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 Cheltenham College | Chemistry IGCSE Revision Guide for Fifth Formers Edexcel IGCSE Chemistry (Triple Award) Contents: •
Conceptual skills Criteria sheets •
Equations you should learn! •
Notes on Tricky Topics (crib notes only – NOT to replace textbooks, revision guides or notes) •
Conceptual skills in Chemistry Over the course of Third, Fourth and Fifth Forms pupils should be developing key skills. A well-­‐prepared IGCSE candidate should be able to: •
explain the differences in solids, liquid and gases in terms of particles •
understand reactants and products in a chemical reaction •
understand how, in a chemical reaction, particles are re-­‐arranged into different groupings to form products •
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•
•
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understand what is meant by atom element molecule ion compound •
say how many atoms of each element are in the formula of a covalent compound •
write a word equation for a chemical reaction •
understand what is meant by atomic number and mass number •
deduce the number of neutrons in an atom from Z and Ar •
explain how mass number is the mass of an atom compared to the mass of the isotope 11H (or more accurately 1/12 12C) •
understand and apply the rules governing how electrons are assigned to shells in elements up to 40C •
understand and explain how atoms form ions and that metals and hydrogen form positive ions and non-­‐
metals form negative ions •
deduce the formula of an ionic compound from the atomic structure of the atoms and charges on the ions •
understand how strong ionic bonds form through electrostatic attraction between oppositely charged ions •
that groups of atoms or ions can form a compound ion, with an overall charge, that behaves as if it were one entity •
understand the idea of spectator ions and, in particular, explain the ionic equation for neutralisation •
understand and explain how many atoms share electrons to form covalent chemical bonds in molecules (and how covalent bonds are different to ionic bonds) •
deduce the empirical formulae and molecular formulae (whichever is appropriate) given suitable data •
re-­‐arrange structural formulae to show the formation of different isomers •
use formulae to write and balance a chemical equation, including the meanings of the state symbols •
understand and use the concept of “amount” in chemistry re. calculation of reacting masses. •
understand the idea that the molar volume of a gas at room temperature and pressure is 24 l; use this idea in calculations •
average the readings from a titration and use the mean value to calculate the concentration of a solution •
write half equations to describe a redox process •
understand and explain the forces of attraction between molecules due to movement of electrons •
understand and explain how ionic and covalent bonding and inter-­‐particle attraction give rise to solid structures Criteria to be a successful in IGCSE Chemistry Topics: IGCSE
Reference
1 (a)
1.1
States of matter
1.2
Atoms
1 (b)
1.3
Atomic structure
1 (c)
1.4
Moles and equations
1.5
Ions & Ionic compounds
1 (f) 1.6
Covalent compounds
1 (g) 1.7
Metallic crystals
1 (h) 1.8
Electrolysis
1 (i) 2.1
The Periodic Table
2 (a) 2.2
The alkali metals
2 (b) 2.3
The halogens
2 (c) 2.4
Oxygen and oxides
2 (d) 2.5
Hydrogen and water
2 (e) 2.6
Reactivity series
2 (f) 2.7
Chemical tests
2 (g) 3.1
Alkanes & alkenes
3.2
Ethanol
3 (d) 4.1
Acids, alkalis & salts
4 (a) 4.2
Energetics
4 (b) 4.3
Rates
4 (c) 4.4
Equilibria
4 (d) 5.1
Metal extraction
5 (a) 5.2
Crude oil
5 (b) 5.3
Polymers
5 (c) 5.3
Industrial processes
5 (d) 1 (d), (e) 3 (a), (b), (c) TOP 1.1 Criteria sheet for the States of Matter To be successful in IGCSE Science you should be able to: Topic
I can….
States of matter
Describe and understand the arrangement of particles in solids, liquids & gases.
Describe how solids, liquids & gases change into other states through the processes of melting, freezing, evaporating, condensing and subliming
Say that particles in a solid only ‘vibrate’ about a fixed position.
Say that particles of gas move around freely and independently of one another. A gas completely occupies the volume of the container it’s in.
TOP I know
To
this
revise
1.2 Criteria sheet for Atoms To be successful in IGCSE Science you should be able to: Topic I can…. Atoms I know To this revise Understand simple experiments to show the smallness of particles and there properties of motion and diffusion e.g. the diffusion of Bromine vapour in a gas jar. Define an atom as the particle of which all matter is composed and which cannot be broken down chemically. Define a molecule as a particle that consists of two or more atoms joined together. Define as element as a pure substance made of only one type of atom. Understand the differences between mixtures & compounds 
Mixture – two or more substances not chemically combined; have the properties of each individual part of the mixture. 
