Why is Lassaigne solution not used for detecting phosphorus?

Phosphorus does not form an extract. In the case of phosphorous, It is oxidised to form oxyacid, where Nitric acid is used.

Why potassium metal is not used in Lassaigne test?

Halogens form sodium halide by fusion with sodium metal in an organic compound. Potassium can, technically, be used in place of sodium. However, since the experiments are conducted in an aqueous solution, the explosive reaction during the application of potassium is difficult to monitor.

Why fluorine is not detected by using the Lassaigne’s test?

Answer: Fluorine does not give Lassaigne’s test because It does not forms Precipitate like other halogens (chlorine ,Bromine,Iodine). Really It forms a precipitate of silver fluoride but the precipitate is soluble in water so we are unable to detect fluorine by lassaigne’s test.

Why only sodium is used in the preparation of Lassaigne filtrate?

2. Why an organic compound is fused with sodium metal for preparing Lassaigne’s extract? Ans. When the organic compound is heated with sodium, the elements such as nitrogen, sulphur and halogens, if present in the compound, are converted into sodium salts which are soluble in water.

Can phosphorus be detected by Lassaigne test?

Nitrogen, sulphur, halogens, and phosphorus present in an organic compound are detected by “Lassaigne’s test”.

Which compound does not give Lassaigne test?

The molecular formula for hydrazine is N2H4. Thus, hydrazine contains nitrogen but it does not contain carbon. On reaction with sodium it cannot form sodium cyanide and thus does not give a positive Lassaigne’s test for nitrogen. Thus, option (B) is correct.

Which is the oxidizing agent used in the test for phosphorus?

Explanation: The phosphorous present in the organic compound is oxidized to phosphate by the oxidizing agent sodium peroxide. This solution is then boiled with nitric acid and treated with ammonium molybdate. As a result, a yellow precipitate is formed, indicating the presence of phosphorous.

Which compound do not give Lassaigne’s test for nitrogen?

hydrazine and hydrazoic acid do not contain carbon. Thus these compounds cannot form NaCN on fusion with sodium. Hence, benzene diazonium chloride, hydrazine and hydrazoic acid cannot give Lassaigne’s test of nitrogen.

Which compound does not give positive Lassaigne’s test for nitrogen?

Thus, hydrazine does not give a positive test in Lassaigne’s test for nitrogen. Thus, the correct option is (B) hydrazine.

Which of the following is not used in making sodium fusion extract?

The correct answer is (c) because hydrazine is not an organic compound and cannot form CNo- whereas a,b,d are organic compounds.

What is the purpose of making sodium extract for the detection of hetero elements in organic compounds?

The red hot tube is plunged into the porcelain basin with cold water. The content is grinded and then filtered. Thus, obtained filtrate is called sodium extract. The sodium extract is subjected to further chemical analysis to decide whether the organic compound has foreign element or not.

How can we detect the presence of phosphorus?

The organic compound is heated with an oxidising agent. The phosphorus present in the compound is oxidized to phosphate. The solution is boiled with nitric acid and then treated with ammonium molybdate . A yellow colouration indicated presence of phosphorus.

Which organic compounds give Lassaigne’s test?

The organic compounds (which have carbon atoms) along with nitrogen give lassaigne’s test. It is because the carbon present will react with nitrogen and sodium metal added during this test to give NaCN (sodium cyanide). Sodium cyanide is converted to sodium ferrocyanide on treating with ferrous sulphate.

What is the use of Lassaigne’s test?

Lassaigne’s test is a test for the detection of halogens, nitrogen and sulphur in an organic compound. These elements are covalently bonded to the organic compounds. In order to detect them, these have to be converted into their ionic forms. This is done by fusing the organic compound with sodium metal.

Why diazonium salts do not give CN – ion test?

This is because both C and N are required to form CN – ion. This test is not given by diazonium salts as they decompose to give nitrogen gas on heating. The extract is treated with sodium nitroprusside. The appearance of violet colour indicates the presence of sulphur. The following reaction occurs:

Why fresh Sol of FeSO4 is used in Fe2+ test?

Fe2+ has great tendency to form Fe3+ (as Fe3+ has d5 config while Fe2+ has d6, former being half filled and hence more stable). [Facts are agreeable to Reduction Potential Values too.] So, in fresh sol of FeSO4 isnt used, sol will have predominant Fe3+ which wont give the test satisfactorily. Thus is the need to use Fresh Sol of FeSO4.