C1.1 The Early atmosphere 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.

C1.2 a changing atmosphere. Carbon dioxide levels fell Oxygen levels rose

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.

A simple carbon cycle 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.

C1.4 The atmosphere today. Our atmosphere today… Gas

Formula

% in dry air

Nitrogen

N2

78

Oxygen

O2

21

Argon

Ar

0.9

Carbon Dioxide other

CO2

0.04 trace

How do scientists use rocks to work out the composition of the Earth’s early atmosphere? Analyse the minerals in them and look for oxides. As more oxygen was present, more oxide mineralswere formed.

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. • Deforestation lead 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.

C1.5 Rocks and their Formation Igneous Rocks • Example – granite. • Formed by the solidification of magma or lava • They contain crystals whose 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.

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

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

The advantages and disadvantages of quarrying.

C1.6 Limestone 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  copper oxide + carbon dioxide CaCO3 CaO + CO2

Problems associated with quarrying: Economic - money Social – the people Environmental - pollution

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 Advantage of quarrying…jobs and valuable building resources.

C1.7 Thermal decomposition

Breaking down with heat

Ease of thermal decomposition of metal carbonates: • Most difficult to decompose is sodium carbonate (10000C), calcium carbonate (8250C), zinc carbonate (3000C) and copper carbonate (2000C).

Copper carbonate  copper 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.

C1.8 Chemical reactions Word equations A word equation gives the names of the substances involved in a reaction. For example: copper + oxygen → copper(II) oxide Copper and oxygen are the reactants, and copper(II) oxide is the product.

Precipitation reactions 1) A simple example of conservation of mass is a precipitation reaction. 2) Transition metals form coloured compounds with other elements. Many of these are soluble in water, forming coloured solutions. If sodium hydroxide solution is then added, a transition metal hydroxide is formed. These are insoluble. They do not dissolve but instead form solid precipitates. As all the reactants and products remain in the sealed reaction container then it is easy to show that the total mass is unchanged. copper sulfate + sodium hydroxide → copper hydroxide + sodium sulfate CuSO4 + 2NaOH → Cu(OH)2 + Na2SO4

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.

C1.9 Reactions of Calcium Compounds

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

CaO(s) +

(s)

CO2 (g)

2. Adding water to 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) NB – large quantities of CO2 will dissolve to form an acid. This reacts with the CaCO3 making it colourless again! Neutralising acids with limestone 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)

1.10 indigestion

Hydrochloric acid is produced in the stomach to kill bacteria and to help digestion.

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 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.

Hydrochloric acid produces chloride salts e.g. calcium chloride Nitric acid produces nitrate salts e.g. calcium nitrate Sulfuric acid produces sulfate salts e.g. calcium sulfate

C1.11Neutralisation •

You need to be able to describe the reactions of hydrochloric acid and sulfuric acid with metal hydroxides, metal oxides and metal carbonates.

Metal hydroxides • Metal hydroxides, such as sodium hydroxide, usually dissolve in water to form clear, colourless solutions. When an acid reacts with a metal hydroxide, the only products formed are a salt plus water. Here is the general word equation for the reaction: acid + metal hydroxide → a salt + water • there is a temperature rise • the pH of the reaction mixture changes Metal oxides • Some metal oxides, such as sodium oxide, dissolve in water to form clear, colourless solutions. Many of them are not soluble in water, but they will react with acids. Copper(II) oxide is like this. When an acid reacts with a metal oxide, the only products formed are a salt plus water. Here is the general word equation for the reaction: acid + metal oxide → a salt + water Metal carbonates • Although sodium carbonate can dissolve in water, most metal carbonates are not soluble. Calcium carbonate (chalk, limestone and marble) is like this. When an acid reacts with a metal carbonate, the products formed are a salt plus water, but carbon dioxide is also formed. Here is the general word equation for the reaction: acid + metal carbonate → a salt + water + carbon dioxide • You usually observe bubbles of gas being given off during the reaction. You can show that the gas is carbon dioxide by bubbling it through

c1.13 electrolysis Electrolysis The process in which electrical energy from a d.c. supply decomposes compounds

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. ELECTROLYSIS OF Hydrochloric Acid • Produces chlorine at the positive electrode • Produces hydrogen at the negative electrode

C1.14 the importance of chlorine/Products from sodium chloride

Learn all of this

1.15 Electrolysis of Water 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.

1.16 ores 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.

