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The Little Book of everything I need to know for Chemistry C1 Targets and test record page 2 Topic checklists and key words C1.1 Fundamental Ideas in Chemistry C1.2 Limestone and Building Materials C1.3 Metals and their Uses C1.4 Crude Oil and Fuels C1.5 Other Useful Substances from Crude Oil C1.6 Plant Oils and their Uses C1.7 Changes in the Earth and its Atmosphere 4 7 10 13 16 19 21 Command words for GCSE How Science works key words 24 26 Basic Standards of Presentation and Marking Laboratory Rules Notes 28 29 30 Data sheet [inside back cover] Periodic table [back cover] 31 32 Challenge grade: Date:………………… Grade: ………… Date:……………………Grade:..…… Topic Test result Comment C1.1 Fundamental ideas C1.2 Limestone and building materials C1.3 Metals and their uses C1.4 Crude oil and fuels C1.5 Other useful substances from crude oil C1.6 Plant oils and their uses C1.7 Changes and the Earth and its atmosphere Targets Due by 2 Done? Targets Due by 3 Done? Topic checklist – C1.1 The fundamental ideas in Chemistry Atoms and elements are the building blocks of chemistry. Atoms contain protons, neutrons and electrons. When elements react they produce compounds. C1.1.1 Atoms All substances are made of atoms. An element is a substance that is made of only one sort of atom. There are about 100 different elements. Elements are shown in the periodic table. The groups (vertical columns) contain elements with similar properties. Metals appear on the left hand side of the Periodic Table and non-metals on the right hand side Atoms of each element are represented by a chemical symbol, eg O represents an atom of oxygen, and Na represents an atom of sodium. Atoms have a small central nucleus, which is made up of protons and neutrons and around which there are electrons. The sub-atomic particles are as shown: Name of particle Charge Proton Neutron Electron +1 0 –1 Relative mass 1 1 1 /1840 In an atom, the number of electrons is equal to the number of protons in the nucleus. Atoms have no overall electrical charge. All atoms of a particular element have the same number of protons. Atoms of different elements have different numbers of protons. The number of protons in an atom of an element is its atomic number. The sum of the protons and neutrons in an atom is its mass number. Mass number no. protons: 35 80 Br no. neutrons: (80-35) = 45 35 Atomic number no. electrons: 35 (same number as the atomic number) 4 Electrons occupy particular energy levels. Each electron in an atom is at a particular energy level (in a particular shell). The electrons in an atom occupy the lowest available energy levels (innermost available shells). The electronic structure of the first 20 elements of the periodic table can be represented in the following forms: and sodium : 2,8,1 C1.1.2 The periodic table Elements in the same group in the periodic table have the same number of electrons in their highest energy level (outer electrons) and this gives them similar chemical properties. e.g. Na: 2,8,1 and K: 2,8,8,1 The elements in Group 0 of the periodic table are called the noble gases. They are unreactive because their atoms have stable arrangements of electrons; they have eight electrons in their outer energy level, except for helium, which has only two electrons i.e. full outer shells. E.g. Ne:2,8 C1.1.3 Chemical reactions When elements react, their atoms join with other atoms to form compounds. This involves giving, taking or sharing electrons to form ions or molecules. Compounds formed from metals and non-metals consist of ions; metals lose electrons to form positive ions, whereas non-metals gain electrons to form negative ions.. Compounds formed from non-metals consist of molecules. In molecules the atoms are held together by covalent bonds. Chemical reactions can be represented by word equations or by symbol equations. No atoms are lost or made during a chemical reaction so the mass of the products equals the mass of the reactants. Notes: 5 C1.1 Fundamental ideas (atomic structure) key words: Word / Phrase Meaning Atom The smallest part of an element that can still be recognised as that element. Atomic number The number of protons in (the nucleus of) an atom. Compound Substance containing atoms of two or more different elements chemically joined together. Covalent bond Type of chemical bond in molecules [see C2] Electron Smallest sub-atomic atomic particle. Electrons have a charge of -1 and a tiny mass (1/1840 amu); they orbit the nucleus of an atom in electron shells. Electron shell [energy level] Area around a nucleus in which an electron is found Electronic structure [electron arrangement] The arrangement of electrons in their shells [energy levels]. E.g. the electronic structure for sodium is 2,8,1 Element Substance containing only one type of atom Energy level See electron shell Group Vertical column of elements in the Periodic Table Ion Charged particle formed by the gain or loss of (outer shell) electrons Mass number The total number of protons and neutrons in the nucleus of an atom. Molecule Group of atoms held together by covalent bonds Neutron Subatomic particle found in the nucleus of an atom. Neutrons have no charge and a mass of 1 amu Noble gases Unreactive group of elements found in group 0 of the Periodic Table. Nucleus Dense, central part of an atom that contains the protons and neutrons Periodic table Arrangement of elements in order of their atomic numbers Proton Subatomic particle found in the nucleus of an atom. Neutrons have a charge of +1 and a mass of 1 amu Sub-atomic particles Small particles that make up an atom. 6 Topic checklist – C1.2 Limestone and building materials Rocks provide essential building materials. Limestone is a naturally occurring resource that provides a starting point for the manufacture of cement and