Alkanes Practice Questions PDF

1. What is the general formula for alkanes? * A) CnH2n * B) CnH2n+2 * C) CnH2n-2 * D) CnHn 2. Which term best describes the bonding in alkanes? * A) Unsaturated * B) Saturated * C) Ionic * D) Aromatic 3. Are alkanes generally considered polar or non-polar molecules? * A) Polar * B) Non-polar * C)...

1. What is the general formula for alkanes? * A) CnH2n * B) CnH2n+2 * C) CnH2n-2 * D) CnHn 2. Which term best describes the bonding in alkanes? * A) Unsaturated * B) Saturated * C) Ionic * D) Aromatic 3. Are alkanes generally considered polar or non-polar molecules? * A) Polar * B) Non-polar * C) Both polar and non-polar * D) Neither polar nor non-polar 4. Due to their polarity and saturation, alkanes are generally: * A) Highly reactive * B) Highly unreactive * C) Moderately reactive * D) Reactive with water 5. What is the solubility of alkanes in water? * A) Highly soluble * B) Slightly soluble * C) Insoluble * D) Soluble at high temperatures 6. How does the boiling point of alkanes change as the carbon chain length increases? * A) Decreases * B) Increases * C) Stays the same * D) Fluctuates randomly 7. What is the primary intermolecular force responsible for the trend in alkane boiling points? * A) Hydrogen bonding * B) Permanent dipole-dipole forces * C) Induced dipole-dipole forces (London dispersion forces) * D) Ionic bonding 8. Which has a higher boiling point: a straight-chain alkane or its branched-chain isomer? * A) Straight-chain alkane * B) Branched-chain isomer * C) They have the same boiling point * D) It depends on the speci c alkane 9. Why do branched-chain alkanes have lower boiling points than their straight chain isomers? * A) smaller surface area so fewer interaction points, weakening the induced dipole intermolecular forces * B) increased surface area so fewer interaction points, weakening the induced dipole intermolecular forces * C) smaller surface area so fewer interaction points, weakening the permanent dipole intermolecular forces * D) increased surface area so more interaction points, weakening the hydrogen bonding intermolecular forces 10. What are the products of the *complete* combustion of an alkane in excess oxygen? * A) Carbon monoxide and water * B) Carbon dioxide and water * C) Carbon and water * D) Carbon monoxide and hydrogen 11. What is the approximate enthalpy change (ΔH) for the combustion of alkanes? * A) Highly positive * B) Slightly positive * C) Highly negative * D) Close to zero 12. Which alkanes are easier to burn: short-chain or long-chain alkanes? * A) long chain alkanes * B) short chain alkanes fi * C) They both burn with the same ease. * D) It is impossible to tell 13. Which releases more energy per mole during complete combustion: short-chain or long-chain alkanes? * A) Short-chain alkanes * B) Long-chain alkanes * C) They release the same amount of energy * D) It depends on the speci c alkanes 14. What highly toxic product can be formed during the *incomplete* combustion of alkanes? * A) Carbon dioxide * B) Carbon monoxide * C) Water * D) Hydrogen 15. How does carbon monoxide affect the human body? * A) It dissolves in water to form acid rain * B) It reacts with sulfur impurities to cause smog * C) It permanently bonds to haemoglobin, preventing oxygen transport * D) It is a greenhouse gas 16. Which pollutant, produced from impurities in alkane fuels, contributes to acid rain? * A) Carbon dioxide (CO2) * B) Sulfur dioxide (SO2) * C) Water (H2O) * D) Carbon monoxide (CO) 17. Nitrogen oxides (NOx), formed from impurities in fuels, contribute to: * A) Global warming * B) Acid rain * C) The depletion of the ozone layer * D) Smog, but not acid rain 18. What is the name of the reaction mechanism by which alkanes react with chlorine? * A) Electrophilic addition * B) Nucleophilic substitution fi * C) Free radical substitution * D) Elimination 19. What is required for the chlorination of alkanes to occur? * A) High pressure * B) A nickel catalyst * C) UV light * D) Concentrated sulfuric acid 20. What is a "free radical"? * A) A molecule with a positive charge. * B) A molecule with a negative charge. * C) A species with a paired electron. * D) A species with an unpaired electron. Answers and Explanations: 1. B) CnH2n+2 - This is the general formula for alkanes. 2. B) Saturated - Alkanes contain only single C-C bonds. 3. B) Non-polar - C-H bonds have very little difference in electronegativity. 4. B) Highly unreactive - Saturation and non-polarity make alkanes unreactive. 5. C) Insoluble - Non-polar alkanes do not mix with polar water. 6. B) Increases - Longer chains have stronger intermolecular forces. 7. C) Induced dipole-dipole forces (London dispersion forces) - These forces increase with molecular size. 8. A) Straight-chain alkane - Straight-chain alkanes have greater surface area contact. 9. A) smaller surface area so fewer interaction points, weakening the induced dipole intermolecular forces Correct de nition of the effect. fi 10. B) Carbon dioxide and water - These are the products of complete combustion. 11. C) Highly negative - Combustion is highly exothermic. 12. B) short chain alkanes Correct, short chain alkanes are easier to burn 13. B) Long-chain alkanes - More bonds are broken and formed, releasing more energy. 14. B) Carbon monoxide - Incomplete combustion produces CO. 15. C) It permanently bonds to haemoglobin, preventing oxygen transport - This is why CO is toxic. 16. B) Sulfur dioxide (SO2) - SO2 from sulfur impurities forms acid rain. 17. B) Acid rain - NOx gases dissolve in water to form acid rain. 18. C) Free radical substitution - This is the mechanism for alkane halogenation. 19. C) UV light - UV light provides the energy for homolytic ssion of Cl2. 20. D) A species with an unpaired electron. - De nition of a free radical. fi fi