4 REVISION OF FACTORS THAT SPEED UP A REACTION Learning intentions Describe using collision theory how rates of reaction are affected by temperature, surface area and concentration.Predict the effect any change to one of the factors above would have before experimental observation.Evaluate from experiment if the factors from above have indeed changed the speed of a chemical reaction in the manner described by collision theory.
5 Reminder from S3: What are the signs of a chemical reaction?
6 Signs of a chemical reaction are: 1. Change in colour (for example silver to reddish brown when iron rusts)2. Change in temperature or energy, such as the production (exothermic) or loss (endothermic) of heat3. Light, heat or sound is given off.4. Change of form (for example, burning paper).5. Formation of gases often appearing as bubbles.6. Formation of precipitate (insoluble solid usually from two solutions when mixed)
7 Important Point to note In order for chemists to monitor the rate of a reaction we must observe a CHANGE in response to a chemical reaction occurring against TIME.REACTANTS PRODUCTSe.g. magnesium + hydrochloric acid magnesium chloride + water + hydrogen
11 Factors Affecting the Rate of Reaction For chemical reactions to take place, the reactant particles must meet and collide with each other.Not all collisions result in a chemical reaction taking place - the collisions must take place with sufficient energy to break any bonds within the reactants.This energy, used to start the reactions is called activation energy.
12 Contents of lesson Rates of Reaction Introduction to collision theory Effect of temperatureEffect of concentrationEffect of surface area
13 Rates of reactionsThe speed of different chemical reactions varies hugely. Some reactions are very fast and others are very slow.ReactionRateBurning magnesiumfastfireworksvery fastchemical weathering of rocksvery slowsodium and waterfastrotting fruitslow
14 Collision theoryReactions occur when particles of reactants collide with enough energy to react (activation energy). Reactants state i.e. solid, liquid or gas will have to be taken into account when thinking about [collision theory].
15 Contents Rates of Reaction Introduction to collision theory Effect of temperatureEffect of concentrationEffect of surface area
17 The effect of temperature on collisions How does temperature affect the rate of particle collision?
18 Temperature and particle collisions Boardworks GCSE Additional Science: ChemistryRates of ReactionTemperature and particle collisionsTeacher notesThis simulation illustrates how increasing the temperature increases the number of collisions between particles.
19 Contents Rates of Reaction Introduction to collision theory Effect of temperatureEffect of concentrationEffect of surface area
20 What is concentration?When a solute (e.g. coffee, salt etc.) is dissolved in a solvent (e.g. water, alcohol etc.) and the resultant mixture is a solutionSoluteSolventAfter they mix it is a solution
21 Concentration has the units (mols/l) which is referring to the amount of solute per unit volume of water we will look at this specifically much later in the topic.For example these examples all have the same volume of solvent but the amount of solute added is changed
23 Video Concentration and reaction rate Dilute hydrogen peroxide solutionAdd more solute (hydrogen peroxide) to the same volumeVideoConcentrated hydrogen peroxide solution
24 ConcentrationReactions in solution involve dissolved particles. The more crowded (concentrated) the solution, the faster the reaction.Higher concentration more particles more collisions faster reaction
25 Contents Rates of Reaction Introduction to collision theory Effect of temperatureEffect of concentrationEffect of surface area
26 Video Surface area and reaction rate video Increased surface area 5g Marble powder20 ml 0.1 mol HCl5g Marble chips medium size20 ml 0.1 mol HCl5g Marble lumps large size20 ml 0.1 mol HCl
27 Extra surface for molecules to collide with. Surface areaReactions of solids can only take place at the surface of the solid. If we break a solid into smaller pieces we get a larger surface area and a faster reaction.Molecules collide with the surface of the solidExtra surface for molecules to collide with.Smaller particles larger surface area more collisions faster reaction
28 Surface area Slow Very fast If we grind up a solid to a powder we massively increase the surface area.We therefore massively increase the rate of any reactionSlowVery fast
29 Summary of the factors which can affect the rate of a reaction are;- Particle size/surface areaConcentration of reactantsTemperature of reactants
30 Particle Size/Surface Area Decreasing the particle size of a solid in a reaction, increases the surface area available for contact between the reactants.Particle size is halvedNew surfaces available for contactIf the surface area available for contact is increased, the rate of collisions will increase and hence the reaction rate will increase.
31 ConcentrationTo increase the concentration of a solution you increase the amount of solute dissolved in the solvent. This means that the number of particles in solution increases.More particles means more collisions which leads to an increase in the rate of reaction.
32 TemperatureAs you increase the temperature of something you give it more energy making the particles move faster, so they collide more frequently. This increases the number of successful collisions and hence the reaction rate.Also, as the particles are now moving faster, the collisions between them have more kinetic energy. This means that more reactions have the required activation energy.
33 Particles and rates of reaction copy and complete
34 NATIONAL 5 CHEMISTRYCHEMICAL CHANGES AND STRUCTURE LESSON 2 MEASURING AND CALCULATING THE RATE OF REACTION
36 Calculating the Rate of Reaction The rate of reaction can be calculated by measuring the :1. Time taken for the reactionand2. One other variable (something that changes) e.g.Volume (cm3)Mass (g)Concentration (moles per litre = moll-1)Rate = Change (in variable)Time taken
37 Example 1Use the graph below to calculate the rate of reaction for the first 20 seconds.Average rate = (change) / time20 cm3/ 20 s1 cm3 S-1
38 Example 2Use the graph below to calculate the rate of reaction between 5.2 and 10.8 seconds.Average rate = (change) / time/ ( )0.2 mol l-1/ 5.6 s0.036 mol l-1 s-1
39 Rates and GraphsThese show the increasing amount of product or the decreasing amount of reactant.Amount of productTimeAmount of reactantTimeSteep gradient Fast reactionShallow gradient Slow reactionSteep gradient Fast reactionShallow gradient Slow reaction
40 Rate graphs and reactant concentrations Amount of productTimeAll productMix of reactantAnd productReactant Concentration fallsRate of Reaction fallsreactantsproductGradient of graph decreasesAll reactant
41 Calcium carbonate + hydrochloric acid calcium chloride + carbon dioxide + water CaCO3 + HCL CaCl2 + CO2 + H2OTime (s)Decrease in mass (g)Concentration of CO2-4.00301.252.86602.922.25902.401.821203.761.491503.061.221803.320.982103.520.802403.680.652703.810.543003.920.443604.110.274204.230.154804.300.095404.350.04600Time (s)Volume of CO2 (cm3)306090130120142150154180162210171240173270174300177360420195480200540600Activity 1 plot either of these graphs on graph paper and work out the average rate for the first 120 seconds and then between 300 – 600 seconds
42 Rate and TimeFor some reactions, a colour change will indicate the end of the reaction.The only measurement carried out during this type of experiment is time. Therefore the rate equation is slightly changed from:No other variable measuredRate = Change (in variable)Time takenTo:Rate =Time takenUnits = per second (s-1)
43 Concentration of Potassium Iodide (KI) Mol/l Concentration of sodium thiosulphate and the time taken for the cross to disappearVideoConcentration of Potassium Iodide (KI) Mol/lTime (S)Rate (1/t) S-11.0230.8290.6390.4600.2111Activity 2 - Plot a Time vs Rate Graph for this reaction and identify the relationship between concentration and rate of reaction0.04350.03450.0270.020.009
44 Rate = (1/t) S-1Concentration of sodium thiosulphate (mol/l)Q) How long did it take for the cross to be obscured when the concentration of sodium thiosulphate was 0.7 mol / l?A) Rate = 1/t… so we must rearrange the equation to Time = 1/rate and obtain the rate from the graph0.7 mol l = S-1 ; Time = 1/0.032 seconds
45 ATOMIC STRUCTURE AND BONDING RELATED TO PROPERTIES OF MATERIALS
46 Atoms and the Periodic Table. We can classify (arrange) elements in different ways:-naturally occurring/made by scientistssolid/liquid/gasmetal/non-metal
47 The Periodic Table of the Elements. The Periodic Table lists the chemical elements in increasing atomic number.The Periodic Table arranges elements with similar chemical properties in groups (vertical columns).All the elements in a group have similar chemical properties as they have the same number of outer electrons.