Uses of metals. Gold= jewellery Copper = wires Silver = jewellery

C1.26 Acid rain 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.

C1.17 Extracting metal

 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.

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

C1.18 Oxidation and reduction Keywords 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 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

Corrosion of metals is oxidation •

Most metals corrode

•

Surface of a metal reacts with oxygen (or sometimes water) This is called OXIDATION reaction More reactive metals 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)

•

• •

C1.19 Recycling metals

Keywords • Recycled metal – when a used metal is melted down and made into something new.

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 Method 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

C1.20 Properties of metals

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

Keywords 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

Aluminium

Copper

Gold

Useful Properties • Low density • Does not corrode (because of layer of oxide that forms quickly)

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

Useful Properties • Very unreactive • Does not corrode • Malleable • Remains shiny • Excellent electrical conductor

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

Uses • Electrical cables • Water pipes

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

Keywords 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

C1.21 Alloys

Pure metal 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 Examples of Alloys 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 fineness of 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

Pure metal

C1.22 Crude Oil Key words • Hydrocarbons are compounds that contain carbon and hydrogen only. • Crude oil is a complex mixture of hydrocarbons

C1.23 Crude Oil Fractions • Crude oil is separated into simpler, more useful mixtures by fractional distillation.

C1.23 Crude Oil Fractions There are 6 fractions you need to know… Fraction

Uses

Gases

Domestic heating and cooking

Petrol

Car fuel

Kerosene

Aircraft fuel

Diesel oil

Fuel for some cars and trains

Fuel oil

Fuel for ships and some power stations

Bitumen

Surfacing roads and roofs

C1.23 Crude Oil Fractions Key words: Ignition – to set alight Viscosity – How thick or runny a substance is

How do the fractions differ? Fraction Gases

Length of molecule

Ease of ignition

Boiling point

Viscosity

Short

Easy

Low

Runny

High

Thick and sticky

Petrol Kerosene Diesel oil

Fuel oil Bitumen

Long

Difficult

C1.24 Combustion Key words: Combustion – a chemical reaction with oxygen (oxidation) to release energy. Complete combustion – where all the hydrocarbon is used up. Oxidation – the addition of oxygen.

+ Energy released

Any hydrocarbon

Tested for using limewater. CO2 will turn it cloudy if present.

C1.25 Incomplete Combustion Keywords: • Incomplete combustion – where there is not enough oxygen for the fuel to completely burn. • Carbon Monoxide – poisonous gas produced during incomplete combustion. Water is formed just like in complete combustion but there are not enough oxygen atoms to form CO2. Soot and Carbon Monoxide are formed instead. 3 different equations show what can happen:

Methane + Oxygen  Carbon (soot) + Water Methane + Oxygen  Carbon Monoxide + Water Methane + Oxygen  Carbon Dioxide + Carbon Monoxide + Carbon (soot) + Water Different percentages of CO2, CO and C are produced depending on the amount of oxygen present.

C1.25 Incomplete Combustion Problems of incomplete combustion:

• Carbon Monoxide is an odourless, colourless, toxic gas. • It reduces the amount of oxygen carried by the Red Blood Cells. • Carbon monoxide poisoning can kill. • Soot can clog pipes carrying waste gases. • Faulty or blocked boilers can produce carbon monoxide.

C1.26 Acid Rain Key word: Acid rain – rain that is more acidic than normal. Impurities in hydrocarbons such as sulfur react with oxygen to produce sulfur dioxide. This dissolves in rainwater to form acid rain. 4 Problems of Acid Rain: • Rivers, lakes and soils become acidic harming living organisms • Damages trees • Speeds up weathering of buildings made of limestone or marble • Corrodes metal

C1.27 Climate Change 3 gases trap heat from the Sun and keep the Earth warm – Greenhouse Effect • Carbon Dioxide • Methane • Water vapour

The Earths temperature varies. Human activity such as burning fossil fuels may influence this

C1.27 Climate Change • 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.

