Question

What happens when
i. Formaldehyde is heated with $N{{H}_{3}}$.
ii. Acetone reacts with Bleaching Powder.
iii. Formaldehyde reacts with Fehling Solution.

Answer 1

When formaldehyde ($C{{H}_{2}}O$) reacts with ammonia ($N{{H}_{3}}$) to give a complex product called urotropine. Acetone (${{C}_{3}}{{H}_{6}}O$) reacts with bleaching powder ($Ca{{(OCl)}_{2}}$) to form trichloroacetone and hydrolysis of trichloroacetone gives chloroform. Formaldehyde ($C{{H}_{2}}O$) reacts with Fehling solution to form anion of formic acid.

Complete answer:
Let us see the solutions of each question.
(i) The chemical formula of formaldehyde is $C{{H}_{2}}O$ , and the name of the compound $N{{H}_{3}}$ , is ammonia. The reaction between both of them takes place to form a product called urotropine, also water is formed as a by-product. The IUPAC name of urotropine is hexamethylene tetramine. The reaction is given below.
$6HCHO+4N{{H}_{3}}\xrightarrow{{}}{{(C{{H}_{2}})}_{6}}{{N}_{4}}+6{{H}_{2}}O$
In this reaction, 6 molecules of formaldehyde react with 4 molecules of ammonia to give 1 molecule of urotropine and 6 molecules of water.

(ii) The chemical formula of acetone is ${{C}_{3}}{{H}_{6}}O$ and the chemical formula of bleaching powder is $Ca{{(OCl)}_{2}}$ , bleaching powder is also known as calcium hypochlorite. The reaction between these two gives chloroform as the main product and calcium acetate as a by-product.
The reaction goes in three steps and is shown below.
$CaOC{{l}_{2}}+{{H}_{2}}O\xrightarrow{{}}Ca{{(OH)}_{2}}+C{{l}_{2}}$
First, bleaching powder or calcium hypochlorite reacts with water to give calcium hydroxide and chlorine as its products.
$C{{H}_{3}}COC{{H}_{3}}+3C{{l}_{2}}\xrightarrow{{}}CC{{l}_{3}}COC{{H}_{3}}+3HCl$
In the second step, acetone reacts with chlorine to give trichloroacetone and hydrogen chloride as its products.
$2CC{{l}_{3}}COC{{H}_{3}}+Ca{{(OH)}_{2}}\xrightarrow{{}}2CHC{{l}_{3}}+{{(C{{H}_{3}}COO)}_{2}}Ca$
In the third step, trichloroacetone reacts with the obtained calcium hydroxide to give chloroform as the main product and calcium acetate as a by-product.

(iii) The chemical formula of formaldehyde is $C{{H}_{2}}O$ and the Fehling’s solution is a mixture of copper and hydroxide ions. Thus, the reaction between them gives out anion of formic acid ${{H}_{2}}C{{O}_{2}}$ as the main product and copper oxide and water as by-products. The reaction is given below.
$HCHO+2C{{u}^{2+}}+5O{{H}^{-}}\xrightarrow{\Delta }HCO{{O}^{-}}+C{{u}_{2}}O+3{{H}_{2}}O$
The solution of formaldehyde and Fehling’s solution is heated and thus we obtain the anion of formic acid.

Note:
The compound urotropine found when formaldehyde reacts with ammonia is used as urinary antiseptic. The compound trichloroacetone can be the final compound in the reaction of acetone with bleaching powder, but its reaction with calcium hydroxide gives chloroform as the final product. The reaction of formaldehyde with Fehling’s solution can be considered as a test to recognize aldehydes, as Fehling’s solution is used in Fehling’s test for the recognition of aldehydes.