48 The Periodic Table of the elements is a useful way of classifying the elements. A vertical column of elements in the periodic table is called agroup.The elements in the same group of the periodic table havesimilar chemical properties.The noble gases are a group of veryunreactive elements.
49 Group 1 - the alkali metals Between groups 2 and 3 - Groups of elements have names: –Group 1 -the alkali metalsBetween groups 2 and 3 -the transition metalsGroup 7 -Group 0 -the halogensthe noble gases
50 Contents Atomic Structure Introducing atoms Atomic number and mass numberElectron configurationIsotopesSummary activities
52 Atoms – the building blocks All substances are made from very tiny particles called atoms.Atoms – the building blocksJohn Dalton had ideas about the existence of atoms about 200 years ago but only relatively recently have special microscopes (called electron microscopes) been invented that can ‘see’ atoms.The yellow blobs in this image are individual gold atoms, as seen through an electron microscope.AcknowledgmentThe image is a false-colour high-resolution transmission electron micrograph (HREM) of the atomic lattice of a thin gold crystal. Magnified 16 million times at 35mm size, each yellow blob represents an individual gold atom. The micrograph has been enhanced by optical image- processing techniques. The centre to centre spacing of the atoms is 2.04 angstroms ( nanometres); this represents the practical limit of resolution of the modern electron microscope.Credit: Graham J Hills/Science Photo Library
53 Elements – different types of atom Elements are the simplest substances. There are about 100 different elements.Each element is made up of just one particular type of atom, which is different to the atoms in any other element.Copper is anelement made up ofcopper atoms only.Carbon is anelement made up ofcarbon atoms only.
54 How small is an atom?Atoms are very small – they are about cm wide.To make an atom the size of a football it would have to be enlarged by about 3,000,000,000 times.NX3,000,000,000If a football was enlarged by the same amount it would stretch from the UK to the USA!
56 Inside an atomWhere are the electrons and nucleus found in an atom?
57 Contents Atomic Structure Introducing atoms Atomic number and mass numberElectron configurationIsotopesSummary activities
58 Even smaller particles For some time, people thought that atoms were the smallest particles and could not be broken into anything smaller.Scientists now know that atoms are actually made from even smaller subatomic particles. There are three types:protonneutronelectron
59 Where are subatomic particles found? Protons, neutrons and electrons are NOT evenly distributed in an atom.The protons and neutrons exist in a dense core at the centre of the atom. This is called the nucleus.The electrons are spread out around the edge of the atom. They orbit the nucleus in layers called shells.
60 The atom: check it out! nucleus electron neutron Draw a labelled diagram of the atom showing the nucleus and labelling protons, neutrons and electrons.nucleuselectronprotonneutron
61 Properties of subatomic particles There are two properties of subatomic particles that are especially important:1. Mass2. Electrical chargeParticleMassChargeprotonneutronelectron1+11almost 0-1The atoms of an element contain equal numbers of protons and electrons and so have no overall charge.
62 How many protons?The atoms of any particular element always contain the same number of protons. For example:hydrogen atoms always contain 1 proton;carbon atoms always contain 6 protons;magnesium atoms always contain 12 protons,The number of protons in an atom is known as its atomic number or proton number.It is the smaller of the two numbers shown in most periodic tables.
63 What’s the atomic number? What are the atomic numbers of these elements?sodiumirontinfluorine1126509
64 More about atomic number Each element has a definite and fixed number of protons. If the number of protons changes, then the atom becomes a different element.Changes in the number of particles in the nucleus (protons or neutrons) is very rare. It only takes place in nuclear processes such as:radioactive decay;nuclear bombs;nuclear reactors.
65 Mass number Atom Protons Neutrons Mass number hydrogen lithium Electrons have a mass of almost zero, which means that the mass of each atom results almost entirely from the number of protons and neutrons in the nucleus.The sum of the protons and neutrons in an atom’s nucleus is the mass number. It is the larger of the two numbers shown in most periodic tables.AtomProtonsNeutronsMass numberhydrogenlithiumaluminium11347131427
66 What’s the mass number? Atom Protons Neutrons Mass number helium Mass number = number of protons + number of neutronsWhat is the mass number of these atoms?AtomProtonsNeutronsMass numberheliumcoppercobaltiodinegermanium2242935642732595374127324173
67 How many neutrons? Atom Mass number Atomic number Number of neutrons Number of neutrons = mass number - number of protons= mass number - atomic numberHow many neutrons are there in these atoms?AtomMass numberAtomic numberNumber of neutronshelium42fluorine199strontium8838zirconium9140uranium238922105051146
69 Contents Atomic Structure Introducing atoms Atomic number and mass numberElectron configurationIsotopesSummary activities
70 How many electrons? Atom Protons Neutrons Electrons helium copper Atoms have no overall electrical charge and are neutral. This means atoms must have an equal number of protons and electrons.The number of electrons is therefore the same as the atomic number.AtomProtonsNeutronsElectronsheliumcopperiodine222293529537453Atomic number is defined as the number of protons rather than the number of electrons because atoms can lose or gain electrons but do not normally lose or gain protons.
71 Calculating the number of electrons What are the missing numbers?AtomProtonsNeutronsElectronsAtomic numberMass numberboronpotassiumchromiummercuryargon565511192019193924282424528012180802011822181840
72 How are electrons arranged? Electrons are not evenly spread but exist in layers called shells.The arrangement of electrons in these shells is often called the electron configuration.1st shell2nd shell3rd shell
73 How many electrons per shell? Each shell has a maximum number of electrons that it can hold. Electrons will fill the shells nearest the nucleus first.1st shell holds a maximum of 2 electrons2nd shell holds a maximum of 8 electrons3rd shell holds a maximum of 8 electrons
76 Summary: the atom so far The nucleus is:Dense – it contains nearly all the mass of the atom in a tiny space.Made up of protons and neutrons.Positively charged because of the protons.Electrons are:Thinly spread around the outside of the atom.Very small and light.Negatively charged.Found orbiting the nucleus in layers called shells.Able to be lost or gained in chemical reactions.
