Question 1: Define an addition reaction in the context of alkenes.

Answer: An addition reaction is a chemical process where atoms or groups are added to the carbon-carbon double bond in an alkene, converting it into a saturated compound.

Question 2: Describe the general mechanism of an electrophilic addition reaction involving alkenes.

Answer: The mechanism involves the alkene's π bond attracting an electrophile, forming a carbocation intermediate, followed by nucleophilic attack to form the addition product.

Question 3: What is the role of the electrophile in addition reactions of alkenes?

Answer: The electrophile accepts a pair of electrons from the alkene's π bond, initiating the addition process.

Question 1: Calculate the volume of hydrogen gas (H₂) required to fully hydrogenate 0.5 mol of ethene (C₂H₄) at standard temperature and pressure (STP). Use the molar volume of a gas as 22.4 L/mol.

Answer: 11.2 L

Question 2: A reaction involves 2.0 g of ethene reacting with hydrogen. How many grams of ethane (C₂H₆) are produced? (Molar mass of ethene = 28 g/mol, ethane = 30 g/mol).

Answer: 2.14 g

Question 1: Identify two variables that must be controlled during the addition of bromine to an alkene in a lab experiment.

Answer: Temperature and concentration of bromine solution.

Question 2: List two safety precautions that should be taken when handling bromine in the laboratory.

Answer: Wearing gloves and eye protection; working in a fume hood.

Question 1: In an experiment, 1.0 g of 1-butene reacts with excess HBr to produce 2.1 g of 1-bromobutane. Calculate the percentage yield of the reaction.

Answer: 50%

Question 2: A sample of alkene reacts with bromine, and the reaction mixture turns colourless. What does this indicate about the reaction progress?

Answer: It indicates that the bromine has reacted completely with the alkene, forming a colourless addition product.

Question 1: Explain the mechanism of addition of hydrogen halides (HX) to alkenes, including any intermediate structures. (6 marks)

Answer: The addition of HX to an alkene proceeds via electrophilic addition. The π bond acts as a nucleophile, attracting the proton (H⁺) from HX to form a carbocation intermediate. The halide ion (X⁻) then attacks the carbocation, resulting in the formation of the halogenated alkane. The regioselectivity depends on carbocation stability, often leading to Markovnikov's rule.

Question 1: Describe how the addition of hydrogen to alkenes is used in the industrial production of margarine.

Answer: Hydrogenation of vegetable oils (alkenes) converts unsaturated fats into saturated fats, producing margarine with a solid consistency.

Question 2: Explain why addition reactions are important in the synthesis of pharmaceuticals.

Answer: Addition reactions allow the functionalisation of alkenes to produce specific molecular structures needed in active pharmaceutical ingredients.