Chemistry (Core)

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  • Created on: 31-08-15 00:38

The early atmosphere

Volcanoes on earth today release mainly carbon dioxide and water vapour  along with ammonia, methane and nitrogen. The atmosphere of Titan is 98% nitrogen which some scientists think was released by volcanoes also. They feel Earth’s early atmosphere may of been like this (nitrogen) there are also volcanoes on Mars and Venus but their atmospheres are mainly carbon dioxide. This has lead other scientist to believe that Earth’s early atmosphere may of been Carbon dioxide. Recent results from space probes have revealed that titan’s interior is icy rather than earth’s rocky one (like Mars, Venus) which doesn’t explain how earth now contains so much nitrogen. Scientists cannot be certain which theory is correct. 

OXYGEN

Scientists are more certain there was little or no oxygen in the early atmosphere on Earth.

Evidence: volcanoes do not release oxygen, iron compounds found in Earth’s oldest rocks are compounds which would only form in the ABSENSE of oxygen

As the Earth became older, it cooled down. Water vapour in hot atmosphere= cooled= condensed in to liquid water=oceans

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A changing atmosphere

After oceans were formed, carbon dioxide in the atmosphere dissolved into the oceans

Scientists feel half of the carbon dioxide in the atmosphere was lost this way.

Some marine organisms (coral, molluscs and star fish) use dissolved carbon dioxide to make shells of calcium carbonate. 

As they die, their shells fell and formed sediment. Over millions of years, the layers of sediment became sedimentary rock. 

Limestone is mostly calcium carbonate.

PHOTOSYNTHESIS

Taking in co2 and releasing o2

Life started 4 billion years ago, 1billion years ago photosynthesis occurred ( believe) 

Increasing level of photosynthesis= sped up rate of co2 removal= same rate of 02 released. 

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The atmosphere today

Nitrogen  and oxygen are the most abundant gases in the atmosphere today (99%) Water vapour changes daily so not included in composition of dry air. Some noble gases, mainly argon are some of the other 1% gas. Small amount of co2 is also found Trace gases: carbon monoxide, sulfur dioxide and methane.

Can be change in amount found.  NATURAL: volcanoes- release a lot of sulfur dioxide. Lightening produces nitrogen oxides

HUMAN ACTIVITIES: deforestation- increase in co2, burning fossil fuels- increase of c02, CO, sulfur dioxide.

Cattle and rice fields- methane Some are harmful to people/environment scientists have to monitor. 

NITROGEN  Nitrogen main gas in atmosphere today

One theory- released by volcanoes

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rocks and their formation

IGNEOUS

Rocks deep in the earth may become hot enough to melt. Molten rock = magma.

Erupt- lava When molten rock cools, it solidifies= solid rock.

Contain crystals which interlock Size of crystal depends of rate of magma/larva to cool. Slower it cools, the larger the crystals. E.g. Granite.

SEDIMENTARY  Rocks are broken into smaller pieces by physical processes such as expansion of water when it freezers. Also by chemical reactions with water/air. Erosion happens when pieces of rock are TRANSPORTED in a river. Rivers carry large amounts of broken rock towards sea where they are DEPOSITED. Most sedimentary rocks are formed this way. Other are formed by hard parts of dead organisms. 

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rocks and their formation continued

METAMORPHIC

 The action of heat and/ or pressure can change rock causing new crystals to form.  changed rock=metamorphic 

Marble is a metamorphic rock formed from chalk/limestone. Grains in chalk are weakly joined with gaps.  When marble forms, grains become new crystals that interlock tightly.  This makes marble harder than chalk

To help, crystals are larger in rocks that cool down slowly think of the crystals growing while the rock is hot. if the rock cools down slowly, the crystals have more time to grow bigger.

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limestone and its uses

USES

Limestone is cut into blocks to be used for construction of buildings

Crushed into smaller lumps to be used to make firm base for railway lines/roads

Raw material for the manufacture of cement, concrete and glass!

QUARRYING

Limestone is removed from the ground at a quarry

Explosives are used to break limestone into pieces.

