Activity 4.2 NCERT Class 10 Science, Carbon, and its Compounds
Activity 4.2 asks us to observe the difference in formulae and molecular masses of various alcohol.
Name: Chemical formula: Difference; Molecular weight: Difference
Methanol: CH3OH —- 32 —–
Ethanol: C2H5OH -CH2 46 14
Propanol: C3H7OH -CH2 60 14
Butanol: C4H9OH -CH2 74 14
Carbon contains four electrons in its valance shell. It needs 4 extra valence electrons to complete the octet. It combines with various other molecules like oxygen, nitrogen, hydrogen but also reacts with other carbon atoms as well. We call such property as polymerisation tendency. Here, a carbon atom attaches to another carbon atom and elongates the chain. The various compounds formed show similar property and gradual change (increase or decrease) in the property, e.g. Boling point, melting point, solubility, polarity. We call such groups as homologous series.
Methanol, ethanol, propanol, butanol etc. are similar in structure and molecular weight increases by 14amu (Atomic Mass Unit). Here Melting point and boiling point also increase with the number of carbon atoms. They all show the polar property due to the presence of polar -OH(hydroxy group). With an increase in the bulkiness of carbon atom, higher alcohols are less polar.
We use such a tendency to predict the behaviour of the molecule.
Similarly, the property of other functional groups like Amide (CONH2), Carboxylic acid (COOH), Primary, secondary, and tertiary Amines (NH) etc. also depend on the number of carbon atoms.
Inference/conclusion: molecules of a homologous series show similar physical and chemical property.