Chem Paper 1 RP

• Filtration


  Separates insoluble solids from liquids
• Filtration


  • Can be used to purify a reaction mixture by separating out solid impurities
  • Can only be used if the product is an insoluble solid
• Soluble


  A solid that can be dissolved in a liquid
• Evaporation


  1. Pour solution into evaporating dish

  2. Slowly heat the solution

  3. Solvent will evaporate and solution will become more concentrated

  4. Crystals will start to form

  5. Keep heating until dry crystals remain
• Evaporation


  A quick way to separate a soluble salt from a solution, but can only be used if the salt doesn't decompose when heated
• Crystallisation


  1. Pour solution into evaporating dish and gently heat

  2. Some solvent will evaporate, making the solution more concentrated

  3. Remove dish from heat and allow solution to cool

  4. Salt will form crystals as it becomes insoluble in the cold, concentrated solution

  5. Filter out the crystals and leave to dry
• Separation of rock salt

  • Grind the mixture to make salt crystals small
  • Dissolve in water, the salt will dissolve but the sand won't
  • Filter the mixture, the sand will be left on the filter paper
  • Evaporate the water to leave dry salt crystals
• Simple distillation


  Used to separate a liquid from a solution by heating and condensing the vapour
• Simple distillation


  • Can only separate substances with very different boiling points
  • Can't separate a mixture of liquids with similar boiling points
• Fractional distillation


  1. Put the mixture in a flask with a fractionating column on top

  2. Heat the mixture, the different liquids will evaporate at different temperatures

  3. The vapour with the lowest boiling point will reach the top of the column first and be collected

  4. Liquids with higher boiling points will only rise part way up the column before condensing and running back down
• Titration


  A method of analysing the concentrations of solutions by neutralising an acid with a base (or vice versa)
• Titration procedure


  1. Add a known volume of alkali to a conical flask

  2. Fill a burette with an acid of known concentration

  3. Slowly add the acid from the burette to the alkali, watching for the colour change (end-point)

  4. Record the volume of acid used and use this to calculate the concentration of the alkali
• Indicator


  Used to estimate the pH of a solution by changing colour at different pH values
• Indicators for titrations


  • Need a single, sharp colour change at the end-point, not a gradual colour change
  • Examples include litmus, phenolphthalein, and methyl orange
• Measuring energy transfer


  1. Mix the reagents in a polystyrene cup and measure the temperature change

  2. Reduce heat loss to surroundings by using insulation and a lid

  3. Can investigate effect of variables like concentration on energy transferred
• Reaction profile


  Also called an energy level diagram, shows the energy changes during a reaction
• Paper Chromatography


  1. Draw line near bottom of filter paper

  2. Add spot of ink to line

  3. Place sheet in beaker of solvent

  4. Solvent seeps up paper, carrying ink

  5. Dyes separate out

  6. Insoluble dyes stay on baseline

  7. Dry paper to get chromatogram
• Chromatography


  Technique to separate different substances in a mixture
• Substances separated by chromatography

  • Dyes in ink
• Solvent used depends on what's being tested
• Pencil marks are insoluble and won't dissolve in the solvent
• Ink shouldn't touch the solvent to avoid dissolving into it
• Each dye moves up the paper at a different rate, forming a separate spot
• Insoluble dyes stay on the baseline
• The end result is a pattern of spots called a chromatogram