77 Contents Atomic Structure Introducing atoms Atomic number and mass numberElectron configurationIsotopesSummary activities
78 What is an isotope?Elements consist of one type of atom, but sometimes these atoms can be slightly different.Although atoms of the same element always have the same number of protons, they may have different numbers of neutrons.Atoms that differ in this way are called isotopes.mass number is differentatomic number is the same
79 Properties of isotopes The isotopes of an element are virtually identical in their chemical reactions.This is because they have the same number of protons and the same number of electrons.The uncharged neutrons make no difference to chemical properties but do affect physical properties such as melting point and density.Natural samples of elements are often a mixture of isotopes.
80 Isotopes of carbon 6 protons 6 neutrons 6 electrons 6 protons Most naturally-occurring carbon exists as carbon-12, about 1% is carbon-13 and a much smaller amount is carbon-14.6 protons6 neutrons6 electrons6 protons6 neutrons7 electrons6 protons6 neutrons8 electrons
81 Isotopes of hydrogen 1 proton 0 neutrons 1 electron 1 proton 1 neutron Hydrogen-1 makes up the vast majority of the naturally-occurring element but two other isotopes exist.hydrogendeuteriumtritium1 proton0 neutrons1 electron1 proton1 neutron1 electron1 proton2 neutrons1 electron
82 Isotopes of chlorineAbout 75% of naturally-occurring chlorine is chlorine-35 and 25% is chlorine-37.17 protons18 neutrons17 electrons17 protons20 neutrons17 electrons
83 Isotopes of oxygen oxygen-16 oxygen-18 protons neutrons electrons Almost all of naturally-occurring oxygen is oxygen-16 but about 0.2% is oxygen-18.What are the particle numbers in each isotope?oxygen-16oxygen-18protonsneutronselectrons8888810
84 Isotopes and RAMMany elements are a mixture of isotopes. The RAM given in the periodic table takes account of this.To calculate the RAM of a mixture of isotopes, multiply the percentage of each isotope by its atomic mass and add them together.For example, chlorine exists as two isotopes: chlorine-35 (75%) and chlorine-37 (25%).= (0.75 x 35) + (0.25 x 37)== 35.5RAM of chlorine = (75% x 35) + (25% x 37)
85 Calculating RAMBromine contains 50.5% bromine-79 and 49.5% bromine-81.What is the RAM of naturally-occurring bromine?= (0.505 x 79) + (0.495 x 81)== 79.99= 80 (the RAM is usually rounded to the nearest whole number)RAM of bromine = (50.5% x 79) + (49.5% x 81)
88 Contents Atomic Structure Introducing atoms Atomic number and mass numberElectron configurationIsotopesSummary activities
89 Glossary (part 1)atom – The smallest particle that can exist on its own.atomic number – The number of protons in the nucleus of an element, also known as the proton number.electron – Negative particle that orbits the nucleus of an atom.element – Substance made up of only one type of atom.isotopes – Different atoms of the same element. They have the same number of protons and electrons, but a different number of neutrons.
90 Glossary (part 2)nucleus – The dense positive centre of an atom, made up of protons and neutrons.neutron – A neutral particle, with a mass of 1. It is found in the nucleus of an atom.mass number – The number of protons and neutrons in an atom.proton – A positive particle, with a mass of 1. It is found in the nucleus of an atom.relative atomic mass (RAM) – The mass of an element compared to the mass of 1⁄12 of the mass of carbon-12.
99 BondingAtoms take part in chemical reactions to achieve a full outer shell of electrons.The molecules or compounds formed are held together by chemical bonds.
100 are invisible forces of attraction. There are 3 main types: Chemical Bondsare invisible forces of attraction.There are 3 main types:Covalent bonds (in covalent molecules)Ionic bonds (in all ionic compounds)Metallic bonds (in all metals)
101 Compounds and Molecules Covalent substances are made up of molecules.Molecules contain 2 or more non-metal atoms held together by covalent bonds.E.g. chlorine moleculeCl
102 Diatomic Molecules Contain 2 atoms only Carbon monoxide Hydrogen chlorideOxygenNitrogenHydrogenGroup 7 elements
103 Forming Covalent Bonds Covalent Bond: Bond formed between two non-metal atoms by sharing a pair of electronsHydrogen Molecule:Hydrogen atom + hydrogen atom = hydrogen gasCovalent bond: the two atoms share a pair of electronsEach hydrogen atoms now has 2 electrons in its outer shell. Therefore the shell is now full.
104 Starter Fill in the table below: Element Symbol Atomic no. Protons ElectronsNeutronsMass NumberCalciumOxygenArgonNitrogen
106 The diagram below shows how a molecule is held together by a covalent bond. A covalent bond is the force of attraction between the nuclei and the shared outer electrons.
107 The only type of covalent bond that has an equal share of electrons between the two atoms is when the two atoms are of the same element. e.g. H2, O2, Cl2. These bonds are called pure covalent bonds.All other covalent bonds are classed as polar covalent bonds.
108 Polar Covalent BondsThe diagram of the covalent bond showed the outer electrons being shared equally between the bonding atoms.When covalent bonds are formed between two different types of atoms, the electrons that are shared between the atoms are not equally shared.
109 This is because some atoms attract electrons more strongly than others This is because some atoms attract electrons more strongly than others. This attraction is called electronegativity.In a molecule of water the bonding electrons are pulled closer to the oxygen atom.OHe-+-= delta- = slightly negative+ = slightly positive
110 These types of bonds are known as POLAR COVALENT BONDS. Because the negative electrons are closer to the oxygen it becomes slightly negative.Molecule: Group of atoms held together by covalent bonds.FHe-+-These types of bonds are known as POLAR COVALENT BONDS.
111 Bonding Diagrams N.B. Only outer electrons are involved in bonding. E.g. chlorine gas, Cl2ClN.B. Outer electrons are grouped together in pairs.
117 The shape of a molecule is determined by the number of bonds. There are 4 basic shapes:TetrahedralAny molecule with the formula XY4
118 Any molecule with the formula XY3 2. PyramidalAny molecule with the formula XY33. AngularAny molecule with the formula XY24. PlanarH ClAny molecule with the formula XYOH
119 Starter What are covalent bonds? Why do molecules form covalent bonds? How is the covalent bond held together?What is a diatomic molecule?
120 Covalent Compounds There are two types of covalent compounds: Discrete covalent moleculese.g. CO2, HF, CH4, N22. Covalent networkse.g. C, SiO2, CS2
121 1. Discrete covalent molecules These are substances made up of discrete (individual) molecules.The bonds between the molecules are weaker than the covalent bonds within molecules.e.g. CO2O=C=OWeak intermolecular forces (Van der Waals)Strong covalent intramolecular bonds
122 Note: The intermolecular forces are weak BONDS (Van der Waals) between the molecules. All discrete molecules have low melting points because only weak intermolecular bonds are broken (Van der Waals)- not covalent bonds.
