Chem calculations

    Cards (9)

    • Calculate % mass of an element in a compound
      (Ar x number of atoms of that element / Mr of compound ) x 100
    • number of moles in a given mass
      mass in g / Mr
    • Conservation of mass
      No atom are destroyed or created. There are the same number and types of atoms on each side of a reaction equationl
    • if mass seems to change, usually a gas is involved
    • Gases and solutions
      • volume of gas = ( mass of gas / Mr of gas ) x 24
      • Concentration = number of moles of solute / volume of solvent
    • Atom economy = ( relative formula mass of desired products/ relative formula mass of all reactants ) x 100
    • percentage yield
      ( mass of product actually made/ maximum thereorical mass of product) x 100
    • yield is always less than 100%

      • not all reactants react to make a product
      • there could be side reactions
    • Titrations
      allow you to find acid amount needed to neutralise a quantity of alkali, vice versa.
      1. use pipette, add set volume of alkali to a conical flask. Add 2-3 drops of indicator.
      2. use funnel to fill a burette with some acid of known concentration.Record initial volume of acid in burette
      3. use burette, add acid to alkali a bit at a time. swirl the flask
      4. the indicator changes colour when alkali has been neutralised(phenolphthalein is pink = alkali and colourless acidic)
      5. record final vol of acid in burette with initial reading and find vol of acid used to neutralise alkali