- All substances are made up of atoms
- The periodic table lists all the chemical elements, with eight main groups each containing elements with similar chemical properties.
- Elements contain only one type of atom.
- Compounds contain more than one type of atom.
- An atom has a tiny nucleus at its centre, surrounded by electrons.
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C1.2 Chemical Equations
- No new atoms are ever created or destroyed in a chemical reaction: the total mass of the reactants = the total mass of the products.
- There is the same number of each type of atom on each side of a balanced symbol equation.
- You can include state symbols to give extra information in balanced symbol equations. These are (s) for solids, (l) for liquids, (g) for gases, and (aq) for aqueous solutions.
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C1.3 Separating Mixtures
- A mixture is made up of two or more substances that are not combined together.
- Mixtures can be separated by physical means, such as filtration crystallisation, and simple distillation.
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C1.4 Fractional Distillation and Paper Chromotogra
- Fractional distillation is an effective way of separating miscible liquids, using a fractioning column.
- Paper chromatography separates mixtures of substances dissolved in a solvent as they move up a piece of chromatography paper. The different solubilities are separated because of their different solubilities in the solvent used.
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C1.5 History of the atom
- New evidence has been gathered from the experiments of scientists who have used their model of the atom to explain their observations and calculations
- Key ideas were proposed successively by Dalton, Thomson, Rutherford and Bohr.
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C1.6 Structure of the Atom
- Atoms are made of protons, neutrons and electrons.
- Protons have a relative charge of +1, and electrons have a relative charge of -1. Neutrons have no charge. They are neutral.
- The relative masses of a proton and a neutron are both 1.
- Atoms contain an equal number of protons and electrons, so carry no overall charge.
- Atomic Number = number of protons = number of electrons.
- Mass number = Number of Protons (or Electrons) + Number of Neutrons
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C1.7 Ions, Atoms, and Isotopes
- Atoms that gain electrons form negative ions. If atoms lose electrons they form positive ions.
- You can represent the atomic number and mass number of an atom using the notation: 2412 Mg. Magnesium's atomic number is 12 and its mass number is 24
- Isotopes are atoms of the element with different numbers of neutrons. They have identical chemical properties but their physical properties, such as density can differ.
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C1.8 Electronic Structures
- The electrons in an atom are arranged in energy levels or shells.
- The electron configuration is 2, 8, 8
- The number of electrons in the outermost shell of an element's atoms determines the way in which that element reacts.
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C2.1 Development of the Periodic Table
- The periodic table of elements developed as chemists tried to classify the elements. It arranges them in an order in which similar elements are grouped together.
- The periodic table is so named because of the regularly repeating patterns in the properties of elements.
- Mendeleev's periodic table left gaps for unknown elements.
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C2.2 Electronic structures and the periodic table
- The atomic (proton) number of an element determines its position in the periodic table.
- The number of electrons in the outermost shell (highest energy level) of an atom determines its chemical properties.
- The group number in the periodic table equals the number of electrons in the outermost shell.
- The atoms of metals tend to lose electrons, whereas those of non-metals tend to gain electrons.
- The noble gases in Group 0 are unreactive because of their very stable electrons arrangements.
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C2.3 Group 1 The Alkali Metals
- The elements in Group 1 of the periodic table are called the alkali metals.
- Their melting points and boiling points decrease going down the group.
- The metals all react with water to produce hydrogen and an alkaline solution containing the metal hydroxide.
- They form 1+ ions in reactions to make ionic compounds. These are generally white and dissolve in water, giving colourless solutions.
- The reactivity of the alkali metals increases going down the group.
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C2.4 Group 7 The Halogens
- The halogens all form ions with a single negative charge in their ionic compounds with metals.
- The halogens form covalent compounds by sharing electrons with other non-metals.
- A more reactive halogen can displace a less reactive halogen from a solution of one of its salts.
- The reactivity of the halogens decreases going down the group,
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C2.5 Explaining Trends
- You can explain trends in reactivity as you go down a group in terms of the attractions between electrons in the outermost shell ant the nucleus.
- This electrostatic attraction depends on:
- The distance between the outermost electrons and the nucleus
- The number of occupied inner shell (energy levels) of electrons, which provide a shielding effect.
- The size of the positive charge on the nucleus (called the nuclear charge).