concrete. C1.2.1 Calcium carbonate Limestone, mainly composed of the compound calcium carbonate (CaCO3), is quarried and can be used as a building material. Calcium carbonate can be decomposed by heating (thermal decomposition) to make calcium oxide and carbon dioxide. heat Calcium carbonate CaCO3 calcium oxide + carbon dioxide CaO + CO2 The carbonates of magnesium, copper, zinc, calcium and sodium decompose on heating in a similar way. Some carbonates, such as potassium carbonate, do not decompose at Bunsen temperature Calcium oxide reacts with water to produce calcium hydroxide, which is an alkali that can be used in the neutralisation of acids. Calcium oxide CaO + + water H2O calcium hydroxide Ca(OH)2 A solution of calcium hydroxide in water (limewater) reacts with carbon dioxide to produce calcium carbonate. Limewater is used as a test for carbon dioxide. Carbon dioxide turns limewater cloudy. Calcium hydroxide + carbon dioxide Ca(OH)2 + CO2 calcium carbonate + water CaCO3 + H2O Carbonates react with acids to produce carbon dioxide, a salt and water. CARBONATE + ACID SALT + WATER + CARBON DIOXIDE e.g. zinc carbonate + nitric acid ZnCO3 + 2HNO3 zinc nitrate + water + carbon dioxide Zn(NO3)2 + H2O + CO2 Limestone is damaged by acid rain. Limestone is heated with clay to make cement. heat Limestone clay cement Cement is mixed with sand to make mortar and Cement + + sand mortar [used to hold bricks together] Cement is mixed with sand and aggregate to make concrete. Cement + sand + aggregate concrete 7 [used for paving slabs, building blocks] LIMESTONE + CLAY HEAT CEMENT + SAND + SAND + AGGREGATE MORTAR CONCRETE limestone is needed for buildings; the positive benefits of using this material must be compared with the negative aspects of quarrying. evaluate the environmental, social and economic effects of exploiting limestone and producing building materials from it Environmental Social Economic pros End of quarry life beautification Improved infrastructure e.g. road network Increased business More jobs cons Habitats destroyed Increased dust Increased traffic/noise pollution Tourism might suffer evaluate the developments in using limestone, cement and concrete as building materials, and their advantages and disadvantages over other materials Notes: 8 C1.2 Limestone and building materials key words: Word / Phrase Meaning Acid Sour substance that can attack metal, clothing or skin. The chemical opposite of an alkali. When dissolved in water, its solution has a pH less than 7. [see also C2] Aggregate Small stones; crushed rock Alkali A solution with a pH greater than 7 Cement A building material made by heating limestone and clay Clay A stiff, sticky earth used in making pottery Concrete A building material made by mixing cement, sand and aggregate with water Limestone Rock containing mainly calcium carbonate Mortar Neutralisation A building material used to bind bricks together. It is made by mixing cement and sand with water. Reaction in which an acid and an alkali cancel each other out [see also C2] Quarry Extract stone for building Thermal decomposition The breakdown of a compound into simpler substances using heat 9 Topic checklist – C1.3 Metals and their uses Metals are very useful in our everyday lives. Ores are naturally occurring rocks that provide an economic starting point for the manufacture of metals. Iron ore is used to make iron and steel. Copper can be easily extracted but copper-rich ores are becoming scarce so new methods of extracting copper are being developed. Aluminium and titanium are useful metals but are expensive to produce. Metals can be mixed together to make alloys. C1.3.1 Extracting metals Ores contain enough metal to make it economical to extract the metal. The economics of extraction may change over time. Metal ores are obtained by mining and that this may involve digging up and processing large amounts of rock. After mining, ores may be concentrated before the metal is extracted and purified. Unreactive metals such as gold are found in the Earth as the metal itself but most metals are found as compounds that require chemical reactions to extract the metal. Metals that are less reactive than carbon can be extracted from their oxides by reduction with carbon, for example iron oxide is reduced in the blast furnace to make iron. [reduction is removal of oxygen] Metals that are more reactive than carbon, such as aluminium, are extracted by electrolysis of molten compounds. The use of large amounts of energy in the extraction of these metals makes them expensive. Copper can be extracted from copper-rich ores by heating the ores in a furnace (smelting). The copper can be purified by electrolysis i.e. copper is extracted from its ores by chemical processes that involve heat or electricity. The supply of copper-rich ores is limited. Copper-rich ores are being depleted and traditional mining and extraction have major environmental impacts. New ways of extracting copper from low-grade ores are being researched to limit the environmental impact of traditional mining. Copper can be extracted by phytomining, or by bioleaching. phytomining uses plants to absorb metal compounds and that the plants are burned to produce ash that contains the metal compounds bioleaching uses bacteria to produce leachate solutions that contain metal compounds. Copper can be obtained from solutions of copper salts by electrolysis or by displacement using scrap iron. During electrolysis positive ions move towards the negative electrode. Aluminium and titanium cannot be extracted from their oxides by reduction with carbon. Current methods of extraction are expensive because: there are many stages in the processes large amounts of energy are needed. We should recycle metals because extracting them uses limited resources and is expensive in terms of energy and effects on the environment. evaluate the social, economic and environmental impacts of exploiting metal ores, of using metals and of recycling metals evaluate the benefits, drawbacks and risks of using metals as structural materials. 