123 2. Covalent NetworksThese consist of a giant lattice of covalently bonded atoms.e.g. Carbon (diamond)Covalent bondCarbon atom
124 All covalent networks have very high melting points because strong covalent bonds must be broken. =Oxygen atoms=Silicon atoms
125 StarterDraw the bonding diagrams for the followingH2OCF4NH3HF
126 Revision of IonsAll atoms become more stable if they have a full outer shell of electrons (like the noble gases).During chemical reactions, atoms can lose electrons or gain electrons. When this happens the atoms become electrically charged particles called ions.
127 Atoms that lose electrons form positive ions Atoms that gain electrons form negative ions.Ion: Particle found when an atom loses or gains electron(s).
128 Ionic Compounds Contain metal and non-metal ions. Contain oppositely charged ionE.g. Sodium chloride Na+Cl-Magnesium sulphate Mg2+SO42-Remember ions are charged because the don’t have the same numbers of protons and electrons.
129 Ca2+ P3- Positive charge therefore more protons than electrons. 20 protons (atomic number)18 electronsNegative charge therefore less protons than electrons.P3-15 protons (atomic number)18 electrons
130 Forming Ions Atom Ion Na Na+ 2,8,1 2,8 Al Al3+ 2,8,3 2,8 2,8,1 2,8Al Al3+2,8,3 2,8Metal atoms ALWAYS lose outer electrons to obtain a full shell when changing to ions.
131 Atom IonF F-2,7 2,8S S2-2,8,6 2,8,8Non-metals (except hydrogen) ALWAYS gain outer electrons to obtain a full shell when changing to ions.
132 Group Number12345678Number of outer electronsCharge on ionExample of ion
133 StarterDraw the bonding diagrams for the followingH2OCF4NH3HF
134 Forming Sodium Chloride The 2 atoms became ions:Na Cl-2, ,8,8
135 Structure of Ionic Compounds All ionic compounds are solid at room temperature with the ions being held in a fixed pattern called an IONIC LATTICE.
136 The ions cannot move and are held in place by the strong forces of attraction between the opposite charges.Ionic Bond: Electrostatic force of attractionbetween oppositely charged ions in a compound.
137 Conductivity Experiment Aim: To investigate the conductivity of different substances.Method:WiresPower supplyBulbElectrodes6 VBeaker containing compound
138 Results: Sucrose (C12H22O11) Sucrose solution (C12H22O11) Name of substanceIs substance solid or in solutionDoes it have a metal in its name?Is the compound ionic, covalent or metallic?ConductorInsulatorSucrose (C12H22O11)Sucrose solution (C12H22O11)Polystyrene ([C8H8]n)Polystyrene in solutionSodium chloride solutionSodium chloride solidCopper sulphate solidCopper sulphate solutionZinc
139 Conclusion:Ionic solutions conduct electricity.Ionic solids and covalent compounds do not conduct electricity.
141 Metals can lose their outer shell electrons to gain a stable electron arrangement. This is what happens in metals.Outer electrons are said to be ‘delocalised’ which allows them to move freely.This effectively creates positively charged metal ions, which are surrounded by these delocalised electrons.
142 Metal atoms form positively charged ions and so they attract the free moving electrons in the lattice. This attraction forms a metallic bond which is very strong.Metallic Bond: The electrostatic force of attraction between the positive ions in a metallic lattice and the delocalised electrons within the structure.
143 Conductivity Experiment Aim: To investigate the conductivity of some metals and non-metals.Method:WiresPower supplyMaterial to be tested6 VAAmmeter
144 Results: Name of substance Is substance a solid or liquid? Is substance a metal or a non-metal?ConductorInsulatorCopper foilIronSulphurMagnesiumSiliconOxygenAluminiumTinLeadCarbon (in form of graphite)Iodine
145 All metals are conductors of electricity. Conclusion:All metals are conductors of electricity.Non-metals are insulators of electricity, except carbon in the form of graphite.
146 Electrical Conductivity Summary Conductivity in Ionic CompoundsIonic compounds will conduct electricity when in solution or when molten (has been melted into a liquid) as the ions are free to move.An ionic compound in solution or as a melt is called an electrolyte.Solid ionic compounds do not conduct electricity because in the solid state the ionic lattice is rigid and the ions are not free to move.
147 Conductivity in Covalent Compounds Covalent solutions do not conduct electricity as they do not contain any charged particles.The exception to this is carbon in the form of graphite which can conduct electricity as it has delocalised electrons.
148 Conductivity in Metals All metals are conductors of electricity whether they are in solid or liquid form.This is because they have electrons moving freely through their structuresNon-metals are insulators of electricity, except carbon in the form of graphite.
149 Starter What type of bonding is present in the following compounds: a) sodium chloride b) carbon dioxidec) potassium bromide d) irone) Silicon dioxide f) chlorine2. Explain why sodium chloride will not conduct in solid form, but will conduct when dissolved in water.
151 Aim: To investigate the relationship between bonding and melting point. Compound being testedMethod:
152 Results: Compound Formula Bonding Melting Point (oC) Shellac Silica Potassium iodidecopperCovalent discreteC60H90O1577-120oCCovalent network1723oCSiO2KIIonic681oCCuMetallic1085oC
153 Conclusion:In generalIonic compounds High melting pointsMetallic elements High melting pointsCovalent networks High melting pointsCovalent compounds (discrete) Low melting points
154 Explanation of Melting Points To melt a substance, the bonding between units (molecules and ionic structures) has to be substantially weakened (or partly broken).To boil a substance, these bonds have to be broken.
155 Ionic Compounds Example: sodium chloride have very high melting and boiling points and are all solids at room temperature. this is because ionic bonds need to be weakened/broken to melt or boil them.
156 Metallic Elements Example: Iron high melting and boiling points. this is because metallic bonds need to be weakened/broken to melt or boil them.
157 Covalent Network Substances Example: Silicon dioxide have high melting and boiling points and are all solids at room temperature. This is because the structure is held together by strong covalent bonds.
158 Discrete Covalent Substances Example: Carbon dioxidehave low melting and boiling points.the Van der Waals forces that exist between covalent molecules are weak and when a discrete covalent substance is heated it is these weak forces that must be weakened or broken.as these forces are weak they do not require much energy to break them and so melting and boiling points of discrete covalent substances are low.
159 N.B. the covalent bonds between atoms in a molecule are not broken during melting or boiling. Almost all substances (except mercury) that exist as gases or liquids at room temperature, are discrete covalent substances.Polar covalent substances have higher melting and boiling points than pure covalent substances due to the increased attraction between molecules.
160 Conclusion:Some covalent substances dissolve in water, but most dissolve in other solvents.Most ionic substance dissolve in water and this involves the lattice being broken up completely.
161 ‘Like dissolves like’ This means that non-polar solutes will dissolve in non-polar solventspolar solutes will dissolve in polar solventsionic solutes will dissolve in ionic/polar solvents
162 Dissolving in water?Ionic substances dissolve in water, but water isn’t ionic, it’s covalent.Remember- water has a special type of covalent bonding known as POLAR COVALENT.This is an unequal sharing of electrons within the bond, leaving one end slightly polar +ve and the other end slightly polar –ve.This is not an ion, but a polarity.Water is still covalent.
