Chemistry C1 GCSE AQA Higher

To help with revision for C1 Chemistry AQA Higher Exams at GCSE

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ATOMS AND ELEMENTS

All substances are made up of ATOMS.

Atoms have a small nucleus made up of PROTONS and NEUTRONS.

Surrounding the nucleus in shells are the ELECTRONS.

Protons have a POSITIVE charge, Neutrons have a NEUTRAL charge and Electrons have a NEGATIVE charge. 

Substances made up of only one type of atom are called ELEMENTS.

The MASS Number is the number at the top of an element's square in the Periodic Table.

The ATOMIC Number is the number at the bottom of an element's square in the Periodic Table. 

If you want to find out the number of neutrons in an atom using the Periodic table, you calculate:
MASS No. - ATOMIC No. 

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COMPOUNDS

Atoms form Chemical bonds with other atoms to form COMPOUNDS.

Making bonds involves ONLY the giving away, taking or sharing of ELECTRONS

A compound formed from a METAL and NON-METAL consists of IONS.

METAL atoms LOSE electrons to form POSITIVE IONS.

NON-METAL atoms GAIN electrons to form NEGATIVE IONS.

The charges of the Ions are OPPOSITE and so are strongly attracted to each other. This is called IONIC BONDING

A compound formed from NON-METALS consists of MOLECULES.

Each atom SHARES an electron with another atom. This is called a COVALENT BOND

Each atom MUST make enough covalent bonds to fill its outer shell

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LIMESTONE

Limestone is QUARRIED out of the ground.

It is mainly CALCIUM CARBONATE (CaCO3).

When heated, it thermally decomposes to make Calcium Oxide and Carbon Dioxide:

Calcium Carbonate -> Calcium Oxide + Carbon Dioxide                                                  CaCO3                              CaO                     CO2

Calcium Carbonate also reacts with acid to make Calcium salt, Carbon Dioxide and water:

Calcium Carbonate + Sulfuric acid -> Calcium Sulfate + Carbon Dioxide + Water              CaCO3                  H2SO4                 CaSO4                    CO2              H2O

The type of salt produced is dependent on the acid used (E.g. If Hydrochloric acid was used, it would make a Chloride). 

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CALCIUM OXIDE

CALCIUM OXIDE reacts with WATER to produce CALCIUM HYDROXIDE.

Calcium Oxide + Water -> Calcium Hydroxide                                                                    CaO             H2O              Ca(OH)2   

Calcium Hydroxide is an ALKALI.

It can be used to neutralise acidic soil in fields as well as powdered limestone, but works much FASTER than powdered limestone. 

It can also be used to test for CARBON DIOXIDE;

Make a solution of Calcium Hydroxide and water (Limewater) and bubble gas through it. The solution will turn CLOUDY if there's Carbon Dioxide in the gas. 

The cloudiness is caused by the formation of Calcium Carbonate:

Calcium Hydroxide + Carbon Dioxide -> Calcium Carbonate + Water                               Ca(OH)2                       CO2                      CaCO3               H2O 

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LIMESTONE PRODUCTS

POWDERED LIMESTONE is HEATED in a kiln with POWDERED CLAY to make CEMENT

CEMENT can be mixed with SAND and WATER to make MORTAR.

CEMENT can also be mixed with SAND and AGGREGATE to make CONCRETE. [Aggregate= Water and Gravel] 


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ADVANTAGES AND DISADVANTAGES OF LIMESTONE

ADVANTAGES
Limestone products are used to neutralise acidic soil and acidity in rivers and lakes.

It provides chemicals used in making dyes, paints and medicine.

Quarrying can provide people with jobs and bring more money into the local economy. 


DISADVANTAGES
Quarrying Limestone makes holes, which permanently change the landscape.

The Quarrying Processes can make noise and dust in quiet areas.

Quarrying destroys habitats of animals and birds.

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EXTRACTING METALS [USING CARBON]

A METAL ORE is a rock which contains enough metal to make EXTRACTION worthwhile. 

