Chemistry

Hydrocarbons

Question:

Which of the following reactions of methane is incomplete combustion?
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Answer:

Dining incomplete combustion of alkanes with insufficient amount of air or dioxygen, carbon black is formed which is used in the manufacture of ink, printer ink, black pigments and as filters. Thus,

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Hydrocarbons

Q 1.

In the alkane, CH3CH2—C(CH3)2—CH2—CH(CH3)2, identify 1 °, 2 °, 3 ° carbon atoms and give the number of H-atoms bonded to each one of these.

Q 2.

Convert ethylene to ethane.

Q 3.

How will you distinguish between propene and propane?

Q 4.

What is the hybridisation of central carbon in 1,2-propadiene (CH2=C=CH2)?

Q 5.

Out of benzene, m-dinitrobenzene and toluene which will undergo nitration most easily and why?

Q 6.

What happens when ethanol is heated with cone. H2SO4?

Q 7.

Nucleophiles and electrophiles are reaction intermediates having electron rich and electron deficient centres respectively. Hence, they tend to attack electron deficient and electron rich centres respectively. Classify the following species as electrophiles and nucleophiles.
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Q 8.

Which of the following are correct?
(a) CH3 – O – CH+2 is more stable than CH3 – CH+2
(b) (CH3)2CH+ is less stable than CH3 – CH2 – CH+2
(c) CH2 = CH – CH+2 is more stable than CH3 – CH2 – CH+2
(d) CH2 = CH+ is more stable than CH3 – CH+2
 

Q 9.

Arrange the following: HCl, HBr, HI, HF in order of decreasing reactivity towards alkenes.

Q 10.

Arrange the following set of compounds in order of their decreasing relative reactivity with an electrophile, E+.
(a) Chlorobenzene, 2, 4-dinitrochlorobenzene, p-nitrochlorobenzene
(b) Toluene,p—H3C—C6H4—NO2, p—O2N—C6H4—NO2.

Q 11.

What is polymerization? Give an example.

Q 12.

Why does benzene undergo electrophilic substitution reactions easily and nucleophilic substitutions with difficulty?

Q 13.

What are conformations?

Q 14.

For the following compounds, write structural formulas and IUPAC names for all possible isomers having the number of double or triple bond as indicated:
(a) C4H8 (one double bond) (b) C5H8 (one triple bond)

Q 15.

Write chemical equations for the combustion reaction of the following hydrocarbons,  (i) Butane (ii) Pentene (iii) Hexyne (iv) Toluene

Q 16.

What happens when benzene is treated with acetyl chloride in presence of AlCl3?

Q 17.

Why is benzene extra-ordinarily stable though it contains three double bonds?

Q 18.

Define resonance energy. What is resonance energy of benzene?

Q 19.

Write the IUPAC names of the following compounds.
(i) (CH3)CCH2C(CH3)3    (ii) (CH3)2C(C2H5)2

Q 20.

Discuss the preparation of alkanes by Wurtz reaction. What is the limitaHon of the reaction?

Q 21.

Arrange the following alkyl halides in decreasing order of the rate of β -elimination reaction with alcoholic KOH.

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Q 22.

Explain why the following systems are not aromatic?
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Q 23.

Which type of isomerism is exhibited by but-l-yne and but-2-yne?

Q 24.

What effect does branching of an alkane chain has on its boiling point?

Q 25.

What will be the product obtained as a result of the following reaction and why?

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Q 26.

The relative reactivity of 1 °, 2 ° and 3 ° hydrogens towards chlorination is 1: 3.8 : 5. Calculate the percentages of all monochlorinated products obtained from 2-methylbutane.
 

Q 27.

(a) What effect the branching of an alkane has on its melting point?
(b) Which of the following has highest boiling point?
(i) 2-methyl pentane
(ii) 2, 3-diethyl butane
(iii) 2, 2-dimethyl butane

Q 28.

How will you demonstrate that double bonds of benzene are somewhat different from that of olefins?

Q 29.

The molecules having dipole moment are________ .
(a) 2,2-Dimethylpropane                                            
(b) trans-Pent-2-ene
(c) cw-Hex-3-ene            
(d) 2,2,3,3-Tetramethylbutane

Q 30.

What happens when benzene is treated with acetyl chloride in presence of AlCl3?

Q 31.

Explain the following with examples:
(i) Wurtz reaction
(ii) Hydrogenation.

Q 32.

(a) Why are alkenes called unsaturated hydrocarbons?
(b) How will you test the presence of double bond in an alkene?
(c) Name the products formed when propene is subjected to ozonolysis.

Q 33.

Which of the following reactions of methane is incomplete combustion?
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Q 34.

Which are the correct IUPAC names of the following compound
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(a) 5-(2′,2′-Dimethylpropyl)decane
(b) 4-Butyl-2,2-dimethylnonane
(c) 2,2-Dimethyl-4-pentyloctane
(d) 5-neo-Pentyldecane

Q 35.

Alkynes on reduction with sodium in liquid ammonia form trans alkenes. Will butene formed on the reduction of but-2-yne show geometrical isomerism?

Q 36.

How will you convert benzene into
(i) p-nitrobromobenzene (ii) m-nitrobromobenzene
 

Q 37.

Why are alkanes called paraffins?

Q 38.

What is electrophile in sulphonation?

Q 39.

Explain the term aromaticity. What are the necessary conditions for any compound to show aromaticity?

Q 40.

How will you separate propene from propyne?

Q 41.

Which of the following alkenes on ozonolysis gives a mixture of ketones only?
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Q 42.

Why do alkenes prefer to undergo electrophilic addition reaction while arenes prefer electrophilic substitution reaction? Explain.

Q 43.

Rotation around carbon-carbon single bond of ethane is not completely free. Justify the statement.

Q 44.

Arrange the following set of compounds in the order of their decreasing . relative reactivity with an electrophile. Give reason.

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Q 45.

Why does the presence of a nitro group-make the benzene ring less reactive in comparison to the unsubstituted benzene ring? Explain.

Q 46.

How do you account for the formation of ethane during chlorination of methane?

Q 47.

An alkene ‘A’ contains three C—C, eight C—H, a-bonds, and one C—C n-bond. ‘A’ on ozonolysis gives two moles of an aldehyde of molar mass 44 u. Write the IUPAC name of’A’.

Q 48.

Draw the cis- and trans-structures for hex-2-ene. Which iosmer will have higher b.p. and why?

Q 49.

What are the necessary conditions for any system to be aromatic?

Q 50.

What is Huckel rule?