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Class 10 Chemistry Chapter 22 Hydrocarbons Class Test 8 PDF | Punjab Board 2027 Model Papers
Grade 10 Chemistry Chapter 22 Hydrocarbons Test 8
Prepare for your exams with the Class 10 Chemistry Chapter 22: Hydrocarbons Class Test 8, designed according to the Punjab Board 2027 Model Papers and the new syllabus issued by PECTAA Punjab. This chapter-wise test is part of our Class 10 Chemistry Test Series and includes a full unit test with exercise-based questions to help students strengthen their concepts, practise important questions, and prepare effectively for Punjab Board examinations. Students can use these chapter-wise tests for revision, self-assessment, and exam preparation.
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PAPER NO.
08
CHEMISTRY
CHAPTER
WISE
WISE
Roll No.(in Figures): (in Words):
ABCD
1ABCD
2ABCD
3ABCD
4ABCD
ABCD
5ABCD
6ABCD
7ABCD
8ABCD
ABCD
9ABCD
10ABCD
11ABCD
12ABCD
NOTE:Four possible answers A, B, C and D to each question are given. The choice which you think is correct, fill that circle in front of that question with Marker or Pen ink. Cutting or filling two or more circles will result in zero mark in that question.
Q1.12
1.Which of the following compounds is expected to give addition reaction?
(A) CH3 – CH3(B) CH2 = CH2(C) CH4(D) CH3–CH2–CH3
Answer: (B) CH2 = CH2 – it has a C=C double bond (unsaturated).
2.The general formula for alkenes is:
(A) CnH2n(B) CnH2n(C) CnH2n+2(D) CnHn
Answer: CnH2n. In the printed paper options (A) and (B) look identical, so both are marked.
3.Which of the followings is not used as a fuel?
(A) LPG(B) CNG(C) Diesel(D) Asphalt
Answer: (D) Asphalt – used for road making.
4.Ethyne is commonly known as:
(A) Methane(B) Ethylene(C) Acetylene(D) Propylene
Answer: (C) Acetylene
5.Which species acts as a reducing agent in the reaction between ethene and KMnO4?
(A) H2O(B) CH2 = CH2(C) KMnO4(D) NaOH
Answer: (B) CH2 = CH2 – ethene is oxidised; KMnO4 is the oxidising agent.
6.The IUPAC name of acetylene is:
(A) Ethane(B) Ethene(C) Ethyne(D) Methyne
Answer: (C) Ethyne
7.Select the name of the petroleum fraction which generates electricity in power plants.
(A) Bitumen(B) Lubricating oil(C) Kerosene oil(D) Fuel oil
Answer: (D) Fuel oil
8.Kerosene oil is used as:
(A) Lubricant(B) Jet fuel(C) Road making(D) Chemical feedstock
Answer: (B) Jet fuel (also used in stoves and lamps).
9.The molecule eliminated in the following reaction is:
CH3 – CH2 – Br + KOHEthanolCH2 = CH2 + KBr + H2O
(A) Br2(B) H2(C) HBr(D) H2O
Answer: (C) HBr – dehydrohalogenation removes H and Br from the alkyl halide.
10.As chain length of petroleum fraction increases, boiling point:
(A) Decreases(B) Remains same(C) Increases(D) First increases then decreases
Answer: (C) Increases
11.Fractional distillation of petroleum is based on:
(A) Viscosity(B) Boiling point range(C) Flammability(D) Melting point range
Answer: (B) Boiling point range
12.Benzene an aromatic hydrocarbon may be produced from:
(A) Methane(B) Ethane(C) Propane(D) n-hexane
Answer: (D) n-hexane (by reforming: cyclization and dehydrogenation).
Here is Subjective Part of Paper.
Roll No.(in Figures):
(in Words):
Chapter 22:
Hydrocarbons
Hydrocarbons
SUBJECTIVE TYPE
(PART – I)
(PART – I)
Maximum Marks: 48
Time Allowed :1.45 Hours
Time Allowed :1.45 Hours
Q2.Write short answers to any FIVE (5) questions:(5×2=10)
- (i)Give two examples of addition reactions.