10 C1.3.2 Alloys Iron from the blast furnace contains about 96% iron. The impurities make it brittle and so it has limited uses. Blast furnace iron is used as cast iron because of its strength in compression. Most iron is converted into steels. Steels are alloys since they are mixtures of iron with carbon. Some steels contain other metals. Alloys can be designed to have properties for specific uses. Low-carbon steels are easily shaped, high-carbon steels are hard, and stainless steels are resistant to corrosion. Most metals in everyday use are alloys. Pure copper, gold, iron and aluminium are too soft for many uses and so are mixed with small amounts of similar metals to make them harder for everyday use. C1.3.3 Properties and uses of metals The elements in the central block of the periodic table are known as transition metals. Like other metals they are good conductors of heat and electricity and can be bent or hammered into shape. They are useful as structural materials and for making things that must allow heat or electricity to pass through them easily. Copper has properties that make it useful for electrical wiring and plumbing. Copper: is a good conductor of electricity and heat can be bent but is hard enough to be used to make pipes or tanks does not react with water. Low density and resistance to corrosion make aluminium and titanium useful metals. Notes: 11 C1.3 Metals and their uses key words: Word / Phrase Meaning Alloy A mixture of metals (and sometimes non-metal such as carbon) Bioleaching Method of extracting metals from ores using micro-organisms Brittle Easily broken/shattered when hit Corrosion Chemical reaction that wears away a metal Density Displacement Amount of substance in a given volume Low density - lightweight Reaction in which one (more reactive) element takes the place of another in a compound Ductile Can be drawn into wires Electrode Conductor through which an electric current enters or leaves an electrolyte Electrolysis Breaking down a substance containing ions by passing an electric current though it as a solution or when molten Electrolyte Substance that conducts electricity in solution as ions are free to move Leachate Solution of metal ions obtained in bioleaching Malleable Can be hammered into shape Molten Melted Ore Rock containing enough metal to make it economically worthwhile to extract the metal Phytomining Method of extracting metals from ores using plants Reduction Loss or removal of oxygen Smelting Heating a metal ore in order to extract its metal Steel Alloy of iron with small amounts of carbon and other metals Transition metal Metal found in the middle block of the Periodic Table 12 Topic checklist – C1.4 Crude oil and fuels Crude oil is derived from an ancient biomass found in rocks. Many useful materials can be produced from crude oil. Crude oil can be fractionally distilled. Some of the fractions can be used as fuels. Biofuels are produced from plant material. There are advantages and disadvantages to their use as fuels. Fuels can come from renewable or non-renewable resources. C1.4.1 Crude oil Crude oil is a mixture of a very large number of compounds. A mixture consists of two or more elements or compounds not chemically combined together. The chemical properties of each substance in the mixture are unchanged. It is possible to separate the substances in a mixture by physical methods including distillation. Most of the compounds in crude oil consist of molecules made up of hydrogen and carbon atoms only (hydrocarbons). Most of these are saturated hydrocarbons called alkanes, which have the general formula CnH2n+2. C1.4.2 Hydrocarbons Alkane molecules can be represented in the following forms: a molecular formula such as C2H6 a displayed formula in which | represents a covalent bond H H I I H –– C –– C –– H I I H H in displayed structures — represents a covalent bond The many hydrocarbons in crude oil may be separated into fractions, each of which contains molecules with a similar number of carbon atoms, by evaporating the oil and allowing it to condense at a number of different temperatures. This process is fractional distillation. Some properties of hydrocarbons depend on the size of their molecules. These properties influence how hydrocarbons are used as fuels. As the hydrocarbon molecules get bigger: boiling points increase as the number of carbon atoms increases (decreases up the fractionating column) viscosity increases as the number of carbon atoms increases (decreases up the fractionating column) flammability decreases as the number of carbon atoms increases (increases up the fractionating column) know the names and formulae of individual alkanes methane, ethane, propane and butane. 13 C1.4.3 Hydrocarbon fuels Most fuels, including coal, contain carbon and/or hydrogen and may also contain some sulfur. The gases released into the atmosphere when a fuel burns may include carbon dioxide, water (vapour), carbon monoxide, sulfur dioxide and oxides of nitrogen (formed at high temperatures). Solid particles (particulates) may also be released. Solid particles may contain soot (carbon) and unburnt fuels. The combustion of hydrocarbon fuels releases energy. During combustion the carbon and hydrogen in the fuels are oxidised. Hydrogen is always completely oxidised to water. In complete combustion, the carbon is fully oxidised to carbon dioxide. In (incomplete) combustion, the carbon may be partially oxidised to carbon monoxide or may not be oxidised at all and released as solid particles (soot). oxides of nitrogen are formed at the high temperatures reached in an engine Sulfur