Presentation on theme: "Standard Grade Chemistry"— Presentation transcript:
1Standard Grade Chemistry This series of presentations is designed to help you revise for Standard Grade Chemistry.Click here for the menu.
2To revise a topic, click on its name, when the cursor appears MenuTo revise a topic, click on its name,when the cursor appearsChemical ReactionsThe Periodic TableSpeed of ReactionHow Atoms CombineHydrocarbonsFuelsChemical ArithmeticProperties of SubstancesReactions of AcidsAcids and AlkalisMetalsCorrosionMetals and ElectricityCarbohydratesPlastics and Synthetic FibresFertilisersClick here to finish
4Chemical ReactionsA chemical reaction involves the formation of new substances.How do we know that a chemical reaction has taken place?There is a change in appearanceA precipitate is formedA gas is given offEnergy is released or taken in
5Chemical Reactions In an exothermic reaction energy is released. In an endothermic reaction energy is taken in.
6Elements and Compounds All the substances in the world are made from about 100 elements, each of which has a name and a symbol. A compound whose name ends in "ide" contains two elements only. A compound whose name ends in "ite" or "ate" contains three elements, one of which is oxygen, ("ite" has less oxygen than "ate“)
7Solutions A solution is formed when a material dissolves in a liquid. The material which dissolves is called a solute.The liquid is called a solvent.A material which can dissolve is soluble.A material which cannot dissolve is insoluble.A saturated solution is one where no more solute can dissolve.A table of solubility is found in the Data Booklet.
8Chemical Reactions Click to repeat this presentation Click to return to MenuClick to End
15The Periodic TableThe elements are classified by arranging them in the Periodic Table.The atoms in the Periodic Table are listed in order of their Atomic Number.
16Elements in the Periodic Table can be classified in different ways. Solid, liquid or gasMetal or non-metal.Naturally occurring or man-made
17The vertical columns are called groups. All the elements in any group will show similar chemical properties.
18Group 1 elements are called the Alkali Metals. Group 7 elements are called the Halogens.Group 0 (or 8) gases are called the Noble Gases.The central block of the Periodic Table contains the Transition Metals.
19Rutherford’s Atom Elements are made of small particles called atoms In the centre of the atom is the nucleus, containing protons and neutrons.Electrons orbit around the nucleus, like planets around the Sun.
20Atoms Most of the mass of the atom is found in the nucleus The nucleus contains positively charged protons.The nucleus also contains neutrons, which have no charge.Negatively charged electrons orbit around the nucleus.
21Sub-Atomic Particles Particle Charge Mass Location Proton positive 1 a.m.u.nucleusNeutronnoneElectronnegativenegligibleIn orbit around the nucleus
22AtomsFor each atom the Atomic Number is equal to the number of protons.The Mass Number is the number of protons + neutrons.The number of neutrons is Mass Number minus Atomic Number.
23The atom is neutral because the positive charge of the nucleus is balanced by the negative charge of the electrons.Thus the number of electrons is the same as the number of protons.
33How Atoms CombineAtoms react in such a way as to achieve a stable electron arrangement where they have a full outer electron shell. (Usually 8 electrons)
34How Atoms Combine They are trying to achieve a Noble Gas structure. This means that they are trying to get the same electron arrangement as the nearest Noble Gas.
35The Covalent BondAs two atoms come together the half-filled electron pair clouds overlap to form a new cloud.
36The Covalent BondAs two atoms come together the half-filled electron pair clouds overlap to form a new cloud. The covalent bond
37The Covalent BondIn a covalently bonded molecule the two atoms are held together because both nuclei are attracted to the shared pair of electrons.e-e-+
38Molecules Atoms are held together by bonds. A covalent bond is formed between two atoms when they share a pair of electrons.Covalent bonds are formed between two non-metal atoms
39MoleculesA molecule is a group of atoms, held together by covalent bonds.The molecular formula gives the number of atoms of each type in a covalent molecule.A diatomic molecule is one containing two atoms.
40We can write formulae by counting the atoms in a model or picture.
41We can write formulae by counting the atoms in a model or picture.
42Diatomic moleculesHydrogen, nitrogen, oxygen, the halogens and carbon monoxide exist as diatomic molecules.
43We can draw diagrams to show the formation of diatomic molecules.
44We can draw diagrams to show the formation of diatomic molecules. +H H
45We can draw diagrams to show the formation of diatomic molecules. +H H H2
48Some diatomic molecules involve more than one covalent bond.
49We can represent these molecules, using as a covalent bond. H2 H HCl2 Cl ClO2 O ON2 N N
50Covalent moleculesWe can draw similar diagrams of discrete covalent molecules.methane CH4ammonia NH3
51Once again we can represent those more simply: H N H H C HH Hammonia NH3methane CH4
52ValencyValency is a number which helps us work out molecular formulae.It is the combining power of the atom.Valency isGroup Number8 minus Group NumberSize of charge on ionNumber after metals name e.g. copper(II)
60Fuels A fuel is a chemical which burns, releasing energy. An exothermic reaction is one in which heat is released.Combustion is the reaction of a substance with oxygen, in which energy is given out.
61The test for oxygen is that it relights a glowing splint. The two main gases in air are oxygen (about 20%) and nitrogen (about 80%).
