CHEM - principals

• States of Matter


  • Solids
  • Liquids
  • Gases
• Solids


  • Distance: Close together
  • Arrangement: Regular
  • Movement: Vibrate
  • Speed of movement: Slowest
  • Energy: Lowest
  • Forces of attraction: Strongest
• Liquids


  • Distance: Close but further apart than solids
  • Arrangement: Random
  • Movement: Move around each other
  • Speed of movement: Faster
  • Energy: Higher
  • Forces of attraction: Weaker
• Gases


  • Distance: Far apart
  • Arrangement: Random
  • Movement: Move in all directions
  • Speed of movement: Fastest
  • Energy: Highest
  • Forces of attraction: Weakest
• Energy required for state changes depends on the strength of forces between particles
• Stronger forces of attraction require more energy to overcome for state changes (higher melting and boiling points)
• Interconversion of state


  When matter changes from one state to another due to temperature or pressure changes
• It is a physical change that involves changes in forces between particles (the particles and chemical properties remain the same)
• Melting


  1. Solid -> liquid by adding heat energy

  2. Occurs at specific temp (melting point), which is unique to each pure solid
• Boiling


  1. Process of a liquid -> gas by adding heat energy

  2. Occurs at a specific temp (boiling point), which is unique to each pure liquid
• Freezing


  1. Liquid -> solid (reverse of melting)

  2. Occurs at the same temp as melting (freezing point)
• Evaporation


  1. Liquid -> gas at the liquid's surface, below the boiling point

  2. Larger surface area, warmer the liquid/surface, faster the rate
• Condensation


  Gas -> liquid, usually by cooling. Loses energy
• Sublimation


  Solid -> gas
• Change from solid to liquid to gas: particles gain more kinetic energy, move around more and become more randomly arranged and further apart
• Diffusion and dilution provide evidence for the kinetic theory of matter
• Dilution of coloured solutions

  Provide evidence for the small size/mass of particles
• Diffusion


  • Random movement of particles from areas of high to lower concentration (not solids(vibrate))
  • Diffusion provides evidence for the movement of particles
  • Fastest in gases (particles far apart+move quickly+randomly+easily mix together)
  • Diffusion fastest with particles of low molecular mass
• Solute


  A substance that dissolves to make a solution
• Solvent


  A liquid a solute dissolves in to make a solution
• Solution


  What's formed when a solute dissolves in solvent
• Saturated solution


  Contains the max amount of dissolved solute at a certain temp (there must be some undissolved solid present)

  
• Solubility


  • The mass of solute that dissolves in 100g water (to make a saturated solution)
  • Measurement of how much of a substance will dissolve in a given volume of liquid
  • Solubility of gas depends on pressure+temp (Pressure increases, gases more soluble; Temp increases, gases less soluble)
  • Solubility of solids affected by temp (Temp increases, solid more soluble)

  
• As temp increases, solids usually become more soluble and gases become less soluble
• Solubility curve for three salts. While the solubility of most salts increases with temperature, sodium chloride, or common salt, hardly changes at all
• Element


  A pure substance that can't be broken down into any simpler substance by chemical means. Only contain one type of atom
• Mixture


  Two or more substances mixed together (not chemically combined). Can be separated by physical means
• Compound


  Two or more elements chemically combined and can't be separated by physical means
• A pure substance has a fixed melting point and boiling point (e.g. water boils at 100C and freezes at 0C)
• Mixture/impure substances melts+boils over range of temps - melting point lower and boiling point higher than pure substances
• Crystallisation


  1. Separate solute (dissolved solid) from solution to produce a soluble salt

  2. Heat solution to boil off some water until the solution is saturated. Allow to cool so that crystals form (due to decreasing solubility). Filter off crystals

  
• Filtration


  1. Separate solid from liquid eg. excess copper oxide from copper sulphate solution

  2. Use filter funnel and filter paper – solid is the residue, liquid is the filtrate

  
• Simple distillation


  1. Separate solute and solvent (liquid and soluble solid) from solution

  2. Heat the solution in a flask with a condenser attached. The water boils, is condensed and can be collected, the solid remains in the flask (bec. Dissolved solute has higher boiling point)
• Fractional distillation


  1. Separate a mix of 2 liquids eg.ethanol and water or fractions in crude oil

  2. Works when liquids have different boiling points

  3. A fractionating column and a condenser used. The lower boiling point liquid distils over and the higher boiling point liquid remains in the flask
• Paper chromatography


  1. Separate a mixture of coloured inks (different solubilities in a solvent)

  2. Pencil line (ink dissolves) above solvent level.

  3. Place spots of the sample.

  4. An impure substance will show multiple spots, while a pure substance show only one spot.

  5. Rf = distance travelled by substance ÷ distance travelled by solvent
• Atoms


  The smallest particles of an element that consists of electrons surrounding a nucleus containing protons+neutrons
• Molecule


  Two or more atoms covalently bonded together
• Atomic number (Proton number)


  Number of protons in nucleus of atom
• Mass number


  Number of protons+neutrons in nucleus of atom
• Isotopes


  Different atoms of the same element with same no. of protons but different no. of neutrons in nucleus. Have identical chemical properties(same no.of electrons) and different physical properties