Most metals need to be extracted using a CHEMICAL REACTION by either REDUCTION or by ELECTROLYSIS

Some metals can be extracted by reduction using CARBON. When an ore is reduced, oxygen is removed from it. E.g:

Iron (III) Oxide + Carbon -> Iron + Carbon Dioxide                                                        2Fe2O3             3C         4Fe           3CO2

The position of the metal in the reactivity series determines whether it can be extracted by reduction with carbon. 

Any element BELOW carbon can be extracted by REDUCTION using CARBON.

This is because carbon can only take oxygen away from metals that are less reactive than itself.  

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EXTRACTING METALS [USING ELECTROLYSIS]

ELECTROLYSIS is the BREAKING DOWN of a substance using ELECTRICITY.

It requires a liquid to conduct the electricity called the ELECTROLYTE, which are often metal salt solutions made from the ore or molten metal oxides.

The electrolyte has FREE IONS which conduct the electricity so the whole thing works. 

Electrons are TAKEN away by ANODE and GIVEN away by CATHODEAs ions gain/lose electrons, they become atoms/molecules and are released. 

Any element ABOVE carbon in The Reactivity Series can be extracted using ELECTROLYSIS of MOLTEN COMPOUNDS.

This process is much more expensive than reduction using carbon as it uses a lot more ENERGY.

Copper is PURIFIED by electrolysis even though it is quite expensive because copper extracted by reduction using carbon is IMPURE so doesn't conduct electricity. 

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COPPER ORES

COPPER ORES are in SHORT SUPPLY so scientists have found new methods to extract copper:

BIOLEACHING
Some bacteria ABSORB copper compounds then produce solutions called LEACHATES, which contain copper compounds.

PHYTOMINING: 
This involves growing plants in soil containing copper. Plants can't use or get rid of the copper so it gradually BUILDS UP in the leaves and can then be harvested, dried or burned in a furnace (copper can be collected from the ASH left in the furnace).

These have a much smaller impact on the environment but are SLOWER.

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IMPACTS OF EXTRACTING METALS

ADVANTAGES
Useful products can be made
Provides people with jobs which brings money into the local economy

DISADVANTAGES
Causes noise
Permanently damages the landscape
Loss of habitats 

RECYCLING METALS 
Mining and extracting takes a lot of energy, coming mostly from burning FOSSIL FUELS
Fossil Fuels are running out so it is important to CONSERVE them.

Burning them also contributes to acid rain, global dimming and climate change.

Recycling metals uses a SMALL FRACTION of the energy used to mine and extract new material and saves MONEY too.  

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PROPERTIES OF METALS

Typical properties of ALL metals:
They are STRONG and can be BENT or HAMMERED into different shapes
They conduct HEAT
They conduct ELECTRICITY

COPPER:
-Good conductor of electricity
-Hard and strong but can be bent 
-Doesn't react with water 

ALUMINIUM 
-Corrosion-resistant
-Low density metal
-Pure aluminium isn't that strong but forms hard, strong ALLOYS

TITANIUM 
-Corrosion-resistant
-Low density metal
-Very strong

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ALLOYS

A mixture of two or more elements where at least one is a metal is an ALLOY
Alloys are used as pure elements aren't always right for certain jobs. 

IRON from a blast furnace is around 96% iron and 4% impurities (i.e. carbon). Because the arrangement of the iron atoms is regular, they slide over each other, making the iron soft and easily shaped. This is too bendy for most uses.  

Iron is changed into STEEL (an alloy), which is formed by adding small amounts of CARBON (and sometimes other metals) to the iron. 

 TYPE OF STEEL                                         PROPERTIES              USES                
Low carbon steel (0.1% carbon)
                 Easily shaped              Car bodies  

High carbon steel (1.5% carbon)                Very Hard, inflexible    Blades, bridges

Stainless Steel (Chromium and Nickel)       Corrosion-resistant      Cutlery, sinks
                                                                                                                                  

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CRUDE OIL

CRUDE OIL is a mixture of many different compounds, which are mostly HYDROCARBON molecules. These are made of just carbon and hydrogen.  

