Read the passage and answer the question :A homologous series is a se...
In homologous series the two consecutive members will differ by 14u or CH2 units
In case of alkanes (General Formula : CnH2n+2)
Example methane and ethane.
CH4 , C2H6, C3H8
Molecules masses are 16, 30, 44
Consecutive ones differ by 14.
And each differs by -CH2 units.
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Read the passage and answer the question :A homologous series is a se...
Difference in Molecular Mass:
- In a homologous series of alkanes, two consecutive members differ in molecular mass by 14 atomic mass units (a.m.u).
- This is because each member of the series has an additional CH2 unit in its main carbon chain compared to the previous member.
- The molecular mass of CH2 is approximately 14 a.m.u, so the difference in molecular mass between two consecutive members is 14 a.m.u.
Difference in Number of Atoms of Elements:
- In a homologous series of alkanes, two consecutive members differ in the number of CH2 units in their main carbon chain.
- Each CH2 unit consists of one carbon atom and two hydrogen atoms.
- Therefore, the difference in the number of atoms of elements between two consecutive members is one carbon atom and two hydrogen atoms, which can be represented as CH2.
Explanation:
- A homologous series is a series of organic compounds that have the same functional group and show similar chemical properties.
- In the case of alkanes, the functional group is the carbon-carbon single bond (C-C) and the chemical properties are determined by the presence of this bond.
- Each member of the alkane homologous series has a main carbon chain with varying numbers of carbon atoms.
- The first member of the series is methane (CH4), which has one carbon atom. The second member is ethane (C2H6), which has two carbon atoms.
- The molecular mass of methane is approximately 16 a.m.u (1 carbon atom + 4 hydrogen atoms), while the molecular mass of ethane is approximately 30 a.m.u (2 carbon atoms + 6 hydrogen atoms).
- The difference in molecular mass between methane and ethane is 14 a.m.u (30 a.m.u - 16 a.m.u), which corresponds to the molecular mass of one CH2 unit.
- Similarly, the difference in the number of atoms of elements between methane and ethane is one carbon atom and two hydrogen atoms, which can be represented as CH2.
- This pattern continues in the homologous series of alkanes, where each consecutive member differs from the previous member by 14 a.m.u in molecular mass and one CH2 unit in the number of atoms of elements.
- Therefore, the correct answer is option 'A': 14 a.m.u and CH2 respectively.
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