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The mole 1 One mole of any substance is defined as the formula mass in grams, i.e. the gram formula mass. The formula mass of any substance is first calculated from the formula. To calculate the mass of one mole of the substance, simply change the units to grams. Example 1: What is the mass of one mole of sodium? Step 1 Symbol Na Step 2 Find the relative atomic mass 23 Step 3 Change units to grams 23 g Example 2: What is the mass of one mole of potassium sulphate, K2SO4? Step 1 Formula Step 2 Find the relative atomic masses K2SO4 K S O 39 32 16 39 x 2 32 x 1 16 x 4 Step 3 Multiply by the number of atoms Step 4 Do the sum Step 5 Formula mass 174 Step 6 Change units to grams 174 g Chemical Changes and Structure 78 + 32 + 64 Chemical calculations 2 The mole 2 Example 3: What is the mass of two moles of sodium chloride? Step 1 Formula Step 2 Find the atomic masses Na 23 Step 3 Multiply by the number of atoms 23 x 1 Step 4 Do the sum 23 Step 5 Formula mass 58.5 Step 6 Change units to grams 58.5 g Step 7 Complete calculation NaCl Cl 35.5 35.5 x 1 + 35.5 1 mol 1 58.5 g 2 mol 1 117 g Example 4: How many moles are there in 36g of water, H2O? Step 1 Formula Step 2 Find the relative atomic masses H 1 Step 3 Multiply by the number of atoms 2x1 Step 4 Do the sum Step 5 Formula mass 18 Step 6 Change units to grams 18 g Step 7 Complete calculation Chemical Changes and Structure H2 O 2 O 16 16 x 1 + 16 1 mol 1 18 g 2 mol 1 36 g Chemical calculations 2 The mole 3 Calculate the mass of one mole of each of the following elements. (Remember that some elements exist as diatomic molecules.) silicon magnesium copper Chemical Changes and Structure hydrogen neon bromine Chemical calculations 2 The mole 4 Calculate the mass of one mole of each of the following compounds. LiF H2S C3H8O K2SO4 NaNO3 Ca(OH)2 CH2CCl2 (NH4)2CO3 Chemical Changes and Structure Chemical calculations 2 The mole 5 Calculate the mass of each of the following substances. 2 mol of C 0.5 mol of Mg 3 mol of H2 0.2 mol of KF 2 mol of Cu2O 0.4 mol of NCl3 5 mol of Na2SO4 0.1 mol of (NH4)3PO4 Chemical Changes and Structure Chemical calculations 2 The mole 6 Calculate the number of moles that are contained in each of the following substances. 20 g of Ca 54 g of H2O 14 g of N2 10 g of CaCO3 10.1 g of KNO3 6.4 g of SO2 6.6 g of (NH4)2SO4 18 g of sugar (C12H22O11) Chemical Changes and Structure Chemical calculations 2