SEMI – MICRO QUALITATIVE ANALYSIS OF SIMPLE INORGANIC SALT _______________________________________________________________ CATIONS: Pb2+ ,Hg2+ ,Cu2+ ,Cd2+ , Ag+ , Fe2+ , Fe3+ , Al3+ , Zn2+ , Mn2+ , Co2+ , Sr2+ , Ba2+ , Mg2+ , NH4+ ANIONS: CO32- , S2- , SO32- , SO42- , NO2- , NO3- , Cl- , Br2- , PO43- , CH3COO-
_______________________________________________________________ PRELIMINARY TESTS
1. Note the state (amorphous or crystalline) and colour of salt. 2. Test the solubility of the salt in the following solutions: i. Water (cold and hot) ii. Dilute HCl (cold and hot) iii. Dilute HNO3 (cold and hot)
_______________________________________________________________ IDENTIFICATION OF ACID RADICALS (ANIONS)
This part is the classified into three groups:
FIRST GROUP OF ACID RADICALS
The acid radicals involved in this group are carbonate(CO32-), Sulphide(S2-), Sulphite(SO32-), Thiosulphate(S2O32-) and nitrate(NO2-). The group reagent is dilute hydrochloric acid. EXPERIMENT Salt + dil. HCl OBSERVATION Effervescence or evolution of gases (a) Colourless, odourless gas turns lime water milky (b) Colourless with rotten eggs smell and turns lead acetate paper black. (c) Colourless gas with suffocating smell. Heat and pass the gas through acidified K2Cr2O7 solution. The solution turns green (d) Colourless gas with suffocating smell with a yellow ppt. of sulphur in the test tube. Heat and pass the gas through acidified K2Cr2O7 solution. The solution turns dark blackish green. (e) Colourless gas followed by brown gas and it turns starch iodide paper blue. (f) Colourless gas with the smell of vinegar. INFERENCE 1st group of acid radicals is present. The acid radical may be CO32- or HCO3Sulphide(S2-) is confirmed.
SO32- is confirmed.
S2O32- is confirmed.
NO2- is confirmed. The acid radical may be CH3COO-
Tests to distinguish between CO32- and HCO3EXPERIMENT Salt + water, boil and pass the gas through lime water OBSERVATION (a) Lime water does not turn milky. (b) Lime water turns milky. Confirmation test for Acetate EXPERIMENT Salt solution + Neutral FeCl3 sol. OBSERVATION Appearance of blood red colour. INFERENCE Acetate is confirmed INFERENCE CO32- is confirmed. HCO3- is confirmed.
The acid radicals involved in this group are Cl-, Br- and NO3- . The group reagent is concentrated sulphuric acid (H2SO4). EXPERIMENT OBSERVATION Effervescence with colourless or coloured gases (a) Colourless gas with a pungent smell and gives dense white fumes when a glass rod dipped in ammonium hydroxide (NH4OH) is exposed. (b) Brown gas and the solution is not blue. (c) Light brown gas and brown gas with pieces of copper turnings and the solution turns blue in the test tube. Confirmation test for Chloride EXPERIMENT (a) Chromyl – Chloride test: Salt + few K2Cr2O7 crystals + conc. H2SO4 and heat Pass the vapours through the test tube which contains NaOH solution. To this yellow solution, add dilute CH3COOH and lead acetate solution. OBSERVATION Red vapours are obtained. The solution turns yellow. Yellow ppt. is formed Chloride is confirmed. INFERENCE INFERENCE 2nd group Acid radical is present The Acid radical may be Cl-
SECOND GROUP OF ACID RADICALS
Salt + Concentrated H2SO4 and heat if necessary.
The acid radical may be BrThe Acid radical may be NO3-
(b) Silver Nitrate test: Salt solution + AgNO3 solution + dilute HNO3
White ppt. is formed which is soluble in NH4OH.
Chloride is confirmed.
Confirmation test for Bromide
(a) Globule Test: Aqueous solution of salt + two drops of CCl4 + 1ml chlorine water and shake well. (b)Silver Nitrate test: Salt solution + AgNO3 solution + dilute HNO3
An orange-red globule is obtained A pale yellow ppt. slightly soluble in NH4OH is obtained.
Bromide is confirmed.
Bromide is confirmed.
Confirmation test for Nitrate
Brown ring test: Strong solution of the substance + 2 or 3 drops of conc. H2SO4, and...
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