C1.27 Climate Change Key words: • Correlation – a pattern which is similar in two variables. It could be due to chance. • Causation – when one variable causes the effect in the other. •

There is a correlation between carbon dioxide levels in the atmosphere and the Earths temperature.

•

Not all scientists are convinced that increasing carbon dioxide levels cause global warning.

Because… • There are fluctuations throughout history • There are other causes of global warning • There are other greenhouse gases • Future predictions are just predictions

C1.28 Biofuels Key words: Biofuel – A fuel made by humans from animal or plant material that has recently died. Ethanol – A fuel made from sugar beet or sugar cane. Biodiesel – Diesel made from plant material. Carbon neutral – a fuel that does not add any carbon to the atmosphere overall. Biofuels are a possible alternative to fossil fuels e.g. ethanol which could reduce demand for petrol. Advantages of Biofuels

Disadvantages of Biofuels

They are renewable

Growing crops for fuels requires land that could be used to grow food

Plants remove carbon dioxide from the atmosphere as they grow

Transportation of the fuels produces carbon dioxide Burning the fuels produces carbon dioxide

C1.29 Choosing Fuels 4 factors that make a good fuel: • How easily it burns. • How much ash or smoke it produces. • The comparative amount of heat energy it produces. • How easy it is to store and transport. •

A fuel cell combines hydrogen and oxygen to make water and releases energy.

Advantages of using hydrogen as a fuel

Disadvantages of using hydrogen as a fuel

When hydrogen burns no carbon dioxide is produced, only water vapour

Hydrogen usually produced from natural gas and the process releases carbon dioxide

Hydrogen fuel cells are more efficient than petrol Hydrogen needs to be readily available first engines Renewable

Petrol stations would have to be converted to store and sell hydrogen too Cost of the above

• •

Petrol, Kerosene and diesel oil are non-renewable fossil fuels made from crude oil. Methane is a non-renewable fossil fuel from natural gas.

C1.31 Alkanes and Alkenes Alkanes are saturated hydrocarbons which are present in crude oil. Learn the formula and be able to draw each of these.

C1.31 Alkanes and Alkenes • Alkenes are unsaturated hydrocarbons Learn the formula and be able to draw each of these. Bromine water is used to distinguish between alkanes and alkenes Ethene + bromine water  colourless (colourless) (orange) Ethane + bromine water  orange (colourless) (orange)

C1.32 Cracking

Why is cracking needed? Crude oil has different amounts of each fraction. These don’t always match customer demand so they crack them to match demand.

Cracking involves breaking down long saturated hydrocarbons (alkanes) into smaller useful ones. Some of these small molecules are unsaturated (alkenes).

Know how to crack paraffin in the lab.

C1.33 Polymerisation Many ethane molecules can combine in a polymerisation reaction.

Learn the formula and equation

C1.33 Polymerisation 4 examples of polymers you need to know…

C1.33 Polymerisation Polymer

Properties

Use

Poly(ethane) – polythene

Flexible, cheap, good insulator

Plastic bags, plastic bottles, cling film, insulation for electrical wires

Poly(propene) – polypropene

Flexible, shatterproof, high softening point

Buckets and bowls

Poly(chloroethene) - PVC

Tough, cheap, long-lasting, good insulator

Window frames, gutters, pipes, insulation for electrical wires

Poly(tetrafluoroethene) PTFE or Teflon

Tough, slippery, resistant to corrosion, good insulator

Non stick coatings for saucepans, bearings for skis, containers for corrosive substances, stain proof coating for carpets, insulation for electrical wires

C1.34 Problems with Polymers 3 problems • Most are not biodegradable. • They persist in landfill sites. • They produce toxic gases when burned. How can we overcome these problems? • Recycling polymers instead of landfill. • Development of biodegradable polymers.