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Chemistry 2: Chemical Analysis (Identification of common gases: (Chemical…
Chemistry 2: Chemical Analysis
Flame tests:
Colour produced:
Lithium - Crimson
Sodium - Yellow
Potassium - Lilac
Calcium - Orange/Red
Copper - Green/ Blue
Difficulties/ Limitations of Flame tests:
If a sample contains a mixture of ions, some colours can be masked
Used to identify metal ions (Cat-Ions):
Pure substances / Formulations:
How can pure substances be distinguished from mixtures?
Using their melting/ boiling points. Pure substances melt/ boil at a specific temp
Formulas
What is a formulation?
Mixture designed as a useful product
Components carefully measured
Ensuring the product has the required properties
Examples:
Fuels, Cleaning agents, paints, medicines, foods & fertillisers
What is a Pure substance:
Single element or compound, not mixed with other substances
(A substance that has nothing added to it, in it's natural state)
Identification of common gases:
Chemical test for Oxygen:
Glowing splint relights
Chemical test for Carbon dioxide:
Lime water turns milky
Chemical test for Hydrogen:
Burning splint makes a squeaky pop
Chemical test for Chlorine:
Damp litmus paper bleaches white
Chromatography:
Differences between the chromatogram of pure substances compared to chromatograms of mixtures:
Pure substances make a single spot
Mixtures separate into different spots
How does paper Chromatography separate mixtures?
Chromatography paper (is the stationary phase)
Solvent (Mobile phase)
The mobile phase flows thru stationary phase & carries components of mixture with it
Different components travel at different rates
What is Chromatography used for?
Separating mixtures to identify substances within a mixture
(Involves: Stationary and mobile phases)
Rf:
What is a substances Rf value?
Ratio of substances : Distance moved by solvent
Rf = Distance moved by substance / Distance moved by solvent
How are Rf values useful?
Different compounds have different Rf values, in different solvents
Rf values can be used to help identify compounds
Metal Hydroxides:
Colour of precipitate:
Aluminium - White (Dissolves in excess)
Calcium - White
Magnesium - White
Copper (II) - Blue
Iron (I) - Green
Iron (II) - Brown
Chemical used to identify Cat-ions:
Copper Sulphate + Sodium hydroxide -> Copper hydroxide + Sodium Sulphate
(CuSO4 + 2NaOH -> Cu(OH)2 + Na2 SO4)
Halides:
2 Chemicals used in the test for halides
Silver nitrate & Dilute Nitric acid
Precipitates colours:
Silver Chloride - White
Silver Bromide - Cream
Silver Iodide - Yellow
3 Halide ions that can be identified:
Bromide
Chloride
Iodide
What happens when Carbonates react with acid :
Fizzing - Carbon dioxide is produced
Instrumental methods &
Flame emission spectroscopy:
Flame emission spectography:
What is it?
Instrumental method used to identify metal ions in a solution
What is the Process of it:
Samples put in a flame
Light given out is passed thru a spectroscope
Output = A line spectrum
Which can be used to identify metal ions & Measure concentrations
3 advantages of instrumental methods:
More accurate
More Sensitive
Quicker
Sulphates:
Colour of precipitate when barium chloride is added to a solution containing a sodium ion:
White
2 Chemicals used in test for sulphates:
Barium chloride & dilute Hydrochloric acid