Question

Give one chemical test each to distinguish between the following pairs of compounds:
$1$ : ethanol and acetic acid
$2$ : Acetaldehyde and benzaldehyde.

Answer 1

Hint: First of all we must know about the basic characters of the ethanol which is an alcohol and acetic acid which is an important carboxylic acid. Here we can differentiate them from the acid base reaction. Now, we need to know more about acetaldehyde. It is an organic chemical known as ethanol while benzaldehyde is a compound with benzene ring with a formyl group substitute. Now we will watch which of them reacts with Fehling’s solution.

Complete step by step solution:
Step 1: At first we need to differentiate between acetic acid and ethanol. Since we know that acetic acid is an acid, so we are sure that it will react with a base. An acid-base reaction produces the $C{{O}_{2}}$. While alcohol are not that good of acids so that would not give the $C{{O}_{2}}$ while reacting with base.
\[C{{H}_{3}}COOH+N{{a}_{2}}C{{O}_{3}}\to C{{H}_{3}}COONa+{{H}_{2}}O+C{{O}_{2}}\uparrow \]
Here we can see that the $C{{O}_{2}}$ is released with a brisk effervescence, while this will not happen when ethanol reacts with bicarbonates.
We can say that with help of bicarbonates we can distinguish the ethanol and acetic acid.
Step2: Acetaldehyde which has the chemical formula of \[C{{H}_{3}}CHO\]. So there is a deep blue alkaline solution called Fehling’s solution which is used to identify the presence of the aldehydes or groups which contain the aldehyde functional group.
So when we will use the Fehling’s solution with acetaldehyde it will give red precipitate of cuprous oxide while benzaldehyde will not give any such precipitate.
\[C{{H}_{3}}CHO+5O{{H}^{-}}+2C{{u}^{2+}}\to C{{H}_{3}}CO{{O}^{-}}+C{{u}_{2}}O\downarrow +3{{H}_{2}}O\]
As we can see there is precipitation of the $C{{u}_{2}}O$ left while this reaction does not take place when Fehlin’s solution is reacted with benzaldehyde.
So the conclusion is that we can use Fehling’s solution to distinguish acetaldehyde and benzaldehyde.

Note: We can often see acetic acid at everybody’s home. One of the most famous uses is the Vinegar. Vinegar is the $4-8%$ solution of acetic acid and water. It is of those compounds whose two names are accepted by IUPAC. Another name you can use is ethanoic acid. Some vinegar with baking soda and red food coloring is often used to make the molten lava project.