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C1- Chemistry in our world 24 May 2017 A Massawe How science works • Independent variable – this is the quantity that you change • Dependent variable - this is what you measure • Control variable – this is what must be kept the same to ensure a fair test • Hypothesis – an idea based on observations without experimental evidence • Secondary evidence - data collected by someone else, you may find it in a book or on the internet 24 May 2017 A Massawe 2 How do scientist validate results? 1. they repeat experiment results 2. they publish their findings in scientific journals 3. conference presentation 4. peer review/other scientists investigate the same findings. 24 May 2017 A Massawe 3 The early atmosphere • The early atmosphere was mostly carbon dioxide, little oxygen, water vapour, ammonia. • As the Earth cooled down, most of the water vapour condensed and formed the oceans. 24 May 2017 A Massawe Changes in the atmosphere • The proportion of oxygen went up because of photosynthesis by plants. • The proportion of carbon dioxide went down because: 1. it was locked up in sedimentary rocks such as limestone 2. it was absorbed by plants for photosynthesis 3. it dissolved in the oceans. 24 May 2017 A Massawe Types of rock 1. Igneous rocks are formed by magma from the molten interior of the Earth When it cools slowly inside the earth it forms intrusive rock e.g. granite. When it cools on the surface is known as extrusive rock e.g. basalt. 24 May 2017 A Massawe Types of rock 2. Sedimentary rocks – As a river enters the sea it slows down and deposits the sediment it was carrying Over millions of years the sediment is buried by more and more sediment. Eventually, as the water is squeezed out, it is cemented together to form sedimentary rock. sandstone 24 May 2017 A Massawe limestone Types of rock 3. Metamorphic rocks – is formed when existing rock is changed by high temperatures and pressures, e.g. marble - which originates from chalk or limestone slate - which originates from clay 24 May 2017 A Massawe Reactions of calcium compounds 24 May 2017 A Massawe What are acids? • Acids have a low pH (1-6) – the lower the number the stronger the acid • Acids react with bases to form salts and water • are corrosive when they are strong • are an irritant when they are weak. 24 May 2017 A Massawe Indigestion remedies • Hydrochloric acid (HCl)is used in the body to help digestion and kill bacteria • Too much acid can cause indigestion and we use gaviscon to neutralise excess acids. 24 May 2017 A Massawe Neutralisation • is the reaction between an acid and a base to form a salt and water. 1. Reaction of acids with metal hydroxides hydrochloric + sodium → sodium + chloride acid hydroxide HCl 24 May 2017 + NaOH → A Massawe NaCl + water H2O Neutralisation 2. Reaction of acids with metal oxides hydrochloric + copper → copper + water chloride acid oxide 2HCl + CuO → CuCl2 + H2O 3. Reaction of acids with metal carbonates hydrochloric + calcium → calcium + water + carbon acid carbonate chloride dioxide CaCO3 24 May 2017 + 2HCl → CaCl2 + H2O + CO2 A Massawe Electrolysis of copper chloride • Electrolysis is the process by which ionic substances are broken down into simpler substances using electricity. positive electrode negative electrode chlorine gas given off copper chloride 24solution May 2017 copper metal deposited A Massawe Electrolysis of water water oxygen + hydrogen 2H2O → O2 2H2 oxygen collected here hydrogen collected here negative electrode 24 May 2017 + positive electrode A Massawe Electrolysis Electrolysis of: dilute hydrochloric acid water Produces: oxygen chlorine hydrogen √ √ sea water 24 May 2017 √ √ A Massawe √ √ Uses of products in the chemical industry Product Test Uses damp blue litmus make bleach paper turns red make plastics e.g. PVC Chlorine (as chlorine is acidic) then treat our water white (chlorine is suppy a bleach) lighted splint gives fuel Hydrogen a squeaky pop Sodium turns red litmus cleaning products hydroxide blue 24 May 2017 A Massawe Problems toxic gas flammable corrosive Metal ores • Ores are naturally occurring rocks that contain metal or metal compounds, e.g. bauxite, Al2O3 24 May 2017 haematite, Fe2O3 A Massawe Reactivity and extraction method most reactive(hard to extract) Metal Reactivity potassium sodium calcium magnesium Aluminium Electrolysis of a molten compound Carbon zinc iron tin lead Copper least reactive(easy to extract) 24 May 2017 Heat an ore with carbon Hydrogen silver gold platinum Found as the uncombined element A Massawe Oxidation and reduction • Oxidation is the gain of oxygen by a substance e.g. magnesium + oxygen → magnesium oxide 2Mg + O2 2MgO • Reduction is the loss of oxygen from a substance e.g. copper oxide + hydrogen → copper + water CuO + H2 Cu + H2O 24 May 2017 A Massawe Rusting • Iron and steel rust when they come into contact with water and oxygen : this is a form of corrosion • iron + oxygen → iron oxide (rust) • Rusting is an oxidation reaction 24 May 2017 A Massawe Uses of metals Metal Properties Uses low density, does not corrode suitable for the bodies of planes good conductor of