Chemistry Spec points covered Starter options Practical activity Teacher-led activity CC8 Masses and C1.43 Calculate relative formula 1) Write five formulae on Students determine the Take the students empirical mass given relative atomic the board, including empirical formula for through worked formulae masses some with brackets, e.g. magnesium oxide. examples one step at a C1.44 Calculate the formulae of MgCl2, Li2O, CuSO4, time. simple compounds from Ca(NO3)2, (NH4)2CO3. The empirical formula of reacting masses and Ask students to work out Digital Relative magnesium oxide is MgO. It is understand that these are the number of atoms of formula mass and unlikely that students will get empirical formulae each element in each empirical formulae and an exact ratio of 1:1. They can C1.45 Deduce: formula and to name the relative molecular suggest reasons for the a the empirical formula of a compounds. masses and empirical difference. For example, some compound from the formula formulae presentation 2) Make up some of the magnesium oxide of its molecule molecular models, e.g. escaped when the crucible lid b the molecular formula of a C2H6, C3H6, C4H10, was lifted, the magnesium had compound from its empirical C3H8, CH3COOH and ask not completely finished formula and its relative students to work out the reacting, magnesium reacts molecular mass formula of the molecules with nitrogen from the air as C1.46 Describe an experiment to from the number of each well as oxygen. determine the empirical type of atom. This is the formula of a simple Equipment: For each group: molecular formula. Then compound such as Bunsen burner, crucible and lid, dismantle one model into magnesium oxide emery paper, heat resistant separate atoms and show mat, pipeclay triangle, tongs, them the simplest ratio tripod, about 3 cm length of of each atom. This is the magnesium ribbon. empirical formula. Students need access to an Challenge students to electronic balance weighing to deduce the empirical at least 2 decimal places. formulae of the other compounds.
Chemistry Spec points covered Starter options Practical activity Teacher-led activity CC8 Masses and empirical formulae C1.43 C1.44 C1.45 C1.46 Calculate relative formula mass given relative atomic masses Calculate the formulae of simple compounds from reacting masses and understand that these are empirical formulae Deduce: a the empirical formula of a compound from the formula of its molecule b the molecular formula of a compound from its empirical formula and its relative molecular mass Describe an experiment to determine the empirical formula of a simple compound such as magnesium oxide 1) Write five formulae on the board, including some with brackets, e.g. MgCl2, Li2O, CuSO4, Ca(NO3)2, (NH4)2CO3. Ask students to work out the number of atoms of each element in each formula and to name the compounds. 2) Make up some molecular models, e.g. C2H6, C3H6, C4H10, C3H8, CH3COOH and ask students to work out the formula of the molecules from the number of each type of atom. This is the molecular formula. Then dismantle one model into separate atoms and show them the simplest ratio of each atom. This is the empirical formula. Challenge students to deduce the empirical formulae of the other compounds. Students determine the empirical formula for magnesium oxide. The empirical formula of magnesium oxide is MgO. It is unlikely that students will get an exact ratio of 1:1. They can suggest reasons for the difference. For example, some of the magnesium oxide escaped when the crucible lid was lifted, the magnesium had not completely finished reacting, magnesium reacts with nitrogen from the air as well as oxygen. Equipment: For each group: Bunsen burner, crucible and lid, emery paper, heat resistant mat, pipeclay triangle, tongs, tripod, about 3 cm length of magnesium ribbon. Students need access to an electronic balance weighing to at least 2 decimal places. Take the students through worked examples one step at a time. Digital Relative formula mass and empirical formulae and relative molecular masses and empirical formulae presentation