They are cut or crushed into useful sizes

Transported by rail/ road to customers

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limestone benefits and drawbacks

benefits - help locals with jobs 

              exporting helps the uks economy 

             valuble natural resource and helps with other materials 

             can be used as a reserve for animals or changed into something usefull 

drawbacks- dusty, noisey 

                 destroy animal habitats 

                 damages tourist attractions 

                heavy lorry pollution and traffic 

               land cannot be used again 

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thermal decomposition and limestone manufacturing

Limestone, chalk and marble are natural sources of calcium carbonate

when they are heated strongly, CACO3 breaks down (Decompose) to form calcium oxide and carbon dioxide

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

Thermal decomposition of limestone is used in the manufacture of cement and glass

Cement is made by heating limestone with powdered clay and used in brick work to hold things together 

Concrete is made by mixing cement with SAND, GRAVEL and WATER. Widely used in construction of buildings/bridges

glass is made by heating limestone with sand and sodium carbonate. Chemical reaction- liquid glass. Cools and hardens to form hard, solid, transparent windows. 

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chemical reactions

Reactants products

In thermal decomposition of zinc carbonate, the REACTANT is zinc carbonate. The PRODUCTS are zinc oxide and carbon dioxide. 

for example

Zinc nitrate decomposes with heat to give zinc oxide, nitrogen dioxide and oxygen: 

Zn(NO3)2 (s) -----> 2ZnO (s) + 4NO2 (g) + O2 (g)

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reactions of calcium compounds

MAKING LIMEWATER  - When limestone is heated, the calcium carbonate it contains forms calcium oxide. A reaction happens when water is added to calcium oxide. A lot of heat is released, which makes the water boil as it touches CaO. Calcium hydroxide dissolves when more water is added, forming calcium hydroxide solution. (limewater) 

TEST FOR CARBON DIOXIDE  -   Limewater turns cloudy in the presence of carbon dioxide.  Calcium hydroxide + carbon dioxide-> calcium carbonate+ water  If a lot of carbon dioxide is bubbled through the limewater, the calcium carbonate disappears and a colourless solution is formed. This is because carbon dioxide dissolves in water to form a acidic solution, which reacts with CaCO3.

NEUTRALISING ACIDS WITH LIMESTONE - Acids are neutralised by alkalis= neutralisation reaction    CaCO3, CaO and Ca(OH)2 can neutralise acids. Farmers need to reduce the acidity of their soil, they spray powdered CaCO3 or Ca(OH)2 over their fields to do so.  Many power stations burn coal. Coal contains sulfur. Nitrogen oxides are also formed  (Sulphur+ oxygen sulfur dioxide)  Both are acidic gases. They produce acid rain if they escape from the chimneys into atmosphere. To stop this, wet powered CaCO3 is sprayed through the waste gases. Neutralised limestone reduces harmful emissions and helps reduce acid rain. 

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limestone cycle

     limestone ( CaC03)

                                 add heat and co2 is released 

    Quicklime (cao) 

                                 add a little amount of water 

    slaked lime (Ca(H0)2)

                                  add a lot of water 

   limewater (Ca(H0)2)

                                  bubble through carbon dioxide (C02)

  limestone 

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indigestion

Your stomach produces hydrochloric acid which kills bacteria which may be in your food. Food in the stomach is digested by digestive enzymes that need acidic conditions. Sometimes the stomach produces too much HCL- cause pain called indigestion. Sometimes acid escapes from top of stomach which leads to oesophagus and cause pain (heartburn).

Medicines called antacids can neutralise excess stomach acid.  Antacid  can contain bases- substances that react with acids. 

Acid+ base--> salt + water                               A base dissolved in water is an  alkali

Ph:  1-ACID        14-ALKALINE

use a Universal indicator to detect which is which 

use Litmus paper

Blue litmus paper to  red means acidic

Red litmus to  blue means  alkaline

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neutralisation

If an acid or alkali is spilled, it can be made safe by diluting it with water or by neutralising it.

ACID+METAL OXIDE = SALT+ WATER

ACID+ METAL HYDROXIDE= SALT+ WATER

ACID+ METAL CARBONATE=SALT+ WATER+ CARBON DIOXIDE

Salts produced depend on acid

SULFURIC ACID PRODUCE SULFATE SALTS

NITRIC ACID PRODUCE NITRATE SALTS

HYRDROCHLORIIC ACID PRODUCE CHLORIDE SALTS

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importance of chlorine

in some reactions, compounds are decomposed to from new compounds. Electricity can be used to break down some compounds, this is called electrolysis. Compounds which can be decomposed by electricity are called electrolytes. Sea water contains many dissolved substances.Most common- sodium chloride (salt) If a direct current (D.C) is passed through the sea, chlorine gas is formed at one of the electrodes. Test for chorine- hold damp, blue litmus paper near gas, if goes red then white  chlorine is present.

Key point- Chlorine BLEACHES blue, litmus paper.

