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IGCSE CHEMISTRY LESSON 2 Section 1 Principles of Chemistry a) b) c) d) e) f) g) h) i) States of matter Atoms Atomic structure Relative formula mass Chemical formulae and chemical equations Ionic compounds Covalent substances Metallic crystals Electrolysis Lesson 2 a) Relative formula mass b) Chemical formulae and Chemical equations 1.15 calculate relative formula masses (Mr) from relative atomic masses (Ar) 1.16 understand the use of the term mole to represent the amount of substance 1.17 carry out mole calculations using relative atomic mass (Ar) and relative formula mass (Mr). What is RELATIVE ATOMIC MASS? By definition: “mass of a particular atom compared to the mass of an atom of hydrogen” Relative atomic mass is also the same as the mass number – it’s that simple! Relative Atomic Mass and Atomic Number Relative Atomic Mass = total number of protons and neutrons 23 ATOMIC NUMBER 11 = number of protons (also electrons) Na Relative atomic mass is always bigger than the atomic number Look up the Mass Numbers of the following elements: Oxygen Carbon Iron Lead Iodine Helium Nitrogen Copper Calcium Tin Look up the Mass Numbers of the following elements: Oxygen 16 Carbon 12 Iron 56 Lead 207 Iodine 127 Helium 4 Nitrogen 14 Copper 63.5 Calcium 40 Tin 119 When atoms join together to form a compound (eg. Magnesium oxide) we can calculate the RELATIVE FORMULA MASS: When atoms join together to form a compound (eg. Magnesium oxide) we can calculate the RELATIVE FORMULA MASS: Magnesium oxide MgO 24 + 16 = 40 Chemical formulae MgO Chemical formulae MgO 1 Mg, 1 O Chemical formulae MgO 1 Mg, 1 O H2SO4 Chemical formulae MgO H2SO4 1 Mg, 1 O 2H, 1 S, 4 O Chemical formulae MgO H2SO4 1 Mg, 1 O 2H, 1 S, 4 O Ca(OH)2 Chemical formulae MgO H2SO4 1 Mg, 1 O 2H, 1 S, 4 O Ca(OH)2 1 Ca, 2 O, 2 H Chemical formulae MgO H2SO4 1 Mg, 1 O 2H, 1 S, 4 O Ca(OH)2 2Na2CO3 1 Ca, 2 O, 2 H Chemical formulae MgO H2SO4 1 Mg, 1 O 2H, 1 S, 4 O Ca(OH)2 2Na2CO3 1 Ca, 2 O, 2 H 4 Na, 2 C, 6 O When atoms join together to form a compound (eg. Magnesium oxide) we can calculate the RELATIVE FORMULA MASS: Magnesium oxide MgO 24 + 16 = 40 Now calculate the Relative Formula Mass for the following compounds: Now calculate the Relative Formula Mass for the following compounds: Compound Formula Calcium oxide CaO Sulphuric acid H2SO4 Sodium nitrate NaNO3 Aluminium hydroxide Al(OH)3 Lead carbonate PbCO3 Relative formula mass Now calculate the Relative Formula Mass for the following compounds: Compound Formula Relative formula mass Calcium oxide CaO 40 + 16 = 56 Sulphuric acid H2SO4 2 + 32 + 64 = 98 Sodium nitrate NaNO3 23 + 14 + 48 = 85 Aluminium hydroxide Al(OH)3 27 + 48 + 3 = 78 Lead carbonate PbCO3 207 + 12 + 48 = 267 Relative Atomic Mass Be aware! Ar Relative Atomic Mass Be aware! Ar Relative Formula Mass Mr The mole The mole You may think that the mole is a very blind animal that lives underground The mole The mole is also a measure widely used in chemistry The mole One mole is the relative formula mass (Mr) of a compound, or relative atomic mass (Ar) of an element, expressed in grams The mole For example, the Ar of carbon is 12. The mole For example, the Ar of carbon is 12. So the mass of one mole of carbon is 12g. The mole For example, the Ar of carbon is 12. So the mass of one mole of carbon is 12g. How simple is that? The mole What’s the mass of one mole of lead? The mole What’s the mass of one mole of lead? Ar of lead (Pb) = 207 So that mass of one mole of lead is 207g The mole Let’s get a little more clever now and calculate the mass of moles from the relative formula mass (Mr) Don’t panic! The mole For example, the Mr of sodium hydroxide: NaOH = 23 + 16 + 1 = 40 The mole For example, the Mr of sodium hydroxide: NaOH = 23 + 16 + 1 = 40 So the mass of one mole of sodium hydroxide is 40g The mole What’s the mass of one mole of calcium carbonate? The mole What’s the mass of one mole of calcium carbonate? Mr of CaCO3 = 40 + 12 + 48 = 100 The mole What’s the mass of one mole of calcium carbonate? Mr of CaCO3 = 