Useful hints in analysis of a mixture of calcium chloride and Iron tetraoxosulphate VI

 

    The analysis requires a good knowledge of the specific reactions of the ions with certain reagents, for example an unknown solution which contains copper ions will give a deep blue solution with excess ammonia solution.

 Related post Qualitative analysis of copper(II)tetraoxosulphate VI

So what we are going do here is to identify these ions using their specific reactions.

  A mixture of calcium chloride and iron (II) tetraoxosulphate (VI) will undergo a double decomposition reaction to yield calcium tetraoxosulphate (VI) and iron (II) chloride.

CaCl_{2 (aq)} + FeSO_{4 (aq)} --------- FeCl_2(aq) + CaSO_4(s)

Since calcium tetraoxosulphate (VI) is insoluble, iron(II)chloride  can easily be filtered off with filter paper or by any other means possible.

How to identify the Cations in the mixture

Cations are positive charged ions. We have two of these types of ions in the mixture which

·        Iron (II) ions

·        Calcium ions

How to identify Iron (II) ions

An unknown solution or solid sample which contains iron (II) ion will react positively to the following test below:

·        Test with sodium hydroxide solution

·        Test with ammonia solution

·        Test with potassium hexacyanoferrate (III) solution

So, we are going to use these tests to identify iron (II) ion

Test with sodium hydroxide solution

Add distilled water into the solid sample of the mixture and then filter with filter paper. Divide the filtrated into four portions, to the first portion add sodium hydroxide solution, in drops and then in excess. If the solution contains iron (II) ion dirty green precipitate will be formed which will be insoluble in excess sodium hydroxide solution. This confirms the present of iron (II) ion.

Test with ammonia solution

To the second portion of the filtrate, add aqueous ammonia, in drops and then in excess, if the unknown solution contains iron (II) ion, pale green precipitate will but formed which is insoluble in excess aqueous ammonia. This shows that iron (II) ion is present.

Test with potassium hexacyanoferrate(III) solution

To the third portion of the filtrate, add hexacyanoferrate (III) solution, if the unknown solution contains iron (II) ion, a dark blue precipitate will be formed. This confirms iron (II) ion.

How to identify calcium ion

Calcium ions can be identified by the following tests:

·        Test with sodium hydroxide solution

·        Test with ammonia solution

·        Test with ammonium solution ethanedioate solution

We are going to discuss the test with sodium hydroxide because others have been discussed on our previous post.

Relatedpost: Qualitative analysis of ions in calcium trioxonitrate V

Test with sodium hydroxide solution

To the residue, add dilute hydrochloric acid and divide the solution into two portions. To the first portion, add sodium hydroxide solution in drops and then in excess. A white precipitate formed which is insoluble in excess sodium hydroxide solution confirms the present of calcium ion.

How to identify the anions in the unknown mixture

The two anions in the mixture are

·        Chloride ion

·        Tetraoxosulphate VI

How to identify chloride ion

To the last portion of the filtrate, add silver trioxonitrate V and then dilute trioxonitrate V acid. If the filtrate has chloride ion, white precipitate will be formed which is insoluble in the dilute acid and is decolourized when exposed to sunlight confirms chloride ion.

How to identify tetraoxosulphate (VI) radical (ion)

To the second portion of solution produced from the residue or make other solution by adding dilute hydrochloric acid to a portion of the residue, then add barium chloride solution. If tetraoxosulphate VI radical is present, white precipitate will be formed, this confirms tetraoxosulphate (VI) radical.

Related post : How to analyse the ions in a mixture of copper sulphate and ammonium carbonate

Example question

J is a mixture of two inorganic compounds. Carry out the tests on the table below, copy and complete the table

 

Test	Observation	Inference
(a ) J plus distilled water, filter and keep both the filtrate and residue		J is likely a mixture of soluble and insoluble compounds
(b ) Divide the filtrate from (a) above into three portions to the first portion add dilute sodium hydroxide solution in drops and then excess	Dirty green precipitate forms which is insoluble in excess sodium hydroxide solution
(c )  to the second portion add ammonia solution, in drops and in excess		Fe2+ confirms
( d) to the third portion add dilute trioxonitrate V acid then silver trioxonitrate V solution	White precipitate forms which is decolourized on exposure to light
( e) to the residue add about 5 cm3 of dilute hydrochloric acid and divide into two portions		Ag+ ,Cu+ and  Pb+ absent
( f) to the first portion from (e) above add sodium hydroxide solution in drops and then in excess	White precipitate forms which is insoluble in excess sodium hydroxide solution
( g) to the second portion add barium chloride solution		SO42+ present

 

 

Answers

 

Test	Observation	Inference
(a ) J plus distilled water, filter and keep both the filtrate and residue	Partly soluble	J is likely a mixture of soluble and insoluble compounds
(b ) Divide the filtrate from (a) above into three portions to the first portion add dilute sodium hydroxide solution in drops and then excess	Dirty green precipitate forms which is insoluble in excess sodium hydroxide solution	Fe2+ present
(c )  to the second portion add ammonia solution, in drops and in excess	Pale green precipitate forms and insoluble in excess aqueous ammonia	Fe2+ confirms
( d) to the third portion add dilute trioxonitrate V acid then silver trioxonitrate V solution	White precipitate forms which is decolourized on exposure to light	Chloride ions confirm
( e) to the residue add about 5 cm3 of dilute hydrochloric acid and divide into two portions	Soluble	Ag+ ,Cu+ and  Pb+ absent
( f) to the first portion from (e) above add sodium hydroxide solution in drops and then in excess	White precipitate forms which is insoluble in excess sodium hydroxide solution	Ca+ present
( g) to the second portion add barium chloride solution	White precipitate forms	SO42+ present