Question

Lassaigne's test for the detection of nitrogen fails in

• A. NH$_2$CONHNH$_2$ . HCI
• B. NH$_2NH_2$ . HCI
• C. $NH_2CONH_2$
• D. $C_6H_5NHNH_2 . HCI$

Hint:

Lassaigne's test is given by only those compounds which contain both carbon and nitrogen. 

Answer 1

The Correct Option is B

Lassaigne's test is given by only those compounds which contain both carbon and nitrogen. 

• When compounds containing C and N are heated with sodium, they form NaCN which is easily detected by FeCl\(_3\).
• Some compounds live hydrazine (NH\(_2\) . NH\(_2\)) contain nitrogen but they do not respond.
• In Lassaigne's test there's no carbon and hence, NaCN is not formed.
• NH₂NH₂.HCl does not pass Lassaigne's test since it contains no carbon.

Discover More Topics From Chapter: Organic Chemistry

Answer 2

The Correct Answer is (B)

Real Life Applications

• substances that interfere with the test and include other ingredients. Other substances can affect the results of Lassaigne's nitrogen test. For instance, fluorine (F) and sodium cyanide can combine to generate other compounds, which will stop the blue precipitate from forming. Lassaigne's test is therefore ineffective for substances containing fluorine. substances that have a strong acidity. 
• For very acidic substances, Lassaigne's test is ineffective. This is due to the fact that the acid will combine with the sodium cyanide to generate other chemicals, preventing the development of the blue precipitate. 
• Lassaigne's technique, for instance, won't work if used to find nitrogen in a chemical that contains HCl since HCl is a very acidic substance. compound types without carbon. The nitrogen in an organic substance is converted to sodium cyanide (NaCN) in the Lassaigne test. When iron(III) chloride (FeCl₃) is added to the solution, a blue precipitate forms, which can be used to diagnose the problem. The test will be ineffective if the chemical doesn't contain carbon since no NaCN will develop. For instance, the Lassaigne test will not be successful for the compound hydrazine (NH₂NH₂) since it includes nitrogen but no carbon.

Question can also be asked as

• Which of the following compounds will not give a positive Lassaigne's test for nitrogen? 
• What is the chemical reason why Lassaigne's test fails for compounds that do not contain carbon? 
• Describe the steps involved in the Lassaigne's test for nitrogen, and explain why the test fails for compounds that do not contain carbon.

Answer 3

The Correct Answer is (B)

Lassaigne's test is used to find out whether organic molecules contain nitrogen, halogen, or sulfur. 

• Take a fusion tube and fill it with the organic component and a trace amount of sodium to conduct this test.
• By doing this, sodium changes every metal into its ionic compounds.

Procedure of Preparing Lassaigne Extract

• First, insert a little piece of dry sodium into a fusion tube.
• Burner heats the fusion tube.
• The sodium then melts.
• After that, reheat the fusion tube while including a little amount of an organic component.
• The chemical and sodium metal begin to react. The tube should be heated until it becomes red.
• Then, use a glass rod to smash the material after pouring it into a china dish.
• Bring the aforementioned stuff to a boil. Stop heating when it reaches boiling, then filter the insoluble material.
• Lassaigne's Extract or Sodium Fusion Extract (SFE) is the name of this filtrate.
• The extracted substance will have an alkaline pH.
• Add a little drop of NaOH if the extract is found to not be alkaline after testing to make it alkaline.

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