- Hydrogenation: CH2=CH2 + H2 → CH3–CH3 (Ni, about 200°C)
- Halogenation: CH2=CH2 + Br2 → CH2Br–CH2Br
- (ii)What is dehydrohalogenation and how are alkenes prepared by this method?Dehydrohalogenation is the removal of a hydrogen halide (H and X) from an alkyl halide. When an alkyl halide is heated with alcoholic KOH, an alkene is formed:
CH3–CH2–Br + KOH (alcoholic) → CH2=CH2 + KBr + H2O - (iii)Give the names of the compounds obtained from coal tar and petroleum.Coal tar: benzene, toluene, xylene, naphthalene, phenol and anthracene.
Petroleum: petroleum gas (LPG), gasoline (petrol), naphtha, kerosene oil, diesel oil, lubricating oil, fuel oil, paraffin wax and bitumen (asphalt). - (iv)Explain why cracking is an important industrial process.
- It converts heavy, less useful fractions into gasoline, which is in high demand.
- It produces alkenes such as ethene and propene, the raw materials for polythene, plastics and many chemicals.
- It gives hydrogen as a by-product.
- (v)How ethene is oxidized by cold aqueous solution of potassium permanganate.Cold, dilute, aqueous KMnO4 adds two –OH groups across the double bond, forming ethylene glycol (ethane-1,2-diol):
CH2=CH2 + H2O + [O] → CH2OH–CH2OH
The purple colour of permanganate disappears. - (vi)What are addition reactions?Reactions in which atoms or groups are added across a carbon–carbon double or triple bond of an unsaturated compound, giving a saturated product. Example: CH2=CH2 + Cl2 → CH2Cl–CH2Cl
- (vii)Differentiate between elimination and addition reactions.
Elimination reaction Addition reaction Atoms or groups are removed from adjacent carbon atoms. Atoms or groups are added across a double or triple bond. A double bond is formed (saturated → unsaturated). The double bond is lost (unsaturated → saturated). CH3CH2OH → CH2=CH2 + H2O CH2=CH2 + H2 → CH3CH3 - (viii)What is catalytic hydrogenation.The addition of hydrogen to an alkene or alkyne in the presence of a finely divided metal catalyst (Ni, Pt or Pd) at about 200°C to form an alkane:
CH2=CH2 + H2 → CH3–CH3
It is used to convert vegetable oils into ghee.
Q3.Write short answers to any FIVE (5) questions:(5×2=10)
- (i)Name the starting materials used to generate oxyacetylene flame:Acetylene gas (made from calcium carbide and water) and pure oxygen.
- (ii)Write general formula of alkene.CnH2n
- (iii)How can an alkene be identified?By bromine water (the reddish-brown colour is decolourised) or by cold dilute KMnO4 (Baeyer’s test: the purple colour disappears).
- (iv)Why is oxyacetylene flame so hot?Acetylene burns in pure oxygen with a very large release of heat: 2C2H2 + 5O2 → 4CO2 + 2H2O + heat. The flame reaches about 3000°C, so it is used for welding and cutting metals.
- (v)What is the difference between the terms dehydration and dehydrohalogenation?Dehydration is the removal of a water molecule (H and OH), for example from an alcohol. Dehydrohalogenation is the removal of a hydrogen halide (H and X) from an alkyl halide.
- (vi)Why is use of calcium carbide prohibited in Pakistan?Calcium carbide is used to ripen fruit artificially, but commercial carbide often contains toxic impurities such as arsenic and phosphorus compounds. These can contaminate the fruit and harm health, so its use for fruit ripening is banned.
- (vii)You have got two test tubes A and B containing a saturated and unsaturated compound (Alkene). How will you identify the two?Add a few drops of bromine water (or cold dilute KMnO4) to both tubes and shake. The tube in which the colour disappears contains the alkene (unsaturated); the other, with no change, contains the saturated compound.
- (viii)Give two uses of acetylene.
- Oxyacetylene flame for welding and cutting metals.
- Manufacture of chemicals such as ethanal, ethanoic acid, PVC and synthetic rubber.
