Chapter 7 Stoichiometry Worksheet_1 Solution

1 Chapter 7 Mole Concept and Stoichiometry 3E Chapter 7 Mole Concept and Stoichiometry Worksheet One Solutions Modified June 2024 1. In an experiment, 4.0 g of sulfur was burnt in 48.0 dm3 of oxygen measured at r.t.p to form sulfur dioxide. (a) Write the equation for the reaction between sulfur and oxygen. S (s) + O2 (g) → SO2 (g) (b) What was the limiting reactant in this reaction? Number of moles of S given = 4.00 32.0 = 0.125 mol (3 s.f.) Number of moles of O2 given = 48.0 24.0 = 2.00 mol (3 s.f.) Mole ratio of S : O2 = 1 : 1 = 0.125 mol : 0.125 mol (< 2.00 mol given) Since 0.125 mol of S is needed to react with 0.125 mol of O2 but 2 mol of O2 was given, O2 is in excess. Thus, S is the limiting reactant. (c) Calculate the volume of sulfur dioxide formed at r.t.p. Mole ratio of S : O2 = 1 : 1 = 0.125 mol : 0.125 mol Volume of SO2 produced = 0.125 × 24.0 = 3.00 dm3 (3 s.f.) Ans: (b) S (c) 3.00 dm3

2 Chapter 7 Mole Concept and Stoichiometry 2. (a) A compound contains 40.0% carbon, 6.70% hydrogen and 53.3% oxygen. What is its empirical formula? Let the mass of compound be 100 g. Element C H O Mass / g 40 6.7 53.3 Relative atomic mass 12 1 16 Number of moles / mol 40.0 12.0 = 3.33 6.70 1.00 = 6.70 53.3 16.0 = 3.33 Mole ratio 1 2 1 Hence, the empirical formula is CH2O. (b) Given that the compound has an Mr of 180, find its molecular formula. Mr of CH2O = 12 + 1 + 1 + 16 = 30.0 (3 s.f.) n = 180 ÷ 30.0 = 6.00 (3 s.f.) Hence the molecular formula of the compound is C6H12O6. Ans: (a) CH2O (b) C6H12O6

3 Chapter 7 Mole Concept and Stoichiometry 3. In an experiment, 1.20 g of magnesium was reacted with excess hydrochloric acid. Magnesium chloride and hydrogen gas were produced. (a) Write a balanced chemical equation for this reaction. Mg + 2HCl → MgCl2 + H2 (b) Calculate the mass of magnesium chloride produced in this reaction. Number of moles of Mg used = 1.20 ÷ 24 = 0.05 mol Mass of MgCl2 produced = 0.05 × 95 = 4.75 g (c) Calculate the volume of hydrogen gas produced at room temperature and pressure. Number of moles of H2 produced = 0.0500 mol (3 s.f.) Volume of H2 produced = 0.05 24 = 1.20 dm3 (3 s.f.) Ans: (b) 4.75 g (c) 1.20 dm3

4 Chapter 7 Mole Concept and Stoichiometry 4. (a) Define relative atomic mass. The relative atomic m