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๐ฌ Think about it
Stir sugar into water and every sip tastes the same. Stir sand into water and you can see the sand settle. Both are mixtures, yet they behave very differently. How do we sort mixtures into types? Let us see.
What is a homogeneous mixture?
- It has a uniform composition throughout.
- Sugar in water is equally sweet in the first and last sip.
- Such a mixture is also called a solution.
- A solution always stays homogeneous.
Example:
Vinegar (acetic acid in water) and soda (carbon dioxide in water) are homogeneous mixtures.
What is a heterogeneous mixture?
- It does not have a uniform composition.
- In sand and water, the sand particles are easily visible.
- The particles settle down with time.
Example:
A mixture of oil and water, where the two stay in separate layers, is heterogeneous.
In this Activity, we will prepare three different mixtures in groups and shine a laser through them to see which ones scatter light and which let it pass.
Procedure
Divide the class into groups A, B and C. Each prepares a mixture in a clear glass beaker:
1. Group A: add one spatula of common salt to 50 mL of water and stir. Label it A.
2. Group B: add one spatula of chalk powder to 50 mL of water and stir. Label it B.
3. Group C: add a few drops of milk to 50 mL of water and stir. Label it C.
4. Are the particles visible in each mixture? Record your observations.
5. Shine a laser pointer through each beaker and look from the side, perpendicular to the beam. Record what you see.
6. Predict what each beaker looks like if left undisturbed for a few minutes.
7. Filter each mixture separately. Is there any residue on the filter paper?
8. Are these the same type of mixture, or different?
1. Group A: add one spatula of common salt to 50 mL of water and stir. Label it A.
2. Group B: add one spatula of chalk powder to 50 mL of water and stir. Label it B.
3. Group C: add a few drops of milk to 50 mL of water and stir. Label it C.
4. Are the particles visible in each mixture? Record your observations.
5. Shine a laser pointer through each beaker and look from the side, perpendicular to the beam. Record what you see.
6. Predict what each beaker looks like if left undisturbed for a few minutes.
7. Filter each mixture separately. Is there any residue on the filter paper?
8. Are these the same type of mixture, or different?
โ Safety first:
Do not look directly into the laser beam. It can cause irreversible eye damage.
Observation
In A (salt) the particles are not visible and the laser path is not seen. In B (chalk) particles are visible and the light path shows clearly; chalk leaves a residue on filtering. In C (milk) the mixture looks uniform but the laser path is still visible.
Explanation
These are three different types of mixtures — a solution (A), a suspension (B) and a colloid (C). We will explore how they differ through the chapter.
โ Summary
- Make salt, chalk and milk mixtures.
- Shine a laser through each.
- See which scatter light.
- Three different mixture types.
Important Points
- A homogeneous mixture (solution) is uniform throughout.
- A heterogeneous mixture is not uniform; particles may settle.
- Salt water, chalk water and milk water behave as three different mixture types.
โ Test Yourself
-
What is another name for a homogeneous mixture?
View Answer
A solution. -
How do you know sand and water is heterogeneous?
View Answer
The sand particles are visible and settle with time. -
Is oil and water homogeneous or heterogeneous?
View Answer
Heterogeneous — they form separate layers.
Important Definitions
- Homogeneous mixture (solution) — a mixture with uniform composition throughout.
- Heterogeneous mixture — a mixture that is not uniform, in which particles may settle.
๐ NCERT Question 1 — Which of the following
Which mixtures are correctly classified as homogeneous (Hm) and heterogeneous (Ht)?
View Answer →
