Chemical Analysis

Cards (17)

  • A chemically pure substance...
    o only contains a single element or compound (not mixed with any other substance)
    o will only melt/boil at a specific temperature, impurities in a sample...
    decrease melting point & increase melting range of the substance
    increase boiling point & increasing boiling range of the substance
    o the closer you measured value is to the actually melting/boiling point, the purer the sample
    o e.g. oxygen gas, carbon dioxide gas
  • • a formulation is...
    o a useful mixture with a particular purpose
    o made by mixing the components in carefully measured quantities to ensure that the product has the
    required properties
  • Chromatography can be used to separate mixtures & can give information to help identify substances
    o The result of a chromatography analysis is called a chromatogram
    • Chromatography involves 2 phases
    o Mobile – where the molecules can move (liquid or gas) – the solvent that moves through the paper
    o Stationary – where the molecules can’t move (solid or viscous liquid) – the paper
  • Separation depends on the distribution of substances between the phases
    • The mobile phase moves through the stationary phase, anything dissolved in the mobile phase (solvent) moves
    with it
    • Each chemical in the mixture will be attracted to the stationary phase (paper) to a different extent
    o Chemicals strongly attracted to the stationary phase won’t move very far (less soluble in the solvent)
    o Chemicals weakly attracted to the stationary phase will move further up (highly soluble in the solvent)
  • Rf = distance travelled by solute / distance traveled by solvent
  • Hydrogen:
    Hold a burning splint at the open end of a test tube of gas
    Hydrogen burns rapidly with a squeaky pop
    (because hydrogen + oxygen → water)
  • Oxygen:
    Inserting a glowing splint into a test tube of gas
    The splint relights
  • Carbon dioxide:
    Bubble through carbon dioxide through lime water (calcium hydroxide)
    The limewater turns cloudy
  • Chlorine:
    Put damp litmus paper into chlorine gas
    The litmus paper is bleached & turns white
    (may temporarily turn red as chlorine is acidic)
  • Lithium - Crimson
    Sodium - Yellow
    Potassium - Lilac
    Calcium - Orange-red
    Copper - Green
  • o Copper (II) – Cu2+ → Blue
    o Iron (II) – Fe2+ → Green
    o Iron (III) – Fe3+ → Brown
    o Calcium – Ca2+ → White
    o Magnesium – Mg2+ → White
    o Aluminium – Al3+ → White, then redissolves in excess sodium hydroxide to form a colourless solution
  • Carbonates (CO32-) react with dilute hydrochloric acid to produce carbon dioxide
    • So to test for carbonates you react the sample with dilute HCl then bubble any gas produced through limewater
    o if the limewater goes cloudy the gas produced was CO2, so the sample contains carbonate anions
  • Halides (anion test)
    Halides are the ions of group 7 elements
    • Add dilute nitric acid to remove any impurities, then add silver nitrate solution
    o chloride (Cl-) produces a white precipitate (Silver chloride)
    ▪ e.g. Ag+ + Cl- → AgCl
    o bromide (Br-) produces a cream precipitate (Silver bromide)
    o iodide (I-) produces a yellow precipitate (Silver iodide)
  • Sulfates (anion test)
    • Sulfates (SO42-) react with barium chloride solution to produce a white precipitate
    o Ba2+ + SO42- → BaSO4
    • Before adding barium chloride, add dilute hydrochloric acid to remove any traces of carbonate ions (which
    would also produce a precipitate confusing the results)
  • Instrumental methods
    Elements and compounds can be detected and identifies using instrumental methods (tests that use machines)
    • Instrumental methods are accurate, sensitive (detect even the tiniest amounts of substances) and rapid
  • Flame emission spectroscopy is an instrumental method used to analyse metal cations in a solution
    • The sample is put into a flame and the light given out (due to excited elections transferring energy as light) is
    passed through a spectroscope which detects the different wavelengths of light
    • The line spectrum produced can be analysed to identify the metal ions contained and their solutions
    o each ion produces a different spectrum due to the different electron arrangements and charges which produce different wavelengths of light
    the intensity of the lines indicates the concentration
  • Describe what you would see when bromine water is added to an unsaturated organic compound.
    Goes colourless from brown