dioxide and oxides of nitrogen cause acid rain carbon dioxide causes global warming Carbon monoxide is toxic as it reduces the ability of blood to carry oxygen Solid particles cause global dimming Sulfur can be removed from fuels before they are burned, for example in vehicles. Sulfur dioxide can be removed from the waste gases after combustion, for example in power stations. Biofuels, including biodiesel and ethanol, are produced from plant material. There are economic, ethical and environmental issues surrounding their use. evaluate the impact on the environment of burning hydrocarbon fuels evaluate the social, economic and environmental impacts of the uses of fuels evaluate developments in the production and uses of better fuels, for example ethanol and hydrogen in terms of: use of renewable resources storage and use of the fuels their products of combustion. evaluate the benefits, drawbacks and risks of using plant materials to produce fuels. Notes: 14 C1.4 Crude oil and fuels key words: Word / Phrase Meaning Acid rain Rain that is acidic due to dissolved gases, such as suulfur dioude, produced by burning fossil fuels. Alkane Saturated hydrocarbon Biodiesel Fuel for cars made from plants Biofuel A biofuel is a fuel whose energy is obtained through photosynthesis i.e. a fuel derived from plants Butane Alkane with four carbon atoms, C4H10 Combustion Burning Condense Change from vapour to liquid by cooling Crude oil Mixture of hydrocarbons Displayed formula Distillation Chemical formula that shows all the atoms and all the bonds in a molecule Separation of a liquid from a mixture by evaporation followed by condensation Ethane Alkane with two carbon atoms, C2H6 Evaporate Turn from a liquid to a vapour Fossil fuel Fuels that contain carbon and hydrocarbons that are the remains of plants and animals Fractional distillation Method of separating a mixture of liquids with different boiling points Fraction Mixture of hydrocarbons with similar boiling points separation from crude oil Fuel Substance burned for energy Global dimming The reflection of sunlight by tiny solid particles in the air Global warming The increasing in the average temperature of the Earth Hydrocarbon Compound containing carbon and hydrogen only. Methane Alkane with one carbon atoms, CH4 Molecular formula Chemical formula that shows the number of each type of atom in the molecule Oxidation Gain of oxygen Propane Alkane with three carbon atoms, C3H8 Saturated (hydrocarbon) A hydrocarbon that has only single covalent bonds Viscosity Resistance to flow 15 Topic checklist – C1.5 Other useful substances from crude oil. Fractions from the distillation of crude oil can be broken down (cracked) to make smaller molecules including unsaturated hydrocarbons such as ethene. Unsaturated hydrocarbons can be used to make polymers and ethene can be used to make ethanol. Ethanol can also be made by fermentation. C1.5.1 Obtaining useful substances from crude oil crude oil is used to produce fuels and chemicals; it is a limited resource Hydrocarbons can be cracked to produce smaller, more useful molecules. This process involves heating the hydrocarbons to vaporise them. The vapours are either passed over a hot catalyst or mixed with steam and heated to a very high temperature so that thermal decomposition reactions then occur The products of cracking include alkanes and unsaturated hydrocarbons called alkenes. e.g. decane octane + ethene C10H22 C8H18 + C2H4 Alkenes have the general formula CnH2n. Unsaturated hydrocarbon molecules can be represented in the following forms: As a molecular formula such as C3H6 As a displayed formula in which ‖ or ══ represents a double covalent bond H H H I I I H –– C –– C C I I H H be able to recognise alkenes from their names or formulae know the names of individual alkenes, ethene and propene. ethene, C2H4 propene, C3H6 Alkenes react with bromine water, turning it from orange to colourless. orange colourless Some of the products of cracking are useful as fuel. 16 C1.5.2 Polymers Alkenes can be used to make polymers such as poly(ethene) and poly(propene). In these reactions, many small molecules (monomers) join together to form very large molecules (polymers). For example: Polymers have many useful applications and new uses are being developed, for example: new packaging materials, waterproof coatings for fabrics, dental polymers, wound dressings, hydrogels, smart materials (including shape memory polymers). Many polymers are not biodegradable, so they are not broken down by microbes and this can lead to problems with waste disposal. Plastic bags are being made from polymers and cornstarch so that they break down more easily. Biodegradable plastics made from cornstarch have been developed. evaluate the social, economic and environmental impacts of the uses, disposal and recycling of polymers C1.5.3 Ethanol Ethanol can be produced by hydration of ethene with steam in the presence of a catalyst. Ethene + water ethanol Ethanol can also be produced by fermentation with yeast, using renewable resources. This can be represented by: sugar carbon dioxide + ethanol evaluate the advantages and disadvantages of making ethanol from renewable and nonrenewable sources. evaluate the social and economic advantages and disadvantages of using products from crude oil as fuels or as raw materials for plastics and other chemicals Notes: 17 C1.5 Other useful substances from crude oil key words: Word / Phrase Alkane Alkene Biodegradable Bromine water Catalyst Cracking Meaning Saturated hydrocarbon [hydrocarbon containing only single covalent bonds] Unsaturated hydrocarbon [hydrocarbon containing a carbon=carbon double covalent bond] Can be broken down by microorganisms Solution used to test for unsaturation (alkenes). Bromine water changes from orange to colourless in the presence of an