The different parts of a mixture aren't chemically bonded to one another, so keep their original properties (i.e. condensing points).   

Crude oil can be split up into its separate fractions by FRACTIONAL DISTILLATION

The fractionating column works continuously, with the heated crude oil piped in at the bottom.
 
The vaporised crude oil rises up the column and the various fractions are constantly tapped off at different levels where they condense

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ALKANES

All the fractions of the crude oil are hydrocarbons called ALKANES.
Alkanes are made up of chains of carbon atoms surrounded by hydrogen atoms.

METHANE         ETHANE              PROPANE                BUTANE
(http://www.science-resources.co.uk/KS3/Chemistry/Chemical_Reactions/Hydrocarbons/Hydroc43.gif)             (http://www.science-resources.co.uk/KS3/Chemistry/Chemical_Reactions/Hydrocarbons/Hydroc44.gif)            (http://www.science-resources.co.uk/KS3/Chemistry/Chemical_Reactions/Hydrocarbons/Hydroc45.gif)            (http://www.science-resources.co.uk/KS3/Chemistry/Chemical_Reactions/Hydrocarbons/Hydroc45.gif)

     CH4                          C2H6                              C3H8                                C4H10

Alkanes are SATURATED because their carbon atoms are joined together by single bonds (Each straight line shows a covalent bond).
The general formula for alkanes is: CnH2n + 2

Shorter molecules:
Less viscous
More volatile (turns into a gas at a lower temperature)
More flammable

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CRUDE OIL AS A FUEL

CRUDE OIL FRACTIONS burn cleanly so make good fuels for many modern transport (e.g. Cars, trains, planes...).

Crude oil provides the raw materials for making various chemicals (i.e. Plastics).

Alternatives to crude oil fractions as fuel include nuclear or wind power, ethanol-powered cars and solar energy to heat water.

ADVANTAGES
Many things are set up for using oil fractions.
Crude oil fractions are often the easiest and cheapest thing to use. 
More reliable.

DISADVANTAGES
Its a non-renewable fuel (it will run out eventually). 
Oil spills can poison birds and sea creatures.
You have to burn the oil, which is a major cause of global warming, acid rain and global dimming.  

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ENVIRONMENTAL PROBLEMS

Burning FOSSIL FUELS releases gases and particles.
Power stations and cars burn fossil fuels.

Fuels like crude oil and coal contain carbon and hydrogen.During combustion, the carbon and hydrogen are oxidised so that carbon dioxide and water vapour are released into the atmosphere

If the fuel contains sulfur impurities, sulfur dioxide will be released when burnt.

COMPLETE COMBUSTION: Plenty of oxygen so all the fuel burns.
PARTIAL COMBUSTION: Not enough oxygen so some fuel doesn't burn - Soot, unburnt fuel and carbon monoxide is released in partial combustion

GLOBAL DIMMING is the reduction of sunlight reaching the earth's surface caused by particles of soot and ash produced when fossil fuels are burnt
These particles reflect sunlight back into space or help produce more clouds to do the same. 
 
Increasing carbon dioxide causes CLIMATE CHANGE

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ACID RAIN

SULFUR DIOXIDE causes ACID RAIN.

When sulfur dioxide mixes with the clouds, it forms dilute sulfuric acid which falls as acid rain.  
Oxides of nitrogen cause acid rain in the same way but form dilute nitric acid.

ACID RAIN
Causes lakes to become acidic, causing animals and plants to die.
Kills trees, damages limestone buildings and ruins stone statues.

Most sulfur can be removed from fuels before they're burnt but it costs more.
It also takes more energy, usually from burning more fuel, releasing more carbon dioxide.

Petrol and diesel are starting to be replaced by low-sulfur versions.

Power stations now have Acid Gas Scrubbers to take harmful gases out before they release fumes into the atmosphere.  

