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SALT ANALYSIS Anions are divided into 3 Groups: i) Dil. H2SO4 Group: CO32-, SO32-, NO2- , S2- ii) Conc. H2SO4 Group: Cl-, Br -, I -, NO3-, CH3-COO – iii) Not identified by i) & ii) (Special group): SO42- , C2O42-, PO43- Detection of Anion: Two types of tests are to be done in order to detect anion: Dry Tests and Wet Tests. 1. Preliminary observations: a. Colour: b. Structure: 2. Dry Tests for Anion Experiment Observation Inference i) Action of dil. HCl Add 2 c.c of dil. HCl to the salt(0.1gm) taken in a clean and dry test tube. a. Colourless, odourless gas evolved with brisk effervescence. b. Turns blue litmus red c. Burning splinter is extinguished d. Lime water turns milky. Gas evolved is CO2. CO32- confirmed. a. Colourless gas is evolved with rotten egg smell b. Lead acetate paper turns black. Gas evolved is H2S. S2- may be present. a. Colourless gas is evolved with suffocating odour. b. Acidified K2Cr2O7 paper turns green c. Acidified KMnO4 paper turns colourless. Gas evolved is SO2. SO32- may be present a. Light brown gas is evolved with pungent odour b. Pass the gas through ferrous sulphate solution, it turns brown Gas evolved is NO2. NO2 – may be present ii) Action with conc. H2SO4. 2 cc of conc. Sulphuric acid is added to a small amount of salt taken in a clean and dry test tube and heated (do not boil) the contents gently. A pinch of MnO2 is added to the above solution and heated. a. Colourless gas is evolved with pungent odour. b. Turns blue litmus red; c. Dense white fumes obtained when a glass rod dipped in NH4OH is brought near the gas. Greenish yellow coloured gas is obtained, which turns starch iodide paper blue black. 1st Gas evolved is HCl. 2nd Gas evolved is Cl2 Cl – may be present. a. Reddish brown gas with pungent odour. More reddish-brown fumes of bromine are evolved when MnO2 is added to the solution and heated. b. Turns moist starch paper yellow Gas evolved may be HBr. Br – may be present. a. Violet vapours of iodine are evolved with pungent odour. More violet vapours are obtained, when MnO2 is added to the solution and heated. b. Turns moist starch paper blue Gas evolved may be HI I – may be present.Salt analysis 2 a. Light brown gas with pungent odour. b. Add Cu-turnings and heat. Formation of brown gas increases. c. Turns starch iodide paper blue. Gas evolved is NO2 NO3– may be present. iii) Action with conc. Sulphuric acid and ethanol. Few ml of conc. Sulphuric acid is added to a small amount of salt. Now few ml of ethanol is added to it and then heated. Gas with vinegar smell. A strong Fruity odour of ethyl acetate is obtained. Acetate may be present. CH3COO – confirmed. 3) Wet Tests for Anion: Wet tests are done with Na2CO3 extract (Soda Extract). i) Preparation of Soda Extract: 1 part of salt is mixed with 3 parts of Na2CO3 in a test tube and about 10 -15 ml of distilled water is added. It is then boiled for 5 minutes taking care that the contents do not boil over. It is then cooled, filtered and the filtrate is called as Soda Extract. ii) Confirmatory tests for anion: Experiment Observation Inference Test for S2- • Add 1 mL of sodium nitro-prusside solution to 1 ml soda extract. • Add 1 mL of lead acetate solution to 1 ml soda extract. A purple or violet colour is formed. Black ppt. formed. S2- confirmed S2- confirmed Test for NO2- Acidify soda extract with acetic acid and add concentrated solution of cobalt chloride. Then add KCl solution. Warm the contents and wait for some time. Yellow ppt. is obtained NO2- is confirmed. Test for Cl- 1 ml soda extract is acidified with dil. HNO3, and then add 1 mL of AgNO3 solution to it. White ppt soluble in cold NH4OH. Cl– confirmed Test for Br- 1 ml soda extract is acidified with dil. HNO3, and then add 1 mL of AgNO3 solution to it. Pale yellow ppt is obtained partially soluble in NH4OH. CS2 test: Acidify about 2 ml of S.E. with dilute hydrochloric acid. Add to it 1 ml of chlorine water (or KMnO4 and conc. HCl) and 4- 5 drops of carbon disulphide. Shake vigorously. Br– confirmed. Test for I- 1 ml soda extract is acidified with dil. HNO3, and then add 1 mL of AgNO3 solution to it. Yellow ppt. insoluble in insoluble in NH4OH. CS2 test: Acidify about 2 ml of S.E. with dilute hydrochloric acid. Add to it 1 ml of chlorine and 4- 5 drops of carbon disulphide. Shake vigorously. Violet colouration is obtained. I– confirmed. Test for SO42- / SO32- White ppt is obtained, which is insoluble in dilute HCl. SO42- confirmedSalt analysis 3 1 ml soda extract + acidify with dil. HCl + BaCl2 solution. White ppt is obtained, which is soluble in dilute HCl SO3 2- confirmed Test for NO3- 1 ml soda extract + 1ml dil. Acetic acid + freshly prepared FeSO4 sol. + add conc. H2SO4 along the side of the test tube. Brown ring is formed at the junction of two liquids NO3 – confirmed Test for CH3COO- 1 ml soda extract neutralized with dil. Mineral acid + neutral ferric Chloride solution + heat Wine/ blood red coloration, which turns into reddish ppt on heating CH3 COO- confirmed Test for C2O42- • Acidify a portion of sodium extract with acetic acid and add calcium chloride solution. • Filter the ppt. from the above and extract with dilute sulphuric acid. Now few drops of KMnO4 solution and warm it. A white precipitate is obtained. Pink colour of KMnO4 is discharged. C2O42- is confirmed. Test for PO43- • Take about 2 ml of SE. add to about 1 ml of conc. HNO3 and heat to boiling. Now add ammonium molybdate solution and heat again. • SE is first acidified with dilute acetic acid and then silver nitrate solution is added to it. Yellow ppt. or colouration is obtained. Yellow precipitate is obtained, which is soluble in dilute nitric acid. PO43- confirmed Cation is to be detected are divided into the following groups. Group Group Reagent Cations Zero NaOH NH4+ Gp-1 Dil. HCl Pb2+ Gp-2 H2S in acidic medium Pb2+, Cu2+ Gp-3 NH4Cl + NH4OH Fe3+, Al3+ Gp-4 NH4Cl + NH4OH + H2S Zn2+, Mn2+ Gp-5 NH4Cl + NH4OH (excess)+ (NH4)2CO3 Ba2+, Sr2+, Ca2+ Gp-6 NH4Cl + NH4OH excess + Na2HPO4 Mg2+Salt analysis 4 4) Preparation of ORIGINAL SOLUTION (OS): The solubility of the salt mixture should be tested in the following order: i) In cold


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AIIMS CHE 112 - SALT ANALYSIS

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