How to Analylse the ions in Copper ( II) tetraoxosulphate VI)

 Copper  tetraoxosulphate VI is  a blue crystal solid if it contains water of crystallization(copper(II)tetraoxosulphate VI pentahydrate,CuSO₄.5H₂O). The anhydrous form is white. Copper(II)tetraoxosulphate VI is electrovalent compound and it is one of the soluble compounds of copper.

       Tests for Copper(II) tetraoxosulphate VI

In qualitative analysis of any compound or substance, the basic idea is to identify the ions in the compound. That means, one has to know the unique reactions of compound which contains any of the ions to be analyzed, for example all chlorides react with acidified silver trioxonitrate to form white precipitate which is soluble in ammonia solution.

 In the case of copper (II)tetraoxosulphate VI, the two ions are copper ion,Cu²⁺ and  tetraoxosulphate VI ion or radical,SO₄^2-.These two ions have some unique reactions which differentiate them from other ions.

How to Test for Copper ion in an unknown sample (copper sulphate)

Copper ion can be identified in an unknown compound by

·       Flame test

·       Its reaction with dilute sodium hydroxide solution

·       Its reaction with ammonia solution

·       Its reaction with potassium hexacyanoferrate (II) solution

·       Its reaction with potassium iodide solution

·       Its reaction with potassium thiocyanate solution

       Flame Test

Dip a clean platinum wire into concentrated hydrochloric acid and then into the sample of the unknown salt. Heat the end which contains the sample in the Bunsen flame. A blue-green flame confirms the presence of copper ion.

      Test with dilute sodium hydroxide solution

Make a solution of the unknown salt; add few drops of dilute sodium hydroxide. A blue gelatinous precipitate which is insoluble in excess sodium hydroxide confirms the presence of copper ion in the salt sample.

        Test with Aqueous Ammonia  

To the solution of the unknown salt; add few drops of ammonia solution, a pale blue precipitate which dissolves in the excess of the solution to form a deep blue solution confirms that copper ion is present in the sample.

       Test with Potassium hexacyanoferrate(II) solution

To the solution, add potassium hexacyanoferrate(II) solution, a reddish-brown precipitate formed confirms copper ion.

      Test with potassium thiocyanate solution

To the solution, add potassium thiocyanate solution, a black precipitate formed also confirms the presence of copper ion.

     How to Test for tetraoxosulphate(VI) ion in an unknown salt

To the solution, add barium chloride solution in drops, white precipitate formed maybe CO₃^2-, SO₃^2- or SO₄^2- but if the precipitate is insoluble in dilute hydrochloric acid, it confirms that tetraoxosulphate (VI) ion is presence.

Note: Barium trioxonitrate V and trioxonitrate V acid can also give similar result.

Example Question:

Carry out the following tests, identify the unknown salt sample G (CuSO₄) and complete the table. You are provided with the following reagents dilute sodium hydroxide, distilled water, boiling tubes, test tubes, source of heat, ammonia solution, barium chloride solution and dilute hydrochloric acid.

	Test	Observation	Inference
1	Put few sample of G into a boiling tube and heat strongly	Water condensed at the cooler end of the boiling tube. G change from blue to white
2	Another sample of G add about 10cm3 of water shake vigorously and divide into three portions		G is a coloured compound, transition metallic ions likely present.
3	To first portion of G from (2) above, add dilute sodium hydroxide solution in drops then in excess	Blue gelatinous precipitate which is insoluble in excess solution
4	To the second portion of G from (2), add ammonia solution in drops then excess		Cu2+ confirmed
5	To the third portion of G from (2) add barium chloride solution	White precipitate formed
6	To mixture from (5) add dilute hydrochloric acid		SO42- confirmed.

 Answers

	Test	Observation	Inference
1	Put few sample of G into a boiling tube and heat strongly	Water condensed at the cooler end of the boiling tube. G change from blue to white	G has water of crystallization. Transition metals like Fe2+, Fe3+, Cu2+ likely present.
2	Another sample of G add about 10cm3 of water shake vigorously and divide into three portions	Soluble to give a blue solution	G is a coloured compound, transition metallic ions likely present.
3	To first portion of G from (2) above, add dilute sodium hydroxide solution in drops then in excess	Blue gelatinous precipitate which is insoluble in excess solution	Cu2+ present
4	To the second portion of G from (2), add ammonia solution in drops then excess	Pale blue precipitate, soluble in excess solution to form a deep blue solution	Cu2+ confirmed
5	To the third portion of G from (2) add barium chloride solution	White precipitate formed	CO32-, SO32-, SO42- likely present.
6	To mixture from (5) add dilute hydrochloric acid	Precipitate insoluble	SO42- confirmed.

 

Note:  transition metals are known to form coloured compound when they combine with d block electrons