6pH pH is a continuous scale of acidity which runs from below 0 to above 14.Acids have a pH of less than 7Alkalis have a pH of more than 7.Pure water, and other neutral solutions have a pH equal to 7.
7Oxides Non-metal oxides which dissolve in water, give acid solutions. Metal oxides and hydroxides, which dissolve in water, give alkaline solutions.Ammonia dissolves in water to produce an alkali.Acids and alkalis are in common use at home or in the laboratory.
8Ions Acids and alkalis both contain ions. Acids contain the H+(aq) ion Alkalis contain the OH-(aq) ionIn water the concentration of ions is very low.
9H+ and OH- ionsWater, and other neutral solutions, contain equal numbers of H+ and OH- ions.Acidic solutions contain more H+ ions than OH- ions .Alkalis contain more OH- ions than H+ ions.
10Dilution When an acid is diluted its acidity decreases and its pH increases.When an alkali is diluted its alkalinity decreases and its pH decreases.
11 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.
12Equilibrium There is an equilibrium in water: H2O(l) H+(aq) + OH-(aq)This means that the concentrations of reactants and products are always the same (but not equal).
13ConcentrationThe concentration of a solution is measured in moles per litre (mol l-1)A 1 mol l-1 solution means 1 mole is divided in each litre of solution.
14To connect the concentration of a solution to the number of moles and concentration use the triangle opposite.c = concentration (m/l)n = number of molesv = volume (l)ncv
15Strong and Weak AcidsA strong acid is one which completely dissociates in water:HCl(aq) H+(aq) + Cl-(aq)A weak acid is one which partially dissociates in water:CH3CO2H(aq)H+(aq) + CH3CO2-(aq)
25Neutralisation Neutralisation is the reaction of an acid with a base. Metal oxides, hydroxides and carbonates are all examples of bases.Bases which dissolve in water are called alkalis.
26During a neutralisation reaction then the pH of the acid involved moves up nearer to 7. During a neutralisation reaction then the pH of the alkali involved moves down nearer to 7.
27In the reaction of an acid and an alkali the hydrogen ions and hydroxide ions form water. H+ + OH- H2OHCl + NaOH NaCl + H2O
28In the reaction of an acid and a metal oxide the hydrogen ions and oxide ions form water. 2H+ + O2- H2OH2SO4 + CuO CuSO4 + H2O
29In the reaction of an acid and a metal carbonate the hydrogen ions and carbonate ions form carbon dioxide and water.2H+ + CO32- CO2 + H2O2HNO3 + CaCO3 Ca(NO3)2 + CO2 + H2O
30Examples of neutralisation involve adding lime to soil or water to reduce its aciditytreating acid indigestion with magnesium hydroxidethe reaction of H+ (aq) to form water.
31Acids and metalsAcids react with some metals to release hydrogen. The hydrogen ions in the the acid form hydrogen molecules.The test for hydrogen is that it burns with a “pop”.
32Acid Rain Sulphur dioxide is produced by the burning of fossil fuels. Nitrogen dioxide is produced by the sparking of air in car engines.Both these gases dissolve in water in the atmosphere to produce acid rain.
33Acid rain has damaging effects on buildings made from carbonate rock, structures made of iron and steel, soils and plant and animal life.
34Acids 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
35Remember 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
36Remember solutions? n c v To connect volume, concentration and the number of moles in a solution use the triangle opposite.c = concentration (m/l)n = number of molesv = volume (l)ncv
37Working 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
38SaltsA salt is the compound formed when the hydrogen ion of an acid is replaced by a metal ion (or an ammonium ion).Salts are formed by the reactions of acids with bases or metals.
39Salts Acid Formula Salt Ion hydrochloric HCl chloride Cl- sulphuric H2SO4sulphateSO42-nitricHNO3nitrateNO3-carbonicH2CO3carbonateCO32-
40Making salts There are three main methods of making salts. Which method to use depends upon solubilities.Those solubilities can be found in the Data Booklet.
41TitrationTitration is experiment where alkali is measured out using a pipette.Indicator is added.Acid is added from a burette, until the indicator changes colour.The water can then be evaporated to get the salt.
42Neutralisation and Evaporation. An easy way to prepare salts is to react an acid with an insoluble metal oxide or metal carbonate.The excess can be removed from the reaction mixture by filtration.The solution is now evaporated to separate the salt.
43PrecipitationPrecipitation is the reaction in which two solutions react to form an insoluble salt.The salt can then be filtered out and dried.
