Homogenous mixture and a heterogeneous mixture

jul 23 2016

Source: TTS Haryana Sci...

Summary Information

Keywords:

Homogeneous mixture, heterogeneous mixture, particles, solution

Topic:

Chemistry

Workplace Skills:

Investigation Design

Discussion

Independent Thinking

Target Grade (Ages):

Grade 6 (Ages 11-12)

Grade 7 (Ages 12-13)

Grade 8 (Ages 13-14)

Diversity Indicators:

This lesson plan is most suitable for Indian rural government school students.

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LESSON

Goals and Prerequisites

Goals:

To prepare and identify a homogenous mixture and a heterogeneous mixture

Instructional Objective(s)

By the end of this lesson plan students will -

Prepare and identify the homogeneous and hetrogeneous mixtures.

Instructional Resources

Background:

Heterogeneous and Homogeneousrefer to mixtures of materials in chemistry. The difference between heterogeneous and homogeneous mixtures is the degree at which the materials are mixed together and the uniformity of their composition.

A homogeneous mixture is a mixture where the components that make up the mixture are uniformly distributed throughout the mixture. The composition of the mixture is the same throughout.
Homogeneous Mixture Examples

air
sugar water
rain water
vinegar
steel

You can't pick out components of a homogeneous mixture or use a simple mechanical means to separate them. You can't see individual chemicals or ingredients in this type of mixture. Only one phase of matter is present in a homogeneous mixture.

Heterogeneous mixture is a mixture where the components of the mixture are not uniform or have localized regions with different properties.

Different samples from the mixture are not identical to each other. There are always two or more phases in a heterogeneous mixture, where you can identify a region with properties that are distinct from those of another region, even if they are the same state of matter (.e.g., liquid, solid).

Heterogeneous Mixture Examples

blood
gravel
mixed nuts
soil

Usually, it's possible to physically separate components of a heterogeneous mixture. For example, you can centrifuge (spin out) solid blood cells to separate them from the plasma of blood.

Materials:

Sodium chloride/sugar
Sand/chalk powder
Water
Micro beaker
Stirring rod
Funnel
Filter paper
Tripod
Starch powder
Kerosene burner

Procedure:

Part A

How to prepare a homogenous mixture (solution)?

1. Take 5 mL of water in a 10 mL micro beaker and add one spatula full of sodium chloride/ sugar to it.

2. Stir it well and filter.

3. What do you observe on the filter paper?

4. Do you observe any particles settling down in the solution?

Part B

How to prepare a suspension?

1. Take 5 mL of water in a micro beaker and add one spatula of sand/chalk powder to it.

2. Stir it well and observe carefully.

3. Filter the solution through a filter paper.

4. What do you observe on the filter paper?

Part C

How to prepare a colloidal solution?

1. Take one spatula of starch powder in a 10 mL micro beaker and make its paste with water.

2. Add the paste gradually by constant stirring to another beaker containing 5 mL water.

3. Heat the mixture with constant stirring. Do not boil.

4. Cool it and filter.

5. What do you observe on the filter paper? Do you observe some turbidity in the filtrate?

In this colloidal solution, you cannot see the particles of starch, whereas you could see the particles of sand in the suspension.

The particles in colloids are so small that you cannot see them with naked eyes. But you can prove them to be present when a33 beam of light is passed through the solution. These become visible by scattering the light.

Mixture in Part A is homogeneous mixture.

Mixture in Part B and Part C are heterogeneous mixtures

(a) Solution of sodium (b) Suspension of (c) Colloidal solution

Chloride/sugar in water chalk in water of starch in water

(Homogenous mixture) (Heterogeneous mixture) (Heterogeneous mixture)

Conclusion:

1. Salt/sugar in water forms a homogenous mixture.

2. Sand/Chalk powder in water forms a heterogeneous mixture.

3. The residue was seen on the filter paper in case of heterogeneous mixture.

4. The homogenous solution is transparent.

5. Suspensions are opaque.

6. Suspended solid can be separated by filtration.

7. Colloidal solutions are translucent and make a heterogeneous mixture.

8. Solid particles of a colloidal solution cannot be separated by filtration.

9. The enamel paint is an example of heterogeneous mixture and colloidal solution.

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