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Application of Gay-Lussac’s Law of Combining Volumes

Gay Lussac’s of combining volumes states that gases react in simple ratio with one another and to volumes of the products provided that temperature and pressure remain constant. In this article, you will understand how to apply this law in calculation by studying the following examples below: 1.     2H 2 + O 2 → H 2 O In the reaction above, what volume of hydrogen would be left over when 300cm 3 of oxygen and hydrogen are exploded in a sealed tube?   1cm 3 of oxygen = 2cm 3 of hydrogen 300cm 3 of oxygen = 2 x 300 = 600cm 3 Volume of left over = 1000 – 600 = 400cm 3 2.     Calculate the volume of carbon (II) oxide required to react with 40cm 3 of oxygen. 2CO + O 2 → 2CO 2 1cm 3 of oxygen = 2cm 3 of CO 40cm 3 of oxygen = 2 x 40 = 80cm 3 3.     Calculate the volume of residual gases that would be produced when 100cm 3 of sulphur (IV) oxide reacts with 20cm 3 of oxygen    2SO 2 + O 2 → 2SO 3 1cm 3 of O 2 = 2cm 3 20cm 3 of O 2 = 2 x 20 = 40cm 3
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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.

H2SO4(aq) + NO-3(s) ---- HNO3(l) + HSO-4(aq)

4HNO3(l)------ 4NO2(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.

H2SO4(aq) + NO3(S)- ------ HNO3(aq) + HSO-4(aq) +  Cu(s) + 4HNO3(aq)

Cu(s) + 4HNO3(aq) ----- Cu(NO3)2(aq) + 2NO2(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.

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