Experiment 14 Topic Purpose Procedure : Qualitative analysis : To determine the cations and anions of inorganic substances : (a) Solids KA1 and KA2 are simple salts. Carry out the following experiments with solid KA1 to identify its cation and anion. (b) You are then required to carry out a few experiments to identify the cation and anion present in solid KA2. In all the experiments, the reagent should be added gradually until no further change is observed. Deduce what you can about KA1 and KA2. Observations should include details of colour changes, precipitates, and tests on gases evolved. Tests on KA1 Test (a) Add dilute hydrochloric acid to a small amount of solid KA1, then warm gently.
(b) Dissolve solid KA1 in distilled water and filter. Use separate portions of the filtrate for the following tests. (i) Add aqueous sodium hydroxide, then in excess. (ii) Add aqueous ammonia, then in excess followed by aqueous ammonium chloride. (iii) Add aqueous iron (III) chloride, then warm. (iv) Add aqueous silver nitrate, followed by dilute nitric acid. (v) Add aqueous disodium hydrogen phosphate. (vi) Add aqueous potassium chromate (VI) followed by dilute hydrochloric acid. Observation Solutions smells like vinegar. Deduction Solution contains CH3COO- ions.
A white precipitate is formed. Solution turns cloudy and a white precipitate is formed.
Solution contains either Pb2+ ions, Zn2+ ions or Al3+ ions. Solution contains either Pb2+ ions or Al3+ ions. Solution contains CH3COO- ions. Solution contains CH3COO- ions. Solution contains Pb2+ ions. Solution contains Pb2+ ions.
Solution turns brown and a white precipitate is formed. A white precipitate is formed.
Solution turns white and a white precipitate is formed. A yellow precipitate is formed.
Identity of KA1: KA1 contains Pb2+ ions and CH3COO- ions. Tests on KA2 Test (a) Add concentrated hydrochloric acid and test for gas(es) evolved by using lime water. (b) Dissolve KA2 in dilute nitric acid. Use separate portions of the solution for the following tests. (i) Add dilute sodium hydroxide. (ii) Add potassium hexacyanoferrate (II). Observation Lime water turns chalky. Deduction The reaction releases carbon dioxide gas. Solution contains CO32- ions.
A blue precipitate is formed. Solution turns dark brown.
Solution contains Cu2+ ions. Solution contains Cu2+ ions.
Identity of KA2: KA2 contains Cu2+ ions and CO32- ions.
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