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

Answer: An addition reaction is a chemical process where two or more molecules combine to form a larger molecule, typically involving the addition of atoms or groups across a carbon-carbon double bond in alkenes.

Question 2: Explain the general mechanism of an addition reaction of an alkene with hydrogen halides.

Answer: The alkene reacts with a hydrogen halide (HX) through electrophilic addition, where the double bond electrons are attracted to the hydrogen atom, forming a carbocation intermediate, which then reacts with the halide ion to produce the addition product.

Question 3: Describe why addition reactions are typical of alkenes and not alkanes.

Answer: Addition reactions are typical of alkenes because they have a carbon-carbon double bond with a region of high electron density, making them more reactive. Alkanes have only single bonds, which are less reactive and do not readily undergo addition reactions.

Question 1: Calculate the molecular formula of an alkene that has 4 carbon atoms and 8 hydrogen atoms.

Answer: C4H8

Question 2: If 0.5 mol of ethene reacts completely with hydrogen bromide (HBr), how many moles of brominated product are formed?

Answer: 0.5 mol

Question 3: Calculate the mass of 2 moles of ethene (C2H4). (Atomic masses: C=12 g/mol, H=1 g/mol)

Answer: 48 grams

Question 1: Describe a safe laboratory procedure for adding hydrogen bromide to an alkene, including safety precautions.

Answer: The procedure involves conducting the reaction in a well-ventilated fume cupboard, wearing appropriate PPE such as gloves and safety goggles, and adding hydrogen bromide slowly to the alkene in a controlled manner. The reaction should be monitored, and all waste should be disposed of according to safety guidelines to prevent inhalation or contact hazards.

Question 2: Identify the independent and dependent variables in an experiment where alkenes react with hydrogen halides.

Answer: The independent variable is the type or concentration of the hydrogen halide used; the dependent variable is the amount or rate of product formed.

Question 1: A set of data shows that adding bromine water to an alkene results in a colour change from orange-brown to colourless. Explain the chemical reason for this observation.

Answer: Bromine water decolourises when it reacts with the alkene via an addition reaction, where bromine molecules add across the double bond, removing the bromine's colour and forming a colourless dibrominated compound.

Question 1: Describe how the addition reaction of ethene with hydrogen halides is utilised in the industry to manufacture halogenated hydrocarbons.

Answer: In industry, ethene reacts with hydrogen halides such as hydrogen chloride or hydrogen bromide in controlled conditions to produce halogenated hydrocarbons like chloroethane or bromoethane, which are used as solvents, refrigerants, or intermediates in chemical synthesis. This process allows large-scale, efficient production of these compounds through electrophilic addition.

Question 2: Explain the significance of addition reactions of alkenes in the development of new polymers and materials.

Answer: Addition reactions of alkenes are fundamental in creating polymers like polyethylene and polyvinyl chloride, where monomers undergo successive addition reactions to form long chain molecules. These polymers are critical in manufacturing plastics, fibres, and advanced materials used in everyday life.