C3-Quantitative Chemistry

• Relative Atomic Mass:

  A$_r$ x number of atoms of that element / M$_r$ of the compound (x100)
• Moles :

  mass (g) of an element or compound / M$_r$ of the element or compound
• Conservation of Mass :

  During a chemical reaction no atoms are created nor destroyed meaning the mass of reactants = mass of products
• If the mass increases, it means the reactants is a gas and all the products are solids, liquids or aqueous
• If the mass decreases, it means one of the products is a gas and all the reactants are solid, liquids or aqueous
• How to balance equations using reacting masses :

  • Work out the Mr of each of the substances in the reaction
  • Calculate the number of moles of each substance
  • Divide the number of moles of each substance by the smallest number of moles in the reaction
  • If any of the numbers aren't whole numbers ,multiply all the numbers by the same amount so that they all become whole numbers
  • Write the balanced symbol equation for the reaction by putting these numbers in front of the chemical formulas
• How to calculate the mass of a product formed in a reaction using the mass of the limiting reactant :

  • Write out the balanced equation
  • Work out the relative formula masses (Mr) of the reactant and product you want
  • Calculate the number of moles there are in the substance you know the mass of
  • Look at the ratio of moles
  • Calculate the mass
• Volume of a gas (dm$^3$) = mass of gas (g) / Mr of gas
• concentration ($\frac{g}{dm^3}$) = mass of solute ($g$) /volume of solvent ($dm^3$)
• concentration ($\frac{mol}{dm^3}$) =number of moles ($mol$)/ volume of solvent ($dm^3$)
• Atom economy :

  relative formula mass of desired products/relative formula mass of all reactants (x100)
• Low atom economy :

  • bad for the environment as it uses up resources very quickly resulting in lots of waste that is disposed off unsustainable
  • isn' t profitable as raw materials which are expensive to buy are not used effectively
• High atom economy :

  • reactions with highest atom economy have 1 product
  • better for the environment that reactions with low atom economies as it creates useful by products
  • more profitable as efficiency increases
• Percentage yield :

  mass of product actually made / maximum theoretical mass of product (x100)
• High percentage yield :

  • reduces waste
  • reduces cost