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ALTERNATIVE FUELS

ETHANOL
PROS
Carbon dioxide released when it's burnt was taken in by plants while growing so it is carbon neutral. The only other product is water
CONS 
Engines need to be converted before they can work with ethanol fuels and not widely available
Increasing demand could mean farmers produce more ethanol instead of food, increasing food prices.  
BIODIESEL 
PROS 
Carbon Neutral
, no need to convert engines and produces less sulfur dioxide.
CONS
Not enough made to replace diesel
, expensive and could increase food prices.  
HYDROGEN GAS 
PROS
Combines with oxygen in air to form just water, so it is very clean.
CONS 
Needs a special, expensive engine, not widely available and hard to store.  

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CRACKING CRUDE OIL

CRACKING means splitting up long-chain hydrocarbons by passing vapour over a hot catalyst

A lot of the longer molecules produced from fractional distillation are turned into smaller ones by cracking.

Cracking produces useful fuel products and ethene, which are needed when making plastics.  

Cracking is a thermal decomposition reaction (breaking molecules down by heating them).

First, you heat the long-chain hydrocarbon to vaporise it.
The vapour is passed over a powdered catalyst at around 400°C-700°C.
Aluminium oxide is the catalyst used.
The long-chain molecules split apart on the surface of the specks of catalyst.

Most products of cracking are alkanes and alkenes.  

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ALKENES

ALKENES are hydrocarbons which have a double bond between two carbons atoms in their chain.

They are unsaturated as they can make more bonds (the double bonds can open up, which allows the two carbon atoms to bond with other atoms).

ETHENE                    PROPENE
(http://www.science-resources.co.uk/KS3/Chemistry/Chemical_Reactions/Hydrocarbons/Hydroc56.gif)          (http://www.science-resources.co.uk/KS3/Chemistry/Chemical_Reactions/Hydrocarbons/Hydroc57.gif) 
       C2H4                            C3H6

The general formula for all alkenes is: CnH2n

To test for an alkene, add the substance to bromine water.
 
If the water turns from orange to colourless, it is an alkene as the double bond has opened to form bonds with the bromine. 

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ETHANOL

Ethene can be reacted with steam while in a catalyst to produce ETHANOL.

It is a cheap process as ethene is cheap and not much is wasted.

Ethene is produced by crude oil with is a non-renewable source, so making it may become more expensive.  

Alcohol in alcoholic drinks is made by fermentation, which has the raw material of sugar. This is converted into ethanol using yeast:

Sugar -> Carbon dioxide + Ethanol

This needs a lower temperature and simpler equipment than when using ethene.

The raw material is renewable and the ethanol produced can be used as a cheap fuel (also, for countries with no oil reserves to make petrol).

It isn't very concentrated, so to increase the strength you need to distil it.
It also needs to be purified.  

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POLYMERS

Many small alkene molecules (monomers) join together to form very large and long-chain molecules called POLYMERS

E.g: Many ethene molecules can be joined up to produce polythene.
In the same way, you can join many propene molecules to make poly(propene)

The properties of polymers depend on their monomers and the conditions used to join them together.

E.g: Polythene made at 200°C and 2000 atmospheres pressure is flexible with a low density. But polythene made at 60°C and a few atmospheres pressure with a catalyst is rigid and dense.

However, most aren't biodegradable so its best to re-use and/or recycle them.

Things made from polymers are usually cheaper than metal, but crude oil resources will eventually be used up, so the prices of crude oil will rise along with the products.  

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USES OF POLYMERS

Light, stretchable polymers (e.g. low density polythene) are used for plastic bags

Elastic polymer fibres are used to make LYCRA fibre for tights.

Waterproof coatings for fabrics are made of polymers, e.g:
 
Dental polymers are used on resin tooth fillings
Polymer hydrogel wound dressings keep wounds moist.

New biodegradable packaging materials made from polymers and cornstarch are being produced. 

Memory foam is an example of a smart material. Its a polymer that gets softer as it gets warmer

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USES OF PLANT OILS

OILS can be extracted from plants, which can be used for food or for fuel
To extract the oil, the plant material is crushed then pressed between metal plates, which squash the oil out. (This is the traditional method to remove olive oil).

Oil can be separated from crushed plant material by a centrifuge or solvents can be used to get oil from plant material.
Distillation refines oil, and removes water, solvents and impurities.