USES OF CHLORINE

Chlorine is a yellow, green toxic gas. it can be used to treat water supply, killing microorganisms, In manufacturing of bleach and other cleaning products and In the manufacture of plastics such as poly(chloroethene PVC)P

POTENTIAL PROBLEMS

Sometimes gases can leak accidentally from a chemical factory or a tanker carrying the gas may be involved in an accident.

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Electrolysis of water

The electrolysis of dilute HCL produces hydrogen and chlorine gas. 

Chlorine can also be produced if sea water is electrolysed

If a D.C is passed through water, hydrogen and oxygen are given off at the electrodes. 

Test for hydrogen- hold a lighted splint in mouth of test tube. If hydrogen present, a squeaky pop will occur.

Test for oxygen- place glowing splint near mouth of test tube, if oxygen is present it will relight.

USES OF HYDROGEN AND OXYGEN

Hydrogen- rocket fuel. 

Oxygen- hospital

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ores

A few metals are found naturally in earth’s crust- unreactive e.g. Gold, platinum which are also found as elements that have never reacted with O2

Very few metals occur as elements. The more reactive the metal is, the more easily it reacts to form compounds.

Compounds mostly metal oxides. Found in rocks called ores. Ores are rocks which contain enough of the compound to extract the metal for profit.

Extracting metals:

Some metals can be extracted by heating compound with Carbon 

Iron oxide+ carbon  iron + carbon dioxide

Other metals such as aluminium are extracted by electrolysis. electrolysis is used as all the elements after zinc are more reactive than carbon, so extraction in that form wouldn't happen as the carbon will get displaced. The way in which an metal is extracted is based upon reactivity. The harder a metal is to extract, the more it costs to extract. Electroysis- expensive- electricty Hence: more reactive the metal the more difficult and expensive it is to extract. 

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oxidation and reduction

Most compounds which are found in ores are metal oxides. In order to obtain the metal, the O2 must be removed. Extraction of metals from their oxides is REDUCTION. 

iron is obtained by removal of o2 from iron oxide by heating it with Carbon. Iron oxide+ carbon iron+ carbon dioxide. Aluminium obtained by removal of oxygen from aluminium oxide by electrolysis Aluminium oxide -> aluminium+ oxygen

CORROSTION OF METAL OXIDES

Most metals corrode. Corrosion of iron (and steel) is called rusting. Corrosion occurs when the surface of a metal changes by reaction with oxygen- sometimes water too.

OXIDATION is the addition of oxygen to a substance

When a metals corrode the metal is oxidised.

The  MORE reactive the metal, the more rapidly it corrodes.

Reactive aluminium does not corrode as much as expected because its surface oxidises quickly- protective layer- aluminium oxide (AL203) stops further corrosion.

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recycling metals

When metals are melted down and made into something new

ADVANTAGES:

Natural reserves of metal ores will last longer

For most metals, less energy is needed to recycle them than need to extract

Recycling reduces need to mine ores. Ores can damage landscape

Less pollution (when electrolysis is used to for extraction.) 

Less landfills are used up

DISADVANTAGES:

- Expensive and use energy in collection, sorting and transporting. 

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properties of metals

alumminium - low density and doesnt corrode 

                    used for aeroplanes and cars as it is a light weight 

copper - electrical conductor, low reactivity and ductile 

            used for electrical cables and water pipes 

gold - does not corrode, attractive and conducts electricity 

         used for jewellry and easily molded devices 

iron and steel - cheap, strong, hard and rusts 

         used for bridges, cars and machinery 

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alloys

Many metals are mixed with small amounts of other metals to improve their properties. A mixture like this= alloy. In pure metal, atoms same size and packed closely= layers of atoms can slide over each other= metal soft

In alloy- varying sizes- prevents sliding layers- alloys harder  and stronger. Different types of alloy steels. Stainless steel, an alloy of iron with small amounts of chromium and nickel. NO CORROSION. Gold too soft to be used in jewellery. Other metals like copper, silver are added. Purity of gold measured in carats or as fineness.

SHAPE MEMORY ALLOYS

Nitinol is an alloy of nickel and titanium. It is a SMART MATERIAL- properties which change under certain conditions, usually temperature. 

Nitinol is a shape memory alloy

Returns to shape when heated

Repair collapsed artery/ glasses frame

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crude oil

Petrol and other useful products are obtained from crude oil. 

Thick, black liquid found in some sedimentary rocks. 

