ChemistryChapter 17: Separation Techniques
Evaporation
Evaporation lets the solvent leave as vapour and leaves the solute behind.
Learning objectives
- State the main idea of evaporation in clear words.
- Explain why evaporation is useful in chemistry.
- Apply the correct method, observation, equation, or comparison.
- Avoid the common mistakes and write a complete exam answer.
Definition
Evaporation lets the solvent leave as vapour and leaves the solute behind. It is useful when the solid is the prize, as in salt from seawater. Drinking water can also be made this way because water is volatile and salt is not.
Important terms
- solvent leave
- Evaporation lets the solvent leave as vapour and leaves the solute behind.
- volatile
- Evaporation lets the solvent leave as vapour and leaves the solute behind.
Overview
Speed of evaporation, then industry:
What Speeds It
Evaporation is faster if T is up, the surface is up, and airflow keeps the air unsaturated. Stronger intermolecular forces (IMF) make it slower. Higher external P also makes it slower, because vapour finds it harder to escape.
Examples Warm, wide dish, fan · Strong IMF: slower · High external P: slower
Industry Uses
Industry uses evaporation for juice concentrates, lactose powder, dyes, and salt / desalination. Seawater can give drinking water because water is volatile: it leaves, and dissolved salts stay.
Examples Fruit juice concentrate · Milk sugar powder · Sea salt pans
WHAT — Core idea
Evaporation lets the solvent leave as vapour and leaves the solute behind. It is useful when the solid is the prize, as in salt from seawater. Drinking water can also be made this way because water is volatile and salt is not.
WHY — Why it matters
Evaporation does not need the liquid to boil. A puddle dries below boiling T if air above it stays unsaturated. A lid or still air slows the same puddle.
HOW — Method, evidence, or comparison
1. 1. WHAT SPEEDS IT: Evaporation is faster if T is up, the surface is up, and airflow keeps the air unsaturated. Stronger intermolecular forces (IMF) make it slower. Higher external P also makes it slower, because vapour finds it harder to escape. 2. 2. INDUSTRY USES: Industry uses evaporation for juice concentrates, lactose powder, dyes, and salt / desalination. Seawater can give drinking water because water is volatile: it leaves, and dissolved salts stay.
HOW — Answer in an exam
If you want the liquid, do not evaporate it into the room: use distillation and collect the distillate. Evaporation keeps the solid and loses the solvent.
Explanation
Evaporation does not need the liquid to boil. A puddle dries below boiling T if air above it stays unsaturated. A lid or still air slows the same puddle.
In simple words
If you want the liquid, do not evaporate it into the room: use distillation and collect the distillate. Evaporation keeps the solid and loses the solvent.
Key points
- solvent leave
- volatile
- T is up
- surface is up
Exam preparation
Exam Focus
Quick revision
Revision Zone
Review the key facts, formulas and checks before you move on.Evaporation
Sticky Notes · Quick Revision
WHAT
- Evaporation lets the solvent leave as vapour and leaves the solute behind.
Key Points
- solvent leave
- volatile
HOW
- Evaporation is faster if T is up, the surface is up, and airflow keeps the air unsaturated.
- Industry uses evaporation for juice concentrates, lactose powder, dyes, and salt / desalination.
Example
- Warm, wide dish, fan
- Strong IMF: slower
- High external P: slower
Common Mistake
- Evaporation can happen below the boiling point.
Exam Tip
- If you want the liquid, do not evaporate it into the room: use distillation and collect the distillate.
- Evaporation keeps the solid and loses the solvent.
60-second revision
- Evaporation lets the solvent leave as vapour and leaves the solute behind.
- It is useful when the solid is the prize, as in salt from seawater.
- Evaporation is faster if T is up, the surface is up, and airflow keeps the air unsaturated.
- Industry uses evaporation for juice concentrates, lactose powder, dyes, and salt / desalination.
- If you want the liquid, do not evaporate it into the room: use distillation and collect the distillate.
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