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Class 10 Chemistry Chapter 22 Hydrocarbons Class Test 7 PDF | Punjab Board 2027 Model Papers
Grade 10 Chemistry Chapter 22 Hydrocarbons Test 7
Prepare for your Class 10 Chemistry Chapter 22: Hydrocarbons Class Test 7 with our Punjab Board 2027 Model Papers test series. This Class 10 Chemistry Chapter 22 test includes a Full Unit Test with Exercise, designed according to the new syllabus issued by PECTAA Punjab. Students can use this chapter-wise test series to revise important concepts, practise exam-style questions, assess their preparation, and improve their performance in the upcoming Punjab Board examinations. Access our Class 10 Chemistry Chapter 22 Hydrocarbons test to prepare effectively for the 2027 board exams.
Full Chapter Test
Test No. 7
CHAPTER # 22
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.
1.General formula of alkene is:
(a) CnH2n+1(b) CnH2n(c) CnH2n-1(d) CnH2n-2
Answer: (b) CnH2n
2.Dehydrohalogenation of alcohol can be carried out at temperature.
(a) 120°C(b) 140°C(c) 160°C(d) 180°C
Answer: (d) 180°C (alcohol heated with conc. H2SO4 gives alkene).
3.Role of Ethylene in plants is:
(a) Photosynthesis(b) Fruit ripening(c) Seed germination(d) Respiration
Answer: (b) Fruit ripening (ethylene is a plant hormone).
4.Alkenes gives undergo reaction
(a) Elimination(b) Substitution(c) Addition(d) All
Answer: (c) Addition
5.Colour of Iodine is:
(a) violet(b) reddish(c) brown(d) purple
Answer: (a) violet (iodine vapour is violet; verify with your textbook key).
6.Alkynes contain carbon-carbon bonds:
(a) Single(b) double(c) Triple(d) None of these
Answer: (c) Triple
7.When a well is drilled through the rock, which substance is released first?
(a) Liquid Petroleum(b) water(c) Natural gas(d) Bitumen
Answer: (c) Natural gas (it lies on top of the petroleum).
8.Petroleum in a crude state is a mixture of many hydrocarbons which burns.
(a) Easily(b) Not easily(c) very fast(d) moderately
Answer: (b) Not easily (crude oil is a thick mixture and burns poorly until refined). Please verify with your textbook key.
9.Each Petroleum fraction mainly contains a mixture of:
(a) Acid(b) Hydrocarbon(c) salts(d) Alcohol
Answer: (b) Hydrocarbon
10.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).
11.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).
12.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
Here is Subjective Part of Paper.
Part - I
2.Write short answers to any Five (5) questions:[5x2=10]
- (i)Define alkene. Give its general formula and example.Alkenes are unsaturated hydrocarbons that contain at least one carbon–carbon double bond (C=C). General formula: CnH2n. Example: ethene, CH2=CH2 (C2H4).
- (ii)Which methods used for the preparation of alkene?
- Dehydration of alcohols
- Dehydrohalogenation of alkyl halides
- Cracking of alkanes
- (iii)Write the method of dehydration of alcohol.Ethanol is heated with conc. H2SO4 at about 180°C (or passed over heated alumina, Al2O3, at about 350°C):
CH3CH2OH → CH2=CH2 + H2O - (iv)How cracking can be carried out?Cracking is the breaking of large alkane molecules into smaller, more useful molecules by heat. Thermal cracking: high temperature (about 500–700°C) and pressure. Catalytic cracking: lower temperature (about 450–500°C) with a catalyst such as silica–alumina or zeolite.
Example: C10H22 → C8H18 + C2H4 - (v)Write application of cracking.
- Converts heavy fractions into gasoline (petrol) to meet demand.
- Produces alkenes such as ethene and propene for polythene, plastics and other chemicals.
- Produces hydrogen as a by-product.
- (vi)Write the addition reaction of halogen with alkene.CH2=CH2 + Br2 → CH2Br–CH2Br (1,2-dibromoethane). The reddish-brown colour of bromine disappears; this is a test for unsaturation.
- (vii)Write the oxidation process of alkene with KMnO4.With cold, dilute, aqueous (alkaline) KMnO4 (Baeyer's reagent), ethene is oxidised to ethylene glycol (ethane-1,2-diol):
CH2=CH2 + H2O + [O] → CH2OH–CH2OH
The purple colour of KMnO4 disappears (brown MnO2 may form). - (viii)Write a reaction of alkene with steam.Hydration: ethene + steam in the presence of phosphoric acid catalyst (H3PO4), about 300°C and 60–70 atm:
CH2=CH2 + H2O → CH3CH2OH
3.Write short answers to any Five (5) questions:[5x2=10]
- (i)What is alkynes? Give example.Alkynes are unsaturated hydrocarbons containing at least one carbon–carbon triple bond (C≡C). General formula: CnH2n-2. Example: ethyne (acetylene), HC≡CH.
