Topic 8 - Chemical analysis

• 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