C3 - Quantitative Chemistry

• What does the law of conservation of mass state?

  No atoms are lost or made in reactions
• How does the law of conservation of mass apply to chemical reactions?

  The mass of products equals the mass of reactants
• What is the balanced equation for magnesium reacting with hydrochloric acid?

  Mg(s) + 2 HCl(aq) → MgCl2(aq) + H2(g)
• What is relative atomic mass (RAM)?

  Average mass of atoms in an element
• What is relative formula mass (RFM)?

  Sum of RAMs of all atoms in a formula
• Why do carbon dioxide and water escape from the test tube in the reaction?

  They are both gases
• What is Avogadro's constant?

  6.02 x 10²³ particles per mole
• What does Avogadro's constant represent?

  Number of atoms, molecules, or ions in a mole
• What is the formula linking mass, molecular mass, and moles?

  Mass = Mr x Moles
• What is a limiting reactant in a chemical reaction?

  The reactant that is completely used up
• How many grams of oxygen gas are produced from 40.8 g of hydrogen peroxide?

  19.2 g of oxygen gas
• What is the first step to calculate the grams of oxygen from hydrogen peroxide?

  Write the balanced equation for decomposition
• How do you calculate the concentration of a solution?

  Concentration = Mass / Volume
• What is the molar volume of a gas at room temperature and pressure?

  24 dm³ per mole
• What is titration used for?

  Finding the concentration of a solution
• What are the steps to conduct a titration?

  1. Rinse pipette with unknown solution
  2. Measure known volume of unknown solution
  3. Add an indicator
  4. Rinse burette with known concentration solution
  5. Gradually add known solution until endpoint
  6. Record the volume added
  7. Perform calculations to find concentration
• Why might the theoretical amount of product not be obtained in a reaction?

  Reactions may not go to completion
• How is the percentage yield of a product calculated?

  % Yield = (Actual mass / Theoretical mass) x 100%
• What is atom economy?

  Measure of starting materials as useful products
• Which reaction has better atom economy: Reaction I or Reaction II?

  Reaction II has better atom economy
• How is atom economy calculated for Reaction II?

  (134.5 / 152.5) x 100% = 88.2%