Topic 8 - Chemical analysis

Cards (67)

  • flame test lithium=crimson
  • flame test sodium=yellow
  • flame test potassium=lilac
  • flame test calcium=orange-red
  • flame test copper=green
  • Sodium hydroxide + aluminium -> aluminium hydroxide (white precipitate but redissolves in excess)
  • Sodium hydroxide + calcium -> calcium hydroxide (white precipitate forms)
  • Sodium hydroxide +copper(II) -> copper hydroxide (blue precipitate forms)
  • A pure substance is something that only contains one compound or element
  • A chemically pure substance will melt or boil at a specific temperature
  • You test purity of a sample by measuring its melting or boiling point and comparing it with the known value
  • Formulations are useful mixtures with a precise purpose that are made by following a formula
  • Paints are formulations composed of:
    Pigment - gives the paint colour (titanium oxide for white)
    Solvent - used to dissolve the other components and add viscosity
    Binder(resin) - forms a film that holds the pigment in place after it's been painted on
    Additives - added to further change the physical and chemical properties of the paint
  • Formations are really important in the pharmaceutical industry (needs to go to the correct part of the body in the correct concentration)
  • In every day life, formations can be found in cleaning products, fuels, cosmetics, fertilisers, metal alloys and food or drink
  • When you by a product, you can find that it has information about its composition on the packaging
  • Test for chlorine:
    • run through damp litmus paper
    • positive result = bleaches the damp litmus paper
  • Test for oxygen:
    • Put a glowing splint inside a test tube containing the gas
    • Positive result = the splint will relight
  • Test for carbon dioxide:
    • Bubble the gas through limewater
    • Positive result = the limewater turns cloudy
  • Test for hydrogen:
    • Hold a lit splint near the gas
    • Positive result = there will be a squeaky pop
  • Tests for anions (negative ions) often gives precipitates
  • Testing for carbonates (CO₃²⁻) = add a dilute acid, if present, carbon dioxide gas will be produced and you should test for this gas (and water)

  • Testing for sulphates (SO₄²⁻) = add a few drops of dilute hydrochloric acid and barium chloride (BaCl₂), if present a white precipitate should form
    Ba2+ + SO4'2- -> BaSO4
  • Testing for halides (Cl-,Br-, I-) = add nitric acid and silver nitrate
  • Positive halide test:
    Cl- = white precipitate of silver chloride forms
    Br- = cream precipitate of silver bromide forms
    I- = yellow precipitate of silver iodide forms
  • Sodium hydroxide + Iron(II) -> Iron hydroxide (green precipitate forms)
  • Sodium hydroxide + Iron(III) -> Iron hydroxide ( brown precipitate forms)
  • Sodium hydroxide + magnesium -> magnesium hydroxide ( white precipitate forms)
  • Flame test method:
    • clean a platinum wire loop by dipping it in some dilute HCL and then holding it in a blue flame from a Bunsen burner until it burns without any colour
    • Then, dip the loop into the sample you want to test and put it back into the flame. Record the colour of the flame.
  • Flame tests only work for samples that contain a single metal ion.
    If the sample tested contains a mixture of metal ions, the flame colours of some ions may be hidden (masked) by the colours of others
  • Some metals form a coloured precipitate with NaOH. Adding a few drops of sodium hydroxide sometimes form specific coloured precipitates
  • When testing for sulfates, you add HCL (as well as barium chloride), to get rid of any traces of carbonate ions before you do the test. These would also produce a precipitate, so they'd confuse the results.
  • An impure substance is a substance made up of two or more elements or compounds that are not bonded together chemically
  • A precipitate is a solid that is created from a solution during a reaction
  • Aluminium, calcium and magnesium ions form a white precipitate with NaOH
  • Only aluminium's precipitate dissolves when excess NaOH is added to the solution
  • Copper(II) produces a blue precipitate
    Iron (II) produces a green precipitate
    Iron(III) produces a brown precipitate
  • When you add a hydroxide to a metal, the half equation always is:
    Metal ion + Hydroxide ion -> Metal Hydroxide
  • Carbonates react with dilute acids to create carbon dioxide
  • To test for halides first add nitric acid, followed by silver nitrate solution