- In deciding how easy it is for atoms to lose or gain electrons from their outermost shell, these three factors must be taken into account. the increased nuclear charge, due to extra protons in the nucleus, going down a group is outweighed by other two factors.
- Therefore electrons are easier for the larger atoms to lose going down a group and harder for them to gain going down a group.
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C2.6 The Transition Elements
- Compared with the alkali metals, transition elements have much higher melting points and densities. They are also stronger and harder but are much less reactive.
- The transition elements do not react vigorously with oxygen or water.
- A transition element can form ions with different charges, in compounds that are often coloured.
- Transition elements and their compounds are important industrial catalysts.
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C3.1 States of Matter
- The three states of matter are solids, liquids and gases.
- The particles in a solid are packed closely together and vibrate around fixed positions. The particles in a liquid are also close together but can slip and slide over each other in random motion. the particles in a gas have, on average, lots of space between them and zoom around randomly.
- In melting and boiling, energy is transferred to the substance. In freezing and condensing, energy is transferred from the substance to the surroundings.
- The simple particle model of solids, liquids and gasses in useful but has its limitations because the atoms, molecules and ions that make up all substances are not solid spheres with no forces between them.
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C3.2 Atoms into Ions
- Elements react together to form compounds by gaining or losing or sharing electrons
- The elements in Group 1 react with the elements in Group 7. Which gives them a stable atomic structure.
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C3.3 Ionic Bonding
- Ionic compounds are held together by strong forces of attraction between their oppositely charged ions. This is ionic bonding.
- Besides elements in Groups 1 and 7, other elements that can form ionic compounds include Group 2 & 6
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C3.4 Giant Ionic Structures
- It takes a lot of energy to break the many strong ionic bonds, operating in all directions, that hold a giant ionic lattice together. So ionic compounds have high melting points. They are all solids at room temperature.
- Ionic compounds will conduct electricity when molten or dissolved in water. This is because their ions can then become mobile and can carry charge through the liquid.
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C3.5 Covalent Bonding
- Covalent bonds are formed when atoms fo non-metals share pairs of electrons with each other.
- Each shared pair of electrons is a covalent bond.
- Many substances containing covalent bonds consist of simple molecules but some have giant covalent structures.
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C3.6 Structure of Simple Molecules
- Substances made up of simple molecules have low melting points and boiling points.
- The forces between simple molecules are weak. These weak intermolecular forces explain why substances made of simple molecules have low melting points and boiling points.
- Simple molecules have no overall charge, so they cannot carry an electrical charge. Therefore, substances made of simple molecules do not conduct electricity.
- Models are used to help understand bonding but each model has its limitations in representing reality.
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C3.7 Giant Covalent Structures
- Some covalently-bonded substances have giant structures. These substances have very high melting points and boiling points.
- Graphite contains giant layers of covalently bonded carbon atoms. However, there are no covalent bonds between the layers. This means they can slide over each other, making graphite soft and slippery. The carbon atoms in diamond have a rigid giant covalent structure, making it a very hard substance.
- Graphite can conduct electricity and thermal energy because of the delocalised electrons that can move along its layers.
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C3.8 Fullerenes & Graphene
- As well as diamond and graphite, carbon also exists as fullerenes, which can form large cage-like structures and tubes, based on hexagonal rings of carbon atoms.
- The fullerenes are finding uses as a transport mechanism for drugs to specific sites in the body, as catalysts, and as reinforcement for composite materials.
- Graphene is a single layer of graphite and so is just one atom thick. Its properties, such as its excellent electrical conductivity, will help create new development in the electronics industry in the future.
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C3.9 Bonding Metals
- The atoms in metals are closely packed together and arranged in regular layers.
- You can think of metallic bonding as positively charged metal ions. which are held together by electrons from the outermost shell of each metal atom. These delocalised electrons are free to move throughout the giant metallic lattice.
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C3.10 Giant Metallic Structures
- Metals can be bent and shaped because the layers of atoms (or positively charged ions) in a giant metallic structure can slide over each other.
- Alloys are harder than pure metals because the regular layers in a pure metal are distorted by atoms of different sizes in an alloy.
- Delocalised electrons in metals enable electricity and thermal energy to be transferred through a metal easily.
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- Nanoscience is the study of small particles that are between 1 and 100 nanometers in size.
