C3-quantitative chemistry

• What does the law of conservation of mass state?

  No atoms are lost or made in reactions
• How can chemical reactions be represented?

  By balanced symbol equations
• What is the relative formula mass (Mr) of a compound?

  Sum of relative atomic masses in the formula
• What must be true in a balanced chemical equation?

  Sum of reactants' Mr equals sum of products' Mr
• Why might some reactions appear to involve a change in mass?

  Gases may not be accounted for in mass
• What happens when a metal reacts with oxygen?

  The mass of the oxide is greater than metal
• What is uncertainty in measurements?

  It indicates the reliability of the result
• What unit is used to measure chemical amounts?

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

  It is numerically equal to its relative formula mass
• What does one mole of a substance contain?

  The same number of particles as any mole
• What is the value of the Avogadro constant?

  $6.02 \times 10^{23}$ per mole
• How can the masses of reactants and products be calculated?

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

  In terms of moles
• What does the equation Mg + 2HCl → MgCl2 + H2 represent?

  One mole of magnesium reacts with two moles of HCl
• What is a limiting reactant?

  The reactant that is completely used up
• How can balancing numbers in a symbol equation be calculated?

  By converting masses to moles and ratios
• How is the concentration of a solution measured?

  In mass per volume, eg g/dm³
• Why might the calculated amount of a product not be obtained?

  Reactions may not go to completion
• What is yield in a chemical reaction?

  The amount of product obtained
• What is percentage yield?

  Yield compared to maximum theoretical amount
• What is atom economy?

  Measure of starting materials as useful products
• How is percentage atom economy calculated?

  Using the balanced equation for the reaction
• How can the concentration of a solution be measured?

  In mol/dm³
• How can the amount of solute in a solution be calculated?

  From its concentration in mol/dm³
• What is true about gases in terms of moles?

  Equal moles occupy the same volume
• What is the volume of one mole of gas at room temperature and pressure?

  24 dm³
• How can the volumes of gaseous reactants and products be calculated?

  From the balanced equation for the reaction