alkene, but remains orange in the presence of saturated compounds Substance used to speed up a reaction (often used so a reaction can take place at a lower temperature) Reaction sued to break down large hydrocarbon molecules into smaller, more useful ones, by passing the hydrocarbon vapour over a hot catalyst. Ethanol Alcohol used as a biofuel Ethene Alkene with two carbon atoms, C2H4 Fermentation Reaction in which the enzymes in yeast turn glucose (sugar) into ethanol and carbon dioxide Hydration Reaction in which water is chemically added to a compound Hydrocarbon Compound containing carbon and hydrogen only Hydrogel Polymer that can absorb many times its weight in water Monomer Small reactive molecules that join together to make long chain molecules Non-renewable Something that cannot be replaced once it is used up Polymer Very long chain molecule, made up of many repeating units Polymerisation The reaction in which many monomers join together to make long chains Propene Alkene with three carbon atoms, C3H6 Renewable Something that can be replaced when it is used up Shape memory polymer An example of a smart material; can return to original shape if deformed, on heating Smart material Material that changes in response to a change in its environment Thermal decomposition Breaking down a compound into simpler substances by heat Unsaturated (hydrocarbon) A hydrocarbon that contains a carbon=carbon double covalent bond 18 Topic checklist – C1.6 Plant oils and their uses Many plants produce useful oils that can be converted into consumer products including processed foods. Emulsions can be made and have a number of uses. Vegetable oils can be hardened to make margarine. Biodiesel fuel can be produced from vegetable oils. C1.6.1 Vegetable oils Some fruits, seeds and nuts are rich in oils that can be extracted. The plant material is crushed and the oil removed by pressing or in some cases by distillation. Water and other impurities are removed Vegetable oils are important foods and fuels as they provide a lot of energy. They also provide us with nutrients. Vegetable oils are high in unsaturated fats compared with saturated fats and so have possible health benefits Vegetable oils have higher boiling points than water and so can be used to cook foods at higher temperatures than by boiling. This produces quicker cooking and different flavours but increases the energy that the food releases when it is eaten C1.6.2 Emulsions Oils do not dissolve in water. They can be used to produce emulsions. Emulsions are thicker than oil or water and have many uses that depend on their special properties. They provide better texture, coating ability and appearance, for example in salad dressings, ice creams, cosmetics and paints. Emulsifiers are added to make emulsions more stable. Higher Tier Emulsifiers have hydrophilic and hydrophobic properties. C1.6.3 Saturated and unsaturated oils Vegetable oils that are unsaturated contain double carbon–carbon bonds. These can be detected by reacting with bromine water. Higher Tier Vegetable oils that are unsaturated can be hardened by reacting them with hydrogen in the presence of a nickel catalyst at about 60 °C. Hydrogen adds to the carbon–carbon double bonds. The hydrogenated oils have higher melting points so they are solids at room temperature, making them useful as spreads and in cakes and pastries. evaluate the effects of using vegetable oils in foods and the impacts on diet and health evaluate the use, benefits, drawbacks and risks of emulsifiers in foods. Notes: 19 C1.6 Plant oils and their uses key words: Word / Phrase Bromine water Distillation Meaning Solution used to test for unsaturation (alkenes). Bromine water changes from orange to colourless in the presence of an alkene, but remains orange in the presence of saturated compounds Separation of a liquid from a mixture by evaporation followed by condensation Emulsifier A substance that helps keep immiscible liquids mixed in a single layer Emulsion A mixture of liquids that do not dissolve in each other Hydrogenated oil* Oil which has had hydrogen added to reduce the degree of unsaturation in the hardening process to make margarine Hydrophilic * Water-loving; the hydrophilic part of an emulsifier is attracted to water Hydrophobic * Water-hating; the hydrophobic part of an emulsifier is a hydrocarbon tail that is attracted to oil Immiscible Liquids that do not mix but form separate layers e.g. oil and water Nutrient Food needed for a healthy diet Saturated fat Fat molecule with single carbon-carbon covalent bonds Unsaturated fat Fat molecule with some double carbon=carbon covalent bonds 20 Topic checklist – C1.7 Changes in the Earth and its atmosphere The Earth and its atmosphere provide everything we need. The Earth has a layered structure. The surface of the Earth and its atmosphere have changed since the Earth was formed and are still changing. The atmosphere has been much the same for the last 200 million years and provides the conditions needed for life on Earth. Recently, human activities have resulted in further changes in the atmosphere. There is more than one theory about how life was formed. Recognise that the Earth’s crust, the atmosphere and the oceans are the only source of minerals and other resources that humans need C1.7.1 The Earth’s crust The Earth consists of a core, mantle and crust, and is surrounded by the atmosphere The Earth’s crust and the upper part of the mantle are cracked into a number of large pieces (tectonic plates). The mantle is mostly solid, but it is able to move slowly. Convection currents within the Earth’s mantle driven by heat released by natural radioactive processes cause the plates to move at relative speeds of a few centimetres per year. The movements can be sudden and disastrous. Earthquakes and / or volcanic eruptions occur at