1.3 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.
• What is relative atomic mass (RAM)?


  RAM is the average mass of atoms in an element, considering the masses and abundance of its isotopes, relative to $^{12}C$.
• What is relative formula mass (RFM)?


  RFM is the sum of the relative atomic masses of all atoms in the formula.
• How can you increase the precision of the results in the magnesium experiment?


  By measuring to more decimal places or using a more sensitive balance/apparatus.
• What is Avogadro’s constant?


  Avogadro’s constant is the number of atoms, molecules, or ions in a mole of a substance, valued at $6.02 \times 10^{23}$.
• What is the formula that links mass, molecular mass, and moles?


  The formula is $\text{Mass} =$$\text{Mr} \times \text{Moles}$.
• What is a limiting reactant in a chemical reaction?


  The limiting reactant is the reactant that is completely used up, limiting the amount of products formed.
• What are the two formulas that link concentration, mole/mass, and volume together?

  • Concentration (g per dm³) = Mass (g) / Volume (dm³)
  • Concentration (mol per dm³) = Number of moles / Volume (dm³)
• What is the molar volume of a gas at room temperature and pressure?


  1 mole of a gas occupies 24 dm³ at room temperature and pressure.
• What is titration?


  Titration is a technique for finding the concentration of a solution by reacting a known volume of this solution with a solution of known concentration.
• Why is it not always possible to obtain the theoretical amount of product in a chemical reaction?


  • The reaction may not go to completion because it is reversible.
  • Some product may be lost when separated from the reaction mixture.
  • Some reactants may react in unexpected ways (side reactions).
• How do you conduct a titration?

  1. Rinse the pipette with the unknown solution and measure out the known volume.
  2. Add an indicator that changes color at the endpoint.
  3. Rinse the burette with the known concentration solution and discard the liquid.
  4. Gradually add the known solution from the burette until the indicator changes color.
  5. Record the volume added and ensure concordant results.
  6. Perform calculations to find the concentration.
• How is the percentage yield of a product in a chemical reaction calculated?


  Percentage yield = $\frac{\text{Actual mass of product}}{\text{Maximum theoretical mass of product}} \times 100\%$.
• What is atom economy?


  Atom economy measures the amount of starting materials that end up as useful products, calculated as a ratio of the relative formula mass of the desired product to the sum of the relative formula masses of reactants.