Colloidal Solution – Long Answer Questions
Medium Level (Application & Explanation)
Q1. Define a colloidal solution and explain why it is called a heterogeneous mixture though it looks uniform.
Answer:
- A colloidal solution is a mixture where tiny particles are spread evenly in another substance.
- The tiny particles are called the dispersed phase.
- The substance in which they are spread is the dispersing medium.
- Colloids look uniform to the eye, but they are actually heterogeneous.
- This is because the small particles are separate and do not form a single uniform phase.
- Example: Milk looks uniform, but it has fat droplets dispersed in water.
Q2. Explain the Tyndall effect in colloids with suitable examples and its importance.
Answer:
- The Tyndall effect is the scattering of light by colloidal particles.
- When light passes through a colloid, the path of the beam becomes visible.
- This happens because the particles are small but still big enough to scatter light.
- Example: A flashlight in fog shows a visible beam due to water droplets.
- Example: Light rays are visible in dusty or smoky air.
- The Tyndall effect helps us identify a mixture as a colloid.
Q3. Describe the particle size in colloids and how it affects their visibility and behavior.
Answer:
- Colloidal particles have a size between 1 nm and 1 µm.
- They are too small to be seen with the naked eye.
- But they are large enough to scatter light, so the beam can be seen.
- These particles remain suspended and do not settle on standing.
- Due to their size, they do not pass easily through ordinary filters.
- This size range is the key to their unique properties.
Q4. What do you mean by stability of colloidal solutions? Explain factors that can disturb it.
Answer:
- Stability means colloidal particles do not settle down on standing.
- Colloids are more stable than suspensions.
- But they can be disturbed by temperature changes.
- They can also be disturbed by changes in pH of the medium.
- Adding some chemicals can also upset the system.
- So, to keep colloids stable, we control heat, pH, and unwanted additives.
Q5. Why cannot colloids be separated by ordinary filtration? Explain with daily life links.
Answer:
- Ordinary filtration removes only large particles.
- Colloidal particles are very small (1 nm to 1 µm).
- They can pass through normal filter paper.
- So, simple filters cannot separate colloids from the medium.
- Example: Milk cannot be separated into fat and water by normal filtering.
- Example: Fog cannot be removed from air by simple cloth filtering.
High Complexity (Analysis & Scenario-Based)
Q6. A lab sample looks clear in a beaker, but a torch beam becomes visible when passed through it. Identify the mixture and justify your answer.
Answer:
- The sample shows a visible light path when a torch passes through.
- This is a sign of the Tyndall effect.
- The Tyndall effect occurs due to light scattering by particles.
- This is a key property of a colloidal solution.
- So, the mixture is a colloid, not a true solution.
- The particles are small yet enough to scatter light.
Q7. A student leaves two mixtures on a table: milk and muddy water. After a few hours, muddy water settles but milk does not. Explain scientifically.
Answer:
- Milk is a colloid (an emulsion of fat in water).
- In colloids, the particles are small and stable.
- They do not settle on standing.
- Muddy water is a suspension with larger particles.
- Suspension particles settle down over time.
- This shows why colloids are more stable than suspensions.
Q8. On a foggy night, car headlights appear as bright beams in the air and cause glare. Use colloid concepts to explain this observation.
Answer:
- Fog is an aerosol (liquid droplets in a gas).
- The water droplets act as colloidal particles in air.
- Headlight beams become visible due to the Tyndall effect.
- Light is scattered by the tiny droplets.
- This scattering causes glare and reduces clear vision.
- Thus, fog behaves like a colloid and scatters light strongly.
Q9. A cosmetic factory stores face cream (an emulsion). In summer, some batches separate into layers. Analyze the reason and suggest control steps.
Answer:
- Face cream is an emulsion (liquid in liquid colloid).
- Emulsions are stable, but can be disturbed by temperature changes.
- In summer, high heat can destabilize the colloid.
- The droplets may coalesce and form layers.
- To control, keep temperature within safe limits.
- Avoid pH changes and unwanted chemicals that can break the emulsion.
Q10. Classify these everyday materials using colloid types and explain: smoke, shaving cream, milk of magnesia, clouds, sponge.
Answer:
- Smoke: solid in gas → an aerosol (tiny solid particles in air).
- Shaving cream: gas in liquid → a foam (gas bubbles in liquid).
- Milk of magnesia: solid in liquid → a sol (solid dispersed in water).
- Clouds: liquid in gas → an aerosol (tiny water droplets in air).
- Sponge: gas in solid → