Chemistry GCSE Exam Revision

Most metals corrode

Surfaceof a metal reacts with oxygen (or sometimes water)

This is called OXIDATIONreaction

More reactivemetals corrode more rapidly  (less reactive may not corrode at all e.g. Gold)

A layer of metal oxide forms (this can stop further corrosion e.g. on Aluminium =  and Al2O3 layer forms)

Metal extraction is reduction

Most metal ores are ‘oxides’

To get the metal we must remove the oxygen

We say the compound has been reduced.  It is a REDUCTION reaction

Example 1 = Iron oxide is heated with Carbon

Iron oxide  +  Carbon  Iron  +  Carbon dioxide

Example 2 = Aluminium is obtained by electrolysis of aluminium oxide

Aluminium oxide  Aluminium   +   Oxygen

Alloy – a metal mixed with small amounts of other metals to improve their properties

Carats – a measure of the purity of gold with pure gold being 24 carats

Fineness– another measure of purity of gold (parts per thousand)

Smart material – a material that’s properties change with a change in conditions

Shape Memory Alloy – an alloy that can return to its original shape when heated

1.All atoms are the same size and therefore closely packed together.

2.This means that layers of atoms slide over each other which makes the metal soft.

3.In an alloy different atoms are added which prevent the atoms sliding so easily = harder and stronger

Alloy steels – iron mixed with other metals

Stronger that Iron

Some resist corrosion.  Stainless steel NEVER corrodes (Iron with Chromium and Nickel)

Gold  - Pure gold (24 carat) too soft.  24 carat gold has a finenessof 1000 parts per thousand

Copper and silver added to make it harder

Nitinol– Smart material made from nickel and titanium

Return to original shape when heated.

Used in repair of arteries (inserted in squashed and cold and warms with body to reshape)

Flexible glasses frames

1.Collecting – requires people to be willing to separate their rubbish

2.Separating different metals

•Iron can be separated using a magnet (quick and easy)

•Others usually separated by hand (time consuming and labour intensive)

3.Purifying – metals are melted down to form blocks

Many metals can be recycled…

Advantages

•Natural reserves will last longer

•Most use less energy to recycle that to extract.  E.g. Aluminium recycling 95% more energy efficient compared to extraction.

•Reduced mining which damages landscapes and causes pollution (dust and noise)

•Recycling produces less pollution.  Examples supporting this are •Lead from its ore ‘galena’ produces sulfur dioxide

•Carbon dioxide is produced during extraction by electrolysis.

Disadvantages

•Costs money and uses energy to collect, sort and transport metals to be recycled

•This can make it more expensive to recycle some metals the extract them

The most recycled metals in the UK are Lead , Iron and Aluminium and Copper

Aluminium

Useful Properties

Low density

Doesnot corrode (because of layer of oxide that forms quickly)

Uses

Aeroplanes and cars to make them lighter (cheaper to run as they need less fuel)

Malleable – can be hammered into shape

Conduct – allows heat or electricity to pass through it

Ductile – can be stretched into wires

Density – the mass of a substance per unit volume; the unit is usually g/cm3

Properties include:– shiny when polished; conduct heat and electricity; malleable; ductile.

Gold

Useful Properties

Very unreactive

Does not corrode Malleable Remains shiny Excellent electrical conductor

Uses

Jewellery

Electronic devices (printed circuit boards and connection strips)

Iron and Steel

Useful Properties

Cheap to extract by heating with carbon Pure iron too soft but in alloys is very useful Steel (Iron mixed with carbon and other metals) is strong and hard Magnetic

Uses (mainly as steel)

Bridges, cars, cutlery, electrical goods, machinery, building frames, magnetic products

 Copper

Useful Properties

Ductile

Low reactivity (does not react with water) •Good electrical conductor

Uses

Electrical cables

Water pipes

Crude oil is a complex mixture of hydrocarbons Hydrocarbons are compounds that contain carbon and hydrogen only.  

Crude oil is a fossil fuel that comes directly from the Earth's crust and is one of the most  important substances in the world. Crude oil is a complex mixture of hundreds of compounds. The compounds in the mixture are chemically compound together. They can be seperated by methods of fractional distillation.

Crude oil is often found trapped in sedimentary rocks under the sea bed. We can use crude oil to make fuel, plastics and hundreds of petrochemicals. It fuels transport, heating and generating electricity.

1) Removing sulphur before fuels are burnt

-very expensive

-takes more energy- releases co2

2) Acid gas scrubbles

-remove harmful gases in power stations

-cars use catalytic converters

3) Iron seeding

-iron is placed into large bodies of water to promote plant growth (phytoplankton)

A rapid reaction between a substance and oxygen that releases heat and light energy. When a substance burns it is said to combust.

