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Tests for ions

Tests for ions. IGCSE Chemistry. Anions. Chloride, Bromide and Iodide To the salt solution, add dilute nitric acid followed by silver nitrate solution . White precipitate soluble in excess ammonia solution – Chloride ( Cl -)

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Tests for ions

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  1. Tests for ions IGCSE Chemistry

  2. Anions • Chloride, Bromide and Iodide • To the salt solution, add dilute nitric acid followed by silver nitrate solution. • White precipitate soluble in excess ammonia solution –Chloride (Cl-) • Cream precipitate partially soluble in excess ammonia solution –Bromide (Br-) • Yellow precipitate insoluble in excess ammonia solution –Iodide (I-)

  3. Carbonate, nitrate and sulphate • To the salt solution, add dilHCl to remove any CO32- if present as CO2 • Vigorous reaction, colourless gas turns lime water white –Carbonate CO3 2- present • (lime water contains Ca(OH)2 which reacts with CO2 to from insoluble calcium carbonate • Ca(OH)2(aq) + CO2(g)  CaCO3(s) + H2O(l) • To the salt solution, add NaOH solution and a piece of Al foil (or Al powder) and warm the mixture. • A gas (ammonia) is formed which turns red litmus to blue –Nitrate NO3- present. • To the salt solution, add dilHCl (or HNO3) and then BaCl2 or Ba(NO3)2 solution. • A white precipitate of BaSO4 shows the presence of sulphate, SO4 2- • Ba2+(aq) + SO4 2-(aq)  BaSO4(s)

  4. Cations • Part A Flame test • Show a little of the salt to a Bunsen flame: • Lithium Li+ Red • Sodium Na+ yellow • Potassium K+ Lilac (Purple) • Calcium Ca2+ Brick red • Copper Cu2+ Green-blue • Iron Fe2+ Green • Iron Fe3+ Red-brown

  5. Part 2 Using sodium hydroxide and ammonia solution. • Make a salt solution. Add sodium hydroxide solution • A blue precipitate dissolves in excess ammonia solution to give a deep blue solution –Cu2+ • A green precipitate (does not dissolve in ammonia) –Fe2+ • Brown Precipitate (does not dissolve in ammonia) –Fe3+ • White precipitate- Ca2+, Al3+, Zn2+

  6. Aluminium, zinc and Calcium ions • Divide the white precipitate in to two test tubes. • To the first, add excess sodium hydroxide solution. • To the second, add excess ammonia solution. • White precipitate dissolves in NaOH but not in ammonia solution –Al3+ • White precipitate dissolves in both NaOH and ammonia solution –Zn2+ • White precipitate does not dissolve in NaOH or ammonia solution –Ca2+

  7. Ammonium ion NH4+ • Warm the salt solution with NaOH. Colourless gas (ammonia) turns red litmus blue produced – Ammonium, NH4+ present. • Note: any ammonium compound when heated with alkali, ammonia gas will be produced. • Why dilute acid is added before the necessary chemical is added in the test for halides and sulphate? • Answer: Carbonate may be present which can give wrong final result. Dilute acid removes carbonate in the form of CO2 gas.

  8. THE END

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