62Fuels In any chemical reaction breaking bonds takes in energy while forming bonds releases energy.In an exothermic reaction the energy released by forming the bonds in the products is greater than the energy taken in to break bonds in the reactants.
63Fossil FuelsFossil fuels are coal, oil and natural gas which have been formed by the decay of natural materials which lived millions of years ago.Coal, oil and gas are finite resources i.e. the Earth has only limited quantities.A fuel crisis will occur when the amount of these fuels is no longer sufficient to supply our needs cheaply.
64Coal was formed from the decay of forests and vegetation which covered the earth million years ago.Layers built up until the heat and pressure changed the organic material to coal.Oil and natural gas were formed in a similar way, except that they probably came from marine plants and animals, compressed by layers of sand on the sea bed.
65Both coal and oil contain sulphur. When the fuels burn the sulphur produces a gas called sulphur dioxide.This causes pollution since it dissolves in water to form sulphuric acid (acid rain).Oil causes pollution problems if it is spilled in water because it does not dissolve in water and is poisonous to marine life.
66OilAll substances have there own particular melting point and boiling point.Crude oil is a mixture of compounds which can be to split it into fractions.A fraction is a group of chemical compounds, all of which boil within the same temperature range. Oil can be separated into fractions by the process of fractional distillation.
67Fractional Distillation of Oil gases(gaseous fuel)petrol (gasoline)(petrol)naphtha(chemicals)paraffin (kerosine)Heatedoil fromfurnace(aircraft fuel)diesel(fuel for lorries etc.)residue(wax, tar)
68Oil Fractions Name Carbon atoms per molecule Uses Gases 1 to 4 Fuel Petrol4 to 9Fuel for carsNaphtha8 to 14ChemicalsParaffin10 to 16Aircraft fuelDiesel15 to 20Lorry fuelResidueMore than 20Lubricating oil, tar, wax etc.
69Oil Fractions Viscosity is a measure of the thickness of a liquid. Flammability is a measure of how easily the liquid catches fire.Volatility means how easy it is to turn the liquid into a gas.
70As the boiling point of a fraction increases then: it will not evaporate as easily.it will be less flammableit will be more viscous (thicker).
71Moving through the fractions from gases to the residue The molecules present in the fraction are longer and heavierThey will find it more difficult to become a gas i.e. they will be less easy to evaporate.
72Moving up the fractions from gases to the residue Since combustion involves the reaction of gas molecules with oxygen flammability will decrease.Increased molecular lengths mean that molecules become more "tangled up", so the liquid will become thicker (more viscous).
73Tests The test for carbon dioxide is that it turns lime water cloudy. The test for water is that it turns anhydrous copper sulphate from white to blue.Hydrocarbons burn to produce carbon dioxide and water only.
75HydrocarbonsWhen a hydrocarbon fuel burns to give carbon dioxide and water then:The carbon in the carbon dioxide and the hydrogen in water must have come from the fuel.Crude oil is mainly made of compounds called hydrocarbons (i.e. made of carbon and hydrogen only).
76Incomplete Combustion When fuels burn in a limited supply of air then incomplete combustion takes place and the poisonous gas, carbon monoxide (CO) is produced.Increasing the amount of air used to burn fuel improves efficiency and decreases pollution.
77Other products of combustion Fossil fuels contain sulphur which produces sulphur dioxide when the fuel is burned.The oil industry tries to remove this sulphur from the fuels before selling them.
78Nitrogen does not react well because of its strong bonds. Air+-HighVoltagesparkIf there is a high temperature the nitrogen and oxygen will combine to make nitrogen oxides.The experiment opposite shows how a high voltage spark, like one provided by the spark plug or lightning will do the same.
79Nitrogen does not react well because of its strong bonds. Air+-HighVoltagesparkBrowngasIf there is a high temperature the nitrogen and oxygen will combine to make nitrogen oxides.The experiment opposite shows how a high voltage spark, like one provided by the spark plug or lightning will do the same.
80Atmospheric Pollution The sulphur and nitrogen oxides produced can dissolve in water, making acid rain.Unburnt hydrocarbons escaping from car exhausts can help cause the destruction of the ozone layer.
81Reducing PollutionAir pollution caused by burning hydrocarbons can be reduced by:using a special exhaust system – a catalytic converter, in which metal catalysts (platinum or rhodium) will convert pollutants into harmless gases.altering the fuel to air ratio.
82Fuels Click to repeat this presentation Click to return to Menu Click to End
84Homologous Series An homologous series is a series of carbon compounds.The alkanes, the alkenes and the cycloalkanes are examples of homologous series.
85In a homologous series: all members can be represented by a general formula.there is a gradation in physical properties.there is a similarity in chemical properties
86IsomersH C C C C HH H H HH C C C HH H HH C HHH H Isomers are compounds with the same molecular formula but different structural formulaeFor example C4H10
87Alkanes Alkanes All members have a name ending in -ane. Alkanes have a general formula CnH2n+2Alkanes are used as gaseous and liquid fuels, as well as wax and tar.
88AlkanesAlkanesAs we move down the alkanes the boiling point increases.This is because the molecular size increases, making it more difficult to change a molecule from liquid into gas.
