States of Matter and mixtures

• Describe the arrangement and movement of particles in solids

  1. Tightly packed together in a regular arrangement

  2. Vibrate in fixed positions
• Describe the arrangement and movement of particles in liquids

  1. Close together but able to move past each other

  2. Vibrate and move around each other
• Describe the arrangement and movement of particles in gases

  1. Well separated with no regular arrangement

  2. Vibrate and move freely at high speeds
• Interconversion of state


  When matter changes from one state to another due to changes in temperature or pressure
• Melting


  Solid → liquid
• Freezing


  Liquid → solid
• Evaporation


  Liquid → gas
• Condensation


  Gas → liquid
• Describe the forces between particles in solids, liquids and gases

  1. Solids - Strong forces of attraction between particles which keeps them in their fixed positions

  2. Liquids - Weaker attractive forces than in solids

  3. Gases - Weakest intermolecular forces so particles are in random movement
• Physical changes are relatively easy to reverse
• Sublimation


  When a solid changes straight into a gas
• Describe what happens, in terms of particles, when a solid is heated and melts into a liquid

  When heated the particles absorb thermal energy which is converted into kinetic energy. The particles in the solid vibrate more. This causes the solid to expand until the structure breaks, and becomes a liquid
• Describe what happens, in terms of particles, when a liquid is heated and evaporates into a gas

  When heated, the particles in a liquid expand and some particles on the surface gain sufficient energy to overcome the intermolecular forces and evaporate. At the boiling point, all of the liquid particles gain enough energy to evaporate
• Substance A melts at -183oC and boils at -50oC. What state is A at -90oC?
• Mixture


  Contains 2 or more elements or compounds that are not chemically combined together. The chemical properties of each substance in the mixture are unchanged
• Pure substance


  A single element or compound, not mixed with any other substance
• Simple distillation


  Used to separate a solvent from a solution. It is useful for producing water from salt solution
• How can ethanol be separated from water?

  1. Ethanol has a lower boiling point than water so can be separated from water by simple distillation:

  2. - Distillation apparatus set up.

  3. - Mixture boiled.

  4. - Ethanol evaporates first.

  5. - Ethanol vapour cools in the condenser, condensing back to a liquid before being collected
• Fractional distillation


  Used to separate all the elements/compounds in a mixture. These chemicals must have different boiling points to be separated
• How does fractional distillation work?

  1. - Oil is heated until it evaporates into the fractionating column.

  2. - Vapours rise up the fractionating column and condense at the different fractions, depending on the relative boiling point of each substance
• Filtration


  Used to separate an insoluble substance from a solution
• Describe how to separate an insoluble substance from a solution

  1. - Place filter paper in a funnel.

  2. - Pour the solution containing an insoluble substance through the funnel into a conical flask.

  3. - The insoluble substance will collect on the filter paper and the solution will collect in the conical flask
• Crystallisation


  Used to separate a soluble solid from a solution if the solid decomposes when heated
• How could you separate a soluble solid from a solution, if the solid decomposes when heated?

  Use the process of crystallisation
• Separate an insoluble substance from a solution

  1. Place filter paper in a funnel

  2. Pour the solution containing an insoluble substance through the funnel into a conical flask

  3. The insoluble substance will collect on the filter paper and the solution will collect in the conical flask
• Crystallisation


  The process used to separate a soluble solid from a solution if the solid decomposes when heated
• Separate a soluble solid from a solution if the solid decomposes when heated


  1. Pour the solution into an evaporating dish and heat gently

  2. When the crystals start to form, remove the dish from the heat and leave to cool

  3. Once cold, filter the crystals out of the solution and leave them in a warm place to dry
• Chromatography


  The process used to identify soluble substances in a mixture
• How paper chromatography works to separate a mixture

  1. The mobile phase (solvent) moves through the stationary phase (paper) so anything dissolved in the mobile phase will move with up the paper

  2. Compounds interact differently with each phase so will move different distances through the stationary phase meaning they will be separated
• Chromatography


  Can show the composition of a mixture by separating different coloured substances as they have different solubilities in the solvent and will travel at different rates
• Pencil should be used to draw the line along the bottom of the chromatography paper as it is insoluble in the solvent
• The water (solvent) in the beaker for paper chromatography should be no deeper than 1 cm deep to prevent washing away the substances placed on the line
• A lid should be used when carrying out paper chromatography to prevent the solvent evaporating
• Pure substance on a chromatogram

  Produces one spot
• Impure substance on a chromatogram

  Produces more than one spot (one spot for each chemical)
• Rf value


  The ratio between the distance travelled by the dissolved substance (the solute) and the distance travelled by the solvent
• Calculate Rf values


  Rf = Distance travelled by substance / Distance travelled by solvent
• When measuring the distance moved by a substance on the chromatography paper, measure from the pencil baseline to the middle of the spot of the substance
• Use chromatography to see if a certain substance is present in a mixture


  1. Run a pure sample of this substance alongside the unknown mixture

  2. If the Rf value of the pure substance matches the value of one of the spots from the mixture, it is likely to be present
• Substances with a higher solubility in the solvent will travel further up the chromatography paper