Chemistry 🧪💚

• Paper chromatography


  Allows separation of substances based on where they move on the paper
• Paper chromatography


  • Paper is the stationary phase
  • Solvent liquid that moves up the paper and dissolves substances
  • Substances move different distances based on solubility
• Paper chromatography procedure


  1. Place a dot of first colour near bottom of paper

  2. Place a dot of second colour near first

  3. Place paper in solvent

  4. Solvent moves up paper and dissolves ink

  5. More soluble substances move further up paper
• More soluble substances move further up paper than less soluble substances
• Water treatment steps


  1. Filtration - uses a wire mesh to stop large particles

  2. Sedimentation - chemicals added to make small particles clump together and sink

  3. Chlorination - chlorine gas bubbled through to kill bacteria
• Normal water often contains ions that can affect chemical reactions
• Deionising water removes ions normally present in water
• Using normal water can give false results in chemical experiments
• Simple distillation


  Separates liquids based on different boiling points
• Simple distillation procedure


  1. Heat solution

  2. Vapour rises up glass tube

  3. Vapour condenses in condenser

  4. Condensed liquid collected in beaker
• Simple distillation can be used to separate water from seawater
• Fractional distillation


  Separates a mixture of liquids with different boiling points
• Fractional distillation procedure


  1. Gently heat mixture

  2. Lower boiling point liquids evaporate first

  3. Vapours pass up column and condense at different temperatures

  4. Liquids with different boiling points collected separately
• Compounds


  Substances made up of two or more elements combined in fixed proportions
• Mixtures


  Contain two or more substances that are not chemically combined
• Separation techniques


  • Filtration
  • Crystallisation
  • Chromatography
• Separation techniques can only be used on mixtures, not compounds
• Chemical formula


  Shows the elements present in a compound and the relative numbers of each
• Chemical formulas


  • CaSO4 - Calcium sulfate
  • NaCl(aq) - Sodium chloride in water
  • Cu2Br2 - Copper (II) bromide
• Crystallisation procedure


  1. Leave solution for days for water to evaporate

  2. Crystals form as solute becomes more concentrated

  3. Can speed up by gentle heating
• Some chemicals break down if heated too much during crystallisation
• Pure water only Contains H₂O molecules
• Portable water contains additional substances
• Steps to treat fresh water

  1. Filtration

  2. Sedimentation

  3. Chlorination
• Filtration


  • Wire mesh stops large bits going through e.g. twigs
  • Gravel, sand beds filter any other solid bits
• Sedimentation


  • Chemicals added make smaller particles clump together and settle at bottom
• Chlorination


  • Chlorine gas bubbled through to kill harmful bacteria and other microbes
• Water used in chemical experiments can affect reactions if it contains ions
• Deionised water has had ions that were in normal tap water removed
• Using normal water can give false results in chemical experiments
• pH


  Measure of acidity or basicity of a solution
• Measuring pH


  1. Use indicator chemical dyes that change colour depending on pH

  2. Use universal indicator

  3. Use pH probe connected to pH meter to electronically measure pH
• pH probe


  • Provides more accurate and precise results than using indicator dyes
• Acid


  • Any substance that forms aqueous solution with pH less than 7
  • Releases hydrogen ions in water making it acidic
• Base


  • Any substance with pH greater than 7
  • Forms hydroxide ions in water
• Neutralisation reaction


  Acid + base -> salt + water
• Bases


  • Sodium hydroxide (NaOH)
  • Calcium hydroxide (Ca(OH)2)
• Salts


  • Sodium chloride (NaCl)
  • Calcium carbonate (CaCO3)
• Making a soluble salt

  1. Add dilute acid (HCl) to insoluble base (copper oxide)

  2. Gently heat

  3. Slowly add more insoluble base until no longer disappears

  4. Filtered solution contains soluble salt (copper chloride)
• Obtaining pure salt crystals

  1. Evaporate some water using water bath

  2. Allow crystals to form and cool

  3. Filter out crystals and dry