89Alkanes The alkanes, general formula CnH2n+2 methane CH4 ethane C2H6 propane C3H8butane C4H10pentane C5H12hexane C6H14heptane C7H16octane C8H18nonane C9H20decane C10H22
90Cycloalkanes The cycloalkanes, general formula CnH2n cyclopropane C3H6 cyclobutane C4H8cyclopentane C5H10cyclohexane C6H12
91Alkenes The alkenes, general formula CnH2n ethene C2H4 propene C3H6 butene C4H8pentene C5H10hexene C6H12
92Alkenes contain a carbon to carbon double bond: C CH C C HH HetheneHH C C C HH H HpropeneH HH C C C C HH H H Hbutene
93Isomers CH3 CH CH2 propene C3H6 CH2 CH2 CH2 cyclopropane C3H6 The alkenes and the cycloalkanes are isomers.They both have the same general formula CnH2nThey have different structural formulae, as shown.CH CH CH2propene C3H6CH CH2CH2cyclopropane C3H6
94Saturated and Unsaturated Saturated hydrocarbons contain only carbon to carbon single bondsUnsaturated hydrocarbons contain carbon to carbon double or triple bonds.
95Unsaturated Hydrocarbons The test for unsaturation is that unsaturated hydrocarbons decolourise bromine water. An addition reaction takes place when a carbon to carbon double bond breaks and other atoms add on.If hydrogen is added to an alkene then an alkane is formed.
96Cracking Hydrocarbons Cracking of long-chain hydrocarbons produces smaller, more useful molecules.These molecules are unsaturated.
98Catalytic CrackingA catalyst lowers the temperature at which cracking takes place.Cracking produces some unsaturated hydrocarbons because there are not enough hydrogen atoms to produce completely saturated products.
99Hydrocarbons Click to repeat this presentation Click to return to Menu Click to End
101Plastics and Synthetic Fibres Most plastics and synthetic (i.e. man-made) fibres come from oil.Plastics are selected for various uses, according to their properties e.g. lightness, durability, electrical and thermal insulation.Biodegradable means "able to rot away". Most plastics are not biodegradable and so cause environmental problems of disposal.
102Burning plasticsCertain plastics burn or smoulder to give poisonous fumes.All plastics can release carbon monoxide.P.V.C. can release hydrogen chloridePolyurethane releases hydrogen cyanide.
103Thermoplastic or Thermosetting? A thermoplastic plastic is one which can be melted or reshaped (examples polythene, polystyrene, P.V.C.)A thermosetting plastic is one which cannot be melted and reshaped (examples bakelite in electrical fittings, formica in worktops)
104PolymerisationA monomer is a small molecule which is able to join together with other, similar, small molecules.A polymer is the large molecule produced.This process is called polymerisation.Plastics and fibres (natural and synthetic) are examples of polymers. The making of plastics and synthetic fibres are examples of polymerisation.
105Naming polymersMany polymers are made from the small unsaturated molecules, produced by the cracking of oil.The name of the polymer is derived from its monomer.
107Addition Polymerisation The small unsaturated molecules add to each other by opening up their carbon to carbon double bonds.This process is called addition polymerisation.CH2=CH2 + CH2=CH2
108Addition Polymerisation The small unsaturated molecules add to each other by opening up their carbon to carbon double bonds.This process is called addition polymerisation.CH2=CH2 + CH2=CH2 -CH2-CH2-CH2-CH2-The repeat unit is (-CH2-)n
109H HC CI*The ethene is attacked by an initiator (I*) which opens up the double bond
110IH HC C*H HC CThe ethene is attacked by an initiator (I*) which opens up the double bondAnother ethene adds on.
111IH HC CC C*H HC CThe ethene is attacked by an initiator (I*) which opens up the double bondAnother ethene adds on.Then another
112IH HC CC C*The ethene is attacked by an initiator (I*) which opens up the double bond….Another ethene adds on.Then another
113Repeat Units You should be able to look at the structure of a polymer and work out the repeat unit and the monomer(s) from which it was formed.The repeat unit of an addition polymer is always only two carbon atoms long.
114Plastics and Synthetic Fibres Click to repeat this presentationClick to return to MenuClick to End
116Carbohydrates Carbohydrates are important food for animals. Carbohydrates contain the elements carbon, hydrogen and oxygen.There are two hydrogen atoms for each oxygen atom in carbohydrates
117PhotosynthesisPhotosynthesis is the process by which plants make carbohydrates and oxygen from carbon dioxide and water, using light energy.6CO H2O + energy C6H12OChlorophyll (the green colour in plants) is used to absorb the light energy.
118Respiration Respiration is the process by which animals AND plants obtain the supply of energy that they need for growth, movement, warmth etc.They obtain this energy by breaking down the carbohydrate, glucose, using oxygen:C6H12O 6CO H energyCarbohydrates burn, releasing energy and producing carbon dioxide and water
119The Atmosphere The combination of respiration and photosynthesis lead to the balance of carbon dioxide/oxygen in the atmosphere.The clearing of forests with the loss of green plants, reduces the amount of photosynthesis taking place. This could alter the balance of the atmosphere, with a consequent danger to life on Earth.
120Glucose Glucose is a carbohydrate Glucose is sweet Glucose dissolves well in waterA beam of light can pass through glucose solution.Benedict's solution will give an orange precipitate with glucose.
121Sucrose Sucrose is a carbohydrate Sucrose is sweet Sucrose dissolves well in waterA beam of light can pass through sucrose solution.Benedict's solution will NOT give an an orange precipitate with sucrose.
