TESTING FOR CATIONS QUALITATIVE ANALYSIS.

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Presentation transcript:

TESTING FOR CATIONS QUALITATIVE ANALYSIS

Calcium (Ca2+) Test with aqueous sodium hydroxide White ppt. insoluble in excess Test with aqueous ammonia No ppt. or very slight white ppt.

Calcium ions: Ca2+(aq) + 2OH-(aq) → Ca(OH)2(s) white ppt. The ppt. is not soluble in excess of NH3 or NaOH. The test for Mg2+ and Ca2+ have similar tests and similar results. You could distinguish Mg from Ca with a flame test

Test for Cations – Ca2+ / Pb2+ / Zn2+ Observation: White ppt. observed. Observation: White ppt., soluble in excess, giving a colourless solution. Conclusion: Pb2+ / Zn2+ is present. Observation: White ppt., insoluble in excess. Conclusion: Ca2+ is present.

Aluminium(Al3+) Ions Test with aqueous sodium hydroxide Solution White ppt. soluble in excess giving a colourless solution Test with aqueous ammonia Solution White ppt. insoluble in excess Al3+ +3OH- →Al(OH)3(s) in excess NaOH forms soluble (Al(OH)4-

Zinc (Zn2+) Ions Test with aqueous sodium hydroxide Solution White ppt. soluble in excess giving a colourless solution Test with aqueous ammonia Solution White ppt. Soluble in excess - Zn2+(aq) + 2OH-(aq) → Zn(OH)2(s) white ppt. The ppt. dissolves in both excess sodium hydroxide and ammonia to give a clear colourless solution.

Lead (Pb2+) Ions Test with aqueous sodium hydroxide Solution White ppt. soluble in excess giving a colourless solution Test with aqueous ammonia Solution White ppt. Soluble in excess -

Fe2+ and Fe3+ In Aqueous Ammonia and NaOH: Aqueous ammonia and NaOH reacts with Fe(II) ions to produce green ppt Fe(OH)2, which oxidizes to form red-brown Fe(OH)3: Insoluble in excess Both Solutions React with Fe(III) ions to produce red-brown Fe(OH)3: Insoluble in excess

Copper (Cu2+) Test with aqueous sodium hydroxide Solution Light blue ppt. insoluble in excess

Copper (Cu2+) Test with aqueous ammonia Solution Light blue ppt. soluble in excess giving a deep-blue solution

Test for Cations Conclusion Observations

Halide tests (Cl-, Br- ,I-) The Acidified silver nitrate Test. The test will give a white precipitate of silver chloride, a cream (off white) precipitate of silver bromide and a yellow precipitate of silver iodide.

SULPHATE IONS. The barium chloride test for sulphate (SO42-) ions. Any soluble sulphate will give a white precipitate of barium sulphate. The test is made in the presence of dilute hydrochloric acid to remove any carbonate or sulphite ions which may be present. These ions will also produce a precipitate which would confuse the results.

Any carbonate will produce carbon dioxide gas when CARBONATE IONS. ACID TEST Any carbonate will produce carbon dioxide gas when you add a dilute acid. The carbon dioxide gas is identified using lime water, which goes milky

Test for Anions Conclusion Observations

Test for Gases – Sulfur Dioxide (SO2) Sulfur dioxide is a reducing agent. Sulfur dioxide turns aqueous acidified potassium manganate (VII) from purple (MnO4-) to colourless (Mn2+). Sulfur dioxide turns aqueous acidified potassium dichromate (VI) from orange (Cr2O72-) to green (Cr3+). Observations : Effervescence observed. Gas evolved turns aqueous acidified potassium dichromate (VI) from orange to green. Conclusion : Sulfur dioxide gas is evolved.

Common Metals iron filings magnesium ribbon zinc powder copper turnings aluminium foil lead