Investigating Separation Techniques in Mixtures

Aim

To investigate different separation techniques and to separate a mixture of sand, salt and water using filtration and evaporation.

Learning Outcome

• Define mixtures and solutions.
• Distinguish between homogeneous and heterogeneous mixtures.
• Identify soluble and insoluble substances.
• Explain how physical properties are used to separate mixtures.
• Select suitable separation techniques.
• Use filtration and evaporation correctly.
• Identify residue and filtrate.
• Explain real-world applications of separation techniques.

Time Allocation

Approximately 60 minutes.

Introduction

Mixtures are formed when two or more substances are combined without a chemical reaction taking place.

The substances in a mixture keep their original physical properties and can therefore be separated using physical methods.

Different separation techniques are used depending on the physical properties of the substances in the mixture.

What Is a Mixture?

A mixture is a combination of two or more substances that are physically combined.

The substances can usually still be identified and separated.

Examples of Mixtures

• Sand and gravel
• Salad
• Trail mix
• Cereal and milk
• Sand and water

What Is a Solution?

A solution is a special type of homogeneous mixture where one substance dissolves completely in another.

The substances mix so well that they appear as one substance.

Examples of Solutions

• Salt water
• Sugar water
• Lemonade
• Vinegar and water

Important Definitions

Term	Definition
Mixture	Two or more substances physically combined.
Solution	A homogeneous mixture formed when a substance dissolves.
Solute	The substance that dissolves.
Solvent	The substance that does the dissolving.
Soluble	Able to dissolve in a liquid.
Insoluble	Unable to dissolve in a liquid.
Filtration	Separating an insoluble solid from a liquid.
Residue	The solid left behind on the filter paper.
Filtrate	The liquid that passes through the filter paper.
Evaporation	Separating a dissolved solid from a liquid by heating.
Decantation	Pouring off a liquid from settled solids.
Distillation	Separating liquids using different boiling points.

Types of Mixtures

Type of Mixture	Description	Example
Homogeneous Mixture	Uniform throughout.	Salt water
Heterogeneous Mixture	Non-uniform composition.	Sand and water

Physical Properties Used in Separation

Physical Property	Separation Method
Particle Size	Sieving
Magnetism	Magnetic Separation
Solubility	Filtration and Evaporation
Density	Decantation
Boiling Point	Distillation

Common Separation Techniques

Hypothesis

If a mixture of sand, salt and water is separated using filtration and evaporation, then the sand and salt can be recovered because they have different physical properties.

Investigation Question

Which separation methods should be used and in what order to separate a mixture of sand, salt and water?

Variables

Independent Variable

Separation technique used.

Dependent Variable

Successful separation of the substances.

Control Variables

• Same quantities of sand, salt and water.
• Same heating method.
• Same apparatus.

Apparatus

• Sand
• Salt
• Water
• Beaker
• Glass stirring rod
• Filter funnel
• Filter paper
• Conical flask or beaker
• Evaporating dish
• Tripod stand
• Gauze mat
• Bunsen burner or hot plate
• Heatproof mat
• Tongs

Safety Precautions

Important Notes

Experimental Setup

Preparing the Mixture

1. Add sand and salt to a beaker.
2. Add water to the mixture.
3. Stir the mixture thoroughly.

Observation: The salt dissolves and the sand remains visible.

Method

Part A: Filtration

1. Fold the filter paper and place it into the funnel.
2. Place the funnel into the conical flask or beaker.
3. Slowly pour the mixture into the filter funnel.
4. Observe the sand remaining on the filter paper.
5. Allow all the liquid to pass through the filter paper.

Observation: Sand remains on the filter paper as residue. Salt solution passes through as filtrate.

Part B: Evaporation

1. Pour the filtrate into the evaporating dish.
2. Place the evaporating dish on the gauze mat above the heat source.
3. Heat the solution gently.
4. Observe the water evaporating.
5. Continue heating until salt crystals remain.
6. Allow the apparatus to cool before handling.

Observation: Water evaporates. Salt crystals remain in the evaporating dish.

Results Table

Observation Stage	Observation
After adding water
During filtration
Residue on filter paper
Filtrate collected
During evaporation
Final substance remaining

Sample Observations

Observation Stage	Observation
After adding water	Salt dissolved while sand remained visible.
During filtration	Liquid passed through the filter paper.
Residue on filter paper	Sand remained on the filter paper.
Filtrate collected	Clear salt solution collected.
During evaporation	Water evaporated and steam formed.
Final substance remaining	White salt crystals remained.

What Learners Should Observe

• Salt dissolves in water.
• Sand does not dissolve.
• Sand is separated by filtration.
• Water evaporates during heating.
• Salt remains after evaporation.

Analysis of Results

The investigation shows that different separation methods are used depending on the physical properties of the substances.

• Sand is insoluble in water.
• Salt is soluble in water.
• Filtration separates insoluble solids from liquids.
• Evaporation separates dissolved solids from liquids.

The separation occurred without any chemical reaction taking place.

Mini Investigations

Sieving

Use a sieve to separate sand from gravel based on particle size.

Magnetic Separation

Use a magnet to separate iron filings from sand.

Decantation

Allow muddy water to settle and carefully pour off the clear liquid.

Accuracy and Reliability

Improving Accuracy

• Use clean apparatus.
• Stir properly.
• Pour carefully during filtration.
• Heat gently during evaporation.

Improving Reliability

• Repeat the investigation.
• Use measured quantities.
• Compare repeated observations.

Sources of Experimental Error

• Torn filter paper.
• Spilling during filtration.
• Incomplete dissolving of salt.
• Overheating during evaporation.
• Loss of salt crystals during transfer.

Conclusion

The investigation successfully separated a mixture of sand, salt and water using filtration and evaporation.

The experiment confirmed that separation techniques depend on physical properties, filtration separates insoluble solids from liquids, evaporation separates dissolved solids from liquids, and mixtures can be separated without chemical change.

Questions for Learners

1. What is a mixture?
2. What is a solution?
3. What is the difference between a homogeneous and heterogeneous mixture?
4. Why did the salt dissolve?
5. Why did the sand not dissolve?
6. What is filtration?
7. What is residue?
8. What is filtrate?
9. Why was evaporation used?
10. Which physical properties were used during separation?
11. Which method would separate iron filings from sand?
12. Which method would separate gravel from sand?

Common Mistakes

• Pouring too quickly during filtration.
• Tearing the filter paper.
• Confusing residue and filtrate.
• Heating too strongly.
• Not dissolving all the salt.

Teacher Notes

• Emphasise the difference between mixtures and solutions.
• Reinforce the idea that separation methods depend on physical properties.
• Demonstrate correct filter paper folding before the investigation.
• Encourage learners to explain why each method works.

Teacher Tip

Ask learners to predict which separation method should be used before beginning the investigation.

Expected Results

• Sand remains on the filter paper.
• Salt solution passes through the funnel.
• Water evaporates during heating.
• Salt crystals remain in the evaporating dish.

Real-World Applications

Separation techniques are used in water purification, recycling, mining, food production, chemical industries, forensic science and waste management.