Qualitative Analysis of the ions in Calcium trioxonitrate V

 

Calcium trioxonitrate V salt is a white deliquescent tetrahydrate crystal, Ca(NO₃)₂. 4H₂O. it is very soluble in water. In the qualitative analysis of calcium trioxonitrate V, the ions present are calcium ion and trioxonitrate V radical. So, the basic methods of identifying these ions in their compounds are employed.

How to identify Calcium ion in an unknown compound or solution

Calcium ion can be identified by its action or reaction with

·        Aqueous ammonia

·        Sodium hydroxide

·        Ammonium ethanedioate

·        Ammonium trioxocarbonate IV

Test with aqueous ammonia

Calcium does not show any visible reaction with aqueous ammonia both in drops of aqueous ammonia and in excess of the aqueous solution.

Test with Sodium hydroxide

If an unknown solution contain calcium ion, it will form white precipitate with few drops of sodium hydroxide solution the precipitate will remain insoluble in excess sodium hydroxide solution.

Test with Ammonium ethanedioate

Add a solution of ethanedioate to the unknown salt solution, if white precipitate is formed, which is soluble in ethanoic acid, indicates the presence of calcium ions.

Test with Ammonium trioxocarbonate IV

Add ammonium trioxocarbonate IV solution to the solution of unknown salt solution, the formation of white precipitate indicates the presence of calcium ions.

    Barium and strontium salts give similar result with ammonium trioxocarbonate IV and ammonium ethanedioate, but calcium ions do not form precipitate with potassium chromate VI solution, unlike barium ions.

 Calcium ions do not form precipitate with saturated calcium tetraoxosulphate VI solution, unlike both barium and strontium.

How to test for trioxonitrate V radical

Trioxonitrate V radical can be identified by the following tests

·        Brown ring test

·        Test with tetraoxosulphate VI acid

·        Test with copper turnings

Brown ring test

To carry out this test, add about 3cm³ of the unknown solution into a test-tube. Acidify the solution with dilute tetraoxosulphate VI acid, then add freshly prepared iron (II) tetraoxosulphate VI solution and shake to mix. Hold the test-tube in a slanting position and carefully pour a stream of concentrated tetraoxosulphate VI acid down the side of the tube.

  If the known solution contains trioxonitrate V compound a brown ring appears at the junction of the acid and aqueous layers. This test is not reliable because the presence of iodine and bromide give coloured rings too.

Test with tetraoxosulphate VI acid

Put the unknown solid compound into the test-tube and warm with concentrated tetraoxosulphate VI. If trioxonitrate V radical or ion is present, some oily drops of trioxonitrate V acid will be formed on the upper part of the test-tube on heating further, the acid will decompose to yield brown  fumes of nitrogen IV oxide.

H₂SO_4(aq) + NO^-_3(s) ---- HNO_3(l) + HSO^-_4(aq)

4HNO_3(l)------ 4NO_2(g) +O₂ + 2H₂O_(l)

Test with copper turnings

Warm a mixture of the unknown solid and copper turnings with some concentrated tetraoxosulphate VI acid. If a trioxonitrate V is present, reddish-brown fumes of nitrogen IV oxide will be formed.

H₂SO_4(aq) + NO_3(S)^- ------ HNO_3(aq) + HSO^-_4(aq) +  Cu_(s) + 4HNO_3(aq)

Cu_(s) + 4HNO_3(aq) ----- Cu(NO₃)_2(aq) + 2NO_2(g) + 2H₂O_(l)

Example question

Q is a sample of an inorganic compound carry out the tests below and copy and completes the table

Test	Observation	Inference
a)  Q plus water shake very well		Insoluble compounds absent, Na+, K+, NH+ ions likely present.
b)  Solution from (a) above plus dilute NaOH ,drops and then in excess	White precipitate form and insoluble in excess NaOH
c)   Put a solid sample of Q into a test-tube and add 5cm3 of concentrated tetraoxosulphate VI acid and heat gently		NO-3 , NO2  present
d)  Another solid sample of Q plus copper turnings and concentrated tetraoxosulphate VI acid and heat	Reddish brown fumes formed

 

 

 Answers

Test	Observation	Inference
a)  Q plus water shake very well	Soluble and gives a clear solution	Insoluble compounds absent, Na+, K+, NH+ ions likely present.
b)  Solution from (a) above plus dilute NaOH ,drops and then in excess	White precipitate form and insoluble in excess NaOH	Ca2+  present
c)   Put a solid sample of Q into a test-tube and add 5cm3 of concentrated tetraoxosulphate VI acid and heat gently	Oily drop on the upper part of the test-tube with brown fumes.	NO-3 , NO2  present
d)  Another solid sample of Q plus copper turnings and concentrated tetraoxosulphate VI acid and heat	Reddish brown fumes formed	NO2 , NO3+  confirmed

 

 

Explaining the tests and inferences

   In test a, the unknown substance is soluble in water and gives a clear solution, this means that coloured ion, insoluble compounds are absent. It also means that ions like sodium, potassium or ammonium are likely to be present because these ions are ver soluble in water in every case.

   In test b, the unknown substance formed white precipitate with sodium hydroxide solution which remain insolution insoluble in excess this is because calcium is known to form insoluble hydroxide which remain insoluble in sodium hydroxide.

  In test c and d, these are peculiar test for trioxonitrate V because of the formation of brown fumes.