40 + 12 + 48 = 100 So one mole of CaCO3 = 100g This isn’t rocket science! Important equation Steady as you go! Important equation Number of moles = mass used Mr Steady as you go! Important equation Number of moles = mass used Mr Eg how many moles are there in 20g of sodium hydroxide? Steady as you go! Important equation Number of moles = mass used Mr Eg how many moles are there in 20g of sodium hydroxide? Number of = moles = 0.5 20 40 Steady as you go! Important equation Number of moles = mass used Mr Eg how many moles are there in 20g of sodium hydroxide? Number of = moles 20 40 = 0.5 We could even re-arrange the equation Steady as you go! Number of moles = mass used Mr Mass used = number of x Mr moles Number of moles = mass used Mr Mass used = number of x Mr moles Eg. What’s the mass of 2 moles of calcium carbonate? Number of moles = mass used Mr Mass used = number of x Mr moles Eg. What’s the mass of 2 moles of calcium carbonate? Mass used = = 2 x 200g 100 The mole Lesson 2 a) Relative formula mass b) Chemical formulae and Chemical equations 1.18 write word equations and balanced chemical equations to represent the reactions studied in this specification 1.19 use the state symbols (s), (l), (g) and (aq) in chemical equations to represent solids, liquids, gases and aqueous solutions respectively 1.20 understand how the formulae of simple compounds can be obtained experimentally, including metal oxides, water and salts containing water of crystallisation 1.21 calculate empirical and molecular formulae from experimental data 1.22 calculate reacting masses using experimental data and chemical equations 1.23 carry out mole calculations using volumes and molar concentrations. Lesson 2 a) Relative formula mass b) Chemical formulae and Chemical equations 1.18 write word equations and balanced chemical equations to represent the reactions studied in this specification 1.19 use the state symbols (s), (l), (g) and (aq) in chemical equations to represent solids, liquids, gases and aqueous solutions respectively 1.20 understand how the formulae of simple compounds can be obtained experimentally, including metal oxides, water and salts containing water of crystallisation 1.21 calculate empirical and molecular formulae from experimental data 1.22 calculate reacting masses using experimental data and chemical equations 1.23 carry out mole calculations using volumes and molar concentrations. Using chemical symbols Using chemical symbols Each element is represented by a different symbol …… eg Fe for iron, Na for sodium, O for oxygen All of these symbols are in the PERIODIC TABLE Using chemical symbols Each element is represented by a different symbol …… eg Fe for iron, Na for sodium, O for oxygen All of these symbols are in the PERIODIC TABLE We can use these symbols to show molecules of compounds, and they can show us the ratio of the different elements which combine to form compounds Using chemical symbols Each element is represented by a different symbol …… eg Fe for iron, Na for sodium, O for oxygen All of these symbols are in the PERIODIC TABLE We can use these symbols to show molecules of compounds, and they can show us the ratio of the different elements which combine to form compounds Eg. H2O CO2 NH3 Using chemical symbols Let’s recap on what we covered earlier. Using chemical symbols Eg. Sodium hydroxide NaOH 1 atom Na: 1 atom oxygen: 1 atom hydrogen Using chemical symbols Eg. Sodium hydroxide NaOH 1 atom Na: 1 atom oxygen: 1 atom hydrogen Eg. Calcium carbonate CaCO3 1 atom Calcium, 1 atom carbon, 3 atoms oxygen Using chemical symbols Eg. Magnesium nitrate Mg(NO3)2 1 atom Magnesium, 2 atoms nitrogen, 6 atoms oxygen Using chemical symbols Eg. Magnesium nitrate Mg(NO3)2 1 atom Magnesium, 2 atoms nitrogen, 6 atoms oxygen Eg. Aluminium sulphate 3Al2(SO4)3 6 atoms aluminium, 9 atoms sulphur, 36 atoms oxygen Equations Equations REACTANTS PRODUCTS Equations REACTANTS Sodium + water PRODUCTS sodium + hydrogen hydroxide Equations REACTANTS Sodium Na PRODUCTS + water sodium + hydrogen hydroxide + NaOH + H 2O H2 Equations