Activity 4.2 Class 10 Science- Explanation

In this activity, we will discuss the differences in molecular formulas and molecular mass in carbon compounds.

Aim of the activity

To compare molecular formulas and molecular masses of alcohols

To understand the homologous series

 

Materials Required

   1.  Periodic table

   2. Calculator

   3. Pen and pencil

Procedure

   1.  We will write the molecular formulas of alcohol – Methanol, ethanol and propanol.

   2. Now we calculate the molecular masses of these alcohols.

   3. We compare the differences in formulas and molecular masses.

   4. Now we arrange the alcohols in increasing number of carbon atoms and observe homologous series.

   5. Finally we use same method for generating homologous series for other functional groups like alkanes, alkenes etc.

 

Observation

We can observe that:

    1. The difference in molecular mass between two successive member is 14g/mol

    2. Each compound of a homologous series differs by a -CH₂ unit.

   3. All members of a homologous series show similar chemical properties.

Explanation

All the compounds given belong to same homologous series because they have same functional group -OH and differs by  -CH₂ unit and 14g/mol mass.

 

Other Examples of Homologous Series

(1)      Alkanes

i.              CH₄

ii.          C₂H₆

iii.       C₃H₈

iv.        C₄H₁₀

(2)      Alkenes

i.              C₂H₄

ii.          C₃H₆

iii.       C₄H₈

(3)      Carboxylic acids

i.   HCOH

ii.   CH₃COOH

iii.  C₂H₅COOH

iv.   C₃H₇COOH

Conclusion

 We can conclude that:

    1.  All members of a homologous series differ by -CH₂ unit in formula.

    2. Molecular mass increases by 14g/mol

    3. All members have same functional group and chemical properties.

Frequently Asked Questions

   1. What is the difference in molecular mass between two successive alcohols?

Answer – 14 g/mol

    2. What is a homologous series?

Answer – Homologous series is a group of organic compounds having same functional group, similar chemical properties and all members have difference of -CH₂ in molecular formula.

   3. What is the difference in molecular formula of two successive members in a homologous series?

Answer - -CH₂   unit