Sciences - Co-ordinated (Double) - 0654 CIE

Alkenes

Overview

If alkanes are the calm members of the organic world, alkenes are the reactive ones. The single feature that makes the difference is a carbon-carbon double bond, and it turns these molecules into the raw material for plastics, ethanol and much of the chemical industry.

In this lesson you will learn that alkenes are unsaturated hydrocarbons with the general formula CnH2n, how their double bond drives addition reactions, and how bromine water provides a quick chemical test to tell an alkene from an alkane.

Objectives

State that the bonding in alkenes includes a double carbon-carbon covalent bond and that alkenes are unsaturated hydrocarbons.
Describe the manufacture of alkenes and hydrogen by the cracking of larger alkane molecules using a high temperature and a catalyst.
Describe the reasons for the cracking of larger alkane molecules.
Describe the test to distinguish between saturated and unsaturated hydrocarbons by their reaction with aqueous bromine.
[Supplement] State that in an addition reaction only one product is formed.
[Supplement] Describe the properties of alkenes in terms of addition reactions with: (a) bromine or aqueous bromine (b) hydrogen in the presence of a nickel catalyst (c) steam in the presence of an acid catalyst and draw the structural or displayed formulae of the products.

Lesson Note

Alkenes are the starting point for an enormous range of products, from polythene bags to ethanol. Their reactivity, all because of one double bond, is what makes them so useful, and it is also the basis of a simple laboratory test you are expected to know.

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Lesson Evaluation

Congratulations on completing the lesson on Alkenes. Now that youve explored the key concepts and ideas, its time to put your knowledge to the test. This section offers a variety of practice questions designed to reinforce your understanding and help you gauge your grasp of the material.

You will encounter a mix of question types, including multiple-choice questions, short answer questions, and essay questions. Each question is thoughtfully crafted to assess different aspects of your knowledge and critical thinking skills.

Use this evaluation section as an opportunity to reinforce your understanding of the topic and to identify any areas where you may need additional study. Don't be discouraged by any challenges you encounter; instead, view them as opportunities for growth and improvement.

Alkenes are unsaturated because they contain a: A. Single bond only B. Carbon-carbon double bond C. -OH group D. -COOH group Answer: B
The general formula of the alkenes is: A. CnH2n+2 B. CnH2n C. CnH2n+1OH D. CnH2n-2 Answer: B
When bromine water is shaken with an alkene, it: A. Stays orange B. Turns blue C. Is decolourised D. Turns red Answer: C
Adding steam to ethene, with a catalyst, produces: A. Ethane B. Ethanol C. Ethanoic acid D. Methane Answer: B
Reactions in which a molecule adds across a double bond are called: A. Substitution reactions B. Addition reactions C. Combustion reactions D. Neutralisation reactions Answer: B