- Nanoparticles may have properties different from those for the same materials in bulk this arises because nanoparticles have a high surface area to volume ratio, with a high percentage of their atoms exposed at their surface.
- Nanoparticles may result in smaller quantities of materials such as catalysts, being needed for industrial processes.
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C3.12 Applications of Nanoparticles
- New developments in nanoparticulate materials are very exciting and could improve many different aspects of modern life.
- The increased use of nanoparticles needs more research into possible issues that might arise in terms of the environment/.
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C4.1 Relative Masses & Moles
- The masses of atoms are compared by measuring them relative to atoms of Carbon12
- One mole of any substance is its relative formula mass, in grams.
- N.O. moles = mass/Ar (or Mr)
- Avogadro's number is 6.02x10^23
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C4.2 Equations and Calculations
- Balanced symbol equations tell you the number of moles of substances involved in a chemical reaction.
- You can use balanced symbol equations to calculate the masses of reactants and products in a chemical reaction.
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C4.3 From masses to balanced equations
- You can deduce balanced symbol equations from the masses of substances involved in a chemical reaction.
- The reactant that gets used up first in a reactant is called the limiting reactant.
- Therefore, the amounts of product formed in a chemical reaction are determined by the limiting reactant.
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C4.4 The yield of a chemical reaction
- The yield of a chemical reaction describes how much product is made
- % yield tells you how much product is made compared to the maximum (100%)
- Factors affecting yield include:
- Amount of product left in apparatus
- Reactants that formed the undesired product
- losses in separating the products
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C4.5 Atom economy
- it is important to maximise atom economy in industrial processes to conserve the Earth's resources and minimise pollution.
- Th atom economy of a reaction uses its balanced equation to compare the relative formula mass of the desired product with the sum of the relative formula masses of the reactants. It is usually expressed as a percentage.
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C4.6 Expressing Concentrations
- Concentration (g/dm^3) = Amount of Solute (g) / Volume of Solution (dm^3)
- To calculate the mass of solute in a certain volume of a solution of known concentration:
1) Calculate the mass 9g) of the solute there is 1dm^3 of the solution.
2) Calculate the mass (in grams) of solute in 1 cm^3 of the solution.
3) Calculate the mass (in grams) of solute there is in the given volume of the solution.
- A more concentrated solution has more solute in the same volume of solution than a less concentrated solution.
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- Titration is used to measure accurately what volumes of acid and alkali react together completely.
- The point at which a reaction between an acid and an alkali is complete is called the endpoint of a reaction.
- You use an acid/base indicator to show the endpoint of the reaction between acid and alkali.
- To calculate the concentration of a solution in mol/dm^3, given the mass of solute in a certain volume:
- Calculate the mass (in grams) of solute in 1 cm^3 of solution
- Calculate the mass (in grams) of solute in 1000 cm^3 of solution
- Convert the mass (in grams) to moles.
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C4.8 Titration Calculations
- You can use titration to find the unknown concentration of a solution.
- You need to know the accurate concentration of one solution, then once the endpoint is established, the balanced equation gives you the number of moles in a certain volume of solution.
- This value is multiplied up to give the concentration in moles per decimetre cubed.
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C4.9 Volumes of Gases
- A certain volume of gas always contains the same number of gas molecules under the same conditions.
- The volume of 1 mole of any gas at room temperature and pressure is 24dm^3
- You can use the molar gas volume and balanced symbol equations to calculate volumes of gaseous reactants or products
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C5.1 The Reactivity Series
- The metals can be placed in order of reactivity by their reactions with water and dilute acid.
- Hydrogen gas is given off when metals react with water or dilute acids. The gas 'pops' with a lighted spill.
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C5.2 Displacement Reactions
- A more reactive metal will displace a less reactive metal from its aqueous solution.
- The non-metals hydrogen and carbon can be given positions in the reactivity series on the basis of displacement reactions.
- OILRIG - Oxidation Is Loss of electrons, Reduction Is Gain of electrons
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C5.3 Extracting Metals
- A metal ore contains enough of the metal to make it economic to extract the metal. Ores are mined and might need to be concentrated before the metal is extracted and purified.
- Gold and some other unreactive metals can be found in their native state.
- The reactivity series helps you decide the best way to extract a metal from its ore. The oxides of metals below carbon in the series can be reduced by carbon to give the metal element.