122Starch Starch is a carbohydrate Starch is not sweet Starch does not dissolve in waterA beam of light cannot pass through starch solution.When iodine is added to starch a blue/ black colour is produced.
123Testing Carbohydrates Benedict's solution (or Fehling's solution) gives a positive test (an orange colour) with glucose, fructose, maltose and other sugars but NOT sucrose.The pairs of carbohydrate glucose/fructose (C6H12O6) and sucrose/maltose (C12H22O11) are isomers because they both have the same molecular formula but different structural formulae.
124Testing Carbohydrates Starch gives a blue/black colour when added to iodine.
125Types of carbohydrates Monosaccharides are simple sugars with formula C6H12O6.Disaccharides are simple sugars with formula C12H22O11.Polysaccharides are complex sugars with formula (C6H10O5)n.
126Condensation Polymerisation Glucose is a carbohydrate made in photosynthesis.Two glucose molecules join to form sucrose.This is a condensation reaction.2C6H12O6 C12H22O H2OGlucose monomers polymerise to form starch.This is a condensation polymerisation.nC6H12O6 (C6H10O5)n nH2O
127HydrolysisHydrolysis takes place when large molecules are broken down into smaller molecules by the addition of small molecules, such as water.The breakdown of sucrose and starch are examples of a hydrolysis reactions.
128DigestionDuring digestion starch molecules are broken down by the body into smaller glucose molecules that can pass through the gut wall into the bloodstream.The breakdown of starch is brought about using acid or the enzyme amylase.Enzymes, such as amylase, are biological catalysts
129Enzymes Enzymes, such as amylase, are biological catalysts An enzyme will work most efficiently within very specific conditions of temperature and pH.The further conditions are removed from the ideal the less efficiently the enzyme will perform.
130DigestionSucrose and starch molecules break down by the addition of water:C12H22O H2O C6H12O C6H12O6sucrose glucose fructose(C6H10O5)n nH2O n C6H12O6starch glucoseMonosaccharides have formula C6H12O6.Disaccharides have formula C12H22O11.
131AlcoholAlcoholic drinks can be made from any fruit or vegetable source that is a source of sugars.The enzymes in yeast act as catalysts in the formation of alcohol.
132FermentationFermentation is the breakdown of glucose to form carbon dioxide and alcoholC6H12O6 2 CO C2H5OHThe maximum concentration of alcohol that can be produced is limited because an increase in alcohol concentration limits the efficiency of the yeast.
133Distillation of alcohol Since alcohol boils at 80oC and water boils at 100oC distillation of an alcohol solution increases the alcohol concentration.Alcohol is a member of the alkanol family, called ethanol
134Carbohydrates Click to repeat this presentation Click to return to MenuClick to End
136Formula MassFormula mass is found by adding together the relative atomic masses of all the atoms present in the formula, e.g. calcium carbonate CaCO3CaCO xFormula Mass
137Percentage Composition The percentage composition is found as follows.Find the formula mass of the compound.Find the fraction made up by the element required.Convert that fraction to a percentage.Percentage = mass of element required x 100formula mass of compound
138Percentage Composition Find the percentage of nitrogen in ammonium nitrate:Formula NH4NO3Formula mass = 80Nitrogen makes up 28 out of 80%N = (28/80) x100 = 35%
139Empirical FormulaThe empirical (simplest) formula is found as follows.Take the masses (or percentages) of each element present.Divide the mass of each element by its relative atomic mass.Convert these numbers into a simple, whole number ratio.
140Empirical FormulaCalculate the empirical formula for the compound which is 54% calcium, 43% oxygen and 3% hydrogen.Symbol % Divide by RAM RatioCaOH5440354/40 = 1.3543/16 = 2.73/1 = 312Formula is CaO2H2 or Ca(OH)2
141MolesTo connect gram formula mass, mass in grams and number of moles use the triangle oppositegfm = mass of 1 molen = number of molesm = mass of substancemngfm
142Chemical EquationsReactants are the materials with which are present at the start of the reaction and are changed by the reaction.Products are the materials produced by the chemical change.These are separated by an arrow (which means “gives”).Reactants Products
143Chemical EquationsWhenever we write a chemical equation we need to knowwhat substances are present at the startwhat are the new substances formed in the chemical reaction.
144propane + oxygen carbon dioxide + water Chemical EquationsTo know the chemical reactants and products means we can write a word equationHere we are naming the reactants and products. e.g.propane + oxygen carbon dioxide + water
145Chemical Equations We need to convert the word equation into symbols: C3H8 + O2 CO2 + H2OIf we look closely at this equation we will realise that it is unbalanced – there are different numbers of atoms on each side:3xC + 8xH + 2xO C + 2xH + 3xO
146Chemical EquationsWe must write a balanced chemical equation where there are equal numbers of moles of each type of atom on both sides.We can balance the equation we have been working with.
147Balancing Equations Propane has 3 carbons so: C3H8 + O2 3CO2 + H2O Propane has 8 hydrogens so:C3H8 + O2 3CO H2OTo balance out the oxygens:C3H8 + 5O2 3CO H2OThis is a balanced chemical equation.
148Using Chemical Equations The numbers we use to balance an equation are the actual numbers of moles which react.This gives us the mole relationship in the reaction.If we look at the example we have been given:C3H O2 3CO H2O1 mole + 5 moles 3moles + 4moles
149Using Chemical Equations Since one mole is the formula weight in grams we can now work out the masses which react.C3H O2 3CO H2O1 mole 5 moles 3mole 4moles1x44g 5x32g 3x44g 4x72g44g g 132g gNow by proportion we can work out any reacting quantities.