Compound – two or more elements chemically combined into a new substance having properties quite different from its elements. Recall the separation techniques: simple distillation, fractional distillation, filtration, crystallisation, paper chromatography. TOP 1.3 Criteria sheet for Atomic structure To be successful in IGCSE Science you should be able to: Topic I can…. Atomic structure I know To this revise Recall that atoms consist of a central nucleus, composed of protons and neutrons, surrounded by orbiting electrons. State the relative mass and relative charge on a proton, neutron and electron. Explain the terms: • Atomic number (symbol, Z) • Mass number (symbol, Mr) • Relative atomic mass (symbol, Ar) • Isotopes Calculate the relative atomic mass (Ar) of an element from the relative natural abundances of its isotopes. Recall the electronic configurations of the first 20 elements in the periodic table, especially the order of filling electron shells ….. 2, 8, 8…… etc . etc. Say that the similarity of chemical properties of elements in a group in the periodic table is because they have the same number of electrons in their outer shells. TOP 1.4 Criteria sheet for Reactions, Calculations and Chemical equations To be successful in IGCSE Science you should be able to: Topic I can…. I know To this revise Relative formula Calculate relative formula mass from given relative atomic masses. masses Understand the term mole to represent the amount of substance. Understand the term mole as the Avogadro number of particles (atoms, molecules, formulae, ions or electrons) in a substance Carry out mole calculations using relative atomic mass (Ar) and relative formula mass (Mr). Understand the term molar volume of a gas and use its values (24 dm3 and 24 000 cm3) at room temperature and pressure (rtp) in calculations. Chemical formulae Write balanced chemical equations including, where specified, state symbols. It is worth noting that 2 and chemical marks are given for chemical equations: 1 for correct formulae, 1 for correct balancing; the second mark will not be given if the equation is balanced but the formulae are incorrect. equations Write word equations for chemical reactions. Use the state symbols (s), (l), (g) and (aq) correctly in chemical equations to represent solids, liquids, gases and aqueous solutions respectively. Understand how the formulae of simple compounds can be obtained experimentally, including metal oxides, water and salts containing water of crystallisation. Given appropriate data calculate: • Empirical and molecular formula • The amounts (in grams) of reactants or products using the chemical equation Calculate percentage yield Carry out mole calculations using volumes and molar concentrations. TOP 1.5 Criteria sheet for Ions and Ionic compounds To be successful in IGCSE Science you should be able to: Topic I can…. Ionic compounds I know To this revise Describe how ions are formed by the loss or gain of electrons from atoms. Recognise and explain OXIDATION as loss of electrons and REDUCTION as gain of electrons: • Oil RiG Recall the charge on common ions – both metals and non-­‐metals – and compound ions e.g. SO42-­‐, CO32-­‐ , NH4+ , NO3-­‐ . Deduce the charge of an ion from the electronic configuration of the atom from which the ion is formed. Use dot and cross diagrams to show how ions are formed from atoms, limited to compounds involving Li+, Na+, K+, Mg2+, Al3+, F-­‐, Cl-­‐, O2-­‐, S2-­‐ and N3-­‐. Say that the similarity of chemical properties of elements in a group in the periodic table is because they have the same number of electrons in their outer shells. Recall that an ionic bond is a strong electrostatic attraction between oppositely charged ions. Say that ionic compounds, such as NaCl and MgO, have high melting point and high boiling points because ionic bonds are strong and a large amount of heat energy is needed to separate the ions. Understand the relationship between ionic charge and the melting point and boiling point of an ionic compound Describe an ionic crystal as a giant three-­‐dimensional lattice structure held together by the attraction between oppositely charged ions Draw a simple diagram to represent the positions of the ions in a crystal of sodium chloride TOP 1.6 Criteria sheet for Covalent substances To be successful in IGCSE Science you should be able to: Topic I can…. I know To this revise Covalent Define a covalent bond as a shared pair of electrons between two atoms. substances Say that covalent bonds are strong chemical bonds between the bonding pair of electrons and the nuclei of the atoms involved in the bond. Use dot and cross diagrams to represent