Chemistry of Hydrocarbons

29 free MDCAT Chemistry MCQs on Chemistry of Hydrocarbons (PM&DC syllabus), each with the answer, an explanation and the textbook line it comes from. Tap to check, no sign-up.

Tap an answer to check it · 29 questions

1. Question 1

   The rule that the positive part of an unsymmetrical reagent adds to the double-bonded carbon holding more hydrogens is:
   • APauli's principle
   • BHund's rule
   • CLe-Chatelier's principle
   • DMarkovnikov's rule
   Show answer and explanation

   Answer: D) Markovnikov's rule

   So propene + HBr gives mainly 2-bromopropane. Source: Chemistry 12 KPK (taleem360.com), p. 139.

2. Question 2

   Organic compounds with a hydroxyl group and a halogen on adjacent carbon atoms are:
   • AHalohydrins
   • BVicinal dihalides
   • CEpoxides
   • DGlycols
   Show answer and explanation

   Answer: A) Halohydrins

   Formed when alkenes react with hypohalous acids (X-OH). Source: Chemistry 12 KPK (taleem360.com), p. 141.

3. Question 3

   Compounds in which carbon atoms are linked alternately by single and double bonds are:
   • ASaturated
   • BIsolated
   • CConjugated
   • DCumulated
   Show answer and explanation

   Answer: C) Conjugated

   1,3-butadiene is the simplest example. Source: Chemistry 12 KPK (taleem360.com), p. 143.

4. Question 4

   In benzene, the carbon-carbon sigma bonds are formed by overlap of type:
   • Asp2-sp2
   • Bsp-sp
   • Csp3-sp3
   • Dsp3-sp2
   Show answer and explanation

   Answer: A) sp2-sp2

   Each ring carbon is sp2 hybridized, with all bond angles 120. Source: Chemistry 12 KPK (taleem360.com), p. 165.

5. Question 5

   Chlorination of benzene with Cl2 and FeCl3 at room temperature is a/an:
   • AElectrophilic addition
   • BElectrophilic substitution
   • CFree radical addition
   • DNucleophilic substitution
   Show answer and explanation

   Answer: B) Electrophilic substitution

   In UV light without a catalyst, chlorine instead adds to give benzene hexachloride. Source: Chemistry 12 KPK (taleem360.com), p. 171.

6. Question 6

   Nitrobenzene undergoing a second electrophilic substitution gives mainly the:
   • APara product
   • BOrtho product
   • CMeta product
   • DOrtho and para mixture
   Show answer and explanation

   Answer: C) Meta product

   -NO2 withdraws electrons and directs to the meta position. Source: Chemistry 12 KPK (taleem360.com), p. 179.

7. Question 7

   Vegetable oil is converted into vegetable ghee by:
   • AHydration
   • BHydrogenation
   • CHalogenation
   • DOzonolysis
   Show answer and explanation

   Answer: B) Hydrogenation

   Catalytic addition of H2 over Ni. Source: Chemistry 12 KPK (taleem360.com), p. 138.

8. Question 8

   Alkanes are called paraffins because they have:
   • AHigh reactivity
   • BMany double bonds
   • CLittle affinity for reagents
   • DA waxy smell only
   Show answer and explanation

   Answer: C) Little affinity for reagents

   Latin parum = little, affinis = affinity. Source: Chemistry 12 KPK (taleem360.com), p. 128.

9. Question 9

   Alkanes do not react with polar reagents under normal conditions mainly because the C-H bond is:
   • AA pi bond
   • BHighly ionic
   • CVery weak
   • DAlmost non-polar
   Show answer and explanation

   Answer: D) Almost non-polar

   C (2.5) and H (2.1) have comparable electronegativities. Source: Chemistry 12 KPK (taleem360.com), p. 128.

