing algae to grow rapidly which releases poisons in the water

micro-organisms are responsible for returning nitrogen compounds to the soil through decomposition of dead animal and plant material

fertilisers need to be soluble before they can be used by plants; e.g. - ammonium salts and nitrates both contain nitrogen and are very soluble- potassium salts are also very soluble- phosphates contain phosphorus

Making Fertilisers: ammonia and nitric acid are nitrogen compounds which are used to

make fertilisers ammonia can be converted to an ammonium compound by reaction

with an acid

Ammonia: ammonia is an invisible gas ammonia has a characteristic strong smell ammonia dissolves easily in water producing ammonium hydroxide ammonia turns wet pH paper/universal indicator blue

The Haber Process:hydrogennitrogen

H2 + N 2 mixturehigh pressure

moderately high temperaturesiron catalyst

separation of mixture AmmoniaunreactedH2 and N 2recycled

the reaction is carried out at a moderately high temperature as:- too low a temperature gives a low yield of ammonia- too high a temperature causes the ammonia to degrade into elements

not all the nitrogen and hydrogen are converted into ammonia

ammonia can be prepared in the laboratory by reaction of an ammonium compound with an alkali

Nitric Acid: nitrogen gas is very unreactive nitric acid is formed when nitrogen dioxide, in the presence of air,

dissolves in water nitrogen dioxide is produced in the air during lightning storms a lot of energy is needed to break the strong nitrogen triple bonds

before nitrogen will react the energy is provided by lightning or the spark in a car engine the nitrogen oxides in air dissolve in rain water and fall to the soil:

- replacing nitrogen compounds in the soil- increasing the acidity of the soil

The Ostwald Process: the combination of nitrogen and oxygen does not provide an

economic route to nitric acidammonia

hot platinum catalystmoderately high

temperature

nitrogen monoxide

nitrogen dioxide

nitric acid

oxygenfrom air

oxygenfrom air

oxygenfrom air+ water

the reaction is carried out at moderately high temperatures at high temperatures the nitrogen dioxide degrades into elements

Catalytic Oxidation of Ammonia (laboratory): catalytic oxidation of ammonia can be carried out in the laboratory it is not necessary to continue heating once the reaction starts as the

reaction is exothermic

The Nitrogen Cycle:

Nitrogen is introduced into the soil by: lightning storms nitrifying bacteria biodegrading of organic material artificial fertilisers

Topic 15 - Carbohydrates and Related SubstancesPhotosynthesis:

photosynthesis is the process by which plants make carbohydrates from carbon dioxide and water, using light energy in the presence of chlorophyll

Nitrogen is lost from the soil by:

harvesting crops denitrifying bacteria

brown fumes of nitrogen dioxide.

glowing hot platinum wire.

ammonia solution

air

oxygen is released in the process the role of chlorophyll in photosynthesis is to absorb light energy carbohydrates made in plants during photosynthesis are an

important food for animals

Respiration: respiration is the process by which animals and plants obtain a supply

of energy by breaking down carbohydrates (using oxygen) to give carbon dioxide and water

carbohydrates release energy, producing carbon dioxide and water when burned

the energy gained is used to produce heat and movement the processes of respiration and photosynthesis are important in

maintaining the balance of carbon dioxide and oxygen levels in the air

the extensive clearing of forests could present a danger to life on earth by decreasing the amount of oxygen produced

Carbohydrates: carbohydrates are a family of compounds including glucose, sucrose

and starch the monosaccharides - glucose and fructose, are isomers with

molecular formula C6H12O6 the disaccharides - maltose and sucrose, are isomers with

molecular formula C12H22O11 the production of oxides of carbon and hydrogen when burning

carbohydrates shows that carbohydrates contain carbon and hydrogen.

carbohydrates contain the elements carbon, hydrogen and oxygen glucose is sweet and dissolves in water starch is not sweet and does not dissolve well in water when a beam of light is shone through a solution of:

- glucose it shines straight through with no trace of its path- starch it is reflected back so that the path of the beam can be seen

Testing Carbohydrates: it is possible to distinguish starch from other carbohydrates using

iodine solution iodine solution turns starch blue/black Benedict’s or Fehling’s Reagent is used to test for glucose,

fructose, maltose and other sugars (except sucrose) Both solutions give an orange colour when heated with these sugars Sucrose shows no change when heated with Benedict’s or Fehling’s

Reagent

Glucose: glucose is a carbohydrate built up in photosynthesis glucose is the carbohydrate which reacts with oxygen during

respiration starch is a polymer made in plants from glucose monomer units the glucose molecules join together with loss of water the joining up of glucose molecules to form starch is an example of

polymerisation

Digestion: during digestion, starch molecules are broken down in the body into

small glucose molecules which can pass through the gut wall the breakdown of starch can be carried out in the laboratory using

acid or amylase (an enzyme) starch molecules break down by reacting with water molecules this is an example of a hydrolysis reaction a hydrolysis reaction is one in which a large molecule reacts with

water and breaks down into two or more smaller molecules enzymes act as biological catalysts in the breakdown of complex

food molecules into smaller ones in the digestive system enzymes are biological molecules and work best under certain

conditions - optimum conditions most enzymes in our body work best at 37˚C (body temperature) and

pH 7

Alcohol: alcohol is a member of the alkanol family and is called ethanol alcoholic drinks can be made from any fruit or vegetable which is a

source of starch or sugars

Types of Alcoholic Drink:Source DrinkGrape WineBarley Beer, WhiskyApples Cider

Potatoes Vodka

Fermentation: fermentation is the breakdown of glucose to form alcohol and

carbon dioxide an enzyme in yeast, a living organism, acts as a catalyst for the

reaction once the concentration of alcohol reaches 15% the yeast is killed by

the alcohol the alcohol concentration can be increased by distillation water and alcohol can be separated by distillation as they have

different boiling points alcohol boils at 79˚C whereas water boils at 100˚C when the mixture is slowly heated to over 79˚C the alcohol boils off

leaving most of the water behind