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Melting and Boiling Points

The general f...

Question

The general formula of three compounds A,B and C are CnH2n, B has highest boiling point whereas C has the lowest. Which has the minimum number of carbon atoms ? Name the homologous series they belong to ?

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Solution

The general formula of alkane is C_nH_2n₊₂
General formula for alkene is C_nH_2n
General formula for alkyne is C_nH_2n-2.
As the general formula of A, B , C is C_nH_2n therefore they all belong to the homologous series of alkene.
As we known in straigh chain hydrocarbons, higher is the molecular mass , higher will be its melting point and boiling point.
Since the boiling point of B is highest therefore it has more number of carbon atoms and thus have higher molecular mass. Whereas C has lowest boiling point therefore it contains minimum number of Carbon atoms and lower molecular mass as compare to B and A.

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Similar questions

Q. (a) Give the general name of the class of compounds having the general formula C_nH_2n₋₂. Write name of the first member of this homologous series.
(b) The general formula of a homologous series of carbon compounds if C_nH_2n. Write the molecular formulae of the second and fourth members of the series.
(c) Write the molecular formulae of the third and fifth members of homologous series of carbon compounds represented by the general formula C_nH_2n₊₂

Q. Fill in the following blanks with suitable words :
(a) The form of carbon which is known as black lead is ___
(b) The form of carbon which is used as a lubricant at high temperature is ___
(c) Compounds of carbon with hydrogen alone are called ___
(d)

C_{n} H_{2 n}

is the general formula of ___ hydrocarbons.
(e) Hydrocarbons having the general formula

C_{n} H_{2 n - 2}

are called ___
(f) Ethene and ethyne are examples of ___ hydrocarbons.
(g) Ethyne has ___ carbon-hydrogen single bonds.
(h) Carbon compounds have usually ___ melting points and boiling points because they are ___ in nature.
(i) The property of carbon atoms to form long chains in compounds is called ___
(j) The general formula

C_{n} H_{2 n}

for cycloalkanes is the same as that of ___
(k) The IUPAC name of ethylene is ___
(l) The IUPAC name of acetylene is ___

Q. (a) Define a homologous series. Give the name and structural formula of one homologue of the following:
CH₃OH
(b) Write the molecular formula of the third member of the homologous series of carbon compounds with general formula C_nH₂_n₊₁OH.
(c) Name any two fossil fuels.

Q. Fill in the following blanks with suitable words:
(a) The form of carbon which is known as black lead is ...........
(b) The form of carbon which is used as a lubricant at high temperature is .........
(c) Compounds of carbon with hydrogen alone are called ..........
(d) C_nH_2n is the general formula of .......... hydrocarbons.
(e) Hydrocarbons having the general formula C_nH_2n−2 are called ..........
(f) Ethene and ethyne are examples of ..... hydrocarbons.
(g) Ethyne has ......... carbon-hydrogen single bonds.
(h) Carbon compounds have usually ... melting points and boiling points because they are ...... in nature.
(i) The property of carbon atoms to form long chains in compounds is called ...........
(j) The general formula C_nH_2n for cycloalkanes is the same as that of ...........
(k) The IUPAC name of ethylene is .........
(l) The IUPAC name of acetylene is ............

Q. A hydrocarbon on ozonolysis gives one mole each of compounds

A

B

A

B

on reduction with sodium borohydride gives compounds

C

D

belonging to same homologous series.

C

has no position isomer whereas

D

has position isomer.

A

B

do not belong to the same homologous series. However, both

A

B

on oxidation with acidified

K M n O_{4}

give same compound. Identify the hydrocarbon.

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