STPM Chemistry Experiment 14Topic: Qualitative analysis

Purpose: To determine the cations and anions of inorganic substances

Procedure:

1. Solids KA1 and KA2 are simple salts. Carry out the following experiments with solid KA1 to identify its cation and anion.2. 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

Add dilute hydrochloric acid to a small amount of solid KA1, then warm gently.Observation: Solutions smells like vinegar.Deduction: Solution contains CH3COO- ions.

Dissolve solid KA1 in distilled water and filter. Use separate portions of the filtrate for the following tests.

Add aqueous sodium hydroxide, then in excess.Observation: A white precipitate is formed.Deduction: Solution contains either Pb2+ ions, Zn2+ ions or Al3+ ions.

Add aqueous ammonia, then in excess followed by aqueous ammonium chloride.Observation: Solution turns cloudy and a white precipitate is formed.Deduction: Solution contains either Pb2+ ions or Al3+ ions.

Add aqueous iron (III) chloride, then warm.Observation: Solution turns brown and a white precipitate is formed.Deduction: Solution contains CH3COO- ions.

Add aqueous silver nitrate, followed by dilute nitric acid.Observation: A white precipitate is formed.Deduction: Solution contains CH3COO- ions.

Add aqueous disodium hydrogen phosphate.Observation: Solution turns white and a white precipitate is formed.Deduction: Solution contains Pb2+ ions.

Add aqueous potassium chromate (VI) followed by dilute hydrochloric acid.Observation: A yellow precipitate is formed.Deduction: Solution contains Pb2+ ions.

Identity of KA1: KA1 contains Pb2+ ions and CH3COO- ions.

Tests on KA2

Add concentrated hydrochloric acid and test for gas(es) evolved by using lime water.Observation: Lime water turns chalky.Deduction: The reaction releases carbon dioxide gas. Solution contains CO32- ions.

Dissolve KA2 in dilute nitric acid. Use separate portions of the solution for the following tests.

Add dilute sodium hydroxide.Observation: A blue precipitate is formed.Deduction: Solution contains Cu2+ ions.

Add potassium hexacyanoferrate (II).Observation: Solution turns dark brown.Deduction: Solution contains Cu2+ ions.

Identity of KA2: KA2 contains Cu2+ ions and CO32- ions.