(a) Give the general formula of alkanes. Write the name, structural formula and physical state of the compound containing:
(i) 3 carbon atoms
(ii) 8 carbon atoms

(b) Which of the compounds named in (a) would show :
(i) Isomerism
(ii) Higher melting point
(iii) Higher density
(v) Lower boiling point? [5 MARKS]

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Solution

a) 2 Marks
b) 3 Marks

(a) General formula of alkanes:
$C_{n} H_{2 n + 2}$ where n = 1, 2, 3......

(i) Alkane with 3 carbon atoms: Propane:

Propane is a gas at room temperature.
(ii) Alkane with 8 carbon atoms :
Octane, $C H_{3} - C H_{2} - C H_{2} - C H_{2} - C H_{2} - C H_{2} - C H_{2} - C H_{3}$
Or

Octane is a liquid at room temperature.

(b) (i) Octane shows isomerism
(ii) Octane has higher melting point
(iii) Octane has higher density
(iv) Propane has lower boiling point.

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Similar questions

Q. (a) Draw the structural formula of a compound with two carbon atoms in each of the following cases:
(i) An alkane with a carbon to carbon single bond.
(ii) An alcohol containing two carbon atoms.
(iii) An unsaturated hydrocarbon with a carbon to carbon triple bond.

(b) Ethane, Ethene, Ethanoic acid, Ethyne, Ethanol
From the compounds given above, name:
(i) The compound with —OH as a part of its structure.
(ii) The compound with —COOH as a part of its structure.
(iii) Homologue of Homologous series with general formula C_nH_2n.

Which of the following statement(s) is/are correct about carbon compounds?

(i) Carbon has the ability to form covalent bonds with other atoms of carbon giving rise to a large number of molecules through a self-linking property.

(ii) Carbon compounds do not show isomerism.

(iii) Carbon compounds are highly unstable compounds.

(iv) Carbon compounds have low melting and boiling points.

Q. Fill in the blanks : [5 MARKS]
(i) Members of the alkene series containing ....... to ....... number of carbon atoms are liquids.
(ii) Among isomers, the one with more branched chain has a ...... boiling point.
(iii) The term ....... is used when one carbon atom is attached to four other carbon atoms.
(iv) The molecular mass of any two homologues differs by ....... amu.
(v) The melting point of alkanes increases with ....... in molecular weight.

Q. The molecules of the alkene family are represented by a general formula C_nH_2n. Answer the following:
(i) What do n and 2n signify?
(ii) What is the name of alkene when n = 4?
(iii) What is the molecular formula of the alkene, if there are six hydrogen atoms in it?
(iv) Write the molecular and structural formula of the first member of alkene family.
(v) Write the molecular formulae of lower and higher homologues of an alkene which contains four carbon atoms.

(a) Give the general formula of (i) Alkene (ii) Alkane (iii) Alkynes

(b) Write the structural formula of propyne & 2,3 dimethylpentane.

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