Incomplete combustion – where there is not enough oxygen for the fuel to completely burn.

Carbon Monoxide – poisonous gas produced during incomplete combustion.

Complete Combustion

Fuel + Oxygen = Carbon dioxide + Water

Incomplete Combustion

Fuel + Oxygen = Carbon Monoxide +Water

Fuel + Oxygen = Carbon (soot) + Water

Biofuel is most commonly defined as a renewable source of energy, whcih is produced from biological material or biomass, such as sugar cane, corn, cellulose or vegetable oils. The most widely spread types of biofuel these days are ethanol and biodiesel.

The key difference between fossil and biofuel os that they are derived from plants that were recently alive.

Advanatges: renewable, sustainable, less carbon emissions, readily available, supposed to be carbon neutral, delivers ten times more energy than what it took to make them.

Disadvantages: poverty, raises food prices, larger contribution to global warming, not carbon neutral, corn for ethanol is then worst.

Large hydrocarbons are broken into smaller molecules using heat and a catalyst. This process is known as catalytic cracking. The smaller molecules produced are seperated by distillation.

An alkane and alkene are always produced

Example

Octane- C8H16 makes Hexane- C6H14 and Ethene- C2H4

Bromine Test:

To test whether something is an alkane or alkene you can do the bromine test. It tests whetehr it is saturated or unsaturated. An alkene would go clear or white and an alkane would go yellow or orange.

Monomers:

The small molecules that join together to form the large polymer chains. They are alkenes, therefore they contain a double bond.

Additon polymerisation:

The double bond breaks so that two monomers can join together. Most polymers are not biodegradable so they stay in a land fill. But they can also be incinerated. The problems of this though are; only some waste is burnt and many produce toxic substances which can be removed from the waste gases but, has to be disposed of carefully.

Name the polymer: Put 'poly' in front of it's name for example, ethene becomes poly(ethene)

Recycling Polymers: Recycling polymers is possible for some types but is more difficult because they have to be sorted into different categories.

• Alkanes are saturated hydrocarbons. This means that their carbon atoms are joined to each other by single bonds.
• Family of hydrocarbons that share the same general formula CnH2n+2. The general formula means that the number of hydrogen atoms in an alkane is double the number of carbon atoms, plus 2.
• Unreactive, apart from their reaction with oxygen in the air, which we call burning or combustion.

Propane- C3H8                       Heptane- C7H16

Methane- CH4

EthAne- C2H6

ButAne- C4H10

Pentane- C5H12

Hexane- C6H14

• Alkanes are unsaturated meaning they contain a double bond.
• Reacts in ways alkanes cannot.
• The number of hydrogen atoms in an alkene is double the number of carbon atoms.

Butene- C4H8

Ethene- C2H4

Propene- C5H10

Hexene- C6H12

Petrol- car fuel

Keorsene- aircraft fuel

Diesel Oil- fuel for some cars and trains

Gases- domestic heating and cooking

Fuel Oil- fuel for ships and some power stations

Bitumen-surfacing roads and roofs 

Crude oil is separated into simpler, more useful mixtures by fractional distillation.  

The amount of carbon dioxide in the atmosphere varies due to human activity – burning fossil fuels.

How to reduce the amount of carbon dioxide in the atmosphere:

Iron Seeding Oceans – Adding iron to the ocean encourages algal growth which photosynthesise and absorb carbon. They are eaten by other organisms which incorporate carbon into their shells which sinks to the bottom of the ocean.

Converting carbon dioxide back to hydrocarbons – trapping gases from power stations and reacting them to make butane or propane to use as fuels

Gold= jewellery

Copper = wires

Silver = jewellery

Iron= steel, machines

What are Hydrocarbons?

A mixture of hydrogen and carbon; many of the compounds in crude oil only contain these.

Most hydrocarbons in crude oil are compounds called Alkanes. Alkanes are made up of a single chain of carbon atoms whith hydrogen atoms bonded to them.

Effects of acid rain

-Fish numbers started to decrease.

-Soils are made acid and can harm plants.

-Trees damaged -Erosion of buildings made of limestone.

Causes of acid rain.

-Dissolved carbon dioxide and acidic gases in water.

-Sulphur dissolved in water from fossil fuels.

-Burning of fossil fuels which create sulphur.

Gold and platinum found naturally in the environment as they are unreactive.

Most metals are found as ores (usually reacted with oxygen)  in the Earths crust.

Ores are rocks which contain metals.

Extraction = getting the metal out of the rock. Sometimes you can…

•Heat the rock to get the metal

•Or use electrolysis.

Example

Hydrochloric acid + sodium hydroxide → sodium chloride + water

HCl + NaOH → NaCl + H2O

Hydrochloric acid contains hydrogen ions and chloride ions dissolved in water. Sodium hydroxide solution contains sodium ions and hydroxide ions dissolved in water.