- Metals more reactive than carbon cannot be extracted by electrolysis of the molten metal compound.
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C5.4 Salts from Metals
- A salt is a compound formed when the hydrogen in an acid is wholly or partially replaced by metal or ammonium ions.
- Salts can be made by reacting a suitable metal with an acid. The metal must be above hydrogen in the reactivity series, but not dangerously reactive.
- The reaction between a metal and an acid produces hydrogen gas as well as a salt. A sample of the salt made can then be crystallised out of solution by evaporating out off the water.
- The reaction between a metal and an acid is an example of a redox reaction. The metal atoms lose electrons and are oxidised, and the hydrogen ions from the acid gain electrons and are reduced.
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C5.5 Salts from Insoluble Bases
- When an acid reacts with a base, a neutralisation reaction occurs.
- The reactions between an acid and a base produce a salt and water.
- The sum of the charges on the ions in a salt adds up to zero. This enables you to work out the formula of salts, knowing the charges on the ions present.
- A pure, dry sample of the salt made in an acid-base reaction can be crystallised out of solution by evaporating off most of the water, and drying with filter papers if necessary.
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C5.6 Making more salts
- An indicator is needed when a soluble salt is prepared by reacting an alkali with an acid/./
- The titration can be repeated without the indicator to make a salt, then a pure, dry sample of its crystals' prepared.
- A carbonate reacts with an acid to produce a salt, water and carbon dioxide gas.
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C5.7 Neutralisation and the pH scale
- Acids are substances that produce H+ ions when you add them to water.
- Bases are substances that will neutralise acids.
- An alkali is a soluble hydroxide. Alkalis produce OH- ions when you add them to water.
- You can use the pH scale to show how acidic or alkaline a solution is.
- Is the solution's pH is:
- Less than 7, It's acidic.
- 7, It's neutral.
- More than 7, It's alklaine
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C5.8 Strong and weak acids
- Aqueous solutions of weak acids, such as carboxylic acids, have a higher pH value than solutions of strong acids with the same concentration.
- As the pH decreases by one unit, the hydrogen ion concentration of the solution increase by a factor of 10.
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C6.1 Introduction to Electrolysis
- Electrolysis breaks down a substance using electricity.
- Ionic compounds can only be electrolysed when they are molten or dissolved in water. This is because their ions are then free to move and carry their charge to the electrodes.
- The cathode is negative, Anode is positive.
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C6.2 Changes at the Electrodes
- In electrolysis, the ions move towards the oppositely charged electrodes.
- At the cathode, positive ions gain electrons.
- At the anode, negative ions lose electrons.
- When electrolysis happens in an aqueous solution, the less reactive element is usually at the cathode. At the anode you either get:
- oxygen gas, from discharged hydroxide ions produced from water
- a halogen, if the solution has a halide.
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C6.3 The extraction of aluminium
- Aluminium oxide, from the ore bauxite, is electrolysed in the extraction of aluminium.
- The aluminium oxide is mixed with molten cryolite to lower its melting point, reducing the energy needed to extract the aluminium.
- Aluminium forms the cathode and oxygen at the anode.
- The carbon anodes are replaced regularly as they gradually burn away as the oxygen reacts with the hot carbon anodes, forming carbon dioxide gas.
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C6.4 Electrolysis of Aqueous Solutions
- When yo electrolyse sodium chloride solution (brine), you get three products - chlorine gas and hydrogen gas given off at the electrodes, plus sodium hydroxide solution left in the solution./
- Hydrogen is produced at the cathode.
- Chlorine is produced at the anode
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C7.1 Exothermic and Endothermic Reactions
- Energy is neither created nor destroyed.
- A reaction in which energy is transferred from the reacting substances to their surroundings is called an exothermic reaction.
- A reaction in which energy is transferred to the reacting substances from their surroundings is called an endothermic reaction
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C7.2 Using energy transfers from reactions
- Exothermic changes can be used in hand warmers and self-heating cans. The crystallisation of a supersaturated solution is used in reusable warmers. However, disposable, one-off warmers heat up the surroundings for longer.
- Endothermic changes can be used in instant cold packs for sports injuries.
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C7.3 Reaction Profiles
- You can show the relative difference in the energy of reactants and products on reaction profiles.