150Using Chemical Equations How much oxygen is needed to burn 0.22g of propane?C3H O2 3CO H2O1 mole 5 moles 3mole 4moles To burn, 1 mole C3H8 needs 5 moles O2 44g C3H8 needs 160g O20.22g C3H8 needs 0.8g O2
151Concentration of Solutions To connect volume, concentration and molarity of a solution use the triangle opposite.c = concentration (m/l)n = number of molesv = volume (l)ncv
152Using Chemical Equations How much sodium carbonate would dissolve in 500ml of 0.5 m/l sulphuric acid?Na2CO3 + H2SO4 Na2SO4 + CO2 + H2O1 mole mole 1mole mole 1 mole500ml of 0.5 m/l sulphuric acid contain0.5 x 0.5 = 0.25 moles of acid.0.25 moles of sodium carbonate react with 0.25 moles of sulphuric acid.1 mole sodium carbonate = 106g0.25 moles sodium carbonate = 26.5g
153Acid/Alkali Titrations Work out unknown concentrations and volumes from the results of volumetric titrations.You use the equation VH MH NH =VOH MOH NOHV = volumeM = molarityN = number of H/OHH = acidOH = alkali
154Chemical Arithmetic Click to repeat this presentation Click to return to MenuClick to End
156Conductivity An electric current is a flow of electrons. Conductors are materials which allow an electric current to pass through.Insulators are materials which do not allow an electric current to pass through.
157ConductorsMetalsGraphite (a form of carbon - the only non-metallic conductor)Solutions of ionic metal compoundsMolten ionic compounds
158Conductivity A metal conducts because of its metallic bonding. In metallic bonding the outer electrons can jump from atom to atom, and thus move through the solid.
159Ions and Conductivity Ions move through liquids. Positive ions are formed when atoms lose electrons.Negative ions are formed when at atoms gain electrons.
160Ions Ions are charged particles Atoms gain or lose electrons to achieve the Noble Gas Structure.Positive ions are formed when metal atoms lose electrons.Negative ions are formed when at non-metal atoms gain electrons.
161IonsGr.1234567e- to losee- to gainion+2+3+3-2--
162An ionic solution or a melt will conduct because its ions are free to move to the electrode of opposite sign.An ionic solid does not conduct because its ions are unable to move.
163Liquid or Gas At room temperature A liquid or gaseous compound will be covalent.A liquid or gas contains small discrete molecules between which there are fairly small forces of attraction.
164Solids At room temperature A solid compound can be ionic or covalent Solids are a result of very strong forces holding the particles together.Ionic solids consist of a lattice of oppositely charged ions.
165Types of SolidIn an ionic solid these forces are the ionic bonds i.e. the forces of attraction between the oppositely charged ions.
166A covalent network solid consists of a huge number of atoms held together by a network of covalent bonds.
167Soluble in water?Most ionic substances are soluble in water, the lattice breaking, to free the ions Most covalent substances are insoluble in water but can dissolve in other solvents.
168An electrolyte is a substance which conducts when molten or in solution. While most ions are colourless, some are coloured. e.g.cobalt - pink/purple;copper - blue;dichromate - orange;nickel - green;permanganate - purple
169ElectrolysisElectrolysis occurs when d.c. (direct current) is passed through a melt, or an ionic solution. This changes the compound, releasing new substances at the electrodes.
170Products of Electrolysis At the positive electrode: chlorine, bromine, iodine or oxygen (from water) are released.At the negative electrode: copper, silver or hydrogen (from water) are released.
171Electrolysis Electrolysis of copper(II) chloride The positive copper ion moves to the negative electrode where:Cu e- Cu-+Cu2+
172Electrolysis Electrolysis of copper(II) chloride The negative chloride ion moves to the positive electrode where:2Cl- Cl e--+Cl-
173Properties of Substances Click to repeat this presentationClick to return to MenuClick to End
175pH pH is a continuous scale of acidity. Acids have a pH of less than 7 Alkalis have a pH of more than 7.Water, and other neutral solutions have a pH of 7.
176Oxides Non-metal oxides dissolve in water, giving acidic solutions. Metal oxides and hydroxides, which dissolve in water, give alkaline solutions.
177Acid Rain Acid RainThis has damaging effects on buildings and other structures, soil and plant and animal life.Sulphur dioxide gas dissolves in water in the atmosphere, producing sulphuric acid.Nitrogen oxides dissolves in water in the atmosphere, producing nitric acid.
178IonsAcids and alkalis both contain ions. In water the concentration of ions is very low.The test for hydrogen is that it explodes with a "pop" when lit.
179H+ and OH- ions Acids contain more H+ ions than water. Alkalis contain more OH- ions than water.Water, and other neutral solutions, contain equal numbers of H+ and OH- ions.
180Dilution When an acid is diluted its acidity decreases and its pH increases.When an alkali is diluted is alkalinity decreases and its pH decreases.
181 When an acid (or alkali) is diluted then the number of H+ (or OH- ) ions per cm3 of solution decrease and so the acidity (or alkalinity) decrease.
