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: Qualitative analysis
Purpose : To determine the cations and anions of inorganic substances
Procedure : (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 Observation Deduction (a) Add dilute hydrochloric acid to a Solutions smells like vinegar. Solution contains CH3COO- ions. 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 A white precipitate is formed. Solution contains either Pb2+ ions, Zn2+ hydroxide, then in excess.
ions or Al3+ ions. (ii) Add aqueous ammonia, then in Solution turns cloudy and a white Solution contains either Pb2+ ions or Al3+ excess followed by aqueous precipitate is formed. ions. ammonium chloride.
(iii) Add aqueous iron (III)
chloride, then warm. Solution turns brown and a white Solution contains CH3COO- ions. (iv) Add aqueous silver nitrate, precipitate is formed.
followed by dilute nitric acid. A white precipitate is formed. Solution contains CH3COO- ions. (v) Add aqueous disodium
(vi) Add aqueous potassium Solution turns white and a white Solution contains Pb2+ ions. chromate (VI) followed by precipitate is formed.
dilute hydrochloric acid. A yellow precipitate is formed. Solution contains Pb2+ ions.
Identity of KA1: KA1 contains Pb2+ ions and CH3COO- ions.
Tests on KA2
Test Observation Deduction (a) Add concentrated hydrochloric acid Lime water turns chalky. The reaction releases carbon dioxide gas. and test for gas(es) evolved by using Solution contains CO 2- 3 ions. lime water. (b) Dissolve KA2 in dilute nitric acid.
Use separate portions of the solution
for the following tests.
(i) Add dilute sodium hydroxide. A blue precipitate is formed. Solution contains Cu2+ ions. (ii) Add potassium Solution turns dark brown. Solution contains Cu2+ ions. hexacyanoferrate (II).
Identity of KA2: KA2 contains Cu2+ ions and CO 2- 3 ions.