Chemical analysis

Chemical analysis

1. Pure Substances and mixtures

   • Pure - only contains atoms of that element/compound
   • Impure - mixture of two or more different elements/compounds
   • Pure elements and compounds melt and boil at specific temperatures - fixed points can be used to identify them
   • Formulation is a mixture that is designed to produce a useful product, each chemical has specific use, mixed in set proportions to give the product required properties
   • Test for water - turns white anhydrous copper sulfate blue if present - pure water - melts at 0 and boils at 100 degrees

2. Analysing chromatograms

   • Chromotography
     • Mobile phase is solvent
     • Stationary phase is paper
     • Solvent moves up paper carrying different substances different distances
     • Substance with stronger force of attraction to the solvent will travel further (in a set time)
       • more soluble substance to solvent goes further
     • Mixtures usually more than one spot while pure substances one spot on paper
   • Can analyse unkown substances in paper chromatography
   • Rf values can be measure and matched against database to identify specific substance
   • Rf = distance moved by substance / distance moved by solvent
   • Rf - Retention factor

3. Gas tests

   • Hydrogen gas burns rapidly with a 'pop' when applied a lightened splint
   • Oxygen gas relights a glowing splint
   • Carbon dioxide gas bubble into limewater turns milky/cloudy
   • Chlorine gas - bleaches damp blue litmus paper white

4. Test for positive ions

   • Some positive ions can be identified using flame test or sodium hydroxide solution
   • Flame Test
     • Some metals produce colours when put in Bunsen
     • Lithium = crimson Sodium = yellow Potassium = lilac Calcium = orange-red Copper = green
   • Hydroxide test
     • Hydroxides of most metal have 2/3+ charge are insoluable in water, when sodium hydroxide solution is added to solution of ions a precipitate of metal hydroxide is present
     • Aluminum, Calcium and magnesium ions all form white precipitates of their hydroxides, when excess sodium hydroxide is added only white precipitate of aluminum hydroxide dissolves - showing aluminum ions are present
     • Copper (II) ions a blue precipitate of Copper(II), hydroxide appears
     • Iron(II) ions, green precipitate of iron(II), hydroxide produced
     • Iron (III) ions, brown precipitate of iron (III), hydroxide formed

5. Tests for negative ions

   • Carbonate ions - add dilute hydrochloric acid to the substance to see if fizzes, If it does and the gas produced turns limewater cloudy then then the substance is a carbonate
   • Halide ions - add nitric acid and then silver nitrate solution
     • Chloride ions give a white precipitate
     • Bromide ions give a cream precipitate
     • Iodide ions give a yellow precipitate
   • Sulfate ions-add dilute hydrochloric acid and barium chloride solution if a white precipitate forms, sulfate ions are present

6. Instrumental analysis

   • Modern instrumental techniques provide fast, accurate and sensitive ways of analysing chemical subtances
   • Flame emission spectroscopy is an example of an instrumental method
     • Method indicates which metal ions are present from their characteristic line spectra, and also gives the concentration of the metal ions in a solution