single covalent bonds in: • Hydrogen • Chlorine • Hydrogen chloride (gaseous molecules) • Water • Methane • Ammonia • Oxygen • Nitrogen • Carbon dioxide • Ethane • Ethene Use dot and cross diagrams to represent the electron arrangement and covalent bonding in the following complex molecules: oxygen, nitrogen, carbon dioxide and ethene. Recall that substances with simple molecular structures are gases or liquids, or solids with low melting points. Explain why substances with simple molecular structures have low melting points in terms of the relatively weak forces between the molecules. Explain the high melting points of substances with giant covalent structures in terms of the breaking of many strong covalent bonds. Draw simple diagrams representing the positions of atoms in diamond and graphite Explain how the uses of diamond and graphite depend on their structures, limited to graphite as a lubricant and diamond in cutting TOP 1.7 Criteria sheet for Metallic crystals To be successful in IGCSE Science you should be able to: Topic I can…. Metallic crystals I know To this revise Describe a metal as a giant structure of positive ions surrounded by a sea of delocalised electrons. Explain the malleability and electrical conductivity of a metal in terms of its structure and bonding. TOP 1.8 Criteria sheet for Electrolysis To be successful in IGCSE Science you should be able to: Topic I can…. I know To this revise Understand an electric current as a flow of electrons or ions. Understand why covalent compounds do not conduct electricity. Understand and explain that ionic compounds conduct electricity when molten and when in aqueous solution since in these states the ions are able to move. Describe simple experiments to distinguish between electrolytes and non-­‐electrolytes. Say that electrolysis is the formation of new compounds when ionic compounds conduct electricity and be able to write chemical equations for these processes. Describe simple experiments for the electrolysis, using inert electrodes, of molten salts such as lead (II) bromide. Describe simple experiments for the electrolysis, using inert electrodes, of aqueous solutions of sodium chloride, copper (II) sulphate and dilute sulfuric acid and predict the products. Write ionic half-­‐equations representing the reactions at the electrodes during electrolysis. Recall that one Faraday represents one mole of electrons Calculate the amounts of products of the electrolysis of molten salts and aqueous solutions. Electrolysis TOP 2.1 Criteria sheet for The Periodic Table To be successful in IGCSE Science you should be able to: Topic I can…. I know To this revise Explain the classification of elements as metals or non-­‐metals on the basis of their electrical conductivity and the acid-­‐base character of their oxides. Say that the similarity of chemical properties of elements in a group in the periodic table is because they have the same number of electrons in their outer shells. Recall the noble gases (Group 0) as a family of inert gases and explain their lack of reactivity in terms of their electronic configurations. The Periodic Table Understand that: • Horizontal rows are called “periods” • Columns are called “groups” Recall the positions of metals and non-­‐metals in the Periodic Table. TOP 2.2 Criteria sheet for Group 1 elements (alkali metals) To be successful in IGCSE Science you should be able to: Topic I can…. Group 1 elements I know To this revise Explain the relative reactivities of the elements in group 1 in terms of distance between the outer electrons and the nucleus Describe the reaction of lithium, sodium and potassium with water including observations and understand that the reactions provide the basis for their recognition as a family of elements. Recall the relative reactivities of the elements in Group 1. TOP 2.3 Criteria sheet for Group 7 elements (halogens) To be successful in IGCSE Science you should be able to: Topic I can…. Group 7 elements I know To this revise Say that hydrogen chloride: + -­‐ • Dissolves in water forming an aqueous solution of ions HCl (g) → H (aq) + Cl (aq), which is acidic. • Is insoluble in methylbenzene (an alternative solvent) which is neither acidic. Recall the relative reactivities of the elements in Group 7. Say that: • Chlorine (Cl2) is a green gas • Bromine (Br2) is a red/brown liquid • Iodine (I2) is a grey solid ...at room temperature. Use your knowledge of the above to predictions about the properties of the other halogens in this group. Explain the difference between hydrogen chloride gas HCl (g), and hydrochloric acid, HCl (aq). Describe experiments to show that a more reactive halogen will