IGCSE CHEMISTRY LESSON 3

Section 1 Principles of Chemistry a)States of matter b)Atoms c)Atomic structure d)Relative formula mass e)Chemical formulae and chemical equations f)Ionic compounds g)Covalent substances h)Metallic crystals i)Electrolysis

Lesson 3 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.

Finding chemical formulae – experimentally! We can conduct experiments with compounds to determine the mass (or percentage) there is of each element.

Finding chemical formulae – experimentally! For example, we could heat magnesium in air. Magnesium oxide will be formed

Finding chemical formulae – experimentally! For example, we could heat magnesium in air. Magnesium oxide will be formed The mass will increase because oxygen is added

Finding chemical formulae – experimentally! Mass of Magnesium (g) Mass of magnesium oxide (g) Mass of oxygen (g)

Finding chemical formulae – experimentally! Mass of Magnesium (g) Mass of magnesium oxide (g) Mass of oxygen (g)

Finding chemical formulae – experimentally! Let’s just stop there a second! What do we mean by the term ‘empirical formula’?

Finding chemical formulae – experimentally! The empirical formula is the simplest whole number ratio of atoms in a compound.

Finding chemical formulae – experimentally! The empirical formula is the simplest whole number ratio of atoms in a compound. Let’s calculate the empirical formula for magnesium oxide.

Finding chemical formulae – experimentally! Mass of Magnesium (g) Mass of magnesium oxide (g) Mass of oxygen (g)

Empirical formula

ElementsMagnesiumOxygen Mass (g) Relative atomic mass2416 Number of moles

Empirical formula ElementsMagnesiumOxygen Mass (g) Relative atomic mass2416 Number of moles

Empirical formula ElementsMagnesiumOxygen Mass (g) Relative atomic mass2416 Number of moles

Empirical formula ElementsMagnesiumOxygen Mass (g) Relative atomic mass2416 Number of moles Most simple ratio

Empirical formula ElementsMagnesiumOxygen Mass (g) Relative atomic mass2416 Number of moles Most simple ratio Reacting atoms11

Empirical formula ElementsMagnesiumOxygen Mass (g) Relative atomic mass2416 Number of moles Most simple ratio Empirical formulaMgO

Empirical formula ElementsIronoxygen Mass (g) Relative atomic mass Number of moles Most simple ratio Reacting atoms

Empirical formula ElementsIronoxygen Mass (g) Relative atomic mass Number of moles Most simple ratio Reacting atoms

Empirical formula ElementsIronoxygen Mass (g) Relative atomic mass5616 Number of moles Most simple ratio Reacting atoms

Empirical formula ElementsIronoxygen Mass (g) Relative atomic mass5616 Number of moles Most simple ratio0.04/ /0.04 Reacting atoms

Empirical formula ElementsIronoxygen Mass (g) Relative atomic mass5616 Number of moles Most simple ratio0.04/ /0.04 Reacting atoms11.5

Empirical formula ElementsIronoxygen Mass (g) Relative atomic mass5616 Number of moles Most simple ratio0.04/ /0.04 Reacting atoms23

Empirical formula ElementsIronoxygen Mass (g) Relative atomic mass5616 Number of moles Most simple ratio0.04/ /0.04 Empirical formulaFe 2 O 3

Empirical formula ElementsMagnesiumOxygen Mass (%) Relative atomic mass Number of moles Most simple ratio Reacting atoms

Empirical formula ElementsMagnesiumOxygen Mass (%)6040 Relative atomic mass Number of moles Most simple ratio Reacting atoms

Empirical formula ElementsMagnesiumOxygen Mass (%)6040 Relative atomic mass2416 Number of moles Most simple ratio Reacting atoms

Empirical formula ElementsMagnesiumOxygen Mass (%)6040 Relative atomic mass2416 Number of moles2.5 Most simple ratio Reacting atoms

Empirical formula ElementsMagnesiumOxygen Mass (%)6040 Relative atomic mass2416 Number of moles2.5 Most simple ratio2.5/2.5 Reacting atoms

Empirical formula ElementsMagnesiumOxygen Mass (%)6040 Relative atomic mass2416 Number of moles2.5 Most simple ratio2.5/2.5 Reacting atoms11

Empirical formula ElementsMagnesiumOxygen Mass (%)6040 Relative atomic mass2416 Number of moles2.5 Most simple ratio2.5/2.5 Empirical formulaMgO