44How to make a salt. Is salt soluble? No Yes Is base soluble? Titration Neutralisation andEvaporationPrecipitation
45Ionic equations Normally when we write equations we do so like this: HNO3 + NaOH NaNO3 + H2O
46We can change to write the equations using ions. H+ + NO Na+ + OH- Na+ + NO H2O
47If we look closely we can see that some ions appear unchanged on both sides. We call these spectator ions.H+ + NO Na+ + OH- Na+ + NO H2O
48We can rewrite the equation, without the spectator ions. This shows the ions that participate in the reaction.H+ + OH- H2O
49Salt Preparation Click here to repeat Salt Preparation Click here to return to the MenuClick here to End.
51CellsChemical changes can bring about the production of electrical energy.The current measures how many electrons flow in the cell each second.The voltage measures how hard those electrons are pushed by the chemicals used.
52A 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.
53The Electrochemical Series We can measure the voltage produced by connecting different metals together to form a simple cell.V
54The Electrochemical Series The voltage between different pairs of metals varies.By listing the metals according to the voltage they produce we get the electrochemical series.
55The electrochemical series shows a “league table”. KNaCaMgAlZnFeSnPbCuHgAgAuThe electrochemical series shows a “league table”.The substances at the top are those best at pushing electrons.
56DisplacementAny metal, in an Electrochemical Series, will displace a metal lower down in the electrochemical series it from one of its compounds.
57Iron will displace copper from copper(II) sulphate solution. KNaAlZnFeSnPbCu
58Iron can displace copper from copper(II) sulphate solution. KNaAlZnFeSnPbCu
64Most displacement reactions will give some visible signs. If zinc reacts with copper(II) sulphate solution:The silver colour of zinc will be replaced by the brown colour of copper.The blue colour of the solution will fade as Cu2+ changes to Cu.
65HydrogenBy considering the metals with which acids will react it is possible to place hydrogen in the Electrochemical Series.
67Metals which react with acid, releasing hydrogen KNaCaMgAlZnFeSnPbCuHgAgAuMetals which react with acid, releasing hydrogen
68Metals which react with acid, releasing hydrogen KNaCaMgAlZnFeSnPbCuHgAgAuMetals which react with acid, releasing hydrogenMetals which donot react with acid.
69Metals which react with acid, releasing hydrogen KNaCaMgAlZnFeSnPbCuHgAgAuMetals which react with acid, releasing hydrogenHMetals which donot react with acid.
70More about cellsElectricity can be produced in a cell by connecting two different metals in solutions of their metal ions.The next slides show how copper and zinc half-cells can be made to make a cell.
71Put a copper rodin a solution containingcopper ions.
72Put a zinc rodin a solution containingzinc ions.
73Connect the two metal rods through a voltmeter There is no reading because the circuit is not complete.V
74Add an ion bridge (also called a salt bridge) Add an ion bridge (also called a salt bridge). This is to allow the movement of ions to complete the circuit.V
75Electricity can be produced in a cell when at least one of the half-cells does not involve metal atoms.Electrons flow through the meter from the substance higher in the electrochemical series to the one lower in the electrochemical series.
76OxidationOxidation is the loss of electrons by a reactant in a chemical reaction.When a metal reacts to form a compound it is an example of oxidation.
77Reduction Reduction is the gain of electrons by a reactant in a chemical reaction.When a metal compound reacts to form a metal it is an example of reduction.
78Oxidation and Reduction OIL RIGOxidation Is Loss of electrons Reduction Is Gain of electronsIn a redox reaction oxidation and reduction go on together.
79RedoxIon-electron equations can be written for oxidation and reduction reactions.These equations can be combined to produce redox equations.
80Magnesium can be oxidised. Mg Mg e oxidationHydrogen ions can be reduced.2H e H2 reductionOverall2H+ + Mg H2 + Mg2+ redox
81In the displacement of copper by zinc the reaction is: CuSO4 + Zn ZnSO4 + CuThis can be written as:Cu e Cu reductionZn Zn e oxidationOverallCu Zn Cu + Zn2+ redox
82Redox and Electrolysis Electrons are released at the negative electrode so reduction takes place there.Electrons are taken in at the positive electrode so oxidation takes place there.
83Common 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.
84Reactions 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.
85Recovering Metals Ores are naturally occurring compounds of a metal. Less active metals, such as silver and gold, do not react well and so occur uncombined in the earth's crust.They were the first metals discovered.
86The extraction of a metal from its ore is an example of reduction. Oxides of reactive metals are most difficult to extract while oxides of unreactive metals are most easily extracted.
87Very unreactive metals , such as gold, silver and mercury, can be obtained from their oxides by heat alone.
88Other 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).
89iron oreIron is produced from iron ore in the blast furnace.iron
90The Blast Furnace The main reactions are: The 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