Chemistry C2

OCR gateway C2 revision cards

Paints and pigments

solvent- dissolves binder so the paint is liquid

binding medium- holds pigment particles together

pigment- gives it colour

Paints are colloids- tiny particles dispersed in a liquid which won't separate because the particles are too light

emulsion= water based paint- dries by evaporating

oil based paint- like gloss- dries when oil reacts with oxygen (oxidation)

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Dyes and special pigments

natural dyes= onion skin, stinging nettles

synthetic dyes= man made, this has increased number of colours available to dye fabric

Thermochromic paint- changes colour when it gets hot and can be used on mugs containing hot drinks, more colours can be obtained by adding acrylic paint

Phosphorescent paint- (glow in the dark) absorb and stores energy when light shines at them and when the light goes off they release energy in the form of light- emergency exit signs, novelty decorations

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Construction materials

aluminium and iron- from ores in rock

glass- melting limestone, sand and soda

bricks are made from clay

Limestone and clay are heated to make cement

concrete= sand and cement

extracting rocks damages the environment

  • quarrying uses up land and destroys habitats
  • transporting rock can cause noise and pollution
  • quarrying produces lots of dust
  • waste materials from mines and quarries looks unattractive
  • disused mines can cause subsidence
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When cement is made limestone undergoes a change

made by heating limestone and clay together

thermal decomposition= single compound breaks down to form 2 or more substances

calcium carbonate-----> calcium oxide + carbon dioxide

     CaCO3           ------>       CaO         +        CO2

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Reinforced Steel

= a composite- has improved qualities

concrete= hard and strong when squashed but week when stretched

steel= flexible and strong when stretched

composite material combines the properties of both

used in making bridges

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Extracting pure copper

Electrolysis is used to obtain very pure copper

  • requires an electrolyte (liquid) which will conduct electricity 
  • In purifying copper the electrolyte is Copper (II) sulfate solution- contains Cu2+ ions

The electrical supply acts like an electron pump

  • it pulls electrons off copper atoms at the anode causing them to go into solution as Cu2+ ions
  • It then offers electrons at the cathode to nearby Cu2+ irons to turn them back into copper atoms
  • The impurities are dropped at the anode as sludge whilst the pure copper atoms bond at the cathode
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Electrolysis of copper

The cathode is the negative electrode, its starts as a thin piece of pure copper and more pure copper adds to it

  • Pure copper is deposited on the pure cathode (-ve)
  • reaction: Cu2+  + 2e- -------> Cu

The anode is the positive electrode. It is a big lump of impure copper which will dissolve

  • Copper dissolves from the impure anode (=ve)
  • reaction: Cu ------> Cu2+  + 2e-

Recycling copper saves money and resources

  • cheaper to recycle copper
  • uses less energy- less use of fossil fuels, so less carbon emissions
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= A mixture of a metal and other elements

  • can be a mixture of 2 or more metals
  • can be a mixture of metal and non metal

Steel is an alloy of iron and carbon (1%)

  • steel is harder than iron, and is also stronger
  • iron will rust on its own but steel is much less likely to rust
  • used for- bridges, engine parts, cutlery, washing machines, saucepans, ships, drill bits
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More alloys

Brass= copper and zinc, used for making musical instruments as it is sonorous

Bronze= copper and tin, harder and stronger than tin and its more resistant to corrosion, used for springs and motor bearings

Solder- lead and tin- doesn't have a definite melting point

Amalgam- mercury and another metal- tooth fillings

  • they all have metal properties e.g. conduct heat and electricity but all have own distinctive properties 

Smart alloys are alloys that can change shape but remember the old one

  • e.g. nitanol which is used for paper-clips- returns to original shape if put into hot water or electric current through
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Iron and steel corrode much more than aluminium

Iron rusts- needs oxygen and water present

Chemical reaction= oxidation reaction

  • iron gains oxygen to form iron (III) oxide
  • word equation= Iron+Oxygen+water-----> hydrated iron (III) oxide

Rust is a soft crumbly solid that flakes off, rusting is quicker if the water is salty or acidic

Aluminium doesn't corrode as it reacts with oxygen in air to form a protective layer of aluminium oxide which stops any further reaction

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Building cars

advantages of aluminium over steel:

  • lower density so car will be lighter so gives car better fuel economy saving fuel resources
  • corrodes less so has longer lifetime

disadvantage- very expensive

Different parts of a car

  • steel-strong- bodywork
  • copper- good electrical conductor- electrical wiring
  • aluminium- strong and low density
  • Glass- transparent- windscreens and windows
  • Plastic- light, hard wearing- coverings for doors and dashboards
  • Fibres- hard wearing- cover seats and floor

Recycling cars is important- save natural resources, money and reduce landfill use, biggest problem is parts of car have to be separated

