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Metallic impurities to be tested
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Procedure
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Reaction Expected
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Signficance of the impurity if present
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Inference
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| 1. Iron
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5 ml of sample n a test tube. Add a few drops of potassium ferrocyanide, test solution
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Appearance of blue colour
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Iron is a persistent impurity. It imparts bitter taste, furbidity and discoloration, Excess iron causes constipation and digestive disturbances. Iron helps bacteria Crenothrix and Gallionela. Leads to corrosion of pipes. MPL 0.3 ppm
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Absence of iron
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| 2. Copper
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5 ml of sample add a few drops of potassium ferrocyadine solution
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Chocolate colour
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If consumed over a long period can cause digestive diturbances. Green staining of clothes and bath. Toxic to biological species if synergistically present along with zn MPL 3 ppm
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Absence of copper
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| 3. Lead
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5 ml of sample add a few drops of potassium iodide solution
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Golden Yellow precipitate. Boil o dissolve the precipitate cool under tap water.
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Cumulative poison. Causes ' plumbism'. Rain ater soft water with organic matter will corrode lead pipes entering the water MPL: 0.1 ppm
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Absence of Lead
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| 4. Zinc
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5 ml of sample, add a few drops of nitric cid, boil to concentrate add a few drops of potassium ferro cyanide solution.
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White haziness/ turbidity or precipitate depending on the level of zinc present
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Not desirable in water. Prolonged consumption will cause diestive disturbances MPL: 15 ppm
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Absence of zinc
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5. Arsenic Gutzeit test
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5 ml of sample in a test tube, add a few granules of zinc little con. H2SO4, plug the test tube with cotton, place a filter paper over this on which a few crystals of AgNO3 is kept.
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Silver nitrate crystals turn yellow and then black due to arsine gas from arsenic
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It is a cumulative poison. It is used in sheep dip and weedicide from which it may have access to water supply. MPL 0.05ppm
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Absence of Arsenic
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b. Copper foil Test
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10 ml of sample in a white china dish add a pinch of Na2CO3 and evaporate to dryness on a water bath. Redissolved in 2-3 ml of distilled water. Add 1 ml of HCl and a few pieces o Cu fil, boil.
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A steel grey deposit will form over the copper foil.
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Copper + Arsenate  Curpic arsenate
(grey)
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Participants