Year 11 Chemistry: Alkenes & Alcohols

Introduction to Alkenes

Alkenes are a type of hydrocarbon. This means they are made only of hydrogen and carbon atoms. Alkenes have at least one double bond between two carbon atoms. This double bond is what makes them different from alkanes, which only have single bonds.

Key Characteristics of Alkenes:

• General Formula: The general formula for alkenes is $$C_nH_{2n}$$ . This means for every “n” carbon atoms, there are “2n” hydrogen atoms.
• Example: The simplest alkene is ethene, which has 2 carbon atoms and 4 hydrogen atoms, written as $$C_2H_4$$ .
• Reactivity: Alkenes are more reactive than alkanes because of the double bond. They can undergo reactions like addition reactions.

Introduction to Alcohols

Alcohols are another type of hydrocarbon but they contain a hydroxyl group (-OH). This group gives alcohols their unique properties.

Key Characteristics of Alcohols:

• General Formula: The general formula for alcohols is $$C_nH_{2n+1}OH$$ .
• Example: The simplest alcohol is ethanol, which has 2 carbon atoms, 6 hydrogen atoms, and a hydroxyl group, written as $$C_2H_5OH$$ .
• Uses: Alcohols are commonly used in drinks, as solvents, and in fuels.

Tips and Tricks for Understanding

1. Visualisation: Draw the structures of alkenes and alcohols. This helps to see the double bond in alkenes and the hydroxyl group in alcohols.
2. Memorise Simple Examples: Remember common alkenes and alcohols like ethene and ethanol.
3. Practice Naming: Learn how to name these compounds. For alkenes, the name ends with “-ene” (like ethene), and for alcohols, it ends with “-ol” (like ethanol).
4. Chemical Reactions: Understand that alkenes react differently from alcohols. For example, alkenes can add hydrogen (hydrogenation), while alcohols can react with acids to form esters.

Questions

Easy Level Questions

1. What is an alkene?
2. What is the main feature that distinguishes alkenes from alkanes?
3. What is the general formula for alkenes?
4. Name the simplest alkene.
5. What is the chemical formula for ethene?
6. What does a hydroxyl group (-OH) signify?
7. What is an alcohol?
8. What is the general formula for alcohols?
9. Name the simplest alcohol.
10. What is the chemical formula for ethanol?
11. Are alkenes more or less reactive than alkanes?
12. What type of bond do alkenes have?
13. What does the suffix “-ene” indicate in a compound?
14. What does the suffix “-ol” indicate in a compound?
15. Which is more reactive: alkenes or alcohols?
16. Can alcohols be used as fuels?
17. Do alkenes have single or double bonds?
18. What type of reaction can alkenes undergo?
19. What is one common use of ethanol?
20. Give an example of an alcohol.

Medium Level Questions

1. Explain why alkenes are more reactive than alkanes.
2. Draw the structure of ethene.
3. Draw the structure of ethanol.
4. What is the formula for butene?
5. Name an alkene with 3 carbon atoms.
6. Name an alcohol with 4 carbon atoms.
7. What reaction occurs when ethene reacts with hydrogen?
8. What happens when alcohols react with acids?
9. What is an ester?
10. How do you determine the number of hydrogen atoms in an alkene?
11. What is the name of the alkene with the formula $$C_5H_{10}$$ ?
12. What is the name of the alcohol with the formula $$C_3H_8O$$ ?
13. Explain the significance of the double bond in alkenes.
14. Describe one method to produce ethanol.
15. What are the two main types of reactions that alkenes can undergo?
16. How does the presence of the hydroxyl group affect the properties of alcohols?
17. Are all alcohols soluble in water? Why or why not?
18. Name one industrial use for alkenes.
19. What type of bond is present in alcohols?
20. Describe how to convert an alkene into an alcohol.

