Chemistry Practical Techniques

    This page summarises the practical techniques required for the exams (i.e. the last chapter in the official textbook). I am not currently planning on further developing this page or adding flashcards since the content is covered within the other Chemistry pages on my site.

Measurements:

       I didn't do notes on these since they're quite simple
    • Weighing a solid
    • Pipette
    • Burette
    • Gas volumes (gas syringe or inverted burette/measuring cylinder)

    Organic:

    • Heating under reflux
      - Water in bottom, out top of condenser
      - Anti-bumping granules burst bubbles, reducing chance of boiling over

    • Purifying an organic liquid product
      - Separating funnel
      - Add sodium hydrogen carbonate or dilute acid
      - Dry by adding anhydrous sodium sulfate
      - Then use distillation

    Inorganic:

    • Making water-soluble inorganic salts
      - Acid + alkali
         - Titration to find how much acid needed for neutralisation
         - Repeat but without indicator
         - Evaporating basin and Bunsen until crystals appear
         - Leave to cool
         - Heat in watch glass and oven, until constant mass
      - Acid + insoluble base
         - Heat mixture until neutral (indicator paper), adding base as needed
         - Filter, evaporating basin until crystals appear
         - Leave to cool
         - Filter, wash, heat in watch glass in oven until constant mass

    • Making water insoluble inorganic salts
      - Mix equal volumes in beaker, forming precipitate
      - Filter, wash
      - Watch glass in oven until constant mass

    Purification:

    • Distillation
      - Water goes in furthest from the pear shaped flask

    • Thin layer (silica plate), paper chromatography

    • Recrystallisation
      - Solvent: desired compound dissolves at high temperatures only, impurities all dissolve at all temperatures
      - Dissolve in the minimum amount of hot solvent
      - Preheat the filter funnel and conical flask
      - Filter (to remove insoluble impurities), keep filtrate. Cool. Filter, keep crystals
      - Dry

    • Vacuum filtration
      - Vacuum pump through side arm of conical flask
      - Damp filter paper in Buchner funnel
      - Disconnect flask from vacuum pump before turning it off (prevent suck-back)

    Analysis:

    • Melting point determination
      - Fill Thiele tube with a liquid/oil
      - Solid sample in capillary tube alongside mercury thermometer
      - Heat, recording the temperature when the sample starts/ends melting
      - Range between two readings is the melting range
      - The higher the melting range, the more impure the sample is

    • Colorimetry
      - Filter (complementary colour to solution colour)
      - Zero with cuvette of solvent (usually water)

    Making standard solutions:

    • From a solid
      - Mix with deionised water in a beaker before pouring into volumetric flask

    • From higher concentration solution

    • Calculations: use

    Titration:

    • Acid-base
    • Iodine-thiosulfate
    • Redox

    Energy transfer:

    • Burning fuel
      - Use spirit burner (keep cap on when not in use to prevent evaporation)
      - Use copper calorimeter, draught excluder

    • Reaction
      - Insulated polystyrene cup
      - Extrapolate backwards if readings were taken every 30 s/60 s etc

    Electro:

    • Electrolysis
      - Use inverted test tubes (filled with water) to collect gases
      - Purification: pure metal cathode, impure anode, (aq) solution

    • Finding standard electrode potentials
      - H+(aq) and platinum wire electrode surrounded by H2(g)
      - Other electrode is the metal to be measured in its solution
      - Salt bridge, voltmeter

    Measuring pH:

    • Calibrate in a neutral solution (pH is temperature dependent)
    • Also calibrate in pH 4.00 for acid measurement, or pH 10.00 for alkali measurement
    • Then rinse electrode and use for testing

    Alkenes:

    • Cracking
      - Porcelain chips to be heated in centre of boiling tube
      - Mineral wool soaked in alkene [e.g. paraffin (l)] at end
      - Discard first tube
      - Heat whilst changing tubes to prevent suck-back

    • Testing for unsaturation
      - Br2(aq) (yellow/orange → colourless if an alkene)