Vegetable oil in food:
-Used in food, has a very high energy content, contain other nutrients (e.g. Vitamin E in oil from seeds), contains essential fatty acids used for many metabolic processes
-Have higher boiling points to cook foods faster and at higher temperatures.

Vegetable oil in fuel:
-Rapeseed and soybean oil can be processed and turned into fuels as they provide a lot of energy.
-Biodiesel is made from vegetable oil and has similar properties to diesel.

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PLANT OILS

Oils and fats are either saturated or unsaturated.
Unsaturated oils contain C=C double bonds, so will decolourise bromine water. Monosaturated fats contain one C=C double bond within their carbon chains. Polysaturated fats contain more than one C=C double bond. 

Unsaturated vegetable oils are liquid at room temp. so can be hardened by reacting them with hydrogen in a nickel catalyst at about 60°C. This is hydrogenation (the hydrogen reacts with the double bonded carbons, opening the bonds).

Hydrogenated oils: 
Higher melting points than unsaturated oils, so more solid at room temp. 
Margarine is made from partially hydrogenated vegetable oil as it would be too hard if all the double bonds were made into single bonds.
However, partially hydrogenated vegetable oils mean you can end up with trans fats, which are very bad for you.

Using vegetable oil to cook is more fattening and partially hydrogenated vegetable oil increases the cholesterol in the blood. 

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EMULSIONS

Oil doesn't dissolve in water so you can mix it with water to make an EMULSION, made up of lots of droplets from one liquid suspended in another liquid.

There are oil-in-water emulsions and water-in-oil emulsions.

Emulsions are thicker than either oil or water and their physical properties make then suited to lots of uses in food (e.g. salad dressings and sauces).

Generally, the more oil in an oil-in-water emulsion, the thicker it is.
Whipped cream and ice cream are oil-in-water emulsions with the addition of air to give whipped cream a fluffy, frothy consistency and ice cream a softer texture.

Emulsions are also have non-food uses (moisturising lotions, so they're easier to rub into the skin).

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EMULSIONS

Oil and water mixtures naturally separate out, so emulsifiers help them mix.
Emulsifiers are molecules with a hydrophilic (attracted to water) part and a hydrophobic (attracted to oil) part. 

The hydrophilic end of each emulsifier latches onto water molecules.
The hydrophobic end of each emulsifier latches onto oil molecules.

When the oil and water mixture is shaken with the emulsifier, the oil forms droplets surrounded by a coating of emulsifier with the hydrophilic part facing outwards.
Other oil droplets are repelled by the hydrophilic part of the emulsifier, while water molecules latch on. This means the emulsion won't separate out.  

Emulsifiers stop emulsions from separating out, giving them a longer shelf life.
They also allow food companies to produce food that's lower in fat and still has a good texture.

However, some people are allergic to certain emulsifiers (e.g. egg yolk).  

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THE EARTH'S STRUCTURE

The CRUST is the first layer; thin, rocky and surrounded by the atmosphere.

The MANTLE is the second layer, which holds properties of a solid, but flows very slowly. In the mantle, radioactive decay takes place, producing a lot of heat, which causes the mantle to flow in convection currents.

The CORE is in the centre, containing nickel and iron.

The upper part of the mantle are cracked into tectonic plates. Because of convection currents in the mantle, these plates move a few cm each year.
Occasionally, the plates move suddenly, causing earthquakes and volcanic eruptions.

It's hard to predict when earthquakes and volcanic eruptions could happen as:
-It is impossible to predict when the plates may suddenly move.
-There are mini-earthquakes near volcanoes when molten rock rises up into chambers near the surface, but sometimes it cools down instead of erupting, so these can be a false alarm.  

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Comments

caitlin

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Shine

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Aaron

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Qasim

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Princeeeee

thanks for summarising it without rambling! some people always go on and on but your notes are quick, to the point, and precise. thanks again!

James Wilson

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lake09__

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shruthy

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mani

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Miriam

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Abdilahi omar

helpfull  indeed!

liya

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saab

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Maary123

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hiraawf

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