3.3 Calculating Mass in Reactions

• What is the mass of sodium used in the reaction to produce sodium oxide?

  1. 00 g
• What is the known substance in the reaction to produce sodium oxide?

  Sodium (Na)
• What is the unknown substance in the reaction to produce sodium oxide?

  Sodium oxide (Na2O)
• What are the steps for calculating mass in chemical reactions?

  1. Write out the balanced equation
  2. Find the moles of the known substance (moles = mass ÷ Mr)
  3. Find the moles of the unknown substance (using the molar ratio from the balanced equation)
  4. Find the mass of the unknown substance (mass = moles x Mr)
• What is the balanced equation for the reaction of nitrogen and hydrogen to form ammonia?

  N2 + 3H2 ➔ 2NH3
• What mass of hydrogen is given in the question about nitrogen's reaction?

  15 g
• What is the balanced equation for the combustion of pentane?

  C5H12 + 8O2 ➔ 5CO2 + 6H2O
• What mass of pentane is used in the combustion reaction?

  21.6 g
• What is the balanced equation for the reaction of aluminium with chlorine?

  2Al + 3Cl2 ➔ 2AlCl3
• What mass of aluminium is given in the question about chlorine's reaction?

  32.4 g
• What is the balanced equation for the reaction of potassium with oxygen?

  4K + O2 ➔ 2K2O
• What mass of oxygen is used in the reaction with potassium?

  1. 0 g
• What is the balanced equation for the reaction of magnesium with sulfuric acid?

  Mg + H2SO4 ➔ MgSO4 + H2
• What mass of magnesium is used in the reaction with sulfuric acid?

  1. 00 g
• What is the significance of giving answers to 3 significant figures?

  It ensures precision in measurements and calculations
• What is the purpose of using a periodic table in these calculations?

  To find the molar masses of the substances
• How do you find the moles of a known substance?

  By using the formula moles = mass ÷ Mr
• How do you find the mass of an unknown substance?

  By using the formula mass = moles x Mr
• What is the molar ratio used to find moles of the unknown substance?

  It is derived from the balanced equation
• Why is it important to write a balanced equation before performing calculations?

  It ensures the conservation of mass and correct stoichiometry
• What is the first step in calculating the mass of a product in a chemical reaction?

  Write out the balanced equation
• What does "3 significant figures" mean in the context of reporting mass?

  It means the answer should be precise to three digits
• How do you determine the mass of chlorine that reacts with aluminium?

  By using the balanced equation and the mass of aluminium
• What is the mass of hydrogen produced when magnesium reacts with sulfuric acid?

  It can be calculated using the balanced equation and the mass of magnesium