182Acids and Alkalis Click to repeat this presentation Click to return to MenuClick to End
184Neutralisation Neutralisation is the reaction of an acid with a neutraliser.Neutralisers are metal oxides, hydroxides and carbonates.Examples of neutralisation involveadding lime to soil or water to reduce its aciditytreating acid indigestion with magnesium hydroxidethe reaction of H+ (aq) to form water.
185NeutralisationDuring a neutralisation reaction then the pH of any acid or alkali involved move nearer to 7.Neutralisation involves the reaction:H+ + OH- H2OA salt is the substance formed when the hydrogen ion of an acid is replaced by a metal (or ammonium) ion.
186Salts Acid Formula Salt Ion hydrochloric HCl chloride Cl- sulphuric H2SO4sulphateSO42-nitricHNO3nitrateNO3-carbonicH2CO3carbonateCO32-
187Acids and carbonatesAn acid reacts with a metal carbonate to release carbon dioxide. Thus acid rain will dissolve rocks or buildings which contain carbonates.The hydrogen ions from the acid react with the carbonate ions, to form carbon dioxide and water.2H+ + CO32- H2O + CO2
188Acids and metalsAcids react with some metals to release hydrogen. The hydrogen ions in the the acid form hydrogen molecules. Acid rain will dissolve iron structures very slowly, since iron reacts with acid to produce hydrogen.
189SaltsWhen dilute hydrochloric acid reacts with acid then hydrogen and a metal chloride are formed.When dilute sulphuric acid reacts with acid then hydrogen and a metal sulphate are formed.
190Acids, Bases and Alkalis A base is a substance which neutralises an acid.ACID + BASE SALT + WATERAn alkali is a soluble base.ACID + ALKALI SALT + WATER
191PrecipitationAn easy way to prepare salts is to react an acid with an insoluble metal oxide or metal carbonate. Excess can be removed from the reaction mixture by filtration. Precipitation is the reaction in which two solutions react to form an insoluble salt.
192Remember Moles?To connect gram formula mass, mass in grams and number of moles use the triangle oppositegfm = mass of 1 molen = number of molesm = mass of substancemngfm
193Remember solutions? n c v To connect volume, concentration and molarity of a solution use the triangle opposite.c = concentration (m/l)n = number of molesv = volume (l)ncv
194Working out about neutralisations Work out unknown concentrations and volumes from the results of volumetric titrations.You use the equation VH MH NH =VOH MOH NOHV = volumeM = molarityNH = number of H+ ions in acidNOH =number of OH- ions in alkaliH = acidOH = alkali
195Reactions of Acids Click to repeat this presentation Click to return to MenuClick to End
197Metals Metals have a metallic lustre i.e. they are shiny Metals conduct electricity when solid or liquid.The world's metal resources are finite and so we must recycle used metals.
198AlloysAn alloy is a mixture of metals, or a mixture of metal with non-metal. Examples:Brasssolder"stainless steel"
199Properties of Metals A metal's properties decide its uses electrical conductivity – electric wiringthermal conductivity – pots and pansmalleability - shaped into many objectsstrength - made into certain objects
200Common reactions of metals. Metals react with oxygen to form metal oxides.Metals react with water (either as liquid or steam) to form the metal hydroxide and hydrogen.Metals react with dilute acid to release hydrogen.
201Reactions of MetalsN.B. Not all metals react as shown on the previous slide.The ease with which these reactions take place is a measure of the reactivity of the metal.We can build up a Reactivity Series from the relative reactivity of the metals.
202OxidationOxidation is the loss of electrons by a reactant in a chemical reaction.When a metal reacts to form a compound it is oxidised.
203Reduction Reduction is the gain of electrons by a reactant in a chemical reaction.When a metal compound reacts to form a metal it is reduced.
204Oxidation and Reduction OIL RIGOxidation Is Loss of electrons Reduction Is Gain of electronsIn a redox reaction oxidation and reduction go on together.
205The Reactivity SeriesKNaCaMgAlZnFeSnPbHCuHgAgAuMetals are listed from most reactive to least reactive.
206ReactivityThe Reactivity Series (also called the Electrochemical Series) lists the metals in order of their ease of oxidation.The least active metals are those whose ions are most easily reduced.
207Recovering MetalsThe less active metals do not react well and so occur uncombined in the earth's crust.Thus they were some of the first elements discovered.
208Ores are naturally occurring compounds of a metal. The more reactive metals are found combined in the earth's crust, as ores.The extraction of a metal from its ore is an example of reduction.
209Very unreactive metals , such as gold, silver and mercury, can be obtained from their oxides by heat alone.
210Recovering MetalsOther metals from the middle of the Reactivity Series, such as zinc, iron, copper and lead, can be obtained from their oxides by heating the oxide with hydrogen, carbon (or carbon monoxide).
211Highly reactive metals, such as magnesium, calcium, sodium and potassium, have to be obtained from their oxides by other electrolysis.
212Recovering MetalsThe more reactive a metal is, the more difficult it is to break down its compounds.Oxides of reactive metals are most difficult to break down.Oxides of unreactive metals are most easily broken down.