10. Question 10

    Cyclopropane undergoes ring-opening addition reactions because of its:
    • AGreater angle strain
    • BStronger C-C bonds
    • CDelocalized electrons
    • DHydrogen bonding
    Show answer and explanation

    Answer: A) Greater angle strain

    Poor orbital overlap makes it unstable; higher cycloalkanes behave like alkanes. Source: Chemistry 12 KPK (taleem360.com), p. 128.

11. Question 11

    At room temperature, the first four alkanes (C1-C4) are:
    • ALiquids
    • BGases
    • CSolids
    • DWaxes
    Show answer and explanation

    Answer: B) Gases

    C5-C17 are liquids; higher alkanes are wax-like solids. Source: Chemistry 12 KPK (taleem360.com), p. 124.

12. Question 12

    Propene reacts with HBr to give mainly:
    • A2-Bromopropane
    • B1-Bromopropane
    • C1,2-Dibromopropane
    • DPropyl alcohol
    Show answer and explanation

    Answer: A) 2-Bromopropane

    Markovnikov's rule: H adds to the CH2 carbon. Source: Chemistry 12 KPK (taleem360.com), p. 139.

13. Question 13

    Rapid decolourization of bromine in CCl4 shows that a compound contains:
    • AOnly carbon-carbon single bonds
    • BA carbon-carbon double bond
    • CA hydroxyl group on carbon
    • DAn ester functional group
    Show answer and explanation

    Answer: B) A carbon-carbon double bond

    Bromine adds across the double bond to give a colourless dibromide. Source: Chemistry 12 KPK (taleem360.com), p. 140.

14. Question 14

    Ethene reacts with oxygen over a silver catalyst at about 300 C to give:
    • AAcetaldehyde
    • BEthylene glycol
    • CEthylene oxide
    • DEthanol
    Show answer and explanation

    Answer: C) Ethylene oxide

    Epoxides give glycols on acid hydrolysis. Source: Chemistry 12 KPK (taleem360.com), p. 141.

15. Question 15

    Ozonolysis of an unknown alkene is used to:
    • AMake polyethene
    • BPrepare its alkane
    • CTest for benzene rings
    • DLocate the double bond
    Show answer and explanation

    Answer: D) Locate the double bond

    Cleavage at the double bond gives carbonyl compounds that reveal its position. Source: Chemistry 12 KPK (taleem360.com), p. 142.

16. Question 16

    Ozonolysis of ethene, followed by warming with Zn and water, gives:
    • AFormaldehyde
    • BAcetaldehyde
    • CAcetone
    • DEthanol
    Show answer and explanation

    Answer: A) Formaldehyde

    Both CH2 halves become HCHO; ozonides are explosive and not isolated. Source: Chemistry 12 KPK (taleem360.com), p. 142.

17. Question 17

    In 1,3-butadiene the C-C single bond (1.48 A) is shorter than a normal one (1.54 A) because of:
    • Asp3 hybridized carbons
    • BDelocalized pi electrons
    • CHydrogen bonding
    • DRing angle strain
    Show answer and explanation

    Answer: B) Delocalized pi electrons

    All four p orbitals overlap, spreading the pi electrons over four carbons. Source: Chemistry 12 KPK (taleem360.com), p. 143.

18. Question 18

    Alkynes are less reactive than alkenes towards electrophiles partly because sp carbon orbitals have:
    • ALarger atomic size
    • BFewer pi electrons
    • CMore s character
    • DNo sigma bonds
    Show answer and explanation

    Answer: C) More s character

    50% s character holds the pi electrons more tightly; the cylindrical pi cloud also has low electron density. Source: Chemistry 12 KPK (taleem360.com), p. 155.

19. Question 19

    Acetylene and terminal alkynes are weakly acidic because the sp-hybridized carbon is:
    • APositively charged
    • BLess electronegative
    • Csp3 hybridized
    • DMore electronegative
    Show answer and explanation

    Answer: D) More electronegative

    It pulls the C-H electrons strongly, so the H is released to strong bases. Source: Chemistry 12 KPK (taleem360.com), p. 156.

