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AimTo qualitatively determine one cation and one anion in a given salt.
Apparatus RequiredTest tubes
Test tube holder
Bunsen burner
Dropper
Glass rod
Filter paper
Distilled water
0.1 M solutions of NaOH, Na2S, BaCl2, AgNO3, and NH4OH
TheoryIn this experiment, a given salt sample will be subjected to various tests to determine the presence of one cation and one anion. The tests are based on the characteristic properties of the cations and anions.
ProcedurePreliminary Tests: a. Flame Test: Take a small amount of the given salt on a platinum wire loop and hold it in the non-luminous flame of a Bunsen burner. Observe the color of the flame and identify the cation present in the salt. b. Heating Test: Heat a small amount of the given salt in a dry test tube. Observe any changes in the color or state of the salt. This test is done to identify the presence of any water of crystallization or decomposition of the salt.
Tests for Cations: a. Ammonium Molybdate Test: Take a small amount of the salt in a test tube and add a few drops of ammonium molybdate solution followed by concentrated HNO3. Heat the solution gently and observe the color of the precipitate. This test is done to identify the presence of Pb2+ and Cu2+ ions. b. Hydrogen Sulphide Test: Take a small amount of the salt in a test tube and add dilute HCl followed by a few drops of freshly prepared hydrogen sulphide gas. Observe the color of the precipitate. This test is done to identify the presence of As3+, Al3+, Fe3+, Mn2+, Zn2+, Ni2+, Ca2+, Sr2+, Ba2+, and Mg2+ ions. c. Flame Test Confirmation: Repeat the flame test for the cation identified in the preliminary test.
Tests for Anions: a. Sodium Carbonate Test: Take a small amount of the salt in a test tube and add a few drops of sodium carbonate solution followed by dilute HCl. Observe the effervescence and the color of the gas evolved. This test is done to identify the presence of (CO3)2- and (SO3)2- ions. b. Dilute Nitric Acid Test: Take a small amount of the salt in a test tube and add dilute HNO3 followed by a few drops of silver nitrate solution. Observe the color of the precipitate. This test is done to identify the presence of (NO2)-, (C2O4)2-, and CH3COO- ions. c. Barium Chloride Test: Take a small amount of the salt in a test tube and add a few drops of barium chloride solution followed by dilute HCl. Observe the color of the precipitate. This test is done to identify the presence of (SO4)2-, (PO4)3-, Cl-, Br-, and I- ions.
Observation and ResultObservations: Record all the observations carefully and note down the color, shape, and size of the precipitates formed in each test.
Results: Based on the observations and tests, identify the cation and anion present in the given salt. For example, if the salt is identified as PbSO4, the cation present is Pb2+ and the anion present is (SO4)2-.