Mixtures

• Mixture


  Made of more than one substance, which are not chemically joined to each other
• Mixtures


  • Air
  • Saltwater
• Composition of air


  • Nitrogen (N2, 78%)
  • Oxygen (O2, 21%)
  • Argon (Ar, 0.96%)
  • Carbon dioxide (CO2, 0.04%)
• Measuring percentage of oxygen in air


  1. React oxygen with another element, often a metal

  2. Air volume decreases until all oxygen has been added to the element
• Results for oxygen measurement experiment

  • Initial volume of air: 100 cm3
  • Final volume of air: 79 cm3
  • Decrease in volume: 100 - 79 = 21 cm3
• Percentage of O2 in original air is: 21 cm3 / 100 cm3 x 100 = 21%
• Air nearly always contains 21% O2: so whatever the initial volume, it should decrease by 21%
• If the air in one of these experiments didn't decrease by 21%, it could be because: the metal wasn't heated for long enough for all the oxygen to be reacted, or there's a leak in the apparatus
• Solution


  A mixture of a liquid (solvent) with at least one other substance mixed through it
• Dissolving terminology


  • Solute
  • Solvent
  • Solution
  • Saturated
  • Suspension
  • Soluble
  • Insoluble
• Adding salt to water

  • Salt = solute
  • Water = solvent
  • Saltwater = solution
• Solubility


  Measured in g per 100 g of solvent
• Solubility of sodium chloride in water is 36.37 g / 100 g
• Up to 36.37 g of sodium chloride can dissolve into 100 g of water
• Solubility can be scaled for different amounts of solvent, e.g. 18.185 g can dissolve in 50 g of water
• Solubility curve


  • Line = saturated (maximum mass of solid which can be dissolved at each temperature)
  • Below line = soluble (less than maximum, so it will all dissolve)
  • Above line = insoluble (more than maximum, so some will dissolve and some won't)

  
• Adding 50 g of sodium chloride to 100 g of water at 40 oC


  • 36.37 g would dissolve to form a saturated solution
  • 13.63 g would stay undissolved as a suspension