Empirical formula ElementsCalciumCarbonOxygen Mass (g) Relative atomic mass Number of moles Most simple ratio Reacting atoms

Empirical formula ElementsCalciumCarbonOxygen Mass (g)10312 Relative atomic mass Number of moles Most simple ratio Reacting atoms

Empirical formula ElementsCalciumCarbonOxygen Mass (g)10312 Relative atomic mass Number of moles Most simple ratio Reacting atoms

Empirical formula ElementsCalciumCarbonOxygen Mass (g)10312 Relative atomic mass Number of moles Most simple ratio Reacting atoms

Empirical formula ElementsCalciumCarbonOxygen Mass (g)10312 Relative atomic mass Number of moles Most simple ratio 0.25/ /0.25 Reacting atoms

Empirical formula ElementsCalciumCarbonOxygen Mass (g)10312 Relative atomic mass Number of moles Most simple ratio 0.25/ /0.25 Reacting atoms113

Empirical formula ElementsCalciumCarbonOxygen Mass (g)10312 Relative atomic mass Number of moles Most simple ratio 0.25/ /0.25 Empirical formula CaCO 3

Lesson 3 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.

? What is ‘water’ of crystallisation?

?

? = water found in the crystal structure of a compound (eg. copper sulphate) but not directly bonded to the compound, eg hydrated calcium chloride crystals CaCl 2.2H 2 O

? What is ‘water’ of crystallisation? When a hydrated salt is heated, the water is evaporated off, and we can use the change in mass to calculate how many molecules of water there would be in the empirical formula.

? What is ‘water’ of crystallisation? When a hydrated salt is heated, the water is evaporated off, and we can use the change in mass to calculate how many molecules of water there would be in the empirical formula. eg. MgSO 4.nH 2 O What will the value of ‘n’ be?

Finding chemical formulae of hydrated salts– experimentally! Mass of hydrated magnesium sulphate (g) Mass of anhydrous magnesium sulphate (g) Mass of water (g)

Finding chemical formulae of hydrated salts– experimentally! Mass of hydrated magnesium sulphate (g) Mass of anhydrous magnesium sulphate (g) Mass of water (g)

Empirical formula CompoundsMgSO 4 H2OH2O Mass (g) Relative molecular mass Number of moles Most simple ratio Reacting molecules

Empirical formula CompoundsMgSO 4 H2OH2O Mass (g) Relative molecular mass Number of moles Most simple ratio Reacting molecules

Empirical formula CompoundsMgSO 4 H2OH2O Mass (g) Relative molecular mass Number of moles Most simple ratio Reacting molecules

Empirical formula CompoundsMgSO 4 H2OH2O Mass (g) Relative molecular mass Number of moles Most simple ratio0.039/ /0.039 Reacting molecules

Empirical formula CompoundsMgSO 4 H2OH2O Mass (g) Relative molecular mass Number of moles Most simple ratio0.039/ /0.039 Reacting molecules16.93 (7)

Empirical formula CompoundsMgSO 4 H2OH2O Mass (g) Relative molecular mass Number of moles Most simple ratio0.039/ /0.039 Empirical formulaMgSO 4.7H 2 O

Phew! Take a break!

Molecular formula

Molecular formula shows the actual number of atoms in a compound and is a simple multiple of the empirical formula.

Molecular formula Eg. Empirical formula = CH 2 Molecular formula = C 3 H 6 (empirical formula x 3)

Molecular formula Eg. Find the molecular formula of a compound which has the empirical formula CH 2 and a relative molecular mass of 56g. Mass of empirical formula CH 2 = = 14g

Molecular formula Eg. Find the molecular formula of a compound which has the empirical formula CH 2 and a relative molecular mass of 56g. Mass of empirical formula CH 2 = = 14g Divide relative molecular mass by empirical mass = 56 / 14 = 4

Molecular formula Eg. Find the molecular formula of a compound which has the empirical formula CH 2 and a relative molecular mass of 56g. Mass of empirical formula CH 2 = = 14g Divide relative molecular mass by empirical mass = 56 / 14 = 4 So the molecular formula = 4 x (CH 2 ) = C 4 H 8

Lesson 3 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 3 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.

End of Lesson 3 (part 1) In this lesson we have covered: Finding chemical formulae – experimentally! Empirical formula Water of crystallisation and hydrated salts Molecular formula