- Bond breaking is endothermic whereas bond making is exothermic.
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C7.4 Bond energy calculations
- In chemical reactions, energy must be supplied to break the bonds between atoms in the reactants.
- When new bonds are formed between atoms in a chemical reaction, energy is released.
- In an exothermic reaction, the energy released when new bonds are formed is greater than the energy absorbed when bonds are broken.
- In an endothermic reaction, the energy released when new bonds are formed in less than the energy absorbed when bonds are broken.
- You can calculate the overall energy change in a chemical reaction using bond energies.
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C7.5 Chemical Cells and Batteries
- Metals tend to lose electrons and form positive ions.
- When two metals are dipped in a salt solution and joined by a wire, the more reactive metal will donate electrons to the less reactive metal. This forms a simple electrical cell.
- The greater the difference in reactivity between the two metals, the higher the voltage produced by the cell.
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C7.6 Fuel Cells
- Much of the world relies on fossil fuels. However, they are non-renewable and they cause pollution.
- Hydrogen is one alternative fuel. It can be burned in combustion engines or used in fuel cells to power vehicles.
- Hydrogen gas is oxidised and provides a source of electrons in the hydrogen fuel cell, in which the only waste product is water
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C8.1 Rate of Reaction
- You can find out the rate of a chemical reaction by monitoring the amount of reactants used up over time.
- Alternatively, you can find out the rate of reaction by measuring the amount of products made over time.
- The gradient of the line at any given time on the graph drawn from such an experiment tells you the rate of reaction at the time. The steeper the gradient, the faster the reaction.
- To calculate the rate of reaction at a specific time draw a tangent of the curve, then calculate its gradient
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C8.2 Collision Theory and Surface Area
- Particles must collide, with a certain minimum amount of energy, before they can react.
- The minimum amount of energy that particles must have in order to react is called the activation energy of a reaction.
- The rate of a chemical reaction increases if the surface area to volume ratio of any solid reactants is increased. This increases the frequency of collisions between reacting particles.
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C8.3 The Effect of Termperature
- The rate of reaction increases as the temperature increases because particles collide more frequently and more energetically.
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C8.4 The effect of concentration and pressure
- Increasing the concentration of the reactants in solutions increases the frequency of collisions between particles, and so increases the rate of reaction.
- Increasing the pressure of reacting gases also increases the frequency of collisions, and son increases the rate of reaction.
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C8.5 The effect of catalysts
- A catalyst speeds up the rate of a chemical reaction however it does not become a product of the reaction. It remains chemically unchanged.
- Different catalysts are needed for different reactions.
- Catalysts are used whenever possible in industry to increase rates of reaction and reduce energy costs
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C8.6 Reversible reactions
- A reversible reaction is where a reaction causes the products to become the reactants again.
- ⇌ is the sign of a reversible reaction.
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C8.7 Energy and Reversible Reactions.
- In reversible reactions, one direction of reaction is exothermic the other is endothermic. The energy transferred either way are equal.
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C8.8 Dynamic Equilibrium
- In a reversible reaction, the products of the reaction can react to re-form the original reactants./
- In a closed, system, the rate of the forward and reverse reactions in equal at equilibrium.
- Changing the reaction conditions can change the amounts of products and reactants in a reaction mixture at equilibrium.
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C8.9 Altering conditions
- Pressure can affect reversible reactions involving gases at equilibrium. Increasing the pressure favours the reaction that forms fewer molecules of gas. Decreasing the pressure favours the reaction that forms the greater number of gas molecules.
- You can change the relative amount of products formed at equilibrium, by changing the temperature at which you carry out a reversible reaction.
- Increasing the temperature favours the endothermic reaction. Decreasing the temperature favours the exothermic reaction./
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- Crude oil is a mixture of many different compounds.
- Most of the compounds of crude oil are hydrocarbons.
- Alkanes are saturated hydrocarbons. They contain as many hydrogen atoms as possible.
- They all conform to the equation CnH2n+2
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C9.2 Fractional Distillation of oil
- Crude oil is separated into fractions using fractional distillation.
- The properties of each fraction depend on the size of the hydrocarbon molecules in it./
- Lighter fractions make better fuels as they ignite more easily and burn well, with cleaner (less smoky) flames.
