state of matter (chemistry)

• The three 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
• The amount of energy needed to change state


  Depends on the strength of the forces between the particles
• The nature of the particles

  Depends on the type of bonding and structure of the substance
• The stronger the forces between the particles

  The higher the melting point and boiling point
• Predicting the physical state of a substance

  1. At temperatures below the melting point, the substance will be solid

  2. At temperatures above the melting point but below the boiling point, the substance will be liquid

  3. At temperatures above the boiling point, the substance will be a gas
• Mixture


  Consists of 2 or more elements or compounds not chemically combined together
• 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 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. Solvent vapour evaporates from the solution, the gas moves away and is cooled and condensed

  4. The remaining solution becomes more concentrated in solute
• Filtration


  Used to separate an insoluble precipitate from a solution
• Crystallisation


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

  2. Warm the solution to evaporate the solvent, leaving a saturated solution

  3. Allow the solution to cool, the solid will come out of the solution and crystals will grow
• Paper chromatography


  1. Used to separate mixtures and 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
• Pure substances should only have one spot on a chromatogram
• Impure substances/mixtures will show up with more than one spot on a chromatogram
• Identifying substances 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 then the substance you're testing is the same as the known substance
• Identifying substances by calculation of Rf values

  Calculate Rf values and compare them to known values for different substances
• Waste and ground water can be made potable by sedimentation, filtration and chlorination
• 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 not contain any dissolved salts
• The kinetic theory of gases explains the behavior of gases based on the motion of their particles.
• Increasing temperature increases the average speed of particles, causing them to collide more frequently with one another.
• Increasing temperature increases the average speed of particles, causing them to collide more frequently with their surroundings.
• Gases are highly compressible compared to liquids and solids.
• The kinetic energy of particles is the reason why they move around.
• Gases have no definite shape or volume and expand to fill the entire container they are in.
• Pressure increases when gas volume decreases or temperature increases.
• Pressure exerted by gas depends on the number of particles hitting the walls per unit time.
• Solids have strong intermolecular forces that hold the atoms together tightly.
• Particles in a gas can travel long distances between collisions due to low intermolecular forces.