the boundaries between tectonic plates. explain why scientists cannot accurately predict when earthquakes and volcanic eruptions will occur Scientists once thought that the features of the Earth’s surface were the result of the shrinking of the crust as the Earth cooled down following its formation. explain why Wegener’s theory of crustal movement (continental drift) was not generally accepted for many years C1.7.2 The Earth’s atmosphere For 200 million years, the proportions of different gases in the atmosphere have been much the same as they are today: about four-fifths (80%) nitrogen about one-fifth (20%) oxygen small proportions of various other gases, including carbon dioxide, water vapour and noble gases. During the first billion years of the Earth’s existence there was intense volcanic activity. This activity released the gases that formed the early atmosphere and water vapour that condensed to form the oceans. There are several theories about how the atmosphere was formed. One theory suggests that during this period the Earth’s atmosphere was mainly carbon dioxide and there would have been little or no oxygen gas (like the atmospheres of Mars and Venus today). There may also have been water vapour and small proportions of methane and ammonia. explain and evaluate theories of the changes that have occurred and are occurring in the Earth’s atmosphere. No knowledge of other theories is required There are many theories as to how life was formed billions of years ago. 21 Higher Tier One theory as to how life was formed involves the interaction between hydrocarbons, ammonia and lightning. e.g. be aware of the Miller-Urey experiment and the ‘primordial soup‘ theory, but remember this is not the only theory. Higher Tier Describe why we do not know how life was first formed. Plants and algae produced the oxygen that is now in the atmosphere. Plants and algae produce oxygen by a process called photosynthesis; this uses carbon dioxide from the atmosphere. Most of the carbon from the carbon dioxide in the air gradually became locked up in sedimentary rocks as carbonates and fossil fuels. Carbon dioxide dissolves in the oceans Limestone was formed from the shells and skeletons of marine organisms. Fossil fuels contain carbon and hydrocarbons that are the remains of plants and animals. The oceans also act as a reservoir for carbon dioxide but increased amounts of carbon dioxide absorbed by the oceans has an impact on the marine environment. Nowadays the release of carbon dioxide by burning fossil fuels increases the level of carbon dioxide in the atmosphere. This increase in carbon dioxide is thought to be causing global warming Higher Tier Air is a mixture of gases with different boiling points and can be fractionally distilled to provide a source of raw materials used in a variety of industrial processes. Notes: 22 C1.7 Changes in the Earth and atmosphere key words: Word / Phrase Meaning Air Mixture of gases Algae Simple plants, including seaweed Atmosphere Protective layer of gases surrounding the Earth Continental drift Theory that continents are able to move Convection current Circular motion caused by heating in liquids (hot liquids rise, causing cooler, more dense liquid to fall) Core Centre of the Earth (the inner core is solid, the outer core is liquid) Crust Outer, solid layer of the Earth Mantle Layer of earth between the crust and the core Marine organisms Living things found in the sea Miller-Urey* Photosynthesis Plate tectonics Experiment designed to re-create the conditions in the early atmosphere to see if life could have formed from the gases present Process in which plants use sunlight to convert carbon dioxide and water into sugar and oxygen Theory describing the movement of the crust and upper part of the mantle Primordial soup Mixture of organic molecules, such as amino acids, needed to start life Sedimentary rock Rock formed Tectonic plate Pieces of the crust and upper part of the mantle * Higher tier 23 Command words For examples of how to answer these types of questions, see the separate booklet on Firefly. Calculate You should use numbers given in the question to work out the answer. As stated on the front of the paper, you should always show their working, as it may be possible for the examiner to award some marks for the method even if the final answer is wrong. You should always give the units when asked to do so. In the question a mark can be awarded for the correct unit/units, even if the calculation is wrong. Compare This requires you to describe the similarities and/or differences between things, not just write about one. If you are asked to ‘compare x with y’, you need to write down something about x compared to y, using comparative words such as ‘better, ‘more than’, ‘less than’, ‘quicker’, ‘more expensive’, ‘on the other hand.’ Complete Answers should be written in the space provided, eg on a diagram, in spaces in a sentence or in a table. Describe You may be asked to recall some facts, events or process in an accurate way. For example you may be asked to describe an experiment you have done, or you may need to give an account of what something looked like, or what happened, eg a trend in some data. Evaluate You should use the information supplied as well as your knowledge and understanding to consider evidence for and against. An evaluation goes further than ‘compare’. For example, you may be given a passage to read and told to ‘Evaluate the benefits of using system x and system y’. This means you will need to write down some of the points for and against both systems to develop an argument. A mark may also be available for a clear and justified conclusion. For example, if a question is worth 5 marks, and does not specifically ask for a conclusion, then you can gain all 5 marks for 5 valid points made for and against. If you only make 4 points but give a justified conclusion then the 5th mark can be gained. However, if a question specifically asks for a justified conclusion then full marks can only be gained if a justified conclusion is given. When giving comparisons you should be encouraged to compare both sides using linking words. For example in a physics question ‘Wind power is a renewable resource whereas fossil fuels are non-renewable.’ Useful words to use could be ’however’, ‘whereas’ ‘but’ and ’on the other hand’. No credit will be given just for giving the information stated directly from the question in either the comparisons or in the conclusion. In the chemistry example a mark is given for ‘waste’ oils being able to be used whereas just saying ‘vegetable’ oils can be used would not gain a mark. Likewise there would be no mark for stating that biodiesel produces fewer carbon particles, but a mark is awarded for linking this to less global dimming. 24 Explain You should make something clear, or state the reasons for something happening. The answer should not be a simple list of reasons. This means that points in the answer must be linked coherently and logically. Suitable linking words could be ‘so’, ‘therefore’, ‘because’, ‘due to’, ‘since’, ‘this means’ or ‘meaning that’. All of the stages/steps in an explanation must be included to gain full marks. State, give, name, write down Only a short answer is required, not an explanation or a description. Often it can be answered with a single word, phrase or sentence. If the question asks you to state, give, or write down one (or two etc) examples, you should write down only the specified number of answers, or you may not be given the mark for some correct examples given. Suggest This term is used in questions where you need to apply your knowledge and understanding to a new situation. Often there may be more than one correct answer as you are expected to base your answers on scientific knowledge and/or principles. Useful words to use are ‘may’, ‘might’, ‘could’, and ‘I think that’. Use the information in the passage/diagram/graph/table to… The answer must be based on the information given in the question. Unless the information given in the question is used, no marks can be given. In some cases you might be asked to use your own knowledge and understanding and credit will be given. 25 How Science Works Key Words Word / Phrase Accuracy Calibration Meaning A measurement result is considered accurate if it is judged to be close to the true value Marking a scale on a measuring instrument. This involves establishing the relationship between indications of a measuring instrument and standard or reference quantity values, which must be applied. For example, placing a thermometer in melting ice to see whether it reads zero, in order to check if it has been calibrated correctly Data Information, either qualitative or quantitative, that has been collected Errors See also uncertainties - measurement error The difference between a measured value and the true value - anomalies - random error - systematic error - zero error These are values in a set of results which are judged not to be part of the variation caused by random uncertainty. These cause readings to be spread about the true value, due to results varying in an unpredictable way from one measurement to the next. Random errors are present when any measurement is made, and cannot be corrected. The effect of random errors can be reduced by making more measurements and calculating a new mean. These cause readings to differ from the true value by a consistent amount each time a measurement is made. Sources of systematic error can include the environment, methods of observation or instruments used. Systematic errors cannot be dealt with by simple repeats. If a systematic error is suspected, the data collection should be repeated using a different technique or a different set of equipment, and the results compared Any indication that a measuring system gives a false reading when the true value of a measured quantity is zero, eg the needle on an ammeter failing to return to zero when no current flows. A zero error may result in a systematic uncertainty Evidence Data which has been shown to be valid Fair test A fair test is one in which only the independent variable has been allowed to affect the dependent variable. Hypothesis A proposal intended to explain certain facts or observations Interval Precision Prediction Range Repeatable The quantity between readings, eg a set of 11 readings equally spaced over a distance of 1 metre would give an interval of 10 centimetres. Precise measurements are ones in which there is very little spread about the mean value. Precision depends only on the extent of random errors – it gives no indication of how close results are to the true value. A prediction is a statement suggesting what will happen in the future, based on observation, experience or a hypothesis. The maximum and minimum values of the independent or dependent variables; important in ensuring that any pattern is detected. For example a range of distances may be quoted as either: "From 10cm to 50 cm" or "From 50 cm to 10 cm" A measurement is repeatable if the original experimenter repeats the investigation using same method and equipment and obtains the same results 26 Reproducible Resolution Sketch graph True value Uncertainty Validity Valid conclusion Variables - categoric - continuous - control - dependent - independent A measurement is reproducible if the investigation is repeated by another person, or by using different equipment or techniques, and the same results are obtained. This is the smallest change in the quantity being measured (input) of a measuring instrument that gives a perceptible change in the reading. A line graph, not necessarily on a grid, that shows