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C9.3 Burning Hydrocarbon Fuels
- When hydrocarbon fuels are burned in plenty of air, the carbon and hydrogen in the fuel are completely oxidised. They produce carbon dioxide and water.
- CO2 turns limewater cloudy.
- Incomplete combustion produces CO as one of its products.
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C9.4 Cracking Hydrocarbons
- Large hydrocarbon molecules can be broken up into smaller molecules by passing the vapours over a hot catalyst, or by mixing them with steam and heating them to a very high temperature.
- Cracking produces saturated hydrocarbons, used as fuels, and unsaturated hydrocarbons (alkenes).
- Alkenes react with orange bromine water, turning it colourless.
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C10.1 Reactions of the Alkenes
- The general formula of the alkenes, containing one C==C bond, is CnH2n.
- Complete combustion of an alkene forms carbon dioxide and water.
- Alkenes react with halogens, hydrogen, and water, (steam) by adding atoms across the C==C bond, forming a saturated molecule.
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C10.2 Structures of alcohols, carboxylic acids and
- The homologous series of alcohols contain the -OH functional group.
- The homologous series of carboxylic acids contain the -COOH functional group.
- The homologous series of esters contains the -COO- functional group.
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C10.3 Reactions and Uses of Alcohols
- Alcohols are used as solvents and fuels, and ethanol is the main alcohol is alcoholic drinks.
- Alcohols burn in air, forming carbon dioxide and water.
- Alcohols react with sodium metal to form a solution of sodium alkoxide, and hydrogen gas is given off.
- Ethanol can be oxidised to ethanoic acid, either by chemical oxidising agents or by the actions of microbes in the air. Ethanoic acid is the main acid in vinegar.
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C10.4 Carboxylic Acids and Esters
- Solutions of carboxylic acids have a pH value of less than 7. Carbonates gently fizz in solutions of carboxylic acids, releasing carbon dioxide gas.
- Aqueous solutions of carboxylic acids, which are weak acids, have a higher pH value than solutions of strong acids of the same concentrations.
- Esters are made by reacting a carboxylic acid with an alcohol, in the presence of a strong acid catalyst.
- Esters are volatile, fragrant compounds used in flavourings and perfumes.
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C11.1 Addition Polymerisation
- Plastics are made of very large, covalently bonded molecules called polymers.
- The large polymer molecules are made when many monomers (small, reactive molecules) join together.
- The reaction between alkene monomers to form a polymer is called addition polymerisation/.
- In addition polymers, the repeating unit has the same atoms as the monomer, because when the C==C bond 'opens up' in polymerisation, no other molecule is formed in the reaction.
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C11.2 Condensation Polymerisation.
- Condensation polymerisation usually involves a small molecule released in the reaction, as the polymer forms.
- The monomers used to make the simplest condensation polymers are usually two different monomers, with two different monomers, with to of the same functional groups on each monomer.
- Polymers are formed from the condensation polymerisation of a diol and dicarboxylic acid, with H2O given off in the reaction.
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C11.3 Natural Polymers
- Simple carbohydrates (monosaccharides) polymerise to make polymers such as starch and cellulose.
- Proteins are polymers made from different amino acid monomers.
- Amino acids have an acidic and a basic functional group in the same molecule.
- Amino acids react together during condensation polymerisation to make polypeptides and proteins made of long sequences of different monomers.
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- DNA (deoxyribonucleic acid) is made up from monomers called nucleotides.
- The nucleotides are based on the sugar deoxyribose, bonded to a phosphate group and a base. There are four possible bases that bond to the sugar.
- A DNA molecule consists of two polymer stands (with sugars bonded to a phosphate group) intertwined into a double helix.
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C12.1 Pure Substances and Mixtures
- Pure substances can be compounds or elements, but they contain only one substance. An impure substance is a mixture of two or more different elements or compounds.
- Pure elements and compounds melt and boil at specific temperatures, and these fixed points can be used to identify them.
- The melting point and boiling point data can be used to distinguish pure substances from mixtures.
- Formulations are useful mixtures, made up in definite proportions, designed to give a product the best properties possible to carry out its function.
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C12.2 Analysing Chromotograms
- Scientists can analyse unknown substances in solution by using paper chromatography.
- Rf values can be measured and matched against databases to identify specific substances./
- Rf = Distance moved by substance / Distance moved by the solvent.