213The Blast Furnace Iron is produced from iron ore in the blast furnace. There are two reactionsThe formation of carbon monoxide from coke (carbon):C(s) + O2 (g) CO2 (g)C(s) + CO2 (g) 2CO(g)The reduction of iron oxide to iron:Fe2O3(s) + 3CO(g) 2Fe(s) + 3CO2
214Metals Click to repeat this presentation Click to return to Menu Click to End
216CellsA cell is made by connecting two different metals together with an electrolyte.An electrolyte is a material, which conducts electricity in solution (it contains ions). The electrolyte is needed to complete the circuit.The voltage generated between different pairs of metals varies, and this gives rise to the Electrochemical Series.
217DisplacementAny metal, in an Electrochemical Series, will displace a metal below it from one of its compounds.This reaction will usually produce some visible signs.
218DisplacementIf zinc reacts with copper sulphate solution the reactions are:Cu e Cu ReductionZn Zn e OxidationOverallCu Zn Cu + Zn2+ RedoxBy considering the metals with which acids will react it is possible to place hydrogen in the Electrochemical Series.
219Chemical Energy in Cells Chemical changes can bring about the production of electrical energy.A cell or battery will run out (“go flat”) when the chemicals which produce electricity are used up.
220Mains or Battery? Mains Electricity Cannot be transported Uses high voltages, which can be dangerous.Cheap to useMade from renewable energy sourcesBatteryIs easily transportedUses low voltages, so is not dangerous.More expensive to useMade from finite energy sources
221Metals and Electricity Click to repeat this presentationClick to return to MenuClick to End
223CorrosionCorrosion is a chemical reaction in which the surface of a metal changes from an element to a compound. Different metals will corrode at different rates. Corrosion results in metals forming compounds and so is an example of oxidation.
224Rusting Rusting is the word used to describe the corrosion of iron. Rusting requires the presence of oxygen (from air) and water.Ferroxyl indicator, which turns blue in the presence of Fe2+ ions can be used to show the extent of rusting.
225RustingThe water must contain dissolved carbon dioxide or some other electrolyte.Salt acts as an electrolyte and so salt, spread on the roads in winter, increases the corrosion of car bodywork.Any other electrolyte would increase corrosion
226RustingWhen iron rusts the iron atom loses electrons to form iron(II) ions:Fe Fe eThis is followed by a further loss of electrons to form the iron(III) ion:Fe2+ Fe e The electrons lost by the iron are taken by the water and oxygen and used to form hydroxide ions:2H20 + O2 + 4e 40H-
227Rusting and electronsIron does not rust when connected to the negative terminal of a battery because the electrons flowing onto the iron prevent it from losing electronsBy using a cell with an iron nail, a carbon rod, an electrolyte, ferroxyl indicator and a centre-zero meter it is possible to show the formation of Fe2+ at the iron nail and the movement of electrons away from the iron.
228Rusting and electronsThe iron atoms rust, losing electrons.
229Rusting and electrons The iron atoms rust, losing electrons. The blue colour shows Fe2+ has been formed.
230Rusting and electrons The iron atoms rust, losing electrons. The blue colour shows Fe2+ has been formedThe centre-zero meter shows the movement of electrons from the iron nail to the carbon rod.
231Electrons flow to ironWhen a cell is set up with iron and a metal (say Mg) higher in the Electrochemical Series then electrons flow to the iron.The reactions taking place are:Mg Mg2+ + 2eFe2+ + 2e FeMagnesiumIron
232Electrons flow from iron When a cell is set up with iron and a metal (say Cu) lower in the Electrochemical Series then electrons flow from the iron.The reactions taking place are:Fe Fe2+ + 2eCu2+ + 2e CuIronCopper
234Electroplating + - Electroplating The metal to be plated on is made the positive electrode.Metal tobe plated on
235Electroplating + - Electroplating The metal to be plated on is made the positive electrode.The object to be coated is made the negative electrode.Metal tobe plated onMetalobjectto be plated
236Electroplating + - Electroplating The metal to be plated on is made the positive electrode.The object to be coated is made the negative electrode.The solution contains the ions of the metal to be plated on.Metal tobe plated onSolution of plating ionsMetalobjectto be plated
237Metal Plating Galvanising occurs when steel (or iron) is coated with zinc.Tin-plating occurs when steel (or iron) is coated with tin.
238Physical ProtectionPutting a barrier over the surface of a metal will provide physical protection against corrosionIt will not allow air and water to come in contact with the metal.PaintingGreasingElectroplatingGalvanisingTin-platingCoating with plastic.
239Sacraficial Protection Sacrificial protectionIf two metals are connected electrons will flow from the more active metal to the less active.The more active metal will corrode in preference to the less active metal.On the Finart-Grangemouth oil pipe bags of scrap magnesium are connected every 200 meters so magnesium corrodes sacraficially to protect the iron.
240Tin-plating Tin-plating If it is scratched then the iron and tin are exposed. Since the iron is higher in the Electrochemical Series it will corrode in preference to the tin.The corrosion of the iron increases.
241Galvanising Galvanising If it is scratched then the iron and zinc are exposed. Since the zinc is higher in the Electrochemical Series it will corrode in preference to the iron.The corrosion of the iron is prevented.
242Corrosion Click to repeat this presentation Click to return to Menu Click to End
244Fertilisers Increasing world population means that we need more efficient means of food production.Growing plants take nutrients from the soil. These nutrients include compounds of nitrogen, phosphorous and potassium.
245FertilisersFertilisers are substances which are added to the soil to replace the essential elements needed for plant growth.Different plants require fertilisers containing different proportions of these nutrient elements.
