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प्रश्न
State any four characteristics of a homologous series
State two characteristics of a homologous series.
उत्तर
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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संबंधित प्रश्न
Write the next homologue of the following: C2H4
Write the next homologue of the following: C4H6
Write the name and formula of the 2nd member of homologous series having general formula CnH2n.
Write the name and formula of the 2nd member of homologous series having general formula CnH2n – 2.
Write the molecular formula of first two members of homologous series having functional group -Cl.
Write the molecular formula of first two members of homologous series having functional group – OH
The following vegetables are kept in a basket :
Potato, Tomato, Radish, Brinjal, Carrot, Bottle-gourd
Which two of these vegetables correctly represent the homologous structures?
(A) Carrot and Tomato
(B) Potato and Brinjal
(C) Radish and Carrot
(D) Radish and Bottle-gourd
Complete the following table which relates to the homologous series of hydrocarbons.
|
General Formula |
IUPAC name of the homologous series | Characteristic bond type | IUPAC name of the first member of the series |
| `C_nH_(2n-2)` | (A)________ | (B)______ | (C)______ |
| C_nH_(2n+1) | (B)________ | (E)______ | (F)______ |
Define a homologous series. Give the name and structural formula of one homologue of the following:
CH3OH
The number of carbon atoms present in the molecule of fifth member of the homologous series of alkynes is:
(a) four
(b) five
(c) six
(d) seven
The molecular formula of the third member of the homologous series of ketones is:
(a) C4H8O
(b) C3H6O
(c) C5H10O
(d) C6H12O
A colourless organic liquid X of molecular formula C2H4O2 turns blue litmus to red. Another colourless organic liquid Y of molecular formula C3H6O has no action on any litmus but it is used as a nail polish remover. A yet another colourless organic liquid Z of molecular formula C2H6O has also no action on litmus but it is used in tincture of iodine.
(a) Name the liquid X. To which homologous series does it belong? Give the name of another member of this homologous series.
(b) Name the liquid Y. To which homologous series does it belong? Write the name of another member of this homologous series.
(c) Can you name an organic compound having the same molecular formula as liquid Y but which belongs to a different homologous series? What is this homologous series?
(d) Name the liquid Z. To which homologous series does it belong? Write the name of another member of this homologous series.
Succeeding members of a homologous series differ by ______.
Give the dot diagram of the first member of the alcohol.
Give the structure of the second member of the alcohol group
What is homologous series ?
Copy and complete the following table which relates to three homologus series of hydrocarbons:
| General formula | CnH2n | CnH2n-2 | CnH2n+2 |
| IUPAC name of the homologus series | |||
| Characteristic bond type | Single bonds | ||
| IUPAC name of the first member of the series | |||
| Type of reaction with chlorine | Addition |
What is a homologous series?
Halo alkanes react with alkalies to produce alcohol. Give the equation for the preparation of the second member of the homologous series of alcohol. State under what condition the reaction occurs.
Two statements are given - one labeled Assertion (A) and the other labeled Reason (R).
Assertion (A): In a homologous series of alcohols, the formula for the second member is C2H5OH and the third member is C3H7OH.
Reason (R): The difference between the molecular masses of the two consecutive members of a homologous series is 144.
The phenomenon in which compounds having different structural formulae have the same molecular formula is called _______.
Complete the following table for the homologous series of alkanes.
| Name | Molecular formula | Condensed structural formula | Number of carbon atom | Number of -CH2- units | Boiling point °C |
| Methane | CH4 | CH4 | 1 | 1 | -162 |
| Ethane | C2H6 | CH3–CH3 | 2 | 2 | -88.5 |
| Propane | C3H8 | CH3–CH2–CH3 | 3 | 3 | -42 |
| Butane | C4H10 | CH3–CH2–CH2–CH3 | ______ | ______ | 0 |
| Pentane | C5H12 | CH3–CH2–CH2–CH2–CH3 | ______ | ______ | 36 |
| Hexane | C6H14 | CH3–CH2–CH2–CH2–CH2–CH3 | ______ | ______ | 69 |
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 |
Observe the structural formula and answer the following questions.
- Write the name of the given hydrocarbon.
- The given hydrocarbon is included in which type of hydrocarbon?
- What is the kind of compounds with the above characteristic structure called?
Which of the following pairs can be the successive members of a homologous series?
The first member of alkyne homologous series is
Study and complete the following table:
| Homologous series | Alkane | Alkyne |
| General formula | CnH2n+2 | 1. ______ |
| IUPAC name | 2. ______ | Ethyne |
| Common name | Marsh gas | 3. ______ |
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.