Q4.Write short answers to any FIVE (5) questions:(5×2=10)
- (i)Give the general formula of alkynes.CnH2n-2
- (ii)How are alkynes named according to IUPAC system?Select the longest chain containing the triple bond, and replace the ending “-ane” of the parent alkane with “-yne”. Number the chain so the triple bond gets the lowest number. Examples: HC≡CH ethyne, CH3–C≡CH propyne, CH3–CH2–C≡CH but-1-yne, CH3–C≡C–CH3 but-2-yne.
- (iii)Do you expect ethyne to decolourize a cold solution of KMnO4?Yes. Ethyne is unsaturated (it has a triple bond), so it is oxidised by cold KMnO4 and the purple colour is decolourised.
- (iv)What are the three major sources of organic compounds?Coal, petroleum and natural gas.
- (v)What is petroleum and how is it extracted?Petroleum (crude oil) is a dark, viscous liquid mixture of hydrocarbons found under the earth’s crust. A well is drilled through the rock to the reservoir; natural gas pressure first pushes the oil out, and when the flow stops the oil is removed with pumps.
- (vi)How do chlorine and hydrogen chloride add to ethene?Both add across the double bond:
CH2=CH2 + Cl2 → CH2Cl–CH2Cl (1,2-dichloroethane)
CH2=CH2 + HCl → CH3–CH2Cl (chloroethane) - (vii)What is the boiling range and use of diesel oil?Boiling range: about 250–340°C. Use: fuel for diesel engines of trucks, buses, trains, tractors and generators.
- (viii)What is naphtha and what is it used for?Naphtha is a light petroleum fraction that boils between gasoline and kerosene (roughly 70–170°C; please verify with your textbook). It is used as a raw material for making petrochemicals (such as ethene by cracking), for producing gasoline by reforming, and as a solvent.
(PART – II)
Note: Attempt any TWO questions.(2 × 9 = 18)
Q5.
(a)Describe two methods of preparation for ethene.5
1. Dehydration of ethanol: ethanol is heated with conc. H2SO4 at about 180°C (or its vapour is passed over heated alumina at about 350°C).
CH3CH2OH → CH2=CH2 + H2O
2. Dehydrohalogenation of ethyl bromide: heated with alcoholic KOH.
CH3CH2Br + KOH (alcoholic) → CH2=CH2 + KBr + H2O
CH3CH2OH → CH2=CH2 + H2O
2. Dehydrohalogenation of ethyl bromide: heated with alcoholic KOH.
CH3CH2Br + KOH (alcoholic) → CH2=CH2 + KBr + H2O
(b)Describe the fractional distillation of petroleum.4
Crude oil is heated to about 400°C in a furnace. The hot vapours enter the lower part of a tall fractionating column that is hotter at the bottom and cooler at the top. Vapours rise and condense at different heights according to their boiling points: gases (below 40°C) at the top, then gasoline, kerosene oil, diesel oil, lubricating oil and fuel oil; the residue (bitumen / asphalt) stays at the bottom. Each fraction is collected from its own tray.
Q6.
(a)Give uses of acetylene.5
- Oxyacetylene flame for welding and cutting metals.
- Manufacture of ethanal, ethanoic acid, vinyl chloride (PVC) and synthetic rubber.
- Used as a source of light in some lamps.
- Starting material for many organic chemicals.
(b)Explain with examples the cracking of alkanes.4
Cracking breaks large alkane molecules into smaller alkanes and alkenes by heat (thermal cracking, about 500–700°C) or by heat with a catalyst (catalytic cracking).
C12H26 → C10H22 + C2H4
C10H22 → C5H12 + C5H10
C2H6 → C2H4 + H2
Importance: more gasoline and the alkenes needed for plastics.
C12H26 → C10H22 + C2H4
C10H22 → C5H12 + C5H10
C2H6 → C2H4 + H2
Importance: more gasoline and the alkenes needed for plastics.
Q7.
(a)Which properties of petroleum fractions change with their boiling points?5
As the boiling point (and molecular mass, chain length) increases: viscosity increases, volatility decreases, ease of burning decreases and the colour becomes darker. Light fractions are colourless, volatile and flow easily; heavy fractions are thick, dark and less volatile.
(b)Identify the major sources from which organic compounds can be obtained.4
The major sources are coal (coal tar gives aromatic compounds), petroleum (the main source of fuels and aliphatic hydrocarbons) and natural gas (mainly methane). Plants and animals are also natural sources.
