Some Basic Concepts Of Chemistry Question 36

Question: An organic compound whose empirical and molecular formula are same, contains 20% carbon, 6.7% hydrogen, 46.7% nitrogen and the rest oxygen. On heating it yields ammonia, leaving a solid residue. The solid residue gives a violet colour with dilute solution of alkaline copper sulphate. The organic compound is

Options:

A) $ NH _2COONH _4 $

B) $ HCOONH _4 $

C) $ NH _2NHCHO $

D) $ NH _2CONH _2 $

Show Answer

Answer:

Correct Answer: D

Solution:

[d]

Element Percentage Atomic mass Relative no. of atoms Simplest ratio
C 20% 12 1.66 1
H 6.7% 1 6.7 4
N 46.7% 14 3.33 2
O 26.6% 16 1.66 1

Empirical formula = Molecular formula $ =CH _4N _2O,or,NH _2CONH _2 $

$ H _2NCONH _2+H _2NCONH _2\xrightarrow{\Delta } $ $ \underset{\text{biuret,}}{\mathop{H _2NCONHCONH _2}},+NH _3 $

When an aqueous solution of biuret is treated with dilute sodium hydroxide and a drop of copper sulphate, a violet colour is produced. This test is known as biuret test, and is characteristic of compounds having the group $ -CONH- $



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