163 When an ionic solid (salt) is added to water, the water molecules arrange themselves round the lattice with the polar +ve end attracted to the –ve ion and the polar –ve end attracted to the +ve ion.If enough energy is present, the ionic lattice breaks and the compound dissolves.
164 If there is not enough energy then the solid doesn’t dissolve i. e If there is not enough energy then the solid doesn’t dissolve i.e. the solid is insoluble.Some covalent compounds also dissolve in water.These compounds must also have polar covalent bonding.
166 State SymbolsState symbols are used in order to show what state a substance is in, suffixes are used;Elements/substances that are solids are often given the suffix (s)e.g. Ca (s) or Calcium (s)Elements/substances that are liquids are often given the suffix (l)e.g. Hg (l) or Mercury (l)
167 Elements/substances that are gases are often given the suffix (g) e.g. Ar (g) or Argon (g)Elements/substances that are dissolved in water are often given the suffix (aq)e.g. Br2 (aq) or bromine (aq)
169 Chemical FormulaeChemical formula – gives elements involved in a compound and the number of each atom of an element in the compound.e.g. H2O: 2 hydrogen atoms and 1 oxygen atom per molecule.
170 Working Out Formulae – Using Valencies The chemical formula for a compound can always be worked out by considering the bonding. There is a shorter method which uses the combining powers (valency).Group12345678Valency
171 Formulae Rules N name S symbols V valency S swap C cancel out common factorF formula
172 Simple Formulae 1. Nitrogen hydride name nitrogen hydrogen symbols N H valencyswapcancel out common factor 1 3formula NH3
173 2. Silicon oxide name silicon oxygen symbols Si O valency 4 2 swap 2 4 cancel out common factor 1 2formula SiO2
174 name phosphorous iodine symbols P I valency 3 1 swap 1 3 formula PI3 3. Phosphorous iodidename phosphorous iodinesymbols P Ivalencyswapcancel out common factor 1 3formula PI3Answer Questions Textbook pg 57 Q1
175 Formulae from Prefixes If a formulae has prefixes in the name, you do not use formulae rules to work out the formula.Prefixes: Mono – 1Di – 2Tri – 3Tetra – 4Penta – 5Hexa - 6
177 Transition Metal Valencies using Roman Numerals The block of metals in the centre of the Periodic Table are the Transition Metals.Transition metals can have more than one valency.Their valency is shown by using Roman Numerals, in the name of the compound.E.g. Iron (III) oxide contains iron with a valency of 3.
179 1. Iron (III) chloride name iron chlorine symbols Fe Cl valency 3 1 swapcancel out common factorformula FeCl3
180 2. Zinc (II) oxide name zinc oxygen symbols Zn O valency 2 2 swap 2 2 cancel out common factorformula ZnOAnswer Questions Textbook pg 61 Q5
181 Compounds ending in ‘ate’ or ‘ite’ These compounds contain 2 elements and oxygen.Magnesium sulphateLithium carbonateSodium hydroxide special caseSulphateCarbonateHydroxideNitrate}These substances are known as COMPLEX ions which have more than one element present.
182 Their formula and VALENCY can be found on databook. Charge = Valency
183 1. Sodium sulphate (pg data book) name sodium sulphate symbols Na SO4 valencyswapcancel out common factor 2 1formula Na2SO4
184 2. Magnesium nitrate (data book) name magnesium nitrate symbols Mg NO3 valencyswapcancel out common factor 1 2formula Mg(NO3)2N.B. Brackets are required here because there is more than one nitrate ion.
185 3. Ammonium carbonate (data book) name ammonium carbonate symbols NH4 CO3valencyswapcancel out common factorformula (NH4)2CO3N.B. Brackets are required here because there is more than one ammonium ion.
187 Revision of Ionic Compounds Ionic compounds contain oppositely charged ions.E.g. Sodium chloride Na+Cl-Magnesium sulphate Mg2-SO42-Ions are charged because they don’t have the same numbers of protons + electrons.
188 Ca2+ P3- Positive charge therefore more protons than electrons 20 protons (atomic number) 18 electronsNegative charge therefore less protons than electronsP3-15 protons (atomic number) 18 electrons
189 Forming ions Atom Ion Na Na+ 2,8,1 2,8 Al Al3+ 2,8,3 2,8 2,8, ,8Al Al3+2,8,3 2,8Metals ALWAYS lose outer electrons to obtain a full shell when changing to ions.
190 Atom IonF F-2, ,8S S2-2,8,6 2,8,8Non-metals (except H2) ALWAYS gain outer electrons to obtain a full shell when forming ions.
191 Valency = Charge Group number 1 2 3 4 5 6 7 Charge on ion 1+ 2+ 3+ / 3-2-1-Valency1234Valency = Charge
192 Ionic FormulaeThe ionic formulae of a compound is just the chemical formula with the charges on the ions shown.Chemical FormulaIonic FormulaNaClNa+Cl-MgOMg2+O2-CaFCa2+(F-)2
193 Working out Ionic Formulae 1. Magnesium oxidename magnesium oxygensymbols of ions Mg2+ O2-valencyswapcancel out common factor 1 1formula Mg2+O2-N.B. no brackets required as only 1 of each ion.
194 name potassium fluoride symbols of ions K+ F- valency 1 1 swap 1 1 2. Potassium flouridename potassium fluoridesymbols of ions K+ F-valencyswapcancel out common factor 1 1formula K+F-N.B. no brackets required as only 1 of each ion.
195 3. Aluminium oxide name aluminium oxygen symbols of ions Al3+ O2- valencyswapcancel out common factor 2 3formula (Al3+)2(O2-)3N.B. Brackets are required here as there are more than 1 of each ion.
196 3. Copper (II) chloride name copper chloride symbols of ions Cu2+ Cl- valencyswapcancel out common factorformula Cu2+(Cl-)2N.B. Brackets are required here as there are more than 1 chloride ion.
197 Group Ions Ionic Formulae 1. Lithium carbonate (pg4 data book)name lithium carbonatesymbols of ions Li+ CO32-valencyswapcancel out common factor 2 1formula (Li+)2CO32-N.B. Brackets are required here as there is more than 1 lithium ion.
198 name ammonium sulphate symbols of ions NH4+ SO42- valency 1 2 swap 2 1 Answer Questions Textbook pg 63 Qs2. Ammonium sulphate (pg4 data book)name ammonium sulphatesymbols of ions NH SO42-valencyswapcancel out common factor 2 1formula (NH4+)2SO42-N.B. Brackets are required here as there is more than 1 ammonium ion.
