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Questions
State any four characteristics of a homologous series
State two characteristics of a homologous series.
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Solution
Characteristics of a homologous series:
- Each member of the series differs from the preceding one by the addition of a -CH2 group and by 14 a.m.u.
- All members of a homologous series share the general formula.
Example: The general formula for alkane is CnH2n+2 and alkene is CnH2n. - The physical properties of the members show a gradation in properties as the molecular mass increases.
- The chemical properties also show a gradient similarity.
Example: Methane and ethane react with chlorine to form methyl chloride and ethyl chloride, respectively.
CH4 + Cl2 → CH3Cl
C2H6 + Cl2 → C2H5Cl - All members of a homologous series can be prepared by the same general method of preparation.
Example: Alcohols can be prepared from alkyl halides.
`CH_3Br+KOH " Boil"/""CH_3OH+KBr`
`C_2H_5Br+KOH " Boil"/""C_2H_5OH+KBr`
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RELATED QUESTIONS
What is meant by homologous series of carbon compounds?
Write the molecular formula of two consecutive members of homologous series of aldehydes. State which part of these compounds determines their
- physical and
- chemical properties
What is a homologous series? Explain with an example.
An organic compound having the molecular formula C3H6O can exist in the form of two isomers A and B having different functional groups. The isomer A is a liquid which is used as a solvent for nail polish. The isomer B is also a liquid. An aqueous solution of one of the lower homologues of B is used for preserving biological specimens in the laboratory
(a) What is compound A?
(b) Write the electron-dot structure of A.
(c) What is compound B?
(d) Write the electron-dot structure of B.
(e) Name the lower homologue of compound B which is used in preserving biological specimens.
Distinguish between homologous organs and analogous organs. In which category would you place wings of a bird and wings of a bat? Justify your answer giving a suitable reason.
Give the names of the first four members of the homologous series of
alkynes.
Give three points to differentiate between saturated and unsaturated
hydrocarbons.
Write the name and formula of the fourth member of the following homologous series:
Alkyne
Saturated hydrocarbon : Single bond : : Unsaturated hydrocarbon : _______
As one ascends in any homologous series, physical properties change gradually.
Complete the following table for homologous series of Alkenes.
| Name | Molecular formula | Condensed structural formula | Number of carbon atom | Number of -CH2- units | Boiling point °C |
| Ethene | C2H4 | CH2 = CH2 | 2 | 0 | -102 |
| Propene | C3H6 | CH3–CH = CH2 | 3 | 1 | -48 |
| 1-Butene | C4H8 | CH3–CH2–CH = CH2 | ______ | ______ | -6.5 |
| 1-Pentene | C5H10 | CH3–CH2–CH2–CH = CH2 | ______ | ______ | 30 |
Which of the following does not belong to the same homologous series?
C3H8 belongs to the homologous series of ______.
A carbon compound ‘A’ having melting point 156K and boiling point 351K, with molecular formula C2H6O is soluble in water in all proportions.
- Identify ‘A’ and draw its electron dot structure.
- Give the molecular formulae of any two homologues of ‘A’.
Define Homologous series.
Write the chemical formula of two consecutive homologous of organic compounds having functional group - OH.
What happens to the (i) boiling point and (ii) solubility of organic compounds of a homologous series as the molecular mass increases?
Consider the following molecular formulae of carbon compounds:
(i) CH3COOH (ii) CH3OH (iii) C2H6 (iv) C3H4 (v) C4H8
- Which one of these compounds belongs to homologous series of alcohols?
- Identify the compound having triple bond between carbon-carbon atoms.
- Write the molecular formula of the first member of the homologous series to which CH3COOH belongs.
- Write the general formula of the series to which the compound C4H8 belongs.
Consider the carbon compounds having following molecular formula:
(i) C3H6 (ii) C3H8 (iii) C4H6 (iv) C6H6 (v) C6H12
- State the number of double covalent bonds present in C3H8.
- Write the formula of first member of the homologous series to which the carbon compound C4H6 belongs.
- Which one of the above compounds forms a ring structure of carbon atoms?
- Identify, which of the above compounds, is a member of alkane series.
Name and draw the electron dot structure of first homologue of alkynes series.
