Alcohols
Q1

Write the molecular formulae of the fourth and fifth members of the homologous series of carbon compounds represented by the general formula CnH2n + 1OH ?

Sol:

The general formula CnH2n +1OH is of alcohol series.
Now, to solve such problems, we should know the number of carbon atoms in the first member of the alcohol series.
Here, the first member of alcohol series is methanol and it has only 1 carbon atom in its molecule.

Knowing this, the above problem can be solved as follows :
(i) Since the first member of alcohol series has 1 carbon atom in its molecule, therefore, the fourth member of alcohol series will have 4 carbon atoms in its molecule.
So, if we put n = 4 in the general formula CnH2n +1OH then the molecular formula of the fourth member of the homologous series will become C4H2* 4 + 1OH or C4H9OH.
(ii) Since the 1st member of alcohol series has 1 carbon atom in it, i.e., the 5th member will have 5 carbon atoms in it. That is, n = 5.
So, if we put n = 5 in the general formula CnH2n + 1OH, then the molecular formula of the fifth member of the alcohol series will become C5H2* 5 + 1OH or C5H11OH.

Q2

An organic compound 'A' is a constituent of wine and beer. This compound, on heating with potassium dichromate or oxygen forms another organic compound 'B'. Identify the compound 'A'. Write the chemical equation of the reaction that - takes place to form the compound 'B'. Name the compound 'B' ?

Sol:

The organic compound which is a constituent of wine and beer is ethyl alcohol (or ethanol).
Thus, the compound 'A' is ethyl alcohol (or ethanol).
Now, ethyl alcohol (or ethanol) on oxidation with acidified potassium dichromate or oxygen produces an acid known as acetic acid (or ethanoic acid).
Thus, the compound 'B' is acetic acid (or ethanoic acid). Please write the chemical equation for the oxidation of ethanol yourself.

Q3

Sugar - cane juice mixed with yeast is kept in an air - tight pot. After a few days, this juice started to give a strong smell. Name and explain the process involved. Name the method used for separating the main product from this mixture ?

Sol:

Sugar - cane juice contains sugar (C12H22O11) and yeast contains the enzymes invertase and zymase.
So, when sugar - cane juice mixed with yeast is kept for a few days, then fermentation of sugar takes place with the production of ethyl alcohol (or ethanol) and carbon dioxide.
The strong smell is due to the formation of ethyl alcohol (or ethanol).
The main product of this fermentation process, ethyl alcohol, is separated from the mixture by the process of fractional distillation.