REACTANTS Sodium PRODUCTS + water sodium + hydrogen hydroxide Na + H 2O NaOH + H2 2Na + 2H2O 2NaOH + H2 Equations REACTANTS Sodium PRODUCTS + water sodium + hydrogen hydroxide Na + H 2O NaOH + H2 2Na + 2H2O 2NaOH + H2 2Na(s) + 2H2O(l) 2NaOH(aq) + H2(g) Equations You need to know your state symbols (s)= solid (l) = liquid (aq) = aqueous solution (g) = gas Equations You also need to be able to: • write word equations when required • recall formulae of simple covalent compounds • write down formulae for simple ionic compounds • interpret chemical formulae of molecules • interpret symbol equations including state symbols Simple covalent formulae Water H2O Carbon dioxide CO2 Ammonia NH3 Hydrogen H2 Oxygen O2 Nitrogen N2 Sulphur dioxide SO2 Methane CH4 Simple Ionic Formulae Sodium chloride NaCl Calcium chloride CaCl2 Magnesium oxide MgO Hydrochloric acid HCl Sulphuric acid H2SO4 Nitric acid HNO3 Sodium hydroxide NaOH Potassium hydroxide KOH Calcium hydroxide Ca(OH)2 Calcium carbonate CaCO3 Aluminium oxide Al2O3 Iron oxide Fe2O3 Writing balanced equations Writing balanced chemical equations can be good / bad for your health! Writing balanced equations The basic rule (golden rule #1) Hydrogen H2(g) + oxygen O2(g) water H2O Writing balanced equations The basic rule (golden rule #1) Hydrogen H2(g) + oxygen O2(g) water H2O Writing balanced equations The basic rule (golden rule #1) Hydrogen H2(g) 2H + oxygen O2(g) 2O water H2O 2H 1O THERE MUST BE EQUAL NUMBERS OF ATOMS OF EACH ELEMENT ON BOTH SIDES OF THE EQUATION Writing balanced equations The basic rule (golden rule #1) Hydrogen H2(g) 2H + oxygen O2(g) 2O water H2O 2H 1O x THERE MUST BE EQUAL NUMBERS OF ATOMS OF EACH ELEMENT ON BOTH SIDES OF THE EQUATION Writing balanced equations The basic rule (golden rule #1) Hydrogen 2H2(g) 4H + oxygen O2(g) 2O water 2H2O 4H 2O THERE MUST BE EQUAL NUMBERS OF ATOMS OF EACH ELEMENT ON BOTH SIDES OF THE EQUATION Writing balanced equations The basic rule (golden rule #1) Hydrogen 2H2(g) 4H + oxygen O2(g) 2O water 2H2O 4H 2O THERE MUST BE EQUAL NUMBERS OF ATOMS OF EACH ELEMENT ON BOTH SIDES OF THE EQUATION Writing balanced equations FOUR important steps: 1 2 3 4 • Write a word equation for the reaction Writing balanced equations FOUR important steps: 1 2 3 4 • Write a word equation for the reaction • Put in the formulae for the elements or compounds Writing balanced equations FOUR important steps: 1 • Write a word equation for the reaction 2 • Put in the formulae for the elements or compounds 3 • Balance the equation – put numbers in front of the reactants and products where necessary 4 Writing balanced equations FOUR important steps: 1 • Write a word equation for the reaction 2 • Put in the formulae for the elements or compounds 3 • Balance the equation – put numbers in front of the reactants and products where necessary 4 • Complete the balanced symbol equation using state symbols Writing balanced equations Example 1: Magnesium + Oxygen Magnesium oxide 1 2 3 4 Writing balanced equations Example 1: Magnesium + Oxygen Magnesium oxide 1 Mg 2 3 4 + O2 MgO Writing balanced equations Example 1: Magnesium + Oxygen Magnesium oxide 1 Mg 2 3 4 + O2 MgO Writing balanced equations Example 1: Magnesium + Oxygen Magnesium oxide 1 2 3 4 Mg 1 + O2 2 MgO 1 1 Writing balanced equations Example 1: Magnesium + Oxygen Magnesium oxide 1 + 2 Mg 1 O2 2 + 3 2Mg 2 O2 2 4 MgO 1 1 2MgO 2 2 Writing balanced equations Example 1: Magnesium + Oxygen Magnesium oxide 1 + 2 Mg 1 O2 2 + 3 2Mg 2 O2 2 2MgO 2 2 2Mg(s) + O2(g) 2MgO(s) 4 MgO 1 1 Writing balanced equations Example 2: nitrogen 1 2 3 4 + hydrogen ammonia Writing balanced equations Example 2: + hydrogen ammonia nitrogen 1 2 3 4 N2 2 + H2 2 NH3 1 3 Writing balanced equations Example 2: + hydrogen ammonia nitrogen 1 + 2 N2 2 H2 2 + 3 N2 2 3H2 6 4 NH3 1 3 2NH3 2 6 Writing balanced equations Example 2: + hydrogen ammonia nitrogen 1 + 2 N2 2 H2 2 + 3 N2 2 3H2 6 4 N2 (g) 2 + NH3 1 3 3H2 (g) 6 2NH3 2 6 2NH3 (g) 2 6 End of Lesson 2 In this lesson we have covered: Relative Formula Mass Chemical Formulae Chemical Equations