- (ii)Write the molecular formula of But-1-yne and But-2-yne.Both have the molecular formula C4H6.
But-1-yne: CH≡C–CH2–CH3
But-2-yne: CH3–C≡C–CH3 - (iii)How acetylene gas ripen the fruits?Acetylene (produced from calcium carbide and moisture) acts like the natural plant hormone ethylene. It triggers the ripening process, so the fruit changes colour and softens quickly. (Calcium carbide ripening is unsafe and is discouraged for food.)
- (iv)How Petroleum is extracted?A well is drilled through the rock to the petroleum reservoir. First natural gas, then petroleum, is pushed out by the gas pressure. When the pressure falls and the flow stops, petroleum is taken out with pumps (water or gas may be forced in to push the oil out).
- (v)Write the uses of Benzene.
- Used as a solvent for fats, resins, paints and rubber.
- Starting material for dyes, drugs, explosives, plastics, detergents and insecticides.
- (vi)Which properties depend upon the physical properties of petroleum fraction.The uses of petroleum fractions depend on their physical properties: boiling point range, volatility, viscosity and ease of burning (flammability).
- (vii)Give two examples of addition reactions.
- Hydrogenation: CH2=CH2 + H2 → CH3–CH3 (Ni catalyst, about 200°C)
- Halogenation: CH2=CH2 + Br2 → CH2Br–CH2Br
- (viii)Give the names of the compounds obtained from petroleum.Petroleum gas / LPG, gasoline (petrol), kerosene oil, diesel oil, lubricating oil, fuel oil, paraffin wax and bitumen (asphalt); also chemicals such as ethene, propene, benzene and toluene.
4.Write short answers to any Five (5) questions:[5x2=10]
- (i)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:
CH2=CH2 + H2O + [O] → CH2OH–CH2OH
The purple colour of permanganate fades. - (ii)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 - (iii)How can an alkene be identified?By adding bromine water (the reddish-brown colour is decolourised) or by Baeyer's test with cold dilute KMnO4 (the purple colour disappears).
- (iv)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 whose colour disappears contains the unsaturated compound (alkene); the tube with no change contains the saturated compound.
- (v)Why is oxyacetylene flame so hot?Acetylene burns in pure oxygen with a large release of heat: 2C2H2 + 5O2 → 4CO2 + 2H2O + heat. The flame reaches about 3000°C, so it is used for welding and cutting metals.
- (vi)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.
- (vii)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) - (viii)Write the uses, Boiling range of Lubricating oil?Boiling range: about 300–370°C (please verify with your textbook). Uses: lubricating machines and engines to reduce friction and wear; making vaseline, polishes and waxes.
NOTE:- Attempt any two questions.[9x2=18]
5.
(a)Describe two methods of preparation for ethene.
1. Dehydration of ethanol: ethanol is heated with conc. H2SO4 at about 180°C.
CH3CH2OH → CH2=CH2 + H2O
2. Dehydrohalogenation of ethyl bromide: heated with alcoholic KOH.
CH3CH2Br + KOH(alc.) → CH2=CH2 + KBr + H2O
CH3CH2OH → CH2=CH2 + H2O
2. Dehydrohalogenation of ethyl bromide: heated with alcoholic KOH.
CH3CH2Br + KOH(alc.) → CH2=CH2 + KBr + H2O
(b)Describe the fractional distillation of petroleum.
Crude oil is heated to about 400°C in a furnace. The hot vapours enter the lower part of a tall fractionating column, which is hotter at the bottom and cooler at the top. The vapours rise and condense at different heights according to their boiling points. Gases (below 40°C) are collected 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.
6.
(a)Which properties of petroleum fractions change with their boiling points?
As the boiling point (and molecular mass) 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)Explain with examples the cracking of alkanes.
Cracking breaks large alkane molecules into smaller alkanes and alkenes by heat (thermal) or heat with a catalyst (catalytic).
C12H26 → C10H22 + C2H4
C10H22 → C5H12 + C5H10
C2H6 → C2H4 + H2
Uses: more gasoline and the alkenes needed for plastics.
C12H26 → C10H22 + C2H4
C10H22 → C5H12 + C5H10
C2H6 → C2H4 + H2
Uses: more gasoline and the alkenes needed for plastics.
7.
(a)Give uses of acetylene.
- 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 and for artificial ripening of fruit.
(b)Write Sources of Organic Compounds.
The main sources are coal, petroleum and natural gas. Plants and animals are also natural sources of organic compounds.
