C8 - Chemical Analysis

C8 - Chemical Analysis

1. Purity

   • Only one compound or element - not mixed with anything else
   • A melting or boiling point can tell you the purity
     • Specific to element/compounds
       • Closer = more pure
     • Impure = lower melting/higher boiling

2. Formulations

   • Useful mixture with precise purpose
   • components measured specifically to perform function
   • Pharmacy
     • Consumption
     • Shelf Life
     • Concentration
   • Packaging - ratio/percent of each component = suitable decisions

3. Paper Chromatography

   • Mobile phase = molecules can move (liquid or gas)
     • more time spent here = quicker movement through stationary
   • Stationary phase = molecules cannot move (solid or thick liquid)
   • Distance dependent on how soluble they are + how attracted to the paper they are
     • higher solubility + low attraction = more time in mobile = further
   • ink = soluble
   • pencil = insoluble
   • Rf values
     • Is a certain substance in a mixture
       • Measure pure substance Rf (reference) - compare to Rf spots in mixture
     • Change of solvent = Rf changes
       • Mixture + Reference spot in all solvents is the same = substance present

4. Gas Tests

   • Chlorine = bleaches litmus paper (may turn red before Cl is acidic
   • Oxygen = relights glowing splint
   • Carbon Dioxide = bubble through limewater turning it cloudy
   • Hydrogen = squeaky pop from lit splint

5. Tests for Anions

   • Dilute acid for carbonates
     • 1. Add drops of dilute acid
     • 2. Connect test tube to test tube of limewater
     • 3. Carbonate = present if limewater turns cloudy (CO2)
   • Sulfates
     • 1. Add HCl
       • gets rid of carbonates which also produce a white precipitate
     • 2. Add barium chloride
     • 3. Sulfate ions = white precipitate forms
   • Halides
     • 1. Add dilute nitric acid
     • 2. Add silver nitrate
     • Chloride = white precip
     • Bromide = cream precip
     • Iodide = yellow precip

6. Tests for Cations

   • Flame Test
     • 1. Clean loop by dipping in HCl + putting through flame
     • 2. Dip in solid/solution
     • 3. Put through flame
     • Lithium
     • Sodium
     • Potassium
     • Calcium
     • Copper
     • Works for single metal ions
       • Flame Emission Spectroscopy
         • Heat causes electrons to change energy levels. Drop back = transfer light
         • Identify wavelengths create line spectrum
           • Higher concentration = more intense
         • No two ions have the same line spectrum - can identify more than one ion
         • Advantages
           • More accurate
             • Flame tests rely on the human eye
           • Very fast/automated
           • Very sensitive
   • Sodium hydroxide forms a precipitate
     • Calcium
     • Copper (II)
     • Iron (II)
     • Iron (III)
     • Aluminium
       • White then redissolves to be colourless
     • Magnesium
     • Most metal hydroxides = insoluble

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