Crude oil and natural gas are normally found deep underground, trapped by layers of rock

Fossil fuels

Crude oil is a mixture of different hydrocarbon molecules.

Hydrocarbon: compound only contains H+C

Can contain impurities like sulfur

Non- renewable resource

Demand increasing 

Pumping oil faster than it being made

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crude oil fractions

(http://www.hazemagazine.co.uk/wp-content/uploads/2014/07/fractioning-column.jpg)

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complete combustion

Hydrocarbon fuels burn they react with oxygen (oxidation) and releases heat and light energy. This is combustion

Used to detect products of a combustion reaction

The U-tube in the middle contains anhydrous copper sulphate. This white substance turns blue when water is added. Limewater turns milky when CO2 is passed through

Testing hydrocarbons: anhydrous copper sulfate turns blue and limewater turns milky. This shows both water and carbon dioxide are present in waste gases. 

All hydrocarbon fuels produce carbon dioxide and water when they burn, as long as enough oxygen is present. Methane: (natural gases main substance) 

Methane oxygen carbon dioxide + water

CH ❹+2O❷ CO❷+2H ❷0

In the combustion of a hydrocarbon the reaction is described as complete combustion, if all hydrocarbons are used up, only carbon dioxide and water can be the  products. 

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incomplete combustion

Incomplete combustion- when fuels burn without enough oxygen. The hydrogen atoms form water but there is not enough oxygen for the carbon atoms to form carbon dioxide. Sine if the carbon may form carbon monoxide and some may just form solid particles of carbon (soot) 

Methane + oxygen carbon + water

Methane +  oxygen carbon monoxide + water

Methane + oxygen carbon monoxide+ carbon (soot)+ water!

Different percentages of c, co and co2 are produced, all depending on levels of oxygen

CARBON MONOXIDE Odourless, colourless toxic gas. Reduces amount of oxygen that can travel around body. People die due to faulty boilers Reduce harm by: Ensure fuel burning appliances are serviced regularly and fitting homes with carbon monoxide detectors

SOOT PROBLEMS Clog pipes, Cause fires if  build up in chimneys, Lung disease and dirty Buildings. 

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acid rain

Wind can transport pollution. RAIN WATER IS NATURALLY ACIDIC. Acid rain is rain that is more acidic than normal and has a pH lower than 5.2. Hydrocarbon fuels (petrol, coal) also have impurities like sulfur. When the fuel is burnt, the sulfur reacts with oxygen to form sulfur dioxide. This dissolves in waster making it more acidic.

effects - Making rivers, lakes and soil more acidic- harm organisms solution - neutralising 

             damaging trees                                                                          reducing amount of                                                                                                                  sulphur in petrol, diesel                                                                                                              and fuel oil                            

            speeds up weathering of buildings                                                 reducing use of fossil                                                                                                                fuels 

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climate change (green house gases)

The surface temperature of the earth varies due to weather patterns and seasons. The mean can also change ( after hundreds of years)  Mean temperature of earth is 14 degrees Celsius

Carbon dioxide, methane and water vapour trap thermal energy and keep earth warm = green house effect ( green house gases). Without gases mean temp would be -18. The concentration of c02 can change due to natural processes. Large increase since 1800 is due to human activity- burning of fossil fuels, Farming increases (methane). 

REDUCING CARBON DIOXIDE

Reduce use of fossil fuels. Chemist investigating- ways of controlling co2 in atmosphere

METHODS: Adding iron compounds to ocean (iron seeding) iron is essential nutrient in plant growth. Adding iron compounds- encourage microscopic plant growth- use for photosynthesis. Then eaten by sea creatures. When die and sink to floor, carbonate buried. This removes carbon from atmosphere for LONG time

Capturing carbon dioxide from fossil fuelled power stations and reacting it to make hydrocarbon compounds (propane and butane). These can be used as fuels.

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biofuels

Petrol used in cars  contain hydrocarbons also contain- ethanol. Biofuels gained from living or recently died organisms. Biofuel include wood and dried animal droppings used for many years and still using plant as biofuels= less plants for food

Biofuels-Waste materials- wheat stalks, peanut shells or branches used from trees cut down

These can be burnt in power stations. Chemists can manufacture BIOFUELS from raw materials. Ethanol is made from processing wheat, sugar cane or sugar beet. Ethanol can be mixed with petrol- fuel for engines. Using ethanol helps reduce demand for petrol and so conserves crude oil supplies. Biodiesel is a fuel made from vegetable oil by chemical reaction. Biodiesel can be made from oil seed **** or soya beans or cooking oil from restaurant. Diesel engines can run on biodiesel, or mixture  of biodiesel and normal diesel oil

ADVANTAGES/ DISADVANTAGES- Renewable as long as trees are replaced quicker than used, our supply of wood will never cease. Crops grow to make into ethanol or biodiesel can be grown continuously. Biofuels may also be used to reduce the overall amount of carbon dioxide. Plants take in carbon dioxide when they photosynthesis . Plants used for biofuel, returned to atmosphere by combustion. So biofuels can be carbon neutral.