Hard Level Questions

1. Explain the process of hydrogenation of alkenes.
2. What is the mechanism of the addition reaction involving alkenes?
3. Compare the boiling points of alkenes and alcohols and explain why they differ.
4. How does the structure of alcohols affect their solubility in water?
5. Discuss the environmental impact of using ethanol as fuel.
6. What are isomers? Provide examples for butene and butanol.
7. Describe the reaction of alkenes with bromine water.
8. Explain how you can distinguish between an alkene and an alkane.
9. What type of polymer can be formed from alkenes? Provide an example.
10. How can alcohols be produced through fermentation?
11. Describe the structural differences between propanol and propan-2-ol.
12. What is a dehydration reaction involving alcohols? Provide an example.
13. Explain why alkenes are important in the petrochemical industry.
14. Discuss how the chain length of alcohols affects their physical properties.
15. What are the health risks associated with ethanol consumption?
16. How does the presence of functional groups influence chemical reactivity?
17. Explain the concept of saturation in hydrocarbons.
18. How can addition reactions lead to the formation of polymers?
19. Discuss the role of catalysts in alcohol reactions.
20. How do alkenes and alcohols contribute to the greenhouse effect?

Answers and Explanations

Easy Level Answers

1. Alkenes are hydrocarbons with at least one double bond.
2. Alkenes have a double bond; alkanes have only single bonds.
3. $$C_nH_{2n}$$ .
4. Ethene.
5. $$C_2H_4$$ .
6. It indicates the presence of alcohol in a molecule.
7. Alcohols are hydrocarbons with a hydroxyl group.
8. $$C_nH_{2n+1}OH$$ .
9. Ethanol.
10. $$C_2H_5OH$$ .
11. More reactive.
12. Double bonds.
13. It indicates a compound is an alkene.
14. It indicates a compound is an alcohol.
15. Alkenes.
16. Yes.
17. Double bonds.
18. Addition reactions.
19. As a solvent and in drinks.
20. Ethanol.

Medium Level Answers

1. Alkenes are more reactive because of the double bond, which can break to form new bonds.
2. (Drawing expected).
3. (Drawing expected).
4. $$C_4H_8$$ .
5. Propene.
6. Butanol.
7. It produces an alkane.
8. They form esters.
9. An ester is formed from an alcohol and acid.
10. $$2n + 2$$ for alkanes; alkenes are $$2n$$ .
11. Pentene.
12. Propanol.
13. The double bond allows for additional reactions.
14. Fermentation of sugars.
15. Addition and polymerization.
16. It makes alcohols polar, which affects solubility.
17. Shorter alcohols are more soluble due to hydrogen bonding.
18. They are used in making plastics.
19. They speed up reactions without being consumed.
20. By removing water from alcohols.

Hard Level Answers

1. Hydrogenation adds hydrogen to the double bond, converting alkenes to alkanes.
2. The double bond opens up to allow new atoms to attach.
3. Alcohols typically have higher boiling points due to hydrogen bonding.
4. Hydroxyl groups can form hydrogen bonds with water.
5. Ethanol is renewable and less polluting than fossil fuels.
6. Isomers have the same formula but different structures; e.g., butene can be 1-butene or 2-butene.
7. A color change occurs, indicating the presence of a double bond.
8. By adding bromine water; alkenes decolourise it.
9. Polyethene, which is made from ethene.
10. Through the fermentation of sugars by yeast.
11. Propanol has the -OH at the end; propan-2-ol has it in the middle.
12. Removal of water from alcohol, e.g., ethanol to ethene.
13. They are used in fuels, plastics, and chemicals.
14. Longer chains have higher boiling points and lower volatility.
15. Ethanol can cause liver damage and addiction.
16. Different functional groups react differently with other chemicals.
17. Saturated means only single bonds; unsaturated means one or more double bonds.
18. Alkenes can link to form long chains (polymers).
19. Catalysts lower the energy needed for a reaction.
20. They contribute to carbon emissions when burned.