Topic 1: Qualitative analysis

Topic 1: Qualitative analysis

1. Qualitative analysis- any method used to identify which chemicals are present for example using an indicator to find out if acids are present.

2. Quantitative analysis- any method used to determine the amount of a particular chemical present for example carrying out an acid-base titration.

3. Flame tests for metal ions: yellow = sodium, lilac = potassium, brick red = calcium, blue/green = copper

4. Precipitate tests for metal ions - add sodium hydroxide (NaOH) to each solution

   • Copper = blue precipitate
   • Iron II = green precipitate
   • Iron III = brown precipitate
   • Aluminium = white precipitate
   • Calcium = white precipitate
   • Aluminium and calcium can be distinguished by adding excess sodium hydroxide
     • Calcium ions would be unchanged but aluminium ions would redissolve to form a colourless solution
   • All preciptates are solid hydroxides of the cation e.g. calcium hydroxide

5. Testing for Halide ions:chloride, bromide and iodide- add silver nitrate (AgNO3)

   • Chloride ions = white precipitate
   • Bromide ions = cream/ pale yellow
   • iodide ions = yellow

6. Anion = negative

7. Cation = positive

8. Identifying ammonium ions: warm the unknown substance (e.g. ammonium chloride) with sodium hydroxide (NaOH)

   • If a smelly gas is given off and damp red litmus paper turns blue then ammonium ions are present
   • NaOH(aq) + NH4Cl(aq) = NH3(g) + H2O(l) + NaCl(aq)

9. Why test for ions in industry?

   • Forensic science, water checked for purity and safety- levels of compounds/ ions can be unsafe, also to identify unknown compounds in water
   • chlorine is used to kill bacteria in our water so the concentrations of chloride ions are monitored by chemists
   • minerals in the diet are very important for health- ions tests our done on our blood to check for mineral defiency
     • Copper, Potassium, Calcium & sodium are tested for - flame test
     • chlorides and iodides are tested for to - halide test
   • water that is too hard will produce alot of scum- impact on industrial and domestic machinery e.g. washing machines