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choosing fuels

In a rocket, hydrogen and oxygen burn energy. Hydrogen and oxygen react and release energy without burning in a device called a fuel cell. A hydrogen fuel cell produces electricity to run an electric motor. Water is the only waste material. Hydrogen is called a clean fuel. Most of the fuels we use cause pollution. Natural gas, petrol, kerosene and diesel are all non-renewable. All produce carbon dioxide and water. Sulfur- sulfur dioxide when burnt. Biofuels are renewable. Leave a lot of ash when burnt

GOOD FUEL? How easily it burns. How much heat is produced. How easily it is stored/transported. A good fuel must burn easily .Easily light can be dangerous. Leaking gas can be explosive Coal and other solid fuels are easy to store but need lorry to transport.Liquid and gas fuels are stored in tanks and can be transported n tankers or through pipes. Hydrogen and methane can be stored at high pressure to reduce size of tanks need to store them

HYDROGEN/ PETROL

Hydrogen needs to be easily and cheaply available

Petrol stations need to be converted to be able to store and distribute hydrogen

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Alkanes

ALKANES

Natural gas is extracted and methane, ethane and propane are processed so that gas piped is almost all methane

These all are part of molecules called alkanes

Mainly used as fuels

A carbon atom can form bonds with maximum of four other atoms

In alkane, each carbon atom is bonded singularly to other four atoms

Hydrocarbons with carbon- carbon bonds that are single are called saturated hydrocarbons

Methane- one carbon atom to four hydrogen

Ethane- two carbon

Propane- 3

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alkenes and bromine test

Alkenes - Double bonded. Unsaturated. Not saturated carbon – carbon as not with maximum amount  of other atoms. Alkenes are hydrocarbons with one double bond between carbon atoms

BROMINE TEST

Used to see is compounds contain double bond

Bromine water is bromine dissolved in water (usually orange)

If mixed with saturated hydrocarbon (alkane) no colour change

If with unsaturated, it reacts with alkene and decolourises.

Ethane + bromine water orange coloured liquid

Ethene + bromine water colourless liquid

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cracking

Longer hydrocarbons being split into smaller, more useful ones done by process called cracking.

In cracking, long-chain alkanes are heated and broken up into smaller molecules by Thermal decomposition. 

Long chained alkanes (heat) shorter alkenes + alkanes

One is saturated and one unsaturated as not enough hydrogen molecules to go around when broken. Mostly used to make plastic (short)

WHY IS CRACKING NEEDED?

Crude oil is obtained from different oil fields

To meet demands (petrol which are short chained but

 not found natural )

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polymerisation

Correct name for polythene is poly(ethene), Poly(ethene)is example of polymer

Polymer- substances made up of thousands of relatively simple repeating units.

Monomers are substances whose molecules react together to form polymers

POLY(ETHENE) IS MADEFROM LOTS OF ETHENE MONOMERS and theyoccur from cracking crude oil. Manufactured polymers are often called plastics

Poly(ethene) is used for plastic bottles and bags

Polymerisation- monomer molecules react together to form long-chained molecules.

a poly(ethene) molecule can have thousands or even millions of carbon atoms in it

Repeating unit- n

Poly(ethene) is made from ethene. Other polymers are made from other unsaturated molecules

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problems with polymers

Materials such as wood and paper are biodegradable this means they rot as microbes can feed on them. Many polymers are useful for many purpose due to the fact they DON’T biodegrade- (long lasting). This also means they don’t rot when thrown away. Most rubbish goes to landfill sights. Some waste is incinerated (burned). Energy released can be used to generate electricity. Many plastics produce toxic substances when burnt. Most toxic can be removed but this forms toxic gas, which must be  disposed off carefully. Chemists are developing polymers which do biodegrade. This will still take time( years) so it is better just to reduce plastic usage.

We can  reduce waste by reusing, reducing and recycling

Reusing and recycling means raw materials will last longer

It is difficult to recycle polymers because each polymer 

         needs to be separated in to each type. 

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