C3 - Quantitative Chemistry

• What must always equal the mass of the product in a chemical reaction?

  The mass of the reactants
• What is the balanced equation for the reaction of hydrogen and oxygen to form water?

  • 2H₂ + O₂ → 2H₂O
• What is the balanced equation for the reaction of sodium and chlorine to form sodium chloride?

  • 2Na + Cl₂ → 2NaCl
• What is the balanced equation for the reaction of bromine and potassium iodide?

  • Br₂ + 2KI → I₂ + 2KBr
• What is the balanced equation for the reaction of nitrogen and hydrogen to form ammonia?

  • N₂ + 3H₂ → 2NH₃
• What is the relative formula mass (Mr) of a compound?

  It is the sum of the relative atomic masses (Ar) of the atoms in the compound
• How do you calculate the relative formula mass of CO₂?

  12 + (16 × 2) = 44
• What is the relative formula mass of H₂O?

  (1 × 2) + 16 = 18
• What is the relative formula mass of CH₄?

  12 + (1 × 4) = 16
• How do you calculate the relative formula mass of NH₄NO₃? Show your working.

  14 + (1 × 4) + 14 + (16 × 3) = 80
• Why might the mass go down when a gas is produced during a reaction?

  The gas may be released into the environment
• What is the balanced equation for the reaction of magnesium with oxygen?

  2Mg + O₂ → 2MgO
• What happens to the mass of the product when magnesium reacts with oxygen?

  The mass increases because oxygen is added from the environment
• How do you calculate the percentage mass of sodium (Na) in NaCl?

  % mass = (Ar of Na × number of atoms × 100) / Mr of NaCl
• What is the % mass of sodium in NaCl if Ar of Na = 23 and Ar of Cl = 35.5?

  % mass = (23 × 1 × 100) / (23 + 35.5) = 39.3%
• If 9g of magnesium reacts completely with 6g of oxygen, what is the mass of magnesium oxide produced?

  15g
• How do you show that mass is conserved in a chemical equation?

  By calculating the Mr of both sides of the equation
• What is the Mr of the left-hand side of the equation 2H₂ + O₂ → 2H₂O?

  36
• What is the Mr of the right-hand side of the equation 2H₂ + O₂ → 2H₂O?

  36
• What is the concentration equation in chemistry?

  • concentration = mass of dissolved substance / volume of solvent
• What is the concentration of a solution with 40g of dissolved substance and 0.5dm³ of solvent?

  80g/dm³
• How do you calculate the mass of the dissolved substance when the concentration is 15g/dm³ and the volume is 0.8dm³?

  mass = concentration × volume = 15 × 0.8 = 12g