electricity, does not react with water electrical wires & water pipes aluminium copper gold very good conductor electrical connections on circuit boards & of electricity, jewellery unreactive cheap and strong 24 May 2017 steel A Massawe suitable for building material Alloys • Alloys are made by mixing a metal with another material e.g. steel (iron and carbon), brass (copper and zinc) and bronze (copper and tin) atoms from different material are smaller hence change arrangement, this makes alloy harder and stronger 24 May 2017 A Massawe Shape memory alloys • Nitinol is a shape memory alloy, its made from nickel and titanium • It returns to its original shape when heated • Used for spectacle frames and hold the artery open 24 May 2017 A Massawe Combustion of fuels 1. Complete combustion methane + oxygen → water + carbon dioxide 2. Incomplete combustion methane + oxygen → water + soot + carbon monoxide 24 May 2017 A Massawe Combustion of fuels • The combustion of a fuel may release several gases into the atmosphere, including: 1. water vapour 2. carbon dioxide 3. carbon monoxide 4. particles 5. sulfur dioxide 24 May 2017 A Massawe Problems with fuels: sulfur dioxide • Sulfur dioxide is produced when fuels that contain sulfur compounds burn. acid rain is formed when sulfur dioxide dissolves in water droplets in clouds. • Effects of acid rain acid rain reacts with metals and rocks such as limestone. buildings and statues are damaged as a result. 24 May 2017 A Massawe Reducing the amount of carbon dioxide • Adding iron compounds to the sea • Capturing carbon dioxide from the fossil-fuelled power stations and reacting it to make hydrocarbon compounds, e.g. propane and butane which can be used as a fuel 24 May 2017 A Massawe Iron seeding flow chart Adding iron compounds encourages small plants to grow Small plants use carbon dioxide for photosynthesis and then eaten by sea animals When these animals die and sink to the ocean floor, the carbonate in their shells is buried This removes the carbon from the atmosphere for along time 24 May 2017 A Massawe Biofuels • Methane biogas comes from decaying manure and sewage. • Some biodiesel is made from waste cooking oil and rapeseed oil. 24 May 2017 A Massawe Advantages and Disadvantages of Biofuels Advantages Disadvantages It is a renewable resources It more expensive than normal diesel fuel It less suitable for use in low temperatures It gives out more nitrogen oxide emissions It can only be used in dieselpowered engines. It causes less pollution It produces 78% less carbon dioxide It contains no sulfur, the element responsible for acid rain. It is relatively less inflammable compared to the normal diesel 24 May 2017 It is made from food crops A Massawe Factors influencing the choice of a fuel • • • • • • the energy value of the fuel in J/g of fuel the availability of the fuel how the fuel can be stored the cost of the fuel the toxicity of the fuel - whether it is poisonous any pollution caused when the fuel is used, such as acid rain • how easy it is to use the fuel 24 May 2017 A Massawe Hydrocarbons and alkanes • Hydrocarbon – contain hydrogen and carbon atoms only, joined together by chemical bonds • The general formula for alkanes is – CnH2n+2 • Alkanes are saturated hydrocarbons alkane formula methane CH4 ethane C2H6 propane 24 May 2017 C3H8 chemical structure A Massawe ball-and-stick model Distillation • Distillation is a process that can be used to separate a pure liquid from a mixture of liquids • This is the sequence of events in distillation: heating → evaporating → cooling → condensing 24 May 2017 A Massawe Cracking • Cracking is the process in which heavy oils are broken down into hydrocarbons of lower molecular weight by heat or catalysis • Cracking allows large hydrocarbon molecules to be broken down into smaller, more useful hydrocarbon molecules. butane 24 May 2017 ethane + A Massawe ethene Alkenes • Alkenes are product of cracking, they all have general formula of CnH2n • Alkenes are unsaturated hydrocarbons alkene formula ethene C2H4 propene C3H6 24 May 2017 chemical structure A Massawe ball-and-stick model Testing for alkenes • An alkene will turn brown bromine water colourless as it reacts with the double bond. 24 May 2017 A Massawe Polymers • Alkenes can be used to make polymers • Polymers are very large molecules made when monomers join together, end-to-end. • Alkenes are monomers because they have a double bond ethene 24 May 2017 poly(ethene) or polythene A Massawe Uses of polymers Monomer ethene Polymer Properties Uses poly(ethene) flexible, cheap, electrical insulator plastic bags and bottles, coating on electrical wires flexible and poly(propene) strong buckets and crates propene chloroethene tetrafluoroethene 24 May 2017 tough, cheap poly(chloroethe and long window frames ne) or PVC lasting tough and poly(tetrafluoro non-stick coating non-stick ethene) or PTFE on pans A Massawe Polymer problems • Polymers are suitable for storing food and chemicals safely • Most polymers are not biodegradable. • This means that microorganisms cannot break them down, so they may last for many years in rubbish dumps. 24 May 2017 A Massawe