Test your knowledge with free interactive questions on Seneca — used by over 10 million students.

Testing for Alkenes

We can test a solution to see if the alkene function group is present.

The test

The test

  • Add bromine water to the solution.
    • If an alkene is present, the solution will lose its orange colour and become colourless.
    • If an alkene is not present, it will NOT decolourise and the solution remains orange.
How the test works

How the test works

  • The test works because:
    • If the alkene is present, it can undergo an addition reaction with the bromine.
    • This removes the bromine (in the bromine water) and forms a halogenoalkane - so the colour is lost.
Bromine water

Bromine water

  • As a quick note, bromine water is just water with a small amount of bromine dissolved in it.
    • Bromine water is what colours the solution orange until it has reacted with the alkene.

Testing for Carboxylic Acids

We can test to see if a carboxylic acid is present in a solution.

The test

The test

  • Firstly we must react the carboxylic acid with sodium carbonates.
    • The reaction with the carbonate ions should form a salt + CO2 + H2O
  • We can then test for the CO2 produced using limewater.
Limewater

Limewater

  • Limewater is a clear solution but it is turned cloudy if CO2 is present.
    • This means we must pump the gas, produced from the reaction between the sample and the carbonate, into limewater.
      • If limewater turns cloudy: carboxylic acid is present in the initial solution.
      • If limewater stays clear: carboxylic acid is NOT present in the initial solution.
Jump to other topics
1

Physical Chemistry

1.1

Atomic Structure

1.2

Amount of Substance

1.3

Bonding

1.4

Energetics

1.5

Kinetics

1.6

Equilibria

1.7

Redox

2

Physical Chemistry 2 (A2 Only)

3

Inorganic Chemistry

4

Inorganic Chemistry 2 (A2 Only)

5

Organic Chemistry 1

6

Organic Chemistry 2 (A2 Only)

6.1

Optical Isomerism (A2 Only)

6.2

Aldehydes & Ketones (A2 Only)

6.3

Carboxylic Acids & Esters (A2 Only)

6.4

Aromatic Chemistry (A2 Only)

6.5

Amines (A2 Only)

6.6

Polymers (A2 Only)

6.7

Biological Organic (A2 Only)

6.8

Organic Synthesis (A2 Only)

6.9

NMR Spectroscopy (A2 Only)

6.10

Chromatography (A2 Only)

6.11

A-A* (AO3/4) - Organic 2

Practice questions on Reactions 2

Can you answer these? Test yourself with free interactive practice on Seneca — used by over 10 million students.

  1. 1
  2. 2
  3. 3
  4. 4
  5. 5
Answer all questions on Reactions 2

Unlock your full potential with Seneca Premium

  • Unlimited access to 10,000+ open-ended exam questions

  • Mini-mock exams based on your study history

  • Unlock 800+ premium courses & e-books

Get started with Seneca Premium