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C12,3 Testing for Gases
- Hydrogen gas burns rapidly with a 'pop' when you apply a lighted splint.
- Oxygen gas relights a glowing splint.
- Carbon dioxide turns limewater cloudy.
- Chlorine gas bleaches damp blue litmus paper white.
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C12.4 Tests for positive ions
- Some metal ions can be identified in their compounds using flame tests.
- sodium hydroxide solution can be used to identify metal ions that form insoluble hydroxides in precipitation reactions/.
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C12.5 Tests for negative ions
- You identify carbonates by adding dilute acid, which produces carbon dioxide gas. The gas turns limewater cloudy.
- You identify halides by adding nitric acid, then silver nitrate solution. This produces silver halide.
- You identify sulfates by adding hydrochloric acid, then barium chloride solution. This produces a white precipitate of barium sulfate.
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C12.6 Instrumental analysis
- Modern instrumental technique provide fast, accurate, and sensitive ways of analysing chemical substances.
- Flame emission spectroscopy is an example of an instrumental method.
- This method will tell us which metal ions are present in their characteristic line spectra, and also the concentration of the metal ions in a solution.
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C13.1 History of our Atmosphere
- The earth's early atmosphere was formed by volcanic activity.
- It probably consisted mainly of carbon dioxide. Threw may also have been nitrogen and water vapour, together with traces of methane and ammonia.
- As plants spread over the Earth, the levels of oxygen in the atmosphere increased.
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C13.2 Our Evolving Atmosphere
- Photosynthesis by algae and plants decreased the percentage of carbon dioxide in the early atmosphere.
- Any ammonia and methane was removed by reactions with oxygen, once oxygen had been formed by photosynthesis.
- Approximately four-fifths (80%) of the atmosphere today is nitrogen, and about one-fifth (20%) is oxygen.
- There are also small proportions of various other gases, including carbon dioxide, water vapour, and noble gases.
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C13.3 Greenhouse Gases
- The amount of carbon dioxide in the Earth's atmosphere has risen in the recent past, largely due to the number of fossil fuels now burnt.
- It is difficult to predict with complete certainty the effects on the climate of rising levels of greenhouse gases on a global scale.
- However, the vast majority of peer-reviewed evidence agrees that increased proportions of greenhouse gases from human activities will increase average global temperatures.
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- When hydrocarbon fuels are burnt in plenty of air, the carbon and hydrogen in the fuel are completely oxidised. They produce carbon dioxide and water.
- Sulphur impurities in fuels burn to form sulphur dioxide, which can cause acid rain. Sulphur can be removed from fuels before they are burned, or sulfur dioxide can be removed from flue gas.
- Changing the conditions in which hydrocarbon fuels are burnt can change the products made.
- In insufficient oxygen, poisonous carbon monoxide gas is formed. Particulates of carbon (soot) and unburnt hydrocarbons can also be produced, especially if the fuel is diesel. They can cause global dimming.
- At the high temperatures in engines, nitrogen from the air reacts with oxygen to form oxides of nitrogen. These cause breathing problems and can also cause acid rain.
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C14.1 Finite and Renewable Resources
- We rely on the Earth's resources to provide us with energy.
- Some of these natural resources are finite (will run out e.g. fossil fuels)
- Others are renewable (can be replaced e.g. biofuels)
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C14.2 Water safe to drink
- Water is made to fit drink by passing it through filter beds to remove solids and adding chlorine, ozone or by passing ultraviolet light through it to reduce microbes.
- Water can be purified by distillation, but this requires large amounts of energy, which makes it expensive.
- Reverse osmosis uses membranes to separate dissolved salts from salty water, but this method of desalination also uses energy to make the high pressures needed.
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C14.3 Treating waste water
- Wastewater requires treatment at a sewage works before being released into the environment.
- Sewage treatment involves the removal of organic matter and harmful microorganisms and chemicals.
- The stages include screening to remove large solids and grit, sedimentation to produce sewage sludge, and aerobic biological treatment of the safe effluent released into the environment.
- The sewage sludge is separated, broken down by anaerobic digestion and dried. It can provide us with fertiliser and a source of renewable energy.
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C14.4 Extracting metals from ores
- Most copper is extracted by smelting copper-rich ores, although supplied of ores are becoming scarcer.