displace a less reactive halogen from a solution of one of its salts. Understand these displacement reactions as redox reactions. TOP 2.4 Criteria sheet for Oxygen and oxides To be successful in IGCSE Science you should be able to: Topic I can…. I know To this revise Recall that sulfur dioxide and nitrogen oxides are pollutant gases which contribute to acid rain, and describe the problems caused by acid rain. Oxygen and oxides Say that the air is made up of: • 78% nitrogen • 21% oxygen • 0.9% argon • 0.04% carbon dioxide Describe how experiments involving the reactions of elements such as copper, iron and phosphorus with air can be used to determine the percentage by volume of oxygen in air Describe how oxygen can be made from hydrogen peroxide in the lab. Describe the reactions with oxygen in air of magnesium, carbon and sulfur, and the acid-­‐ base character of the oxides produced. Describe the laboratory preparation of carbon dioxide from calcium carbonate and dilute hydrochloric acid. Describe the formation of carbon dioxide from the thermal decomposition of metal carbonates such as copper (II) carbonate. Recall the solubility and density of carbon dioxide and how this is used in carbonating drinks and in fire extinguishers. Recall the reactions of carbon dioxide and sulfur dioxide with water to produce acidic solutions. TOP 2.5 Criteria sheet for Hydrogen and water To be successful in IGCSE Science you should be able to: Topic I can…. Hydrogen and water I know To this revise Describe the reaction of dilute hydrochloric and dilute sulfuric acids with magnesium, aluminium, zinc and iron. Describe the combustion of hydrogen. Describe the use of anhydrous copper (II) sulfate in the chemical test for water. Describe a physical test to show whether water is pure. TOP 2.6 Criteria sheet for the Reactivity series To be successful in IGCSE Science you should be able to: Topic I can…. Reactivity series I know To this revise Recall that metals can be arranged in a reactivity series based on the reactions of the metals and their compounds: K, Na, Li, Ca, Mg, Al, Zn, Fe, Cu, Ag and Au. Use the reactions with water & dilute acids to work out an order of reactivity for: K, Na, Li, Ca, Mg, Zn, Fe & Cu. Explain that an element can remove oxygen from the compounds of elements lower down the series. Explain that a metal can displace a less reactive metal from a solution of it’s compound(s) e.g. zinc metal displaces copper ions from copper sulphate solution forming copper metal and zinc ions (i.e. zinc sulphate). Understand oxidation and reduction as the addition and removal of oxygen respectively. Understand the terms redox, oxidising agent and reducing agent. Recall that iron is a moderately reactive metal that rusts. Rusting is the formation of iron oxide, which occurs in the presence of both oxygen and water together. Describe how rusting can be prevented by coating iron or steel with grease, oil, plastic, paint. Describe how iron and steel can be protected from rusting by contact with a more reactive metal, such as magnesium, that reacts with oxygen in preference to the iron; this is called sacrificial protection since the more reactive metal is ‘sacrificed’ or reacted. TOP 2.6 Criteria sheet for Tests for ions and gases To be successful in IGCSE Science you should be able to: Topic I can…. Tests for ions and gases Recall simple test for cations, along with expected observations: • Li+, Na+, K+, Ca2+ using flame tests •
NH4+ using aqueous sodium hydroxide and identifying the ammonia evolved •
Cu2+, Fe2+ and Fe3+ using aqueous sodium hydroxide Recall simple tests for the anions, along with expected observations: • Chloride (Cl-­‐), bromide (Br-­‐) & iodide (I-­‐) using dilute nitric acid followed by silver nitrate I know To this revise solution. •
Sulphate using dilute hydrochloric acid and barium chloride solution •
Carbonate, using dilute hydrochloric acid and identifying the CO2 gas evolved (by using limewater) Recall simple tests and expected observations for: • hydrogen, H2 (g) • oxygen, O2 (g) • carbon dioxide, CO2 (g) • ammonia, NH3 (g) • chlorine, Cl2 (g) TOP 3.1 Criteria sheet for Alkanes & Alkenes To be successful in IGCSE Science you should be able to: Topic Introduction Alkanes Alkenes I can…. I know To this revise Draw displayed formulae for methane, ethane, propane, butane & pentane and their named isomers. Recall that the products of complete combustion are carbon dioxide and water and the products of incomplete combustion are carbon monoxide and water. Recall the reaction of methane with bromine to form bromomethane in the presence of UV light. Draw displayed formulae for ethene, propene & butene and their named straight-­‐chained isomers. Describe and write a chemical equation for the addition of bromine to alkenes. Explain the terms ‘homologous series’, ‘hydrocarbon’, ‘saturated’, ‘unsaturated’, ‘general formula’ and ‘isomerism’. Recall that alkanes have the general formula CnH2n+2. Recall that alkenes have the general formula CnH2n. Say that on addition of bromine water to an alkene the bromine changes colour from brown to colourless and that this is a standard test for an alkene. TOP 3.2 Criteria sheet for Ethanol To be successful in IGCSE Science you should be able to: Topic Ethanol I can…. Describe the manufacture of ethanol by the passing of ethene and steam over a phosphoric acid catalyst at a temperature of about 300C and a pressure of about 60 – 70 atmospheres Describe the manufacture of ethanol by the fermentation of sugars, for example glucose, at a temperature of about 30C. Evaluate the factors relevant to the choice of method used in the manufacture of ethanol, for example the relative availability of sugar cane and crude oil Describe the dehydration of ethanol to ethene, using aluminium oxide I know To this revise 4.1 Criteria sheet for Acids, alkalis & salts To be successful in IGCSE Science you should be able to: Topic I can…. I know To this revise Acids, alkalis & Say that blue Litmus indicator turns red in acid and that red Litmus indicator turns blue in alkali. salts Describe the use of methyl orange and phenol phthalein indicators in titrations, saying what the colour of each is in acid or alkaline solution. Acid Alkali • methyl orange red yellow • phenol phthalein colourless pink Describe the pH scale as a series of numbers from 0 to 14. Say that pH < 7 is acidic pH > 7 is alkaline pH = 7 is neutral (neither acid nor alkaline) Describe the use of universal indicator to measure the approximate pH value of a solution. Define acids as sources of hydrogen ions, H+, and alkalis as sources of hydroxide ions, OH-­‐. Write chemical equations for the reaction of an acid with alkalis, bases, metals and carbonates. Recall the general rules for predicting the solubility of salts in water: • all common sodium, potassium and ammonium salts are soluble • all nitrates are soluble • common chlorides are soluble, except silver chloride • common sulfates are soluble, except those of barium and calcium • common carbonates are insoluble, except those of sodium, potassium and ammonium Describe how a titration is performed to neutralise an acid or alkali exactly making a soluble salt in the process. Explain how solutions of salts can be made by reacting an acid with: metals, alkali, insoluble base or a carbonate. Describe how to prepare insoluble salts using precipitation reactions. TOP 4.2 Criteria sheet for Energetics To be successful in IGCSE Science you should be able to: Topic I can…. Energetics I know To this revise Recall that chemical reactions in which heat energy is given out are described as exothermic and those in which heat energy is taken in are endothermic. Describe simple calorimetry experiments for reactions such as combustion, displacement, dissolving and neutralisation in which heat energy changes can be calculated from measured temperature changes. Calculate molar enthalpy change from heat energy change Understand the use of ΔH to represent molar enthalpy change for exothermic and endothermic reactions. Represent exothermic and endothermic reactions on a simple energy level diagram. Understand that: • breaking bonds endothermic • forming bonds is exothermic Use average bond energies to calculate the enthalpy change during a simple chemical reaction TOP 4.3 Criteria sheet for Rates of reaction To be successful in IGCSE Science you should be able to: Topic I can…. Rates of reaction I know To this revise Describe experiments to investigate the effects of changes in surface area of a solid, concentration of solutions, temperature and the use of a catalyst on the rate of a reaction. Describe the factors that affect the rate of a reaction, namely: • Concentration of solutions • Particle size [surface area] • Temperature • Use of a suitable catalyst Understand the term activation energy and represent it on a reaction profile. Represent exothermic and endothermic reactions on a simple energy level diagram. Describe how the effects of particle size, concentration and temperature can be explained using collision theory: • collision theory – particles of reactant must collide with a minimum amount of energy and in the right direction for a successful reaction (a collision like this is called a ‘successful collision’. The minimum energy for a successful collision is called the ‘activation energy’. • Effect of temperature – higher temperature increases the speed and energy of particles so more particles have the activation energy giving more successful collisions • Effect of concentration-­‐ if there are more particles in a given volume there will be more collisions giving a faster reaction • Effect of particle size – smaller particle size gives larger surface area exposing a greater number of particles increasing the number of successful collisions. •
