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Chemical Analysis

Chemical Analysis. How can we test for the presence of positive and negative ions?. Starter : Why might we need to know what chemicals are present in different substances? . Flame Tests. Metal ions (+ ve ) produce flames with particular colours. Watch the demo on how flame tests are done.

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Chemical Analysis

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  1. Chemical Analysis How can we test for the presence of positive and negative ions? Starter: Why might we need to know what chemicals are present in different substances?

  2. Flame Tests Metal ions (+ve) produce flames with particular colours. Watch the demo on how flame tests are done.

  3. Method 1) Put a Small amount of compound in a cleaned nichrome wire loop. 2) Hold the loop in a roaring flame. 3) Observe the colour. (to clean use conc. Hydrochloric acid and heat)

  4. Results

  5. 2) Reactions with sodium hydroxide (NaOH) • Useful in identifying certain positive (metal) ions.

  6. Aluminium nitrate • Copper II sulfate http://www.youtube.com/watch?v=VONKsXtUS7M

  7. 3) Coloured precipitates with NaOH How could I tell if a substance contained Iron II or Iron III ions?

  8. 3) Testing for negative ions • A) Carbonates React a carbonate with acid to release CO2, - test with lime water.

  9. Nitrates (NO3-) • Add NaOH (sodium hydroxide) and Aluminium powder. • Ammonia gas will be released with a pungent smell.

  10. Halides (Halogen compounds) • Chlorides, Bromides and Iodides. • Add dilute Nitric acid • Add silver nitrate (we say it is silver nitrate acidified with nitric acid) • Look for precipitate – if present, Halide present. • Check colour

  11. More Halide tests • 1) add an unsaturated organic compound to bromine water – it will go from red to colourless.

  12. Results What do you think the precipitates are?

  13. Sulfates • Test for sulfates by adding dil. Hydrochloric acid to remove carbonate ions that would react with barium ions. • Then add barium chloride solution. • White precipitate forms = barium sulfate.

  14. Recognising Ions

  15. Recognising Ions – pair these up SO42- Acid ion CO32- Barium Ions OH - Carbonate ions Ag+ Sulfate ions Silver ions H+ Alkali ion Ba 2+

  16. Recognising Ions – pair these up SO42- Sulfate ions CO32- Carbonate ions OH - Alkali ion Ag+ Silver ions H+ Acid ion Ba 2+ Barium Ions

  17. Positive ion tests

  18. Positive ion tests

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