246Fertilisers Artificial fertilisers are soaked out of the soil by rain. They are carried into lakes and rivers where they increase the number of river plants.When these plants die then there is an increase in the bacteria which digest them leading to a decrease in oxygen in the water.This results in the death of fish.
247Fixed nitrogenCertain plants have nitrifying bacteria present in nodules in their roots. These bacteria can convert atmospheric nitrogen (called free nitrogen) into nitrogen compounds (fixed nitrogen). These nitrogen compounds increase the fertility of the soil.Bacterial methods of increasing the nitrogen content of soil are cheaper than chemical methods.
248Fixed nitrogenRecycling of nitrogen compounds into the soil is brought about by the decomposition of plant and animal protein by bacteria in the soil.Ammonium salts, potassium salts, nitrates and phosphates make good fertilisers because:they contain some of the essential elements for plant growth (P, N and K).they are soluble and pass easily into the soil and up the plant's roots.
249The Nitrogen Cycle All living things need nitrogen to make proteins. They cannot use free nitrogen from the atmosphere.They need to get fixed nitrogen in their food.The Nitrogen Cycle describes the place of nitrogen compounds in Nature.
250The Nitrogen Cycle Animals need nitrogen to make substances called proteinsANIMALS
251The Nitrogen Cycle They get this nitrogen by eating protein which has been made by plants.ANIMALSPLANTS
252The Nitrogen Cycleplant protein eatenANIMALSPLANTS
253The Nitrogen Cycle Plants absorb nitrates through their roots nitrates plant protein eatenANIMALSPLANTS
254The Nitrogen Cycle nitrates taken in by roots plant protein eaten ANIMALSPLANTS
255The Nitrogen Cycle ammonia Ammonia, NH3 comes from animal waste nitratestaken inby rootsplant protein eatenANIMALSPLANTS
256The Nitrogen Cycle ammonia sewage and manure nitrates taken in by rootsplant protein eatenANIMALSPLANTS
257The Nitrogen Cycle ammonia bacteria sewage and manure Bacteria convert ammonia intonitratesnitratestaken inby rootsplant protein eatenANIMALSPLANTS
258The Nitrogen Cycle atmospheric nitrogen ammonia Thunderstorms bacteria make nitratesfrom N2bacteriasewageandmanurenitratestaken inby rootsplant protein eatenANIMALSPLANTS
264The Nitrogen CycleDue to the way in which we live, food, containing nitrogen compounds, is sent from the country to the city.This means that the nitrogen compounds are not returned to the area from which they came.To replace that nitrogen, artificial fertilisers are needed.The Haber Process is used to make ammonia from free nitrogen.
265The Nitrogen Cycle atmospheric nitrogen Haber Process ammonia thunder stormsbacteriasewageandmanurebacteria onlegumesnitratescompostdecaying animalsafter deathtaken inby rootsplant protein eatenANIMALSPLANTS
266The Haber Process Ammonia is produced by the Haber Process. Nitrogen and hydrogen react over an iron catalyst to produce ammonia:N H2 2NH3Since the formation of ammonia is a reversible reaction then not all of the nitrogen and hydrogen are converted into ammonia.
267The Haber ProcessAt low temperatures a large amount of ammonia is produced slowly.At high temperatures a smaller amount of ammonia is produced more quickly.This means that the Haber Process is carried out at a moderately high temperature to produce ammonia at the most economical rate.
268The Haber Process Nitrogen (air) Hydrogen (Oil industry) Unreacted Nitrogen andhydrogenReactionChamberWith FecatalystAmmoniaCooler
269Ammonia Ammonia: has no colour. has a distinctive sharp smell. is highly soluble in water, producing an alkaline solution.can be converted into an ammonium compound by its reaction with acid:2NH H2SO (NH4) 2SO4ammonia sulphuric acid ammonium sulphate
270NH4Cl + NaOH NaCl + H2O + NH3 AmmoniaAmmonia can be prepared by the reaction of ammonium compound with alkali:NH4Cl + NaOH NaCl + H2O + NH3This is also used as a test for the ammonium ion NH4+
271Nitric Acid Nitrogen is a very unreactive gas. Nitric acid (HNO3) is formed when nitrogen dioxide (NO2), in the presence of air, dissolves in water.The presence of nitrogen oxides in the air means that they will dissolve in rain to produce a mildly acidic solution. This has the result that:nitrogen compounds are added to the soil.the acidity of the soil will be increased.
272Nitric AcidNitrogen dioxide is produced by the passage of a high voltage spark through air since a large amount of energy is required to break the bonds between the nitrogen atoms in the molecules.These conditions occur whenlightning passes through aira spark passes in the spark plug of a car engineThis does not provide an economic way of making nitrogen dioxide.
273Nitric AcidAmmonia normally reacts with oxygen to give nitrogen and water.It will only produce nitrogen oxides if a platinum catalyst is used.This is a step in the Ostwald Process, by which nitric acid is produced. This can also be carried out in the laboratory.
275The Ostwald ProcessThis process is carried out at a moderately high temperature to allow it to proceed fairly quickly.Since the reaction is exothermic it is not necessary to continue heating it after the reaction has started since it will supply sufficient energy to continue at a reasonable rate.
276Fertilisers Click to repeat this presentation Click to return to Menu Click to End
277Hope you found the revision useful. The EndHope you found the revision useful.Come back soon!!