the general shape of the relationship between two variables. It will not have any points plotted and although the axes should be labelled they may not be scaled This is the value that would be obtained in an ideal measurement The interval within which the true value can be expected to lie, with a given level of confidence or probability, eg “the temperature is 20 °C ± 2 °C, at a level of confidence of 95 %. Suitability of the investigative procedure to answer the question being asked. For example, an investigation to find out if the rate of a chemical reaction depended upon the concentration of one of the reactants would not be a valid procedure if the temperature of the reactants was not controlled. A conclusion supported by valid data, obtained from an appropriate experimental design and based on sound reasoning. These are physical, chemical or biological quantities or characteristics Categoric variables have values that are labels. Eg names of plants or types of material Continuous variables can have values (called a quantity) that can be given a magnitude either by counting (as in the case of the number of shrimp) or by measurement (eg light intensity, flow rate etc). A control variable is one which may, in addition to the independent variable, affect the outcome of the investigation and therefore has to be kept constant or at least monitored. The dependent variable is the variable of which the value is measured for each and every change in the independent variable The independent variable is the variable for which values are changed or selected by the investigator 27 Basic Standards of Presentation and Marking Presentation All work is to have a title describing what it is about (not just ‘Prep ‘or ‘Classwork’). All work is to be dated. Headings and dates are to be underlined with a ruler in the same colour as the writing ink used. A line space is to be left after the heading and date. Tippex or other correcting fluid must not be used; a neat, single straight line through the incorrect word is all that is required. Spelling Key spelling errors will be identified and the correct spelling written out by your teacher for guidance. Science text books contain spelling lists of essential vocabulary. Diagrams These need to be drawn in pencil. Any shading is to be done neatly using coloured pencils, if appropriate. Labeling should be done in ink. Labeling and headings must be able to be read while looking at the diagram and without having to turn the paper. If arrows or lines are needed to connect the labels with the diagram, they should be drawn in pencil with a ruler. Graphs and tables All graphs and tables are to be drawn in pencil. Tables are to be titled and boxed in, have the independent variable in the first column and only have units in the headings. Graphs are to be titled and have the independent variable along the x axis. Axes should be labeled and have units e.g. Time (seconds) Bar charts are to be used for discontinuous data, while line graphs are to be used for continuous data. Technical writing errors The following indicators are used: sp and the underlining of a misspelling p to indicate incorrect or missing punctuation exp to indicate inaccurate expression with a wiggly line under the relevant area, or down the margin. gr to indicate an area of inaccurate grammar, with a wiggly line under the relevant area, or down the margin. ^ to show where a word, phrase or key point is missing. Target setting T or indicates a target for you to work on in future pieces of work. 28 RHS Chemistry Department - Laboratory Rules The Health and Safety at Work Act holds teachers and pupils responsible for their actions if others are harmed by them. The biggest danger in the laboratory is YOU! You are a danger whenever you are either thoughtless or careless or both. Remember this, because the person most likely to suffer from your mistakes is YOU! 1. You should only go into a lab if you have permission to do so from a teacher. 2. You must wear eye protection when told to do so and at all times during Chemistry practical work and keep it on until all practical work (including tidying up) is finished. 3. Long hair must be tied back and loose garments should be tucked in before any experiment. 4. Never put anything in your mouth (food or drink) in the lab. This includes fingers and pencils. 5. You must not be seated during experimental work, unless you are specifically told to do so by your teacher. 6. If you are not sure of what you are supposed to do during a practical ASK for help. 7. Don't touch apparatus, electrical equipment or chemicals (or gas taps, water taps and electricity supplies) unless you have been told to do so. 8. When heating substances, use small amounts and take care not to point test tubes at yourself or anybody else, and never look directly down a test tube. 9. Only place hot objects on a heat proof mat using appropriate apparatus. Allow hot equipment or substances to cool before you touch them, store them or throw them away. 10. If you get burnt, or get chemicals on your skin, immediately wash the affected part with lots of cold water and alert your teacher. 11. Report ANY accident, however slight (including breakages and spillages), to your teacher. 12. Waste, or surplus, materials should be disposed of as instructed by your teacher. DON'T throw solids into sinks. 13. Keep your bench clean and tidy. Make sure it is wiped clean at the end of any experiment. 14. Wash your hands after laboratory work; this is especially important before meals. 15. Apparatus and chemicals must NEVER be removed from a lab. ANY INAPPROPRIATE OR DANGEROUS BEHAVIOUR WILL RESULT IN EXCLUSION FROM PRACTICAL ACTIVITIES. I have read and understood the laboratory rules listed above. Name:______________________________________________ Form: _______________ 29 Notes 30