SCIENCE 6-LESSON PRESENTATION-COLLOID-Wk3.pptx

PRESENTATION

1. Science VI Week 3 Colloids

2. Gelatin is said to be a mixture. What kind of mixture is it?

3. Pictures of colloids : CHEESE mayonnaise

4. Pictures of colloids : milk gelatin

5. What is common among these pictures?

6. SOLID Properties Do not change shape easily Will not allow another solid to pass through them easily Are usually visible Have a definite shape Have a definite size Becomes liquid when heated Remain solid when cooled

7. Liquid Properties Change shape easily (take the shape of the container) Will allow solid to pass through them easily May be visible or invisible Have a definite size (volume) becomes gas when heated becomes solid when cooled

8. C OLLOID A homogeneous-looking heterogeneous mixture . Examples: Milk, Office paste (gum), Blood, Toothpaste, Mist (water vapor dispersed in air), Jelly

9. Properties of colloid Some characteristics properties of colloids are described below:   Heterogeneous nature: A colloid (or sol) is heterogeneous in nature. The particles in a colloid can be seen only with a powerful microscope.   Particle size: The size of particles in a colloid lies between 10 -9  m – 10 -7  m.

10.   Separation of colloidal particles by filtration : Colloidal particles can easily pass through the pores of a filter paper. Therefore, colloidal particles cannot be separated by filtration.  

11. Stability : Colloids are unstable unless stabilized by adding suitable stabilizer. The colloidal particles tend to come together and settle down   Brownian movement of colloidal particles : When seen under a microscope, the colloidal particles in a colloid are seen to be moving in a random (zigzag) fashion. This zigzag motion of particles in a colloid is called Brownian motion .

12. Light scattering by colloidal particles: Tyndall effect. When a strong beam of light is passed through a colloid kept in a dark room, the path of the light beam through the colloid becomes visible. This occurs due to scattering of light by the colloidal particles. The scattering of light by the particles in a colloid is called Tyndall effect. True solutions do not scatter light. Therefore, true solutions do not show Tyndall effect.

13. Colloids and their applications : Purification of water Food Items Medicine Artificial rain

14. Based on the lesson, how can you characterize the properties of colloids? Question:

15. Thank you!