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CBSE · Class 11 · Chemistry

Hydrocarbons

Standard difficulty · 20 questions · 40 marks

Name: Date: Score: ____ / 40

Show your working for Sections B and C. Answers are on the last page — try every question first!

Section A — Choose the correct answer8 × 1 = 8 marks
1.
The general formula of alkanes is:
  1. CnH2n−2
  2. CnHn
  3. CnH2n
  4. CnH2n+2
2.
But-1-ene reacts with HBr in the presence of a peroxide. The main product is:
  1. 1-bromobutane
  2. ethanal (two molecules)
  3. propanone and methanal
  4. methanal (two molecules)
3.
An open-chain hydrocarbon C5H8 has at most one multiple bond. It is an:
  1. arene
  2. alkene
  3. alkyne
  4. alkane
4.
In electrophilic substitution of a benzene ring carrying –NH2, the group is:
  1. meta (activating)
  2. ortho and para (deactivating)
  3. ortho and para (activating)
  4. meta (deactivating)
5.
Which of these is aromatic?
  1. Pyridine
  2. The cyclopentadienyl cation
  3. Cyclopenta-1,3-diene
  4. Cyclooctatetraene
6.
Ethanol is treated with concentrated H2SO4 at 443 K. The product is:
  1. ethyne
  2. propene
  3. but-2-ene (main product)
  4. ethene
7.
Which of these shows cis–trans (geometrical) isomerism?
  1. propene
  2. but-2-ene
  3. 2-methylbut-2-ene
  4. pent-1-ene
8.
Assertion (A): The addition of water (acid catalyst) to 2-methylpropene gives mainly 2-methylpropan-2-ol.
Reason (R): In the addition to an unsymmetrical alkene, H+ adds first to the carbon with fewer hydrogens.
  1. Both A and R are true, and R is the correct explanation of A.
  2. Both A and R are true, but R is not the correct explanation of A.
  3. A is true, but R is false.
  4. A is false, but R is true.
Section B — Short answer8 × 2 = 16 marks
9.
State Markovnikov’s rule, with an example.
10.
Write the balanced equation for the complete combustion of methane. How many moles of oxygen are needed to burn 1 mol of it?
11.
What happens when 2-methylpropene reacts with ozone, then zinc and water? Name the product and give its formula.
12.
Name the products of ozonolysis (ozone, then zinc and water) of pent-2-ene.
13.
Benzene is treated with Br2 with anhydrous FeBr3. Name the reaction and the product, and give the electrophile.
14.
Complete and name: ethene + H2 over nickel at 523 K → ?
15.
28 g of ethene (C2H4) burns completely. Find the masses of carbon dioxide and water formed. (Atomic masses: H = 1 u, C = 12 u, O = 16 u)
16.
A mixture of CH3CH2CH2Br and C2H5Br is heated with sodium in dry ether. Which alkanes are formed? Why is this not a good way to make one pure alkane?
Section C — Word problems4 × 4 = 16 marks
17.
Describe three methods of preparing alkanes, with equations.
18.
An alkene A gives propanone and ethanal on ozonolysis. (a) Identify A and write its structure. (b) What is the main product when A reacts with HBr? (c) What is it with HBr in the presence of a peroxide?
19.
105 g of propene is burnt completely in oxygen. (a) Write the balanced equation. (b) Find the mass of oxygen used. (c) Find the masses of carbon dioxide and water formed. (d) Check that mass is conserved. (Atomic masses: H = 1 u, C = 12 u, O = 16 u)
20.
How will you obtain the following? Give the reagents and conditions. (a) ethylbenzene from benzene; (b) benzene from ethyne; (c) nitrobenzene from benzene
AmbifulWorksheets
Practice that never repeats
CBSE · Class 11 · Chemistry

Answer key

Hydrocarbons · AW-11C-HYD-2026-V1 · For parents — fold back or tear off before handing the sheet to your child.

QAnswerWorking
1(d) CnH2n+2—
2(a) 1-bromobutaneanti-Markovnikov (peroxide effect)
3(c) alkyneCnH2n−2
4(c) ortho and para (activating)it releases electrons into the ring
5(a) Pyridinepyridine: 6 π electrons, cyclic, planar and conjugated (4n + 2)
6(d) etheneacidic dehydration
7(b) but-2-eneeach carbon of the C=C must carry two different groups
8(c) A is true, but R is false.A is true: the main product is 2-methylpropan-2-ol. R is false.
9When HX adds to an unsymmetrical alkene, the negative part (X) goes to the carbon with fewer hydrogen atoms. CH3CH=CH2 + HBr → CH3CHBrCH3 (2-bromopropane).—
10CH4 + 2O2 → CO2 + 2H2O; 2 molbalance C, then H, then O
11Propanone and methanal: CH3COCH3 + HCHOozonolysis breaks the C=C into two C=O
12ethanal and propanaleach C=C carbon becomes C=O
13Bromination; bromobenzene; electrophile Br+electrophilic substitution
14Ethane (catalytic hydrogenation)—
1588 g CO2; 36 g H2OC2H4 + 3O2 → 2CO2 + 2H2O; 1 mol of C2H4
16butane, pentane, hexane; three products form, and they are hard to separateany two alkyl groups can join
17From alkenes and alkynes by hydrogenation over Ni, Pt or Pd: CH2=CH2 + H2 → CH3CH3. From alkyl halides by the Wurtz reaction: 2CH3Br + 2Na → C2H6 + 2NaBr (dry ether). From carboxylic acid salts by decarboxylation with soda lime: CH3COONa + NaOH → CH4 + Na2CO3; or by Kolbe’s electrolysis.—
18(a) 2-methylbut-2-ene; (b) 2-bromo-2-methylbutane; (c) 2-bromo-3-methylbutanejoin the carbonyl carbons with a double bond; Markovnikov without peroxide
19(a) 2C3H6 + 9O2 → 6CO2 + 6H2O; (b) 360 g; (c) 330 g CO2, 135 g H2O; (d) 465 g on each side2.5 mol of C3H6
20(a) Treat benzene with C2H5Cl with anhydrous AlCl3; (b) Pass ethyne through a red-hot iron tube at 873 K; (c) Treat benzene with concentrated HNO3 and concentrated H2SO4electrophilic substitution for groups on the ring