Module 1 practical skills

• The full procedure for purifying an organic liquid product

  1. heat under distillation to produce an impure product

  2. use a separating funnel to remove an organic layer from an aqueous layer

  3. dry the organic liquid using an anhydrous salt eg CaCl2 (s)

  4. redistil to produce the must pure liquid product possible.
• How to measure rate of reaction

  The rate of a reaction can be followed by measuring how any quantity that is proportional to the concentration of a reactant or product changes with time eg the volume of a gaseous product.

  A graph of the quantity measured is then plotted against time and a smooth curve drawn through the points. The gradient of this curve at any time is proportional to the rate of reaction at that time. The initial rate of reaction is the gradient drawn at t = 0.

  gradient = change in quantity / change in time
• The classes of chemical hazards in the laboratory

  The classes of chemical hazard met in the laboratory include irritant, corrosive, toxic and flammable. Steps should be taken to minimise the risks arising from using these eg a hot water bath can be used to heat a flammable liquid, appropriate eye protection should be worn when using irritant and especially corrosive substances.
• Test for aqueous cations (ammonium)

  ammonium ions add warm NaOH (aq) test for an alkaline gas damp red litmus turns blue

  Ionic equation: NH4+ (aq) + OH- (aq) -> NH3 (g) + H2O (l)
• Test for aqueous anions (carbonate)

  add HCl (aq) bubbles of colourless gas (effervesce)

  Ionic equation: CO32- (aq) + 2 H+ (aq) -> CO2 (g) + H2O (l)
• Test for aqueous anions (sulfate)

  add BaCl2 (aq) white precipitate

  Ionic equation: SO42- (aq) + Ba2+ (aq) -> BaSO4 (s)
• Test for aqueous halide ions (chloride)

  add AgNO3 (aq) precipitates distinguished with aqueous NH3

  Ionic equation: Cl- (aq) + Ag+ (aq) -> AgCl (s) white precipitate dissolves in dilute NH3 (aq)
• Test for aqueous halide ions (bromide)

  add AgNO3 (aq) precipitates distinguished with aqueous NH3

  Ionic equation: Br- (aq) + Ag+ (aq) -> AgBr (s) cream precipitate does not dissolve in dilute NH3 (aq) does dissolve in concentrated NH3 (aq)
• Test for aqueous halide (iodide)

  add AgNO3 (aq) precipitates distinguished with aqueous NH3

  Ionic equation: I- (aq) + Ag+ (aq) -> AgI (s) yellow precipitate does not dissolve in NH3 (aq) at all
• Order of the precipitate tests

  CaSHA