Suspensions and Colloids - Tyndall Effect - UNSOLVED PRACTICE SET

Q7. What is the Tyndall effect? Name two everyday examples where you can observe this effect.

Q8. Differentiate between a suspension and a colloid on the basis of: (i) particle size, and (ii) stability.

Q9. Your teacher shows you three beakers containing: (A) salt solution, (B) milk, and (C) muddy water. When a torchlight is passed through each, only beaker B shows a visible light path. Explain why.

Q10. Why do the particles of a suspension settle down when left undisturbed, while the particles of a colloid do not? Explain in terms of particle size and gravity.

Q11. What is Brownian motion? How is it related to colloidal particles?

Q12. Classify the following as true solution, colloid, or suspension: (i) Blood, (ii) Sugar in water, (iii) Chalk powder in water, (iv) Cheese. Give one reason for each classification.

Q13. With the help of a diagram, explain the Tyndall effect. Describe an experiment to demonstrate the Tyndall effect using a torchlight, three beakers (containing salt solution, milk, and muddy water), and a dark room. What conclusions can you draw from your observations?

Q14. A student argues that since both suspensions and colloids scatter light, they are essentially the same. Do you agree? Present a detailed comparison of suspensions and colloids based on particle size, stability, filterability, and the Tyndall effect. Use a table for clarity.

Q15. "The Tyndall effect has both scientific and practical importance." Discuss this statement by explaining: (i) how the Tyndall effect helps distinguish between true solutions and colloids, (ii) its application in understanding atmospheric phenomena like the blue colour of the sky, and (iii) its use in detecting impurities in drinking water.

Q16. In a laboratory experiment, a student prepares three mixtures:

Mixture P: 2 g of starch in 100 mL water

Mixture Q: 2 g of sodium chloride in 100 mL water

Mixture R: 2 g of sand in 100 mL water

(a) Classify each mixture as true solution, colloid, or suspension.

(b) Which mixture(s) will show the Tyndall effect? Explain.

(c) If the student filters each mixture, which one will leave a residue on the filter paper?

(d) After leaving all three mixtures undisturbed for 2 hours, describe what you would observe in each beaker.

Q17. A science teacher demonstrates the Tyndall effect in the classroom using a laser pointer and various samples:

Sample A: Clean water

Sample B: Dilute milk solution

Sample C: Dilute sulphur colloid

Sample D: Salt solution

(a) Predict which samples will show the Tyndall effect and which will not.

(b) The teacher adds a few drops of dilute HCl to Sample C. The Tyndall effect disappears. Explain why this happens at the particle level.

(c) If the particle size in Sample B is approximately 50 nm, in which category of colloids does it fall?

(d) Calculate the approximate number of particles if the total mass of dispersed phase in 100 mL of Sample B is 0.5 g and each particle has a mass of 10⁻¹⁸ g.

Q18. In a city, the air quality is monitored using the Tyndall effect. On a foggy winter morning, the visibility drops to 50 metres.

(a) Is the fog a colloid or a suspension? Identify the dispersed phase and dispersion medium.

(b) Explain why visibility is reduced using the concept of the Tyndall effect.

(c) If the concentration of water droplets in the fog is 0.1 g per cubic metre of air, calculate the mass of water droplets in 500 cubic metres of foggy air.

(d) Suggest two measures that city authorities can take to reduce fog-related visibility problems.