ChemistryChapter 17: Separation Techniques
Filtration
Filtration separates by particle size.
Learning objectives
- State the main idea of filtration in clear words.
- Explain why filtration is useful in chemistry.
- Apply the correct method, observation, equation, or comparison.
- Avoid the common mistakes and write a complete exam answer.
Definition
Filtration separates by particle size. The residue is the solid left on the filter. The filtrate is the liquid that goes through. Gravity filtration uses filter paper in a funnel. Vacuum filtration uses a Buchner funnel to pull liquid through faster.
Important terms
- particle size
- Filtration separates by particle size.
- residue
- Filtration separates by particle size.
- filtrate
- Filtration separates by particle size.
- Gravity
- Filtration separates by particle size.
- filter paper
- Filtration separates by particle size.
- vacuum
- Filtration separates by particle size.
Overview
What filtration can and cannot do:
Sand and Sugar
To separate sand and sugar: dissolve the sugar in water, filter off the sand (residue), then evaporate or crystallise the sugar from the filtrate. The sand never dissolves, so it stays on the paper.
Examples Sand on the paper · Sugar water through · Sugar crystals later
What Will Not Filter
Heterogeneous sand-water can be filtered. Homogeneous brine cannot: the salt is dissolved, so it passes through with the water. Filtration needs a solid that is bigger than the holes in the paper.
Examples Sand-water: yes · Chalk-water: yes · Salt water: no
WHAT — Core idea
Filtration separates by particle size. The residue is the solid left on the filter. The filtrate is the liquid that goes through. Gravity filtration uses filter paper in a funnel. Vacuum filtration uses a Buchner funnel to pull liquid through faster.
WHY — Why it matters
Name both products in an exam answer: residue on the paper, filtrate in the flask. Vacuum with a Buchner funnel is the same idea as gravity, only faster.
HOW — Method, evidence, or comparison
1. 1. SAND AND SUGAR: To separate sand and sugar: dissolve the sugar in water, filter off the sand (residue), then evaporate or crystallise the sugar from the filtrate. The sand never dissolves, so it stays on the paper. 2. 2. WHAT WILL NOT FILTER: Heterogeneous sand-water can be filtered. Homogeneous brine cannot: the salt is dissolved, so it passes through with the water. Filtration needs a solid that is bigger than the holes in the paper.
HOW — Answer in an exam
You cannot filter dissolved salt from brine. First evaporate or distil if you need the solid or the water.
Explanation
Name both products in an exam answer: residue on the paper, filtrate in the flask. Vacuum with a Buchner funnel is the same idea as gravity, only faster.
In simple words
You cannot filter dissolved salt from brine. First evaporate or distil if you need the solid or the water.
Key points
- particle size
- residue
- filtrate
- Gravity
- dissolve
- filter
Exam preparation
Exam Focus
Quick revision
Revision Zone
Review the key facts, formulas and checks before you move on.Filtration
Sticky Notes · Quick Revision
WHAT
- Filtration separates by particle size.
Key Points
- particle size
- residue
- filtrate
- Gravity
- filter paper
HOW
- To separate sand and sugar: dissolve the sugar in water, filter off the sand (residue), then evaporate or crystallise the sugar from the filtrate.
- Heterogeneous sand-water can be filtered.
Example
- Sand on the paper
- Sugar water through
- Sugar crystals later
Common Mistake
- Residue stays on the paper; filtrate passes through it.
Exam Tip
- You cannot filter dissolved salt from brine.
- First evaporate or distil if you need the solid or the water.
60-second revision
- Filtration separates by particle size.
- The residue is the solid left on the filter.
- To separate sand and sugar: dissolve the sugar in water, filter off the sand (residue), then evaporate or crystallise the sugar from the filtrate.
- Heterogeneous sand-water can be filtered.
- You cannot filter dissolved salt from brine.
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