Effect of a catalyst – a catalyst provides a different path for a chemical reaction having a lower activation energy so more of the collisions are likely to be successful. TOP 4.4 Criteria sheet for Equilibria To be successful in IGCSE Science you should be able to: Topic I can…. Equilbria I know To this revise Recall that some reactions are reversible and are indicated by the symbol ⇌ in equations. Describe a simple reversible reaction like: • Hydration of anhydrous copper (II )sulphate • The effect of heat on ammonium chloride. Explain that a dynamic equilibrium is a reversible reaction in which the reaction ‘goes’ in both directions at the same rate so that there is a balance of reactants and products, which stays the same. Deduce how changing the temperature affects a reversible reaction (effect on yield) e.g. in the Haber process for ammonia. Deduce how changing pressure affects a reversible reaction (effect on yield) e.g. in the Haber process for ammonia. TOP 5.1 Criteria sheet for Extraction & uses of metals To be successful in IGCSE Science you should be able to: Topic I can…. Extraction & uses of metals Explain how the methods of extraction of the metals in this section are related to their positions in the reactivity series. Describe and explain the process for extracting aluminium from purified aluminium oxide (alumina; Al2O3) by electrolysis, including: • The use of molten cryolite. • The need to replace positive carbon anodes because they burn off in the process. • The cost of the electricity as a major factor Write ionic half-­‐equations for the reduction of Al3+ at the cathode and the oxidation of O2-­‐ at the anode. Say that iron can be extracted from iron (III) oxide by reacting with carbon, which is higher in the reactivity series. Understand what is meant by an ‘ore’ and say that the main ore of iron is haematite, which consists mainly of iron (III) oxide. Describe the blast furnace process for extracting iron on an industrial scale, including the role of coke and limestone and recalling the three key equations (chemical equations) for processes that occur in the blast furnace. Explain the uses of: • Aluminium – aerospace & cars – strong; corrosion resistant • Iron – construction – strong; easily shaped by casting TOP I know To this revise 5.2 Criteria sheet for Crude oil To be successful in IGCSE Science you should be able to: Topic I can…. Crude oil I know To this revise Describe how the process of fractional distillation can be used on an industrial scale to separate the hydrocarbons in crude oil into useful products. Give names of several useful products derived from crude oil: • refinery gas, • petrol (gasoline) • kerosene (aviation fuel) • diesel (fuel for heavy vehicles) • fuel oil (fuel for ships) • bitumen (used for ‘tar’ in road making) Describe the trend in boiling point and viscosity of the main fractions. Recall that crude oil is a complex mixture of hydrocarbons. Recall that incomplete combustion of hydrocarbon fuels produces carbon monoxide (CO), which is poisonous because it reduces the capacity of the blood to carry oxygen. Recall that, in car engines, the temperature reached is high enough to allow nitrogen and oxygen from air to react, forming nitrogen oxides. Recall that fractional distillation of crude oil produces more long-­‐chain and fewer short-­‐chain hydrocarbons than desired. Describe how long-­‐chain hydrocarbons are cracked by heating (600-­‐700 °C) and/or in the presence of a catalyst (silica or alumina) to give more short-­‐chain hydrocarbons, which are more useful. TOP 5.3 Criteria sheet for Synthetic polymers To be successful in IGCSE Science you should be able to: Topic I can…. I know To this revise Draw the repeat unit of the following addition polymers: • poly(ethene) • poly(propene) • poly(chloroethene) Deduce the structure of a monomer from the repeat unit of an addition polymer. Recall that nylon is a condensation polymer Understand the formation of a condensation polymer is accompanied by the release of a small molecule such as water or hydrogen chloride Recall the types of monomers used in the manufacture of nylon Draw the structure of nylon in block diagram