ChemistryChapter 17: Separation Techniques
Distillation
Distillation means vaporise then condense.
Learning objectives
- State the main idea of distillation in clear words.
- Explain why distillation is useful in chemistry.
- Apply the correct method, observation, equation, or comparison.
- Avoid the common mistakes and write a complete exam answer.
Definition
Distillation means vaporise then condense. The distillate is the collected liquid. A liquid boils when its vapour pressure equals the external P. Heat the flask; the lowest boiling point (BP) substance leaves first; a condenser cools the vapour back to liquid.
Important terms
- vaporise
- Distillation means vaporise then condense.
- condense
- Distillation means vaporise then condense.
- distillate
- Distillation means vaporise then condense.
- vapour pressure
- Distillation means vaporise then condense.
- external P
- Distillation means vaporise then condense.
- lowest
- Distillation means vaporise then condense.
Overview
The flask and the condenser do different jobs:
In the Flask
Heat raises vapour pressure until it matches the outside pressure. The liquid then boils. The substance with the lowest BP turns to vapour first. Keep the thermometer where the vapour leaves, not in the liquid, if you are reading BP.
Examples Water leaving salt · Alcohol leaving water · Light oil leaving crude
In the Condenser
The condenser cools vapour so it becomes liquid again. That liquid is the distillate. Cold water usually runs in the jacket. Forms of distillation have been known since ancient civilisations (around 3000 BC).
Examples Water from seawater · Solvent recovery · Early stills for oils
WHAT — Core idea
Distillation means vaporise then condense. The distillate is the collected liquid. A liquid boils when its vapour pressure equals the external P. Heat the flask; the lowest boiling point (BP) substance leaves first; a condenser cools the vapour back to liquid.
WHY — Why it matters
Distillation is vaporise + condense, not just heating. If you only boil and do not collect, you have evaporation, not distillation.
HOW — Method, evidence, or comparison
1. 1. IN THE FLASK: Heat raises vapour pressure until it matches the outside pressure. The liquid then boils. The substance with the lowest BP turns to vapour first. Keep the thermometer where the vapour leaves, not in the liquid, if you are reading BP. 2. 2. IN THE CONDENSER: The condenser cools vapour so it becomes liquid again. That liquid is the distillate. Cold water usually runs in the jacket. Forms of distillation have been known since ancient civilisations (around 3000 BC).
HOW — Answer in an exam
Boiling is not a random hot moment. It is the point where vapour pressure = external P. Lower the outside pressure and the BP falls (vacuum distillation).
Explanation
Distillation is vaporise + condense, not just heating. If you only boil and do not collect, you have evaporation, not distillation.
In simple words
Boiling is not a random hot moment. It is the point where vapour pressure = external P. Lower the outside pressure and the BP falls (vacuum distillation).
Key points
- vaporise
- condense
- distillate
- vapour pressure
- lowest BP
Exam preparation
Exam Focus
Quick revision
Revision Zone
Review the key facts, formulas and checks before you move on.Distillation
Sticky Notes · Quick Revision
WHAT
- Distillation means vaporise then condense.
Key Points
- vaporise
- condense
- distillate
- vapour pressure
- external P
HOW
- Heat raises vapour pressure until it matches the outside pressure.
- The condenser cools vapour so it becomes liquid again.
Example
- Water leaving salt
- Alcohol leaving water
- Light oil leaving crude
Common Mistake
- Distillation includes both vaporising and condensing.
Exam Tip
- Boiling is not a random hot moment.
- It is the point where vapour pressure = external P.
60-second revision
- Distillation means vaporise then condense.
- The distillate is the collected liquid.
- Heat raises vapour pressure until it matches the outside pressure.
- The condenser cools vapour so it becomes liquid again.
- Boiling is not a random hot moment.
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