199 Word equations Reactants Products We use word equations to describe what is happening in a chemical reaction.Reactants ProductsAlways shown on left hand side- These are the starting materials for the reaction.Always shown on right hand side- These are the new substances formed in the reaction.Changes into
200 Burning of carbon with oxygen: carbon + oxygen carbon dioxide2. Magnesium reacting with chlorine gas:magnesium + chloride magnesium chloride3. Iron reacting with oxygen to produce iron oxideIron + oxygen iron oxide
201 1. Write word equations for the reaction between a) magnesium + oxygenb) sodium and chlorineAnswermagnesium + oxygen magnesium oxideSodium + chlorine sodium chloride
202 Formula EquationsThis is when we write the chemical formula for the substances.e.g.1. potassium hydroxide reacts with nitric acid to form potassium nitrate and water.This can be written asPotassium hyroxide + nitric acid potassium nitrate + waterKOH HNO3 KNO3 + H2O
203 2. Calcium hydroxide reacts with hydrochloric acid to produce calcium chloride and water. This can be written as:Calcium hydroxide+ hydrochloric acid calcium chloride + waterCa(OH) HCl CaCl H2O
204 Chemical Formula You Must Know! Name of diatomic elementFormulaHydrogenH2NitrogenN2OxygenO2FluorineF2ChlorineCl2BromineBr2IodineI2
205 Chemical Formula You Must Know! Name of CompoundFormulaWaterH2OCarbon dioxideCO2Hydrochloric acidHClSulphuric acidH2SO4Nitric acidHNO3Sodium hydroxideNaOHAmmoniaNH3
206 Identifying atoms Compound Element No of atoms Salt (NaCl) Sodium 1 ChlorineCarbon dioxide (CO2)CarbonOxygenWater (H2O)HydrogenMethane (CH4)Hydrogen sulphide (H2S)SulphurCalcium carbonate (CaCO3)Calcium
207 Identifying atoms Compound Element No of atoms Salt (NaCl) Sodium 1 ChlorineCarbon dioxide (CO2)CarbonOxygen2Water (H2O)HydrogenMethane (CH4)Hydrogen sulphide (H2S)SulphurCalcium carbonate (CaCO3)Calcium
208 Identifying atoms Compound Element No of atoms Salt (NaCl) Sodium 1 ChlorineCarbon dioxide (CO2)CarbonOxygen2Water (H2O)HydrogenMethane (CH4)Hydrogen sulphide (H2S)SulphurCalcium carbonate (CaCO3)Calcium
209 Identifying atoms Compound Element No of atoms Salt (NaCl) Sodium 1 ChlorineCarbon dioxide (CO2)CarbonOxygen2Water (H2O)HydrogenMethane (CH4)4Hydrogen sulphide (H2S)SulphurCalcium carbonate (CaCO3)Calcium
210 Identifying atoms Compound Element No of atoms Salt (NaCl) Sodium 1 ChlorineCarbon dioxide (CO2)CarbonOxygen2Water (H2O)HydrogenMethane (CH4)4Hydrogen sulphide (H2S)SulphurCalcium carbonate (CaCO3)Calcium
211 Identifying atoms Compound Element No of atoms Salt (NaCl) Sodium 1 ChlorineCarbon dioxide (CO2)CarbonOxygen2Water (H2O)HydrogenMethane (CH4)4Hydrogen sulphide (H2S)SulphurCalcium carbonate (CaCO3)Calcium3
212 Balancing Formula Equations Three things are balanced in a chemical equation:1. Atoms2. Mass3. Charge
213 When hydrogen burns in oxygen, water is formed When hydrogen burns in oxygen, water is formed. The formula equation for this reaction is: H2 + O2 H2O This equation is not balanced. The same amount of chemicals must be present on both sides of the reaction because atoms cannot be created or destroyed.
214 H2 + O2 H2OThere are more oxygen atoms on the left hand side than on the right hand side.
215 Steps to balance an equation Putting a number in front of formulae will multiply the number of atoms after it.e.g H2 + O2 H2OLHS RHS2 H atoms 4 H atoms2 O atoms 2 O atoms2. We need to fix the LHS now. Do this by putting a 2 in front on H on the LHS.H2 + O2 2H2O4 H atoms 4 H atoms22
220 One mole of a substance is equal to the formula mass expressed in grams. It is also called the gram formula mass (GFM).In the previous example for ammonium phosphate, the formula mass was calculated to be 149. This means that one mole of ammonium phosphate has the mass of 149g.
221 m n FM The units for the mole is mol. When working out calculations involving formula masses and moles, you can use the triangle below to convert from mass to moles.mnFM
222 m n FM Rearrange the triangle as follows: m = n x FM n = m FM = m FM n Here n= no. of moles m= mass FM= Formula massRearrange the triangle as follows:m = n x FMn = m FM = mFM n
223 Example 1What is the mass of 2 moles of hydrogen chloride? STEP 1: write the chemical formula. Symbols : H Cl Valency : 1 1 Cross over valencies : 1 1 Simplest ratio : 1 1 Formula : HCl
224 STEP 2: calculate the gram formula mass STEP 2: calculate the gram formula mass. 1 x H = 1 x 1 = 1 1 x Cl = 1 x 35.5 = 35.5 So, Gram Formula mass = 36.5g The formula mass of the compound hydrogen chloride is This means that one mole of hydrogen chloride has a mass of 36.5g.
225 STEP 3: Rearrange triangle to calculate the mass. m = n x FM1 mole NaCl 36.5g2 x 36.5 = 73g
226 Example 2Q. How many moles of copper (ll) carbonate are there in 494g of the substance? A. STEP 1: write the chemical formula. Symbols : Cu2+ CO32- Valency : 2 2 Cross over valencies : 1 1 Simplest ratio : 1 1 Formula : CuCO3
227 STEP 2: Calculate the GFM CuCO3 1 x Cu= 1 x 63. 5 = 63 STEP 2: Calculate the GFM CuCO3 1 x Cu= 1 x 63.5 = x C = 1 x 12 = 12 3 x O= 3 x 16 = 48 So, Gram Formula Mass = 123.5g
228 STEP 3: Rearrange triangle for n. Use formula n= m/FM So, n = m = = 4 molesFMTherefore, 494g contains 4 moles of copper (ll) carbonate.mnFM
229 Example 3 (shortened answer) Q. Calculate the number of moles in 12.05g of magnesium sulphate.Chemical Formula MgSO4MgSO41xMg = 1 x 24.5 = 24.51xS = 1 x 32 = 324xO = 4 x 16 = 64GFM =
230 mnFMn = m = = molesFMTherefore, there are 0.1 moles in 12.05g in magnesium sulphate.
231 Mole Ratios 2 2 CH4 + O2 CO2 + H2O We can use the mole ratios from balanced equations to calculate:Mass of REACTANT required for a reaction.Mass of PRODUCT formed.221 mole2 moles
232 Mole Ratio Calculations Q. What mass of oxygen is needed to react with 2.4g of carbon.A. C O2 CO2C : O21 mole : 1 mole12g : 32g1g : 32/122.4g : 32/12 x 2.4 = 6.4g
233 Q. What mass of carbon dioxde is produced when 0 Q. What mass of carbon dioxde is produced when 0.5 moles of propane is burned.A. C3H O2 3CO H2OC3H8 : CO21 mole : 3 moles1 mole : 132g0.5 moles : 0.5 x 132= gCO2 = 44g3CO2 = 132g
234 Q. What mass of hydrogen is burned to produce 100g of water. A. H ½ O2 H2O1 mole H2 : 1 mole H2O1 mole H2O : 1 mole H218g : 2g1g : 2/18g100g : /18 x 100= gH2 = 2gH2O = 18g
236 The pH ScaleThe pH scale is a continuous range of numbers from 1 to 14, which indicate the acidity or alkalinity of solutions.Acids have a pH of less than 7 (pH<7)Alkalis have a pH of more than 7 (pH>7)Pure water and neutral solutions have a pH equal to 7 (pH=7)
237 The pH of a solution can be measured using universal indicator or pH paper. The pH of a solid cannot be measured – it must first be dissolved in water or the pH paper dampened.