format Synthetic polymers Recall that an addition polymer is formed by joining up many small molecules called monomers. TOP 5.4 Criteria sheet for The industrial manufacture of chemicals To be successful in IGCSE Science you should be able to: Topic I can…. Industrial manufacture of chemicals I know To this revise Recall how nitrogen, from air, and hydrogen, from natural gas or the cracking of hydrocarbons, are used in the manufacture of ammonia. Recall the conditions used in the Haber process for the manufacture of ammonia from nitrogen & hydrogen: • temperature of about 450°C • a pressure of about 200 atmospheres • an iron catalyst How the ammonia is liquefied to remove it from the process once formed and to make transportation easier. How since the reaction is reversible, unreacted hydrogen & nitrogen is recycled back into the process. Recall important uses of ammonia, including the manufacture of nitric acid and the manufacture of nitrogenous fertilisers. Recall the raw materials used in the manfacture of sulfuric acid Describe the manufacture of sulfuric acid by the Contact process, including the essential conditions: • a temperature of about 450C • a pressure of about 2 atmospheres • a vanadium (V) oxide catalyst (vanadium pentoxide) Recall the use of sulfuric acid in the manufacture of detergents, fertilisers and paints Describe the manufacture of sodium hydroxide and chlorine by the electrolysis of concentrated sodium chloride solution (brine) in a diaphragm cell (the Chlor-­‐Alkali process) Write ionic half-­‐equations for the reactions at the electrodes in the diaphragm cell Recall the important uses of sodium hydroxide, including the manufacture of bleach, paper and soap; and of chlorine, including sterilising water supplies and in the manufacture of bleach and hydrochloric acid TOP Learn these equations for your IGCSE exams. There are a great many equations that you will have to work out on the day of the exam. However, these are the most common reactions which you can learn and be very familiar with. Ionic equation for the neutralisation of an acid by an alkali H+ (aq) + OH-­‐ (aq)
H2O (l) Harber process for making ammonia 3 H2 (g) + N2 (g) ⇌ 2NH3 (g) 4 Al (l) + 3 O2 (g) Extracting iron from iron(III)oxide in three stages using a blast furnace C (s) + O2 (g)
CO2 (g) CO2 (g) + C (s)
2 CO (g) Fe2O3 (s) + 3 CO (g) 2 Fe (l) + 3CO2 (g) Extracting aluminium from alumina using electrolysis Overall equation: 2 Al2O3 (s) Half equation for the electrodes: Positive electrode (anode) 6 O2-­‐ 3 O2 + 12 e-­‐ Negative electrode (cathode) 4 Al 3+ + 12 e-­‐
4 Al (l) Reaction of sodium (an alkali metal) with water – a regular reaction seen in GCSE papers 2 Na (s) + 2 H2O (l) 2 NaOH (aq) + H2 (g) Test for an alkene using bromine water Br2 (aq) + C2H4 C2H4Br2 TOP ACIDS + BASES ACID ACID ACID + + ALKALI → SALT + WATER + BASE → SALT + WATER CARBONATE → SALT + WATER + → SALT + + ACID METAL HYDROGEN IONIC EQUATION FOR NEUTRALISATION H+ (aq) INDICATORS: METHYL ORANGE PHENOL PHTHALEIN + OH-­‐ (aq) H2O (l) → ACID ALKALI RED YELLOW PINK COLOURLESS TOP CARBON DIOXIDE BONDING shared pair of electrons between two atoms. COVALENT BOND: ××
H ×
N IONIC BOND: ×
H ×
H shared pair
electrostatic attraction between oppositely charged ions. ×
Na
Cl (shows outer electrons only)
[Na]
+
[Cl]
-
TOP POYLMERISATION Making polymers from monomers: e.g. draw the polymer made from “propene”: H
H
H
H
C
C
C
H
H
• Redraw the molecule like this: CH3
H
C
C
H
H
ANSWER CH3
H
CH3
H
C
C
C
C
H
H
H
H
[ ] shows that th
1000s of times
n
propene
polypropene
Another example: C6H5
H
C6H5
H
C
C
C
C
H
H
H
H
n
styrene
TOP polystyrene
ISOMERS Draw the isomers of pentane (C5H12). H
H
H
H
H
H
H
C
H
H
C
C
C
C
C
H
H
H
C
C
C
H
H
H
H
H
H
C
H
H
C
H
H
H
H
C
C
H
•
All have the same formula. •
Each is made by breaking off a carbon and attaching it elsewhere on the chain. H
C
H
H
H
H
H
H
H
What is a (structural) isomer? Isomers are molecules that have the same molecular formula, but different structures. TOP TESTING FOR IONS Tests for Fe2+, Fe3+ and Cu 2+ iron (II) Fe2+ (aq) + + hydroxide → OH-­‐ (aq) → iron (III) hydroxide Fe(OH)2 (s) green iron (III) Fe3+ (aq) + + hydroxide → OH-­‐ (aq) → iron (III) hydroxide Fe(OH)3 (s) brown copper (II) + Cu2+ (aq) + hydroxide → OH-­‐ (aq) → iron (III) hydroxide Cu(OH)2 (s) blue TOP RATES OF REACTION 4 factors that affect the “RATE” • Surface area • Concentration • Temperature • Catalyst N.B. A catalyst changes the path of a reaction to one with a lower activation energy. COLLISION THEORY factors that increase the rate of reaction by increasing the number of successful collisions that lead to a reaction between particles. TOP