Hydrocarbons quiz

The general formula of alkynes is:

The more stable conformation of ethane is:

Bromine water is decolourised by:

Addition of HBr to propene in the presence of peroxide gives:

Ethyne is prepared in the laboratory from:

Which of these is aromatic?

The electrophile in nitration of benzene is:

Which group is meta-directing?

Baeyer's reagent is:

Partial reduction of an alkyne with Lindlar's catalyst gives:

Why do alkanes undergo substitution while alkenes undergo addition reactions? (2 marks)

What is aromatisation? Give an example. (2 marks)

Why is benzene extraordinarily stable despite having three double bonds? (2 marks)

What is Friedel-Crafts alkylation? Give an equation. (2 marks)

How is propene prepared from 2-bromopropane? (2 marks)

What is ozonolysis? What is its use? (2 marks)

Why does cis-but-2-ene have a higher boiling point than trans-but-2-ene? (2 marks)

Write the reaction for the cyclic polymerisation of ethyne. (2 marks)

What is pyrolysis? Give an example. (2 marks)

Why are some polynuclear hydrocarbons dangerous? (2 marks)

Calculate the mass of carbon dioxide formed by complete combustion of 32 g of methane (C = 12, O = 16, H = 1). (3 marks)

Calculate the number of sigma and pi bonds in benzene. (3 marks)

How many structural isomers are possible for C5H12? Name them. (3 marks)

Calculate the percentage of carbon in benzene (C = 12, H = 1). (3 marks)

What volume of hydrogen at STP is needed to convert 5.2 g of ethyne completely into ethane (22.4 L/mol)? (3 marks)

Read the passage and answer the questions. Propene reacts with HBr. In the absence of peroxide, the major product is 2-bromopropane. In the presence of benzoyl peroxide, the major product is 1-bromopropane. Kharasch explained this using a free radical mechanism. (i) Name the rule followed in the first case. (ii) What is the intermediate formed in the first case? (iii) Why does HCl not show the peroxide effect? (5 marks)

Read the passage and answer the questions. Benzene undergoes electrophilic substitution reactions. In nitration, a mixture of concentrated nitric acid and concentrated sulphuric acid is used. The reaction proceeds by the formation of an electrophile, followed by a carbocation intermediate, and then the loss of a proton. (i) Write the equation for the formation of the electrophile. (ii) What is the intermediate called? (iii) Why does benzene undergo substitution rather than addition? (5 marks)

Read the passage and answer the questions. Alkanes are used as fuels. Methane is the main component of CNG, while LPG contains mainly butane and propane. When alkanes burn in sufficient air, they release a large amount of heat. In insufficient air, carbon monoxide and soot are formed. (i) Write the equation for the combustion of butane. (ii) Why is incomplete combustion dangerous? (iii) Why is methane a cleaner fuel than coal? (5 marks)

Read the passage and answer the questions. Alkenes show geometrical isomerism due to restricted rotation around the carbon-carbon double bond. For example, but-2-ene exists as cis and trans isomers. The cis isomer has a dipole moment, while the trans isomer has almost zero dipole moment. (i) Why is rotation restricted? (ii) Why does the trans isomer have nearly zero dipole moment? (iii) Can but-1-ene show geometrical isomerism? Explain. (5 marks)

Read the passage and answer the questions. Ethyne can be converted into benzene by passing it through a red-hot iron tube at 873 K. Benzene can also be prepared by decarboxylation of sodium benzoate with soda lime, or by reducing phenol with zinc dust. (i) Write the equation for decarboxylation of sodium benzoate. (ii) Name the reaction converting ethyne to benzene. (iii) Write the equation for the reduction of phenol. (5 marks)

Describe the methods of preparation of alkanes and their chemical properties with equations. (6 marks)

Explain the conformations of ethane with Newman and sawhorse projections. Why is the staggered form more stable? (6 marks)

Describe the preparation and chemical properties of alkenes, including Markovnikov's rule and the peroxide effect. (6 marks)

Describe the preparation of ethyne. Explain its acidic character and addition reactions. (6 marks)

Explain the structure and aromaticity of benzene. Describe its electrophilic substitution reactions with mechanism and the directive influence of substituents. (6 marks)