C3 : Quantitative Chemistry

• What is the conservation of mass

  No atoms are lost or gained in a chemical reaction
• What happens to the reactants and products according to conservation of mass during a reaction

  The mass of the reactants equal the mass of the products
• What happens if a reactant or product changes in a reaction


  The reactant or product is a gas and it’s mass has not been accounted for
• What happens to mass if a gas is involved in a reaction?

  Mass may appear to change due to gas
• If the mass of a reaction vessel increases, what could be a reason?

  A gas from air reacted and is contained
• What occurs if the mass of a reaction vessel decreases?

  A gas product escapes from the vessel
• How do you show that mass is conserved in a chemical reaction?

  By balancing the total mass of reactants and products
• What are the two explanations for mass change in a reaction vessel?

  1. Mass increases if a gas reacts and is contained.
  2. Mass decreases if a gas escapes during the reaction.
• What does the relative formula mass represent?

  Sum of relative atomic masses in a compound
• What is the formula to calculate the percentage mass of an element in a compound?

  • Percentage mass of an element =

  $\frac{A_r \times \text{number of atoms of that element}}{M_r \text{ of the compound}} \times 100$
• What is the mole in chemistry?

  It is an amount of a substance.
• What does the mole represent in terms of particles?

  It represents $6.022 \times 10^{23}$ particles.
• What is Avogadro's number?

  $6.022 \times 10^{23}$
• How is the mass of a substance related to its relative atomic mass?

  The mass in grams equals its relative atomic mass.
• What is the mass of one mole of carbon?

  12 g
• What is the mass of one mole of oxygen?

  16 g
• What is the mass of one mole of carbon dioxide (CO₂)?

  44 g
• What is the formula to find the number of moles in a given mass?

  • Number of moles = mass in g / Mr
• What is the mass of carbon in 4 moles of carbon dioxide?

  48 g
• What is a limiting reactant?

  • The reactant that gets used up first
  • Stops the reaction from continuing
• What happens when one reactant is used up in a reaction?

  The reaction stops when the limiting reactant is used up.
• How does the amount of product formed relate to the limiting reactant?

  More limiting reactant produces more product.
• What are the steps to calculate the mass of a product formed in a reaction?

  1. Write the balanced equation.
  2. Find relative formula masses (M_r).
  3. Calculate moles of reactants.
  4. Use mole ratios to find product moles.
  5. Calculate mass of product.
• How many moles of aluminium are in 135 g?

  5 moles