C3: Quantitative Chemistry

• What does the law of conservation of mass state?

  No atoms are lost or made during a chemical reaction, so the mass of the products equals the mass of the reactants.
• How can chemical reactions be represented?

  Chemical reactions can be represented by balanced symbol equations.
• What is the relative formula mass (Mr) of a compound?

  The relative formula mass (Mr) is the sum of the relative atomic masses of the atoms in the numbers shown in the formula.
• What does a balanced chemical equation indicate about the relative formula masses?

  In a balanced chemical equation, the sum of the relative formula masses of the reactants equals the sum of the relative formula masses of the products.
• Why might some reactions appear to involve a change in mass?

  This can usually be explained because a reactant or product is a gas and its mass has not been taken into account.
• What happens when a metal reacts with oxygen in terms of mass?

  The mass of the oxide produced is greater than the mass of the metal.
• What occurs during the thermal decomposition of metal carbonates?

  Carbon dioxide is produced and escapes into the atmosphere, leaving the metal oxide as the only solid product.
• How are chemical amounts measured?

  Chemical amounts are measured in moles.
• What is the symbol for the unit mole?

  The symbol for the unit mole is mol.
• What is the relationship between the mass of one mole of a substance and its relative formula mass?

  The mass of one mole of a substance in grams is numerically equal to its relative formula mass.
• What does one mole of a substance contain?

  One mole of a substance contains the same number of particles, atoms, molecules, or ions as one mole of any other substance.
• What is the value of the Avogadro constant?

  The value of the Avogadro constant is $6.02 \times 10^{23}$ per mole.
• How can the masses of reactants and products be calculated?

  The masses of reactants and products can be calculated from balanced symbol equations.
• What does the equation Mg + 2HCl → MgCl2 + H2 represent in terms of moles?

  It shows that one mole of magnesium reacts with two moles of hydrochloric acid to produce one mole of magnesium chloride and one mole of hydrogen gas.
• What is a limiting reactant?

  The limiting reactant is the reactant that is completely used up and limits the amount of products formed.
• How is the concentration of a solution measured?

  The concentration of a solution can be measured in grams per dm³ (g/dm³).
• What are the reasons why it is not always possible to obtain the calculated amount of a product in a chemical reaction?

  • The reaction may not go to completion because it is reversible.
  • Some of the product may be lost when separated from the reaction mixture.
  • Some reactants may react in ways different from the expected reaction.
• What is the term for the amount of product obtained in a chemical reaction?

  The amount of product obtained is known as the yield.
• How is percentage yield calculated?

  Percentage yield is calculated using the formula: % Yield = (Mass of product actually made / Maximum theoretical mass of product) × 100.
• What is atom economy?

  Atom economy is a measure of the amount of starting materials that end up as useful products.
• Why is high atom economy important?

  High atom economy is important for sustainable development and economic reasons.
• How is percentage atom economy calculated?

  Percentage atom economy is calculated using the formula: (Relative formula mass of desired product / Sum of relative formula masses of all reactants) × 100.
• How can the concentration of a solution also be measured?

  The concentration of a solution can also be measured in mol/dm³.
• How can the amount in moles of solute be calculated?

  The amount in moles of solute can be calculated from its concentration in mol/dm³.
• How can the concentration of one solution be calculated if the volumes of two solutions that react completely are known?

  The concentration of the other solution can be calculated if the concentration of one solution is known.
• What is the relationship between gases and moles under the same conditions of temperature and pressure?

  Equal amounts in moles of gases occupy the same volume under the same conditions of temperature and pressure.
• What is the volume of one mole of any gas at room temperature and pressure?

  The volume of one mole of any gas at room temperature and pressure (20°C and 1 atmosphere pressure) is 24 dm³.
• How can the volumes of gaseous reactants and products be calculated?

  The volumes of gaseous reactants and products can be calculated from the balanced equation for the reaction.
• What is the unit used to measure chemical amounts?

  Mole
• What is the symbol for the unit mole?


  The symbol is mol
• How is the mass of one mole of a substance related to its relative formula mass?


  The mass in grams is numerically equal to its relative formula mass
• If the Mr of iron is 56, what is the mass of one mole of iron in grams?


  56g
• What is the mass of one mole of nitrogen gas, N2, if its Mr is 28?


  28g
• What does one mole of a substance contain in terms of particles?


  It contains the same number of stated particles as one mole of any other substance
• What is the Avogadro constant?


  1. 02 x 10²³ per mole
• How can masses of reactants and products be calculated?


  From balanced symbol equations
• How can chemical equations be interpreted?


  In terms of moles
• In the equation Mg + 2HCl -> MgCl₂ + H₂, how many moles of HCl react with 1 mole of Mg?


  2 moles
• What must be true about the total moles of one element in a balanced equation?


  They must be the same on both sides of the equation
• What are the steps to balance a symbol equation using moles?


  1. Convert the masses in grams to amounts in moles
  2. Convert the numbers of moles to simple whole number ratios
  3. Determine how many moles you have of one element/compound compared to another