Amount of Substance-NOTES

• What is the definition of relative atomic mass (Ar)?

  The mean mass of an atom of an element, divided by one twelfth of the mean mass of an atom of the carbon-12 isotope.
• What is the definition of relative molecular mass (Mr)?

  The mean mass of a molecule of a compound, divided by one twelfth of the mean mass of an atom of the carbon-12 isotope.
• What is the term used for relative molecular mass in ionic compounds?

  Relative formula mass.
• What is the mole a unit of measurement for?

  Substances.
• What does the Avogadro Constant (L) represent?

  The number of particles in a mole of a substance.
• How can the number of particles in a sample of a substance be found?

  By using the Avogadro Constant (L) with the known mass.
• Why is the mole considered a very important unit of measurement?

  It is used in many calculations involving substances.
• What is the ideal gas equation?

  pV = nRT
• What must the variables in the ideal gas equation be in?

  Correct standard units.
• What is the value of the ideal gas constant (R)?

  1. 31 JK$-1$mol$-1$.
• What is the empirical formula?

  The simplest whole number ratio of atoms of each element in a compound.
• How is the empirical formula found?

  Using molar ratios of each element.

  
• What is the molecular formula?

  The true number of each atom in the molecule.
• How can the molecular formula be determined?

  Using the Mr of the empirical formula and the true Mr of the molecule.

  
• Why must chemical equations be balanced before calculations?

  To ensure the reacting ratios are correct.
• What can balanced chemical equations be used to calculate?

  Reacting masses, percentage yield, and atom economy.

  
• What is percentage yield?

  The ratio of the actual yield to the theoretical yield, expressed as a percentage.

  
• What does high atom economy mean in industrial chemical processes?

  There is little or no waste product, only the desired product.
• Why is high atom economy beneficial for the environment?

  It uses less natural resources and often less energy.