Hydrocarbons

Chemistry, SSC-KPK Class 10. This chapter is split into 29 topics and has 715 practice questions. The topics covered are listed below, followed by 10 free sample questions from the chapter.

Topics in this chapter

1. Inertness of Alkanes and Paraffins 21 questions
2. Introduction to Alkenes 30 questions
3. Combustion of Alkanes 22 questions
4. Addition Reactions of Alkenes 22 questions
5. Comparison of Alkanes Alkenes and Alkynes 28 questions
6. Key Points and Exercise Questions 30 questions
7. Molar Mass and Composition of Alkanes 29 questions
8. Dehydration of Alcohols to Alkenes 24 questions
9. Oxidation of Alkynes with KMnO4 20 questions
10. Structural Formulae up to Five Carbon Atoms 26 questions
11. Preparation of Alkynes from 1,2-Dihalides 25 questions
12. Halogenation of Alkynes 23 questions
13. Bonding in Alkanes 23 questions
14. Names Formulas and Table 12.1 30 questions
15. Reduction of Alkyl Halides 25 questions
16. Addition of Halogens to Alkenes 24 questions
17. Introduction to Alkynes 30 questions
18. STS Hydrocarbons as Fuels 20 questions
19. Halogenation of Alkanes 28 questions
20. Preparation of Alkynes from Tetrahalides 23 questions
21. Combustion Stoichiometry of Alkanes 21 questions
22. Oxidation of Alkenes with KMnO4 and Baeyers Test 28 questions
23. Addition of Hydrogen Halides to Alkenes 21 questions
24. General Formula of Alkanes 24 questions
25. Hydrogenation of Alkenes 24 questions
26. Dehydrohalogenation of Alkyl Halides 25 questions
27. Preparation of Alkanes by Hydrogenation 25 questions
28. Introduction to Hydrocarbons 22 questions
29. Physical Properties of Alkanes 22 questions

Sample questions: Hydrocarbons

10 sample questions with the correct answer and an explanation. Try to answer each one before reading the explanation.

Q1. Hydrocarbons are considered the ___ organic compounds.

• A. parent(correct answer)
• B. derived
• C. terminal
• D. secondary

Answer: A.The book calls hydrocarbons the parent organic compounds because other organic compounds can be regarded as derived from them.

Q2. Why are hydrocarbons called the parent organic compounds?

• A. Other organic compounds can be viewed as derived from them by replacing hydrogen(correct answer)
• B. They are the only organic compounds that can be burnt in air
• C. They are always formed first when any organic compound is heated
• D. They are the only organic compounds that occur in living cells

Answer: A.Alcohols, halides and acids can be viewed as derivatives of hydrocarbons, so the hydrocarbons are the parent compounds (standard knowledge).

Q3. The chapter objective says you should be able to explain why a ___ method of naming chemical compounds is necessary.

• A. random
• B. traditional
• C. systematic(correct answer)
• D. historical

Answer: C.Chapter 12 begins by stating the need for a systematic method of naming compounds, so each compound has one clear name.

Q4. According to the key points, the reactivity of alkynes is

• A. the same as that of alkanes
• B. less than alkenes but greater than alkanes(correct answer)
• C. less than both alkenes and alkanes
• D. greater than both alkenes and alkanes

Answer: B.The book explains the very high electron density in the triple bond; alkynes are less reactive than alkenes but more reactive than alkanes.

Q5. How many atoms are eliminated in total from ethanol (C₂H₅OH) when ethene is formed?

• A. One atom (O)
• B. Two atoms (1 C and 1 H)
• C. Four atoms (4 H)
• D. Three atoms (2 H and 1 O)(correct answer)

Answer: D.The water eliminated is H₂O: one H from a carbon and the OH from the adjacent carbon, 3 atoms in all (2 H and 1 O).

Q6. Which list contains only reactions of alkenes given in the book?

• A. Reduction of alkyl halides and dehydrohalogenation
• B. Addition of halogens, addition of HX, oxidation by KMnO₄, hydrogenation(correct answer)
• C. Halogenation by substitution, combustion only, dehydration
• D. Hydrolysis, saponification, polymerization

Answer: B.Section 12.2.2 lists the four reactions: addition of halogens, addition of hydrogen halides, oxidation with KMnO₄ and hydrogenation.

Q7. Activity 3: starting from ethane, which is the correct order of reactions to synthesise ethyne?

• A. Bromination, dehydrohalogenation, Br₂ addition, double dehydrohalogenation(correct answer)
• B. Addition of HBr, hydrogenation, dehalogenation and halogenation
• C. Combustion, reduction with Zn/HCl, addition of HBr, hydrogenation
• D. Hydrogenation, dehydration, oxidation with KMnO₄ and combustion

Answer: A.Ethane → bromoethane (halogenation) → ethene (alc. KOH) → 1,2-dibromoethane (Br₂/CCl₄) → ethyne (alc. KOH, two steps).

Q8. The final product X in HC≡CH + 2HBr → X (Exercise Q1 iii) is

• A. CHBr₂-CHBr₂
• B. CHBr=CHBr
• C. CHBr₃
• D. CH₃-CHBr₂(correct answer)

Answer: D.Two HBr add to the triple bond, giving a dibromoethane (the standard answer is the 1,1-isomer, CH3CHBr2; standard knowledge).

Q9. Which of the following is a method of preparing an alkyne? (Exercise Q2 ix)

• A. Dehydration of an alkane with H₂SO₄
• B. Halogenation of an alkane in sunlight
• C. Hydrogenation of an alkene with nickel
• D. Dehydrohalogenation of a 1,2-dihalide with alcoholic KOH(correct answer)

Answer: D.The book gives two methods: dehydrohalogenation of 1,2-dihalides with alcoholic KOH and dehalogenation of tetrahalides with zinc.

Q10. What is the main reason why addition reactions take place in ethene and ethyne but not in ethane?

• A. They have fewer carbons
• B. They are soluble in water
• C. They are gases
• D. They are unsaturated(correct answer)

Answer: D.Ethene and ethyne have double or triple bonds that open and add atoms; saturated ethane cannot (Exercise Q2 viii).