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Chemistry

Chemistry. Qualitative Analysis. What is qualitative analysis.

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Chemistry

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  1. Chemistry Qualitative Analysis

  2. What is qualitative analysis • Qualitative analysis is used to determine the chemical composition of an unknown substance. Below is a list of some simple tests used to determine the presence of numerous anions and cations using the bench reagents present in the laboratory.

  3. Test for carbonates and hydrogen carbonates • Carbonates react with dilute acid with effervesce, liberating carbon dioxide. • Test for carbon dioxide- carbon dioxide outs a lit wooden splint. • Carbonates are present when a dilute acid is added to an unknown substance and carbon dioxide is liberated.

  4. Test for the chloride and bromide ions • chloride and bromide ions react with aqueous lead nitrate to form a white precipitate (ppt.) • This ppt. dissolves when heated and solidifies when cooled.

  5. Conformation of chloride ions (done after test for halides) • Chlorides react with silver nitrate solution to form a white ppt. • This ppt. then dissolves in a solution of aqueous ammonium

  6. Test for the metal ions lead, zinc and aluminum • Lead, zinc and aluminum ions react with aqueous sodium hydroxide to form a white ppt. • White ppt. is soluble in excess sodium hydroxide.

  7. Conformation of zinc ions (done after test for lead, zinc and aluminum) • Zinc ions react with aqueous ammonia to form a white ppt. • Precipitate soluble in excess aqueous ammonia.

  8. Conformation of aluminum ions (done after test for lead, zinc and aluminum) • Aluminum ions react with aqueous ammonia to form an white gelatinous ppt. • Precipitate insoluble in excess aqueous ammonia.

  9. Test for calcium ions • Calcium ions form a white ppt. in aqueous sodium hydroxide • Precipitate insoluble in excess aqueous sodium hydroxide.

  10. Conformation of calcium ions (done after test for calcium) • Add aqueous ammonia solution to an unknown solution until in excess- • No ppt. formed.

  11. Test for absence of lead and copper ions • Add aqueous potassium iodide to an unknown solution • No visible reaction.

  12. Test for copper ions • Copper ions react with aqueous sodium hydroxide to form a pale blue ppt. • Insoluble in excess aqueous sodium hydroxide

  13. Conformation of copper ions (done after test for copper) • Copper ions react with aqueous ammonia to form a pale blue ppt. • Precipitate dissolves in excess ammonia to form a dark blue solution • Or add aqueous potassium iodide • Dark brown ppt. formed (formation of the brown copper iodide).

  14. Test for sulphate • Sulphate ions react with barium chloride solution to form a white ppt. • This ppt. is soluble in dilute HCl without effervescence

  15. Test for nitrate • Heat solid in test tube- colorless gas evolved followed by a pungent brown gas. Colorless gas relights a glowing wooden splint and brown gas turns damp blue litmus red. • Colorless gas is oxygen • Brown gas is NO2

  16. Example of Qualitative Analysis • Identify the ions in the unknown Z using the bench reagents.

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