M, avogadros, the mole

• What is the basis for measuring the mass of an atom?

  Relative to the mass of a carbon-12 atom
• What is relative atomic mass (Ar)?

  The weighted mean mass of an atom compared to carbon-12
• How is the relative atomic mass of chlorine calculated?

  Weighted average of isotopes 35Cl and 37Cl
• What is the relative atomic mass of chlorine?

  35.5
• What is relative molecular mass (Mr)?

  Average mass of a molecule compared to carbon-12
• How is the relative molecular mass of Cl2 calculated?

  2 x 35.5 = 71.0
• What is relative formula mass (Mr)?

  Average mass of a formula unit compared to carbon-12
• What are the steps to calculate relative atomic mass (Ar)?

  1. Multiply each isotope's mass by its abundance
  2. Sum these quantities
  3. Divide by the sum of the abundances
• How does mass spectrometry help in calculating Ar?

  It provides data on isotopic abundances
• What does the y-axis of a mass spectrum represent?

  Relative isotopic abundance
• What does the x-axis of a mass spectrum represent?

  Mass/charge ratio (m/z)
• What does a peak in a mass spectrum indicate?

  The relative abundance of an isotope
• What are the steps to calculate relative formula mass (Mr)?

  1. Write down the compound's formula
  2. Identify the number of atoms of each element
  3. Multiply the number of atoms by their relative atomic mass
  4. Sum the values obtained
• What is Avogadro's constant?

  1. 6.02 x 10^23
• What does the mole unit allow us to do?

  Count large numbers of atoms and molecules
• What is the equation linking moles, particles, and Avogadro's constant?

  Number of moles = Number of particles / Avogadro's constant