Separation & Purification Techniques: Filtration, Evaporation And Crystallisation (Copy)
Separation & Purification Techniques
Filtration, Evaporation And Crystallisation
Purpose of Separation and Purification in ATP
- Separation and purification techniques are used to:
- Isolate desired products from mixtures
- Remove impurities
- Obtain solid or solution for further analysis
- ATP questions test:
- Correct technique selection
- Stepwise method description
- Correct observations
- Understanding of purpose
Core Examiner Rule
- Answers must include:
- Name of technique
- Step-by-step method
- Key observation(s)
- Logical sequence
- Marks lost if:
- Steps missing
- Observations incorrect
- Wrong technique chosen
1. Filtration
Purpose
- Separates insoluble solid from liquid
Apparatus
- Filter funnel
- Filter paper
- Beaker or conical flask
Method
- Fold filter paper into a cone
- Place in funnel
- Pour mixture slowly into funnel
- Collect filtrate (liquid) in beaker/flask
- Wash solid residue if needed
Observations
- Solid collected on paper
- Filtrate is clear
Examiner Notes
- Must mention folded paper
- Slow pouring prevents overflow
- Residue may be washed to remove impurities
Written and Compiled By Sir Hunain Zia, World Record Holder With 154 Total A Grades, 7 Distinctions and 11 World Records For Educate A Change O Level And IGCSE Chemistry Full Scale Course
2. Evaporation
Purpose
- Removes solvent to leave dissolved solute behind
- Useful for soluble salts
Apparatus
- Evaporating dish
- Bunsen burner
- Tripod and gauze
Method
- Pour solution into evaporating dish
- Heat gently over Bunsen burner
- Continue until solvent evaporates
- Solid remains in dish
Observations
- Solution level decreases
- Crystals may start forming
- Eventually, dry solid remains
Examiner Notes
- Do not overheat: avoids decomposition
- Useful for soluble salts that are not hydrated
3. Crystallisation
Purpose
- Purifies solid by forming pure crystals from solution
- Often follows dissolving and filtering
Apparatus
- Evaporating dish
- Filter funnel and paper
- Beaker
Method
- Dissolve impure solid in minimum hot solvent
- Filter to remove insoluble impurities
- Allow filtrate to cool slowly
- Crystals form as solution becomes saturated
- Collect crystals by filtration
- Dry crystals using filter paper
Observations
- Clear solution becomes cloudy
- Crystals appear gradually
- Dry crystals collected on filter paper
Examiner Notes
- Cooling must be slow for larger, pure crystals
- Fast cooling produces small, impure crystals
Written and Compiled By Sir Hunain Zia, World Record Holder With 154 Total A Grades, 7 Distinctions and 11 World Records For Educate A Change O Level And IGCSE Chemistry Full Scale Course
Summary Table of Techniques
| Technique | Purpose | Key Observation |
|---|---|---|
| Filtration | Separate insoluble solid from liquid | Solid on paper, filtrate clear |
| Evaporation | Remove solvent to get solid | Solution level decreases, solid remains |
| Crystallisation | Purify solid by crystal formation | Solution becomes cloudy, crystals form |
Common Examiner Traps
- Confusing evaporation and crystallisation
- Forgetting to filter before crystallisation
- Overheating in evaporation
- Not describing slow cooling for pure crystals
High-Yield ATP Tips
- Always name apparatus
- Follow stepwise logical sequence
- Mention key observations
- Explain purpose briefly if asked
- Distinguish clearly between evaporation and crystallisation
Core Scientific Principle
- Separation and purification techniques exploit:
- Solubility differences
- Physical state differences (solid vs liquid)
- Correct technique ensures:
- Pure product
- Maximum ATP marks
- Mastery of these techniques:
- Avoids common exam pitfalls
- Guarantees high-yield practical marks