Indigestion remedies contain substances to neutralise excess stomach acid.

When an acidic compound dissolves in water it produces hydrogen ions, H+. These ions are responsible for the acidity of the solution.When an alkaline compound dissolves in water it produces hydroxide ions, OH−.  These ions are responsible for the alkalinity of the solution.Acids react with alkalis to form salts. These are called neutralisation reactions. In each reaction, water is also formed:

Acid + alkali → salt + water

Keywords

•Neutralisation reaction - reaction in which a base or an alkali reacts with an acid.

•Limewater – Solution of calcium hydroxide.  It is used to test for the presence of CO2 as it turns from colourless to cloudy.

Making Limewater

1.Heating limestone - Calcium carbonate (CaCO3) turns it into Calcium oxide (CaO)

CaCO3  (s)                CaO(s)  +       CO2 (g)

2.Adding waterto CaO – vigorous reaction that creates calcium hydroxide (crumbly solid)

CaO(s)     +       H2O (l)  Ca(OH)2(s)

Testing for CO2  - limewater turns cloudy/milky as calcium carbonate forms.

 Ca(OH)2(s)   + CO2 (g)                                           CaCO3  (s)    +    H2O (l)

1.Calcium compounds that neutralise acids:

–Calcium carbonate (CaCO3) –Calcium oxide (CaO) –Calcium hydroxide (Ca(OH)2) 2.Uses of these alkalis 1.Farmers neutralise soil 2.Power stations use wet powdered CaCO3 to neutralise acidic waste gases like Sulfur dioxide and nitrous oxides.  ( below is the equation for sulfur dioxide production)

    S  (g)     +     O(g)  SO2 (g)

• income benefits local people
• more jobs available
• income benefits local businesses
• limestone is a valuable resource
• benefit's countries economy as limestone is a UK export

TEST: lighted splint gives a squeaky pop.

Uses: many uses incluidng as a fuel.

Problems: flammable

Hydrogen Fuel:

Advantages: clean fuel, renewable, more efficent

Disadvanatges: needs to be readily available and it is not, process to make it releases co2, stations would need to be converted to stone to store it and imagine the cost of the above.

TEST: damp blue litmus paper turns red (as chlorine is acidic0 then turns white (chlorine is a bleach). It may also smell like chlorine.

Uses: manufacture of bleach and PVC (polyvinylchloride) and used in water treatment.

Problems: it a toxic gas

Most difficult to decompose is sodium carbonate (10000C), calcium carbonate (8250C), zinc carbonate (3000C) and copper carbonate (2000C)

Copper carbonate àcopper oxide + carbon dioxide

CaCO3(s)   =     CaO(s)  +  CO2(g)

Copper carbonate will start to decompose to form carbon dioxide and copper oxide. The reaction will absorb some of the heat from the fire. The carbon dioxide can help to put out the fire by reducing the amount of oxygen available for combustion.

Copper carbonate  = copper oxide + carbon dioxide

Zinc carbonate  =  zinc oxide +  carbon dioxide

The mass of reactants do not change, the particles just get rearranged. The atoms take part in a chemical reaction they are very small. When calcium hydroxide is dissolved in water it makes Limewater.

CaO + H2O =Ca(OH)2. The word equation for this is Calcium Oxide +Water = Calcium Hydroxide. From this reaction a lot of heat is produced.

Another word for Calcium Hydroxide is slaked lime. Quick lime + Water = Slaked lime

Definition: chemical decomposition produced by passing an electric current through a liquid or solution containing ions.

The process of electrolysis

Positively charged ions move to the negative electrode during electrolysis. They receive electrons and are reduced.

Negatively charged ions move to the positive electrode during electrolysis. They lose electrons and are oxidised.

Limestone is made of calcium carbonate (CaCO3)

It is used in:

–Building materials- glass, cement, concrete –Improving the pH of acid soil

Thermal Decomposition of Calcium Carbonate

When metal carbonates are heated they break down into a metal oxide and carbon dioxide is given off

Copper carbonate àcopper oxide + carbon dioxide

           CaCO3                       CaO           +     CO2

ELECTROLYSIS OF Hydrochloric Acid

•Produces chlorine at the positive electrode •Produces hydrogen at the negative electrode

Water

Produces oxygen at the positive electrode

Produces hydrogen at the negative electrode If the gas relights a glowing splint, it is oxygen.

Electrolysis of Seawater

This produces chlorine gas at the electrode.

The level of carbon dioxide in the atmosphere is maintained by several processes, photosynthesis, respiration and combustion

Green plants remove carbon dioxide from the atmosphere by photosynthesis. Respiration and combustion both release carbon dioxide into the atmosphere.