- Copper can be extracted from solutions of copper compounds by electrolysis or by displacement using scrap iron. Electrolysis is also used to purify impure copper, e.g. the copper metal obtained from smelting./
- Scientists are developing ways to extract copper that use low-grade copper ores. Bacteria are used in bioleaching and plants in phytomining.
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C14.5 Life Cycle Assesments
- Life Cycle Assessments (LCAs) are carried out to assess the environmental impact of products, processes or services.
- They analyse each of the stages of a life cycle, from extracting and processing raw material to disposal at the end of its useful life, including transport and distribution at each stage including all transport and distribution.
- Data is available for the use of energy, water, resources and production of some wastes.
- However, assigning numerical values to the relative effects of pollutants involves subjective judgements, so LCAs using this approach must make this uncertainty clear.
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C14.6 Reduce, reuse, recycle.
- There are social, economic and environmental issues associated with exploiting the Earth's limited supplies of raw materials, such as metal ores.
- Recycling metals save energy and our limited, finite metal ores (and fossil fuels). The pollution caused by the mining and extraction of metals is also reduced by recycling.
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- Both air and water are needed for iron to rust
- Providing a barrier between iron and any air and water protects the iron from rusting.
- Sacrificial protection provides protection against rusting, even when the iron is exposed to air and water. The iron needs to be attached to a more reactive metal.
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C15.2 Useful alloys
- Alloys are harder than pure metals because the regular layers in a pure metal are distorted by differently sized atoms in an alloy.
- Copper, gold and aluminium are all alloyed with other metals to make them harder.
- Pure iron is too soft for it to be very useful.
- Carefully controlled quantities of carbon and other elements are added to iron to make steel alloys with different properties.
- Important examples of steels are:
- High carbon steels, which are very hard but brittle.
- Low carbon steels, which are softer and easily shaped
- Stainless steels, which are resistant to corrosion.
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C15.3 The Properties of Polymers
- Monomers affect the properties of the polymers that they produce.
- Changing reaction conditions can also change the properties of the polymer that is produced.
- Thermosoftening polymers will soften or melt easily when heated because their intermolecular forces are relatively weak. Thermosetting polymers will not soften because of their 'cross-linking', but will eventually char if heated very strongly.
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C15.4 Glass, ceramics and composites
- Soda glass is made by heating a mixture of sand, limestone, and sodium carbonate. Borosilicate glass is made from sand and boron trioxide and melts at a higher temperature than soda-lime glass.
- Clay ceramics include pottery and bricks. They are made by shaping wet clay then heating in a furnace.
- Composites are usually made of two materials, with one material acting as a binder for the other material, improving a desirable property that neither of the original materials could offer alone.
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C15.5 Making Ammonia -The Harber Process
- Ammonia is an important chemical for making products like fertilisers.
- Ammonia is made from nitrogen and hydrogen in the Harber process.
- We carry out the Harber process at 450ᵒC and 200 atmospheres of pressure, using an iron catalyst.
- Any unreacted nitrogen and hydrogen are recycled back into the reaction vessel in the Harber process
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C15.6 The Economics of the Harber Process
- The Harber process uses a pressure of around 200 atmospheres to increase the amount of ammonia produced.
- Although higher pressures would produce higher yields of ammonia, they would make the chemical plant too expensive to build and run.
- A temperature of about 450ᵒC is used for the reaction. Although lower temperatures would increase the yield of ammonia, it would be produced too slowly.
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C15.7 Making fertilisers in the lab
- Ammonia is used to make nitric acid.
- The nitric acid made can be reacted with more ammonia to make ammonium nitrate fertiliser.
- Ammonia can also be neutralised by sulfate fertiliser, and with phosphoric acid to make ammonium phosphate fertiliser.
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C15.8 Making Fertiliser in Industry
- Fertilisers are used to supply nitrogen, phosphorus and potassium to plants. These can all be added to land the same time in mixtures of compounds called NPK fertilisers.
- The nitrogen comes from ammonia, made in the Harber process, which is reacted with acids to make fertilisers, such as ammonium nitrate and ammonium sulfate.
- The source of phosphorus is phosphate rock, which is mined and then treated with acids to form fertilisers, such as ammonium phosphate and calcium phosphate.
- The potassium comes from potassium salts mined from the ground for use as fertilisers, such as potassium chloride and potassium sulfate./
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