quantitative chemistry

• What does the law of conservation of mass state?

  No atoms are lost or made
• What does it mean for a chemical equation to be balanced?

  Same number of atoms on both sides
• How is relative formula mass (Mr) calculated?

  Sum of relative atomic masses in formula
• What is the relative formula mass of HCl?

  $Mr =$$1 +$$35.5 =$$36.5$
• What must be true in a balanced chemical equation regarding Mr?

  Sum of Mr of reactants equals products
• What happens to mass when a gas is involved in a reaction?

  Mass may appear to change if gas is lost
• What should you check if a reaction shows a mass change?

  If a gas was released or not
• What is an example of mass change in a reaction?

  Metal reacting with oxygen produces more mass
• What is always present in measurements made in chemistry?

  Some uncertainty about the result
• What should you be prepared to do regarding uncertainty in measurements?

  Make estimations of uncertainty
• What is the unit for measuring chemical amounts?

  Mole
• What is the symbol for the unit mole?

  mol
• How is the mass of one mole of a substance expressed in grams?

  It equals its relative formula mass
• What is the mass of one mole of iron?

  56g
• How much does one mole of nitrogen gas weigh?

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

  The same number of particles as any mole
• 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
• What is the formula for percentage yield?

  Percentage yield = (Amount of product produced / Maximum amount of product possible) x 100
• What does the equation Mg + 2HCl -> MgCl₂ + H₂ indicate?

  1 mol Mg reacts with 2 mol HCl
• Why might the calculated amount of a product not be obtained?

  Because reactions may not go to completion
• What must be the same on both sides of a balanced equation?

  Total moles of one element
• What is one reason for product loss during a reaction?

  Some product may be lost during separation
• What are the steps to balance a chemical equation using moles?

  1. Convert masses in grams to moles
  2. Convert moles to simple whole number ratios
  3. Determine moles of one element/compound compared to another
• What can happen to reactants during a reaction?

  They may react differently than expected
• What is a limiting reactant?

  The reactant that is used up
• What does 'yield' refer to in a chemical reaction?

  Amount of product obtained
• What happens if a limiting reactant is used in a reaction?

  It restricts the amount of product produced
• For calculations, which reactant should be used when a limiting reactant is present?

  The amount of the limiting reactant
• How do you calculate the theoretical mass of a product from a given mass of reactant?

  1. Calculate moles of reactant: mol = mass / molar mass
  2. Use balancing numbers to find moles of product
  3. Calculate theoretical mass: mass = mol x molar mass
• How can concentration of a solution be measured?

  In mass per volume, e.g., g/dm³
• What is atom economy?

  A measure of useful products from starting materials
• What is the formula to calculate mass of solute in a solution?

  mass = concentration x volume
• Why is atom economy important?

  For sustainable development and economic reasons
• What effect does a smaller volume of solute have on concentration?

  It gives a higher concentration
• What effect does a larger volume of solute have on concentration?

  It gives a lower concentration
• How is atom economy calculated?

  =(Mr of desired product / sum of Mr of all reactants) x 100
• What factors influence the choice of a reaction pathway?

  • Atom economy
  • Yield
  • Rate
  • Equilibrium position
  • Usefulness of by-products
• How is the concentration of a solution measured?

  In mol per given volume