These processes form a carbon cycle in which the proportion of carbon dioxide in the atmosphere remains about the same.

Limestone is heated with clay to make cement

Cement is added to sand and water to make mortar

Cement is added to sand, aggregate and water to make concrete

Changes in the atmosphere occur through;

Natural activities:

•Volcanic activity can lead to a rise in sulphur dioxide; lightening can lead to a rise in nitrogen oxides.

Human activity:

•burning fossil fuels can lead to an increase of carbon dioxide, carbon monoxide and sulphur dioxide.

•Deforestationlead to an increase in carbon dioxide; burning trees releases carbon dioxide (combustion), fewer trees to photosynthesise and absorb carbon dioxide; engines and furnaces release nitrogen oxides.

•Farming: increasing numbers of cattle and rice fields can lead to an increase of methane.

Carbon dioxide fell because:

•Some carbon dioxide dissolved into the oceans.

•Some was absorbed by marine creatures who stored it tin their shells as calcium carbonate which later formed carbonate rocks.

As the number of plants increased, the oxygen levels rose through photosynthesis. These plants absorb carbon dioxide too.

Carbon dioxide levels fell

Oxygen levels rose

Gas                 Formula                 % in dry air

Nitrogen                N2                                        78

Oxygen                  O2                                        21

Argon                     Ar                                         0.9

Carbon Dioxide    CO2                                       0.04

Other                                                                    trace

Factors which affect how a metal is extracted are cost and position in the reactivity series.

Iron is heated with carbon in a reduction reaction to extract it from its ore.

Iron oxide + carbon = iron + carbon dioxide

Aluminium is extracted from its ore by electrolysis because it is more reactive.

Aluminium oxide = aluminium + oxygen

Keywords:

anode – The positive electrode used in electrolysis.

cathode– The negative electrode used in electrolysis.

electrolysis – The use of an electric current to separate out the elements in a compound.

electrolyte – An ionic compound that conducts electricity when in a liquid state.

ore– A rock that contains a metal combined with other elements in concentrations that make it profitable to mine

Reduction – occurs when oxygen is removed from a compound

Corrosion – when a metal is converted to its oxide by the action of moist air

Oxidation – occurs when oxygen is added to an element or compound

Rusting – the corrosion of iron

The first gases came from the eruption of Volcanoes and formed the Earth’s early atmosphere.

The main gases in the early atmosphere were:

•Lots of carbon dioxide

•Some nitrogen

•Little or no oxygen

•Water vapour

•Ammonia Volcanoes release these gases today (and so scientists think the same processes operated in the past).

The oceans were formed from the condensation of the water vapour to make liquid water.

Sedimentary rocks

•Sedimentary rocks contain fossils

•They are formed from compaction of layers of rock over a long time.

•They are not as strong as other rocks so erode easily.

•Examples -  chalk and limestone

Limestone, chalk and marble are all forms of calcium carbonate and exist in the Earths crust.

• dusty and noise pollution
• loss of wildlife habitats
• disturbance of wildife
• extra traffic
• original landscape destroyed
• visual impact- destroys view of landscape

Metamorphic – A rock changed by pressure and heat.

Sedimentary – A rock formed by the deposition of sediments.

Thermal decomposition– The breakdown of a compound into simpler substances by heating.

Electrolysis – The use of electricity to split a compound.

Granite – A type of igneous rock that is harder than limestone and marble.

Igneous – A rock formed from cooled magna.

Limestone – A type of sedimentary rock containing calcium carbonate.

Limewater – A limestone product made by fully dissolving quicklime in water. It is used to test for carbon dioxide.

Marble – A type of metamorphic rock that is harder than limestone but softer than granite

Igneous Rocks

•Example – granite.

•Formed by the solidification of magma or lava •

They contain crystalswhose size depends on the rate of cooling.

•Quick cooling = small crystals

•Fast cooling = large crystals

Metamorphic Rocks

•Example – marble

•Formed when heat or pressure is applied to other rocks.

•Marble is formed from chalk or limestone being heated and pressurised.

To neutralise an acid you add/put an alkali in/on it. CaCo3 can be used in neutralising soils, acidic gases in the air and acidic lakes. Calcium hydroxide is an alkali used in soils and lakes that are acidic to neuralise them. They can also be neutralised with magnesium carbonate.

Acid + Alkaline = Salt + Water

                     acid + metal hydroxide    →    a salt + water

                        acid + metal oxide    →    a salt + water

         acid + metal carbonate    →    a salt + water + carbon dioxide

CaCo3 heated = CaO + Co2. Calcium Carbonate can be turned into Calcium Oxide through the proccess of thermal decomposition. CaCo3 breaks down when strongly heated.

The word equation for this reacton is Calcium Carbonate apply heat = Calcium Oxide + Carbon Dioxide