238 Non-Metal OxidesWhen a non-metal elements burns in oxygen the non-metal oxide is formed.Soluble non-metal oxides will dissolve in water to produce acidic solutions.e.g. CO2, NO2, SO2, SO3.Non-metal oxides which are insoluble, will not affect the pH.
239 Metal OxidesWhen metal elements burn in oxygen, the metal oxide is formed.e.g.Soluble metal oxides will dissolve in water to form the metal hydroxide.Metal oxides or hydroxides, which dissolve in water produce alkaline solutions.
240 Not all metal oxides are soluble. A general rule is that the oxides of the Group 1 and Group 2 metals produce alkaline solutions with water.Ammonia gas (NH3), is soluble in water and will dissolve to produce an alkali. Insoluble metal oxides/hydroxides will not affect the pH of water.
241 AcidsAcids are compounds which dissolve in water to form solutions which have a pH less than 7.The table below shows the most commonly used acids both in the lab and the home.Chemical NameFormulapHUsesHydrochloric acidHCl1-3Common lab acidNitric acidHNO3Sulphuric acidH2SO4VinegarN/A4-6Common household acidLemon juiceCar battery acid
242 Acid solutions are made by adding a substance to water which will lower its pH. The substance added could be a solid, a liquid or a gas.H+(aq) and Cl-(aq)H+(aq) and SO42-(aq)H+(aq) and HCOO-(aq)
243 The substance added is made up of molecules – atoms of non-metal elements joined by covalent bonds. When the substance is added to water the covalent bonds break to form ions which become attached to water molecules.An acid solution is one which contains H+(aq) ions
244 Acid solutions are made by adding a substance to water which will lower its pH. The substance added could be a solid, a liquid or a gas.Ions involvedH+(aq) and Cl-(aq)H+(aq) and SO42-(aq)H+(aq) and HCOO-(aq)
245 When the substance is added to water the covalent bonds break to form ions which become attached to water molecules.An acid solution is one which contains H+(aq) ions
246 Electrolysis of AcidsAcids can be electrolysed and the products collected.REMEMBER: electrolysis is the breaking up of an ionic compound in solution or the molten state using electricity.
247 All acids contain the H+ ion. When electricity is passed through a solution of an acid the positively charged hydrogen ions are attracted to the negative electrode where they gain electrons to form hydrogen gas.
248 AlkalisAlkalis are compounds which dissolve in water to form solutions which have a pH greater than 7.Chemical NameFormulapHUsesSodium hydroxideNaOH11-14Common lab alkaliPotassium hydroxideKOHCalcium hydroxideCa(OH)2Cleaning fluidsN/A8-14Common household alkaliToothpaste8-11Indigestion tablets
249 Water Water is a covalent compound. Covalent compounds do not conduct electricity.But we know that water can act as a conductorIt is believed that in pure water, and all aqueous solutions, a reversible reaction takes place.
250 In water and aqueous solutions there is an equilibrium between hydrogen ions (H+) and hydroxide ions (OH-) and water molecules.However, there are more water molecules than there are ions and so water conducts only slightly.Pure water contains an equal concentration of hydrogen and hydroxide ions.H2O(l) H+(aq) + OH-(aq)
251 To summarise:In water and any neutral solution, the concentration of H+ ions and OH- ions is equal and this gives a pH = 7 (neutral).In an acid solution the concentration of hydrogen ions (H+(aq)) is greater than the concentration of hydroxide ions (OH-(aq)).In an alkaline solution the concentration of hydroxide ions (OH-(aq)) is greater than the concentration of hydrogen ions (H+(aq)).
252 In water and aqueous solutions there is an equilibrium between hydrogen ions (H+) and hydroxide ions (OH-) and water molecules.However, there are more water molecules than there are ions and so water conducts only slightly.Pure water contains an equal concentration of hydrogen and hydroxide ions.H2O(l) H+(aq) + OH-(aq)
253 To summarise:In water and any neutral solution, the concentration of H+ ions and OH- ions is equal and this gives a pH = 7 (neutral).In an acid solution the concentration of hydrogen ions (H+(aq)) is greater than the concentration of hydroxide ions (OH-(aq)).In an alkaline solution the concentration of hydroxide ions (OH-(aq)) is greater than the concentration of hydrogen ions (H+(aq)).
254 Diluting acids and alkalis Adding water to an acid increases the pH of the solution towards 7, making it less acidic by decreasing the H+(aq) ions concentration. (The acidity decreases and the pH value increases).Adding water to an alkali decreases the pH of the solution towards 7, making it less alkaline by decreasing the OH-(aq) ions concentration. (The alkalinity decreases and the pH value decreases).
255 Strength and Concentration Strength and concentration are terms that are often used incorrectly. They do not have the same meaning.Strength is used to describe the extent of dissociation into ions.Concentration is used to describe the number of moles of solute in a certain volume of solution.
256 ConcentrationThe concentration of a solution is the number of moles of solute present in one litre of solution i.e. moles per litre (mol l-1).A 1 mol l-1 solution is made by dissolving 1 mole of the substance in 1 litre of solution.
257 n C V so Number of moles of solute Volume of solution in litresConcentration of solution in mol l-1Number of moles of soluteso
258 Sometimes, before calculating the concentration, there is a need to convert grams into moles. GFMGram formula massNumber of moles of soluteMass in grams
259 Example calculation using Concentration Triangle Q. Calculate the concentration of a 500cm3 solution that contains 0.1 moles.A. V= 500cm3 = 0.5ln= 0.1 molesc= ?From trianglec= n/v = 0.1 / 0.5= 0.2 mol l-1 solutionTherefore the concentration is 0.2 mol l-1.nCV
260 Example calculation using both triangles Q. Calculate the mass of sodium hydroxide required to prepare 2 litres of mol l-1 solution.A. Look at the information we’re given first:V= 2 litres = 2lc= mol l-1n= ?First we will calculate nn= c x v = x 2 = 0.03 moles
261 Now we know the number of mole, we can use the other triangle n= 0.03 molesFM= NaOH = = 40m= ?m= n x FM = 0.03 x 40 = 1.2g Therefore the mass of sodium hydroxide is 1.2gmnGFM
263 NeutralisationWhen you add a base to an acid, the acid is slowly cancelled out or neutralised.The reaction of acids with alkalis is an example of a neutralisation.Neutralisation: reaction that moves the pH of an acid toward 7
264 Bases Bases: metal oxides, metal hydroxides and metal carbonates. Any substance which neutralises an acid by reacting with the hydrogen ions (H+) of the acid to form water.Bases: metal oxides, metal hydroxides and metal carbonates.Neutralisation will move the pH of an acid up towards 7 and the pH of an alkali down toward 7.
