03- 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 relative atomic mass (RAM)?

  Average mass of atoms in an element
• How is relative atomic mass calculated?

  Based on isotopes' masses and abundance
• What is relative formula mass (RFM)?

  Sum of RAMs of all atoms in a formula
• Write the balanced equation for magnesium reacting with hydrochloric acid.

  Mg(s) + 2 HCl(aq) → MgCl2(aq) + H2(g)
• How do you calculate the relative formula mass of CaF2?

  40 + 19 + 19 = 78
• What is the relative formula mass of C2H12O6?

  (12 x 6) + (1 x 12) + (16 x 6) = 180
• Why do carbon dioxide and water escape from the test tube?

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

  6.02 x 10^23 particles per mole
• How do you calculate the mean of magnesium produced from 3.3, 3.5, and 3.2 grams?

  (3.3 + 3.5 + 3.2) / 3 = 3.3
• How can you increase the precision of magnesium measurement results?

  Measure to more decimal places
• What is the mass of 20 moles of calcium carbonate (CaCO3)?

  100 x 20 = 2000 g
• What is the formula linking mass, molecular mass, and moles?

  Mass = Mr x Moles
• How do you calculate the moles of carbon dioxide in 0.32 g?

  0.32 / 44 = 0.007
• How do you calculate the mass of nitrogen needed to form 6.8 tonnes of ammonia?

  5600000 g = 5.6 tonnes
• What is a limiting reactant in a chemical reaction?

  The reactant completely used up limits products
• What are the two formulas linking concentration, mole/mass, and volume?

  • Concentration (g per dm³) = Mass (g) / Volume (dm³)
  • Concentration (mol per dm³) = Number of moles / Volume (dm³)
• How do you calculate the concentration of potassium hydroxide solution?

  0.05 / 0.031 = 1.61
• What is titration?

  A technique to find solution concentration
• What is the molar volume of a gas at room temperature and pressure?

  24 dm³ per mole
• 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 solution
  5. Add known solution from burette
  6. Record volume at endpoint
  7. Perform calculations for concentration
• Why is it not always possible to obtain the theoretical amount of product 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 the % yield of NH3 if 40.5 g is produced from 20.0 mol H2?

  40.5/227 x 100 = 17.8%
• What is atom economy?

  Measure of starting materials as useful products
• Which reaction has a better atom economy?

  Reaction II: (134.5/152.5) x 100% = 88.2%