C3: Quantitative Chemistry

• What is relative formula mass denoted as?

  Mr
• How is relative formula mass calculated?

  Add relative atomic masses of all atoms
• What is the relative formula mass of MgCl₂?

  95
• Why do you multiply the relative atomic mass of chlorine by 2 in MgCl₂?

  There are two chlorine atoms in MgCl₂
• What is the formula for calculating percentage mass of an element in a compound?

  Percentage mass = (Ar × number of atoms) / Mr × 100
• What is the percentage mass of sodium in sodium carbonate, Na₂CO₃?

  43%
• How do you find the mass of iron in a mixture containing 20% iron ions by mass?

  Calculate 20% of the total mass
• What mass of iron chloride is needed to provide 10 g of iron ions in a 50 g mixture?

  23 g
• What is the Avogadro constant?

  6.02 × 10^23
• What does one mole of a substance contain?

  Avogadro number of particles
• What is the mass of one mole of carbon?

  12 g
• How is the mass of one mole of nitrogen gas (N₂) calculated?

  It weighs exactly 28 g
• What is the mass of one mole of carbon dioxide (CO₂)?

  44 g
• How do you find the number of moles in a given mass?

  Number of moles = mass / Mr
• How many moles are in 66 g of carbon dioxide (CO₂)?

  1.5 mol
• What mass of carbon is there in 4 moles of carbon dioxide?

  48 g
• What does conservation of mass state in a chemical reaction?

  No atoms are created or destroyed
• What happens to the mass in a balanced chemical equation?

  Mass is conserved
• How do you show that mass is conserved in a reaction?

  Add relative formula masses on both sides
• What happens if the mass of a reaction vessel seems to change?

  Usually a gas is involved
• Why does mass increase in a reaction with a gas reactant?

  The gas is contained after reaction
• Why does mass decrease in a reaction with a gas product?

  The gas escapes from the vessel
• How can you calculate the mass of a product formed in a reaction?

  Use the mass of the limiting reactant
• What mass of aluminium oxide is formed from 135 g of aluminium?

  255 g
• What is the yield of a product in a reaction?

  The mass of product formed
• What are the steps to balance a chemical equation using reacting masses?

  1. Divide mass by relative formula mass
  2. Divide by smallest number of moles
  3. Multiply to get whole numbers
  4. Write the balanced equation
• What are the explanations for mass changes in reactions?

  • Mass increases if a gas reacts and is contained.
  • Mass decreases if a gas escapes during reaction.
• What is the relationship between limiting reactants and product formation?

  • Limiting reactant determines the amount of product.
  • More limiting reactant leads to more product formed.
• What is the significance of the balanced equation in reactions?

  • Indicates the ratio of moles of reactants and products.
  • Essential for calculating masses in reactions.
• What is the first step to calculate moles from mass?

  Divide mass by molar mass
• How do you determine the moles of a product from reactants?

  Use the balanced equation ratios
• If you have 5 moles of reactant, how many moles of product will be produced?

  Depends on the balanced equation
• What does the yield of a reaction refer to?

  The mass of product formed
• What is the balanced equation for aluminium oxide formation?

  4Al + 3O₂ → 2Al₂O₃
• How do you calculate the relative formula mass of Al₂O₃?

  (2 × 27) + (3 × 16) = 102
• How many moles are in 135 g of aluminium?

  5 moles
• Why is the molar mass of oxygen not needed in the calculation?

  Oxygen is in excess
• What is the mole ratio of Al to Al₂O₃ in the reaction?

  4 moles of Al produce 2 moles of Al₂O₃
• How do you calculate the mass of 2.5 moles of aluminium oxide?

  mass = moles × M_r
• What is the theoretical yield of aluminium oxide from 135 g of aluminium?

  255 g