265 We will look at 4 different neutralisation reactions;
266 Reactions of Acids with Alkalis When an acid is neutralised by an alkali, a salt and water are formed.Remember: an alkali is a soluble metal oxideThe general word equation to represent this reaction is;acid + alkali salt + water
267 Nitric + sodium sodium + water acid hydroxide nitrate HNO NaOH NaNO3 + H2OIn the reaction of an acid with an alkali the hydrogen ions and hydroxide ions form water.
268 Reactions of Acids with Metal Oxides When a metal is burned the metal oxide is formed. If that metal oxide dissolves in water it is called an alkali.Metal oxides which do not dissolve in water can still neutralise an acid.Acids react with metal oxides to form a salt and water.
269 Acid + metal oxide salt + water In the reaction of an acid with a metal oxide the hydrogen ions and the oxide ions form water.
270 Reaction of Acids and Metal Carbonates When an acid reacts with a metal carbonate a salt, water and carbon dioxide are formed.
271 Test for CO2: Limewater turns milky if carbon dioxide if present. The H+ ions from the acid react with the CO32- from the metal carbonate to form CO2 and H2O.Test for CO2: Limewater turns milky if carbon dioxide if present.
272 Reactions of Acids and Metals Most metals react with acids to form a salt and hydrogen gas.The reaction that occurs is a neutralisation reaction.Copper, mercury, gold, silver and platinum do not react with acids.
273 In the reaction between a metal and an acid, the hydrogen ions of the acid from hydrogen molecules. Test for H2: Hydrogen burns with a pop!
274 Acid Rain Fossil fuels can burn to produce sulphur dioxide (SO2). Nitrogen dioxide (NO2) is produced by the sparking of air in car engine.Both SO2 and NO2 dissolve in water in the atmosphere to produce acid rain.
275 Acid rain damages… Buildings made from carbonate rock by eroding them. Structures made of iron and steel by making them corrode.Plant life by making the soil too acidic.Animal life by making the water in ponds and lakes too acidic.
276 Volumetric Titrations The concentration of acids/alkalis can be calculated from the results of volumetric titrations.
277 Pipette Burette Acid solution e.g. dilute hydrochloric acid (HCl) Conical flask with alkali solution e.g. sodium hydroxide (NaOH) + universal indicatorWhite tile
278 Pacid x Vacid x Cacid = Palkali x Valkali x Calkali P= power V= volume in litres C= concentrationPower of an acid is the number of H+ ions.For HCl, p=1For H2SO4, p=2For HNO3, p=1Power of an alkali is the number of OH- ions.For NaOH, p=1For Ca(OH)2, p=2For Al(OH)3, p=3
279 Example 1 Pacid x Vacid x Cacid = Palkali x Valkali x Calkali In a titration 10cm3 of sodium hydroxide solution with a concentration of 0.2 mol l-1 was neutralised by 25 cm3 of dilute hydrochloric acid.Calculate the concentration of the acid solution in moles per litre.Pacid x Vacid x Cacid = Palkali x Valkali x Calkali1x x Cacid = 1 x 0.01x 0.21x x Cacid = 1 x 0.01x 0.20.025 x Cacid = 0.002Cacid = / 0.025Cacid = mol l-1
280 Example 2 Pacid x Vacid x Cacid = Palkali x Valkali x Calkali What volume of 2M sodium hydroxide will be required to neutralise 40cm3 of 2M sulphuric acid?Pacid x Vacid x Cacid = Palkali x Valkali x Calkali2 x 0.04 x 2 = 1 x Valkali x 20.16 = Valkali x 2Valkali = 0.16 / 2Valkali = 0.08 litresValkali = 80 cm3
281 Example 3 Pacid x Vacid x Cacid = Palkali x Valkali x Calkali What volume of 1M sulphuric acid will be needed to neutralise 2 litres of 0.1M potassium hydroxide?Pacid x Vacid x Cacid = Palkali x Valkali x Calkali2 x Vacid x 1 = 1 x 2 x 0.1Vacid x 2 = 0.2Valkali = 0.2 / 2Valkali = 0.1 lValkali = 100 cm3
282 Everyday Examples of Neutralisation Taking antacid tablet to treat acid indigestionUsing lime (CaO) to reduce acidity in soil and lochs.
284 SaltsSalts are ionic compounds which are produced in neutralisation reactions.They contain a positive ion, which comes from the acid (H+) and a negative ion, which comes from the neutraliser.Salt: a substance in which the hydrogen ion of an acid has been replaced by a metal ion (or the ammonium ion).
285 Naming SaltsFirst part of the name comes from the metal in the alkali.Second part of the name comes from the acid.Hydrochloric acid always forms a chloride salt.Sulphuric acid always forms a sulphate salt.Nitric acid always forms a nitrate salt.
286 Acid Alkali Salt formed hydrochloric acidsodium hydroxidesulphuric acidcalcium hydroxidenitric acidammonium hydroxideSodium chlorideCalcium sulphateAmmonium nitrate
287 Spectator IonsThe neutralisation of hydrochloric acid by sodium hydroxide can be shown as follows;The Na+(aq) and Cl-(aq) ions are not changed.We call these ions spectator ions as they do not take part in the reaction.
288 If we remove the spectator ions from the equation, the ionic equation for the reaction is; In the reaction of an acid with an alkali the hydrogen ions and hydroxide ions form water.
289 More Spectator Ions Omitting spectator ions... The spectator ions are SO42-(aq) and Mg2+
290 Making Soluble Salts Using Soluble Bases Soluble salts can be prepared by reacting acids with alkalis or bases.When an acid is neutralised by a soluble base (alkali) a salt and water are produced.An indicator is used to show when the acid has been neutralised.E.g. Sodium chloride reacts with hydrochloric acid to produce sodium chloride (soluble salt) and water.
291 Using Metals and Insoluble Bases It is easy to make soluble salts from acids using metals.e.g. magnesium chloride (soluble salt) can be made using hydrochloric acid and magnesium metal powder.Add metal powder to acid until no more reacts.Filter off unreacted metal powderEvaporate off the water to a small volume and then allow crystals to form naturally
292 The same filtration procedure can be used as above when producing a soluble salt using Acid + MetalAcid + Metal oxideAcid + Metal carbonate
293 Preparation of Insoluble Salts by Precipitation Insoluble salts can be prepared by precipitation reactions.Precipitation Reaction: the reaction of two solutions to form an insoluble product called a precipitate.
294 For example, silver iodide (insoluble salt) can be prepared by the following method; dissolve a soluble silver salt in waterdissolve a soluble iodide salt in watermix the two solutions together and a solid should formfilter the solution – the solid will be retained in the filter paper and the solutionwash the solid with water and allow to dry
295 The reaction taking place in this experiment is: The sodium nitrate formed is a soluble salt and so stays in solution.omitting spectator ionsshows the ions which actually react