Topic 2 - states of matter and mixtures

• States of matter


  Solid, liquid and gas
• Melting and freezing


  1. Solid → liquid: melting

  2. Liquid → solid: freezing
• Boiling and condensing


  1. Liquid → gas: boiling

  2. Gas → liquid: condensing
• Particle model


  • Particles represented by small solid spheres
• Gas


  Particles have the most energy, most spread apart
• Liquid


  Particles have more energy than solid, less than gas
• Solid


  Particles have the least energy, fixed in place
• State changes (melting, boiling, freezing, condensing) are physical changes - they involve the forces between the particles but the particles themselves don't change
• Chemical changes are where a new product has been formed
• Particle theory can explain melting, boiling, freezing and condensing

  • Amount of energy needed to change state depends on strength of forces between particles
  • Nature of particles depends on type of bonding and structure
  • Stronger forces = higher melting and boiling points
• Predicting physical state given melting and boiling points

  1. Below melting point = solid

  2. Above melting, below boiling = liquid

  3. Above boiling = gas
• Mixture


  Consists of 2 or more elements or compounds not chemically combined together, chemical properties of each substance are unchanged
• Pure substance


  A single element or compound, not mixed with any other substance
• In everyday language, a pure substance = substance that has had nothing added to it, so it is unadulterated and in its natural state, e.g. pure milk
• Pure substances


  • Melt and boil at specific/exact temperatures
• Mixtures


  • Melt over a range of temperatures
• Fractional distillation


  1. Used to separate a pure liquid from a mixture of liquids

  2. Works when the liquids have different boiling points

  3. Commonly used to separate ethanol from water

  4. Ethanol has a lower boiling point than water so it evaporates first, the ethanol vapour is then cooled and condensed

  5. Sequence of events: heating -> evaporating -> cooling -> condensing
• Simple distillation


  1. Used to separate a solvent from a solution

  2. Works because the dissolved solute has a much higher boiling point than the solvent

  3. When the solution is heated, solvent vapour evaporates from the solution, the gas moves away and is cooled and condensed

  4. The remaining solution becomes more concentrated in solute as the amount of solvent decreases
• Filtration


  Used to separate a precipitate (insoluble salt) from a salt solution, by filtering the solution and leaving the precipitate on the filter paper
• Crystallisation


  1. Used to separate a soluble salt from the solution it is dissolved in

  2. Warm the solution in an open container to allow the solvent to evaporate, leaving a saturated solution

  3. Allow the solution to cool, the solid will come out of the solution and crystals will start to grow, which can then be collected and dried
• Paper chromatography


  1. Used to separate mixtures and give information to help identify substances

  2. Involves a stationary phase and a mobile phase

  3. Separation depends on the distribution of substances between the phases

  4. Rf value = distance moved by substance / distance moved by solvent

  5. Different compounds have different Rf values in different solvents, which can be used to help identify the compounds

  6. Compounds in a mixture may separate into different spots depending on the solvent, but a pure compound will produce a single spot in all solvents
• You need to identify which types of substance you have in the mixture and so which technique is most appropriate (from 2.7)
• Pure substances should only have one spot on a chromatogram
• Impure substances/mixtures will show up with more than one spot on a chromatogram
• To identify by comparing with known substances, carry out paper chromatography with both the known substance and substance you're testing on the same paper. If both spots are at the same height up the paper at the end then you know the substance you're testing is the same as the known substance.
• To identify by calculation of Rf values, you can calculate Rf values and then compare them to known values for different substances
• Potable water must have low levels of microbes and low levels of contaminating substances, it is not the same as pure water but is still safe
• Making waste and ground water potable

  1. Sedimentation: large insoluble particles will sink to the bottom

  2. Filtration: water is filtered through beds of sand which removes small insoluble particles

  3. Chlorination: chlorine gas is put through water to kill microbes
• Making sea water potable using distillation

  1. Filter the seawater

  2. Boil it

  3. Water vapour is cooled and condensed
• Water used in analysis must be pure because any dissolved salts could react with the substances being analysed, leaving you with a false result
• Particle model of solids

  • Particles in a regular pattern, touching, vibrating about a fixed position
• Particle model of liquids

  • Particles in a random arrangement, touching, can flow and move past each other
• Particle model of gases

  • Particles far apart, not touching, moving randomly in all directions
• State changes


  • Melting
  • Evaporating
  • Condensing
  • Freezing
  • Sublimation
  • Deposition
• Pure substance


  Contains only one type of substance, either one element or one compound
• Mixture


  Contains more than one type of substance that can be separated
• Melting point and boiling point of a substance


  Determines its state at room temperature
• Filtration


  Separates insoluble solids from liquids or solutions
• Crystallization


  Separates soluble solids from solutions by evaporation
• Simple distillation


  Separates two liquids based on their different boiling points