20. Question 20

    Acetylene reacts with sodium amide in liquid ammonia to give:
    • ASodium acetylide
    • BEthane
    • CSodium ethoxide
    • DAcetaldehyde
    Show answer and explanation

    Answer: A) Sodium acetylide

    Evidence of the acidic C-H in terminal alkynes. Source: Chemistry 12 KPK (taleem360.com), p. 155.

21. Question 21

    Benzene prefers electrophilic substitution to addition because its:
    • AC-H bonds are ionic
    • BDouble bonds are localized
    • CCarbon atoms are saturated
    • DDelocalized electrons give stability
    Show answer and explanation

    Answer: D) Delocalized electrons give stability

    Addition would destroy the stable delocalized pi system. Source: Chemistry 12 KPK (taleem360.com), p. 170.

22. Question 22

    Benzene reacts with chlorine in ultraviolet light to give:
    • ABenzene hexachloride
    • BChlorobenzene
    • CDichlorobenzene
    • DBenzyl chloride
    Show answer and explanation

    Answer: A) Benzene hexachloride

    An addition reaction; with FeCl3 in the dark it gives chlorobenzene by substitution. Source: Chemistry 12 KPK (taleem360.com), p. 171.

23. Question 23

    Benzene treated with n-propyl chloride and AlCl3 gives mainly:
    • An-Propyl benzene
    • BIsopropyl benzene
    • CChlorobenzene
    • DPropene
    Show answer and explanation

    Answer: B) Isopropyl benzene

    The carbonium ion rearranges before attacking the ring - a drawback of Friedel-Crafts alkylation. Source: Chemistry 12 KPK (taleem360.com), p. 174.

24. Question 24

    Friedel-Crafts acylation of benzene with acetyl chloride and AlCl3 gives:
    • AToluene
    • BBenzaldehyde
    • CAcetophenone
    • DBenzoic acid
    Show answer and explanation

    Answer: C) Acetophenone

    Acylation gives aromatic ketones. Source: Chemistry 12 KPK (taleem360.com), p. 175.

25. Question 25

    The -OH group attached to benzene is:
    • AOrtho/para directing, deactivating
    • BMeta directing, deactivating
    • CMeta directing, activating
    • DOrtho/para directing, activating
    Show answer and explanation

    Answer: D) Ortho/para directing, activating

    It releases electrons to the ring by resonance. Source: Chemistry 12 KPK (taleem360.com), p. 178.

26. Question 26

    Meta-directing groups such as -NO2:
    • AWithdraw electrons from ring
    • BDonate electrons to ring
    • CActivate the benzene ring
    • DDirect to ortho position
    Show answer and explanation

    Answer: A) Withdraw electrons from ring

    The electron-deficient ring reacts more slowly with electrophiles. Source: Chemistry 12 KPK (taleem360.com), p. 179.

27. Question 27

    Ethyl alcohol and dimethyl ether (both C2H6O) are:
    • APosition isomers
    • BChain isomers
    • CFunctional group isomers
    • DMetamers
    Show answer and explanation

    Answer: C) Functional group isomers

    Same molecular formula, different functional groups (-OH vs -O-). Source: Chemistry 12 KPK (taleem360.com), p. 149.

28. Question 28

    Diethyl ether and methyl propyl ether show:
    • APosition isomerism
    • BTautomerism
    • CChain isomerism
    • DMetamerism
    Show answer and explanation

    Answer: D) Metamerism

    Unequal distribution of alkyl groups on either side of the same functional group. Source: Chemistry 12 KPK (taleem360.com), p. 149.

29. Question 29

    The keto and enol forms of propanone, which exist in dynamic equilibrium, show:
    • ATautomerism
    • BMetamerism
    • CChain isomerism
    • DPosition isomerism
    Show answer and explanation

    Answer: A) Tautomerism

    A special type of functional group isomerism. Source: Chemistry 12 KPK (taleem360.com), p. 149.

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