ExamsLogic | Where Exams Make Sense | www.examslogic.com
Topic: Organic Chemistry
Level: OL/HL
Exam Focus: Section A Practical Skills
1. Experiment Snapshot
Feature
Details
Experiment
Preparation of Ethyne
Difficulty
⭐⭐⭐ Practical exam standard
Exam Importance
⭐⭐⭐⭐ Organic practicals are common Section A targets
Typical Marks
5–15 marks
2. Aim
To prepare ethyne gas from calcium carbide and water, collect it safely, and test for unsaturation.
3. Quick Theory
Calcium carbide reacts with water to produce ethyne gas and calcium hydroxide. Ethyne is an unsaturated hydrocarbon, so it decolourises bromine water.
Examiner Tip: Link the practical step to its purpose. This is where students gain easy explanation marks.
4. Apparatus and Chemicals
Apparatus
Chemicals
Dropping funnel, conical flask, delivery tube, gas jar, water trough, stopper.
Calcium carbide, water, bromine water.
Safety: Wear goggles. Take care with hot apparatus, organic liquids, bromine water, acids, alkalis and flammable substances.
5. Labelled Practical Diagram
6. Step-by-Step Procedure
Place a small amount of calcium carbide in the flask.
Add water slowly using a dropping funnel.
Allow the first gas produced to escape to remove air.
Collect ethyne over water in a gas jar.
Test the gas with bromine water.
Record the colour change.
7. Observations / Results
Stage
Expected Observation
Gas production
Effervescence / gas bubbles are produced.
Bromine water test
Orange/brown bromine water becomes colourless.
Conclusion
Ethyne is unsaturated.
8. Sources of Error and Improvements
Source of Error
Improvement
Incorrect heating or poor timing.
Heat gently and follow the sequence carefully.
Product loss or contamination.
Use clean apparatus and correct collection/filtration technique.
Incorrect observation wording.
Use exact exam words such as colourless, precipitate, crystals, reflux, or melting range.
9. Student Common Mistakes
Adding water too quickly and making the reaction uncontrolled.
Collecting the first gas jar before air is displaced.
Forgetting that ethyne is unsaturated.
Writing that bromine water turns blue instead of colourless.
Confusing ethyne with ethene.
10. Examiner Tips and Traps
Examiner Tip: Organic practicals often ask why a step is done, not just what was done.
Examiner Trap: Do not write vague observations like “changed colour” or “gas formed” without the exact result.
11. 🎮 Interactive Simulator
Try It Yourself
What should be added slowly to calcium carbide?
What is the positive bromine water result?
Result Window
Ready
Choose the correct actions to complete the practical.
Score:0/0
12. Past Paper Style Questions
State the aim of this experiment. [2]
Describe the preparation method in correct order. [4]
State one safety precaution. [2]
State one observation and its conclusion. [3]
State one common source of error and one improvement. [4]
13. Mark Scheme
Aim correct [2].
Method in correct order with key apparatus/chemicals [4].
Safety point suitable for chemicals/heating [2].
Observation and conclusion linked correctly [3].
Valid error and improvement [4].
14. Quick Revision Card
Aim: To prepare ethyne gas from calcium carbide and water, collect it safely, and test for unsaturation.
Key theory: Calcium carbide reacts with water to produce ethyne gas and calcium hydroxide. Ethyne is an unsaturated hydrocarbon, so it decolourises bromine water.
Most common mistake: Adding water too quickly and making the reaction uncontrolled.
Exam rule: Use exact observations and state the purpose of key steps.