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Sedimentary rock

Formation of sedimentary rock

1. layers of sediment laid down in lakes or seas

2. layers get buried and the weight pressing down squeezes out the water

3. fluids flowing through the pores deposit natural mineral sediment

Limestone is a sedimentary rock formed from sea shells

its mostly calcium carbonate and grey/white in colour

when limestone is heated thermal decomposition occurs:

  • calcium carbonate -------> calcium oxide + carbon dioxide
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Metamorphic rock

Metamorphic rocks are formed from other rocks

1. formed by the action of heat and pressure on sedimentary rocks over long periods of time

2. the mineral structure and texture may be different but chemical composition is often the same

Marble is a metamorphic rock formed from limestone

  • it is another form of calcium carbonate but the very high temperatures break down the limestone so it reforms as small crystals
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Igneous rock

Igneous rocks form when molten magma pushes up into the crust before cooling and solidifying

they contain various different minerals in randomly arranged interlocking crystals

There are two types of Igneous Rock

  • Extrusive igneous rocks cool quickly above ground forming small crystals e.g. Basalt and Rhyolite
  • Intrusive Igneous rocks cool slowly underground forming big crystals e.g. granite and gabbro
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Earths structure

crust= thin outer layer of solid rock- two types, continental crust (land) and oceanic crust (under oceans)

lithosphere- includes crust and upper part of mantle

Mantle- flows very slowly

Core- iron and nickel and where the earth's magnetic field originates

inner core- is solid

Heat inside earth cause convection currents which cause some plates to move

Tectonic plate movement can cause volcanoes and earthquakes where the plates meet

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Evidence for tectonic plates

Alfred wegener came up with the idea that the lithosphere was broken into tectonic plates that are continually moving


  • Jigsaw fit
  • matching fossils
  • identical rock sequences
  • living creatures are the same
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Volcanic eruptions

oceanic and continental crusts colliding cause volcanoes

  • oceanic crust is denser than the continental crust, when the two types collide the oceanic crust is forced underneath- subduction
  • as oceanic crust is pushed down it melts
  • molten rock finds its way to surface and volcanoes form
  • earthquakes happen when two plates slowly grind past eachother
  • where the oceanic crust is forced down you get a deep trench in ocean

volcanic activity forms igneous rock

  • if lava is poor in silica it will be runny
  • if rich in silica will be very explosive
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The Atmosphere

Today's atmosphere= 79% nitrogen, 20% oxygen, 1% carbon dioxide

carbon dioxide- decreased, some dissolved in oceans and plants took in carbon dioxide in respiration

Ammonia (NH3)- some of the oxygen reacted with ammonia producing nitrogen and water

water vapour- condensed to form oceans

oxygen- increased due to photosynthesis of plants

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The carbon cycle

respiration, combustion and decay of plants and animals adds CO2 to the air and removes oxygen

photosynthesis does the opposite and removes CO2 and adds oxygen

Human activity affects air composition

  • population increasing- more respiration- more CO2 given out
  • more energy needed for electricity and transport, more countries are becoming industrialised so increase energy consumption- burning fossil fuels releases CO2
  • more people means more houses and more food so trees are chopped down to make space so less CO2 absorbed in respiration
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Air pollution and Acid rain

Acid rain is caused by sulfur dioxide and oxides of nitrogen- when fossil fuels are burnt these are released

Acid rain kills fish, trees and statues (damages limestone on buildings)

Oxides of nitrogen also cause photochemical smog

  • caused by sunlight acting on oxides of nitrogen, these combine with oxygen to produce ozone (O3) which can cause breathing difficulties

Carbon monoxide is a poisonous gas that can stop blood carrying oxygen- formed when petrol or diesel in car engines are burnt without enough oxygen (incomplete combustion)

Has to be controlled- catalytic converters on motor vehicles reduce amount of carbon monoxide and nitrogen oxides by using a catalyst which is normally a mixture of platinum and rhodium

carbon monoxide+nitrogen oxide----> nitrogen + carbon dioxide

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Chemical reaction rates

reactions go at different rates

  • slowest- rusting of iron
  • moderate speed- reactive is a metal with an acid
  • fast- burning but really fast is an explosion

you can do an experiment to follow a reaction

  • observing how quickly a gas is produced
  • measure the change in mass and measure the volume of gas given off

Particles must collide with enough energy in order to react

Rate of reaction depends on 4 things- temperature, concentration (or pressure), catalyst, size of particles (surface area)

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Collision Theory

  • Increasing temperature means the particles are moving faster so there are more collisions
  • Increasing the concentration (or pressure) means the particles are more crowded together which means there will be more collisions
  • Smaller solid particles (more surface area) means other particles can get to it more easily so there are more useful collisions
  • A catalyst increases the number of successful collisions without being used up or changed, they reduce the energy needed by the particles to react.
  • Faster collisions increase the rate of reaction- this is only done by increasing the temperature
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