Lesson focus: filtrationSeparating an insoluble solid from a liquid by pouring it through filter paper, like sand from water. separates an insolubleDoes not dissolve, like sand in water. solidA state of matter that keeps its own shape and volume, because its particles are held in place. from a liquidA state of matter that can flow and takes the shape of its container, but keeps the same volume. by particle size.
Label filtration apparatus and predict residueThe solid left behind in the filter paper after filtration. and filtrateThe liquid that passes through the filter paper. contents.
Build on earlier learning
SolubilityUse solubility to decide which particles can be filtered.
Practical
Separating sand and salt
- Add water to the mixture and stir to dissolve the salt.
- Filter: sand stays in the filter paper as the residue; salt solution passes through as the filtrate.
- Evaporate the filtrate gently to leave salt crystals.
Record: A flow diagram of the method with what each step separates and why.
Safety: Stop heating before all the water has gone so the salt does not spit.
You will be successful when you can…
- Label funnel, paper and receiver.
- Define residue and filtrate.
- Predict dissolved and insoluble destinations.
- Evaluate contamination causes.
Words that carry the science
- filtration
- Separation using a porous barrier.
- residue
- Solid retained by filter paper.
- filtrate
- Liquid passing through the filter.
- insoluble
- Not dissolving appreciably in the stated solvent.
- filter pore
- Small opening allowing liquid and dissolved particles through.
Follow every component through the filter
01The apparatus
Fold filter paper into a funnel, place it securely and pour carefully, using a glass rod where appropriate. The steps: fold the filter paper and put it in a funnel over a beaker or flask. Pour the mixture slowly into the paper.
02The products
In muddy salt water, mud/sand is residueThe solid left behind in the filter paper after filtration.; salt solution is filtrateThe liquid that passes through the filter paper.. Dissolved salt is too dispersed to be retained by ordinary paper. The solid left on the paper is called the residueThe solid left behind in the filter paper after filtration.. The liquid that passes through is called the filtrateThe liquid that passes through the filter paper..
03Common failures
Torn paper or pouring above its edge can place solid in filtrate. Fine particles may require different pore size or another method.
Filtration and crystallisation
Filtration separates an insoluble solid from a liquid: the filter paper has tiny holes that let water particles and dissolved salt through but stop sand. Crystallisation then gets the salt back by evaporating the water.
Brown: sand grains. Blue: water particles. Purple: dissolved salt.
Controls
Particle sizes are exaggerated. Stop heating when crystals start to form and leave the rest to evaporate slowly: slower evaporation gives bigger crystals.
Predict both products
A mixture contains chalk, dissolved copper sulfate and water.
- Chalk is insolubleDoes not dissolve, like sand in water. and larger than pores.
- Chalk remains as residue.
- Water passes through.
- Dissolved copper sulfate passes with water as filtrate.
How to make the reasoning visible: Filtrate is a solution, not necessarily pure liquid.
Filtration diagnoses
Identify expected products and faults.
| Situation | Residue | Filtrate | Evaluation |
|---|---|---|---|
| Sand + water | Sand | Water | Suitable |
| Salt solution | None | Salt solution | Does not separate salt |
| Torn paper | Some solid | Cloudy liquid + solid | Invalid separation |
| Paper overfilled | Solid may bypass | Contaminated filtrate | Improve pouring |
Why can filtrate be coloured?
How could dissolved salt then be recovered?
Use the table. Why does the torn filter paper give an invalid separation?
Check your understanding
Answer from memory, then check against the suggested answer.
What is filtration?
What is residue?
What is filtrate?
What does insoluble mean?
Why can water pass through filter paper but sand cannot?
A filtrate is cloudy. Give one procedural cause.
Why can pore size be a trade-off?
Muddy salty water is filtered. What is left in the filter paper and what passes through?
Exam Question Practice
Exam Question Practice
Mark points shown after marking
You have a mixture of sand and salt water. Answer the parts to describe how to separate them by filtering.
Where do you put the filter paper?
(1)What do you do with the mixture?
(1)What stays on the paper? What is it called?
(1)What goes through the paper? What is it called?
(1)Total for this question: 4 marks
Command word: For describeA command word: say what happens or what something is like, step by step, without needing to give reasons., give the steps in order and name both products.