1.5 Chemical Formulae

• Mole


  A unit representing 6.022 × 10^23 particles of a substance.
• Avogadro's Number


  6.022 × 10^23, the number of particles in one mole.
• Molecular Weight


  The mass of one mole of a substance, expressed in grams per mole (g/mol).
• Mass to Moles Conversion

  Moles = Mass (g) ÷ Molecular Weight (g/mol).
• Moles to Mass Conversion

  Mass (g) = Moles × Molecular Weight (g/mol).
• Moles to Particles Conversion

  Particles = Moles × Avogadro's Number (6.022 × 10^23).
• Particles to Moles Conversion

  Moles = Particles ÷ Avogadro's Number (6.022 × 10^23).
• What is the relative atomic mass (Ar) of an element based on?

  The weighted average mass of an element's isotopes, measured on a scale where carbon-12 has a mass of exactly 12.
• How is the relative formula mass (Mr) of a compound determined?

  By summing the relative atomic masses of the atoms in the formula.
• What is the mole (mol) in chemistry?


  The unit of substance amount in chemistry.
• What does the mass of one mole of a substance in grams equal?

  Its relative formula mass.
• If you have a substance with a relative formula mass of 58 g/mol, what is the mass of one mole of this substance?

  58 grams.
• What is an empirical formula?

  The simplest whole-number ratio of atoms in a compound.
• How does a molecular formula differ from an empirical formula?

  A molecular formula shows the actual number of atoms of each element, which may be a multiple of the empirical formula.
• What is the purpose of combustion in determining the formula of a metal oxide?

  To determine the formula of a metal oxide, such as magnesium oxide.
• What does reduction help determine in the context of metal oxides?

  The formula of a metal oxide, such as copper oxide.
• How can you calculate the percentage composition of an element in a compound?

  Using the formula: (mass of element in compound/Mr of compound)×100.
• What do state symbols in chemical equations indicate?

  The physical state of substances in a reaction.
• What does the state symbol (s) represent in a chemical equation?

  Solid.
• What does the state symbol (l) represent in a chemical equation?

  Liquid.
• What does the state symbol (g) represent in a chemical equation?

  Gas.
• What does the state symbol (aq) represent in a chemical equation?

  Aqueous solution.
• How can the percentage by mass of an element in a compound be calculated?

  Using the formula: (mass of element in compound/Mr of compound)×100
• What is an example of a metal oxide determined by combustion?

  Magnesium oxide
• What is an example of a metal oxide determined by reduction?

  Copper oxide
• What is an empirical formula?

  The simplest whole-number ratio of atoms in a compound
• What does a molecular formula show?


  The actual number of atoms of each element in a molecule or compound
• What is the mole (mol) in chemistry?


  The unit of substance amount
• How is the mass of one mole of a substance related to its relative formula mass?

  It is numerically equal to its relative formula mass in grams
• How would you calculate the mass of a substance in moles?

  Using the formula: Mass (g) = Moles × Mr
• What is relative atomic mass (Ar)?

  The weighted average mass of an element's isotopes
• On what scale is relative atomic mass measured?

  A scale where carbon-12 has a mass of exactly 12
• What is relative formula mass (Mr)?

  The sum of the relative atomic masses of the atoms in the formula
• How is relative formula mass also known?

  Relative molecular mass
• What must be true for an equation to be balanced?

  Each element must have the same number of atoms on both sides of the equation
• What is the purpose of a combustion practical in determining formulae?

  It helps determine the formula of a metal oxide by reacting the metal with oxygen.
• What is the purpose of a reduction practical in determining formulae?

  It helps determine the formula of a metal oxide by reducing it to the metal.
• Coefficients and subscripts are used to balance equations.
• What is the law of conservation of mass?

  The total mass of reactants equals the total mass of products in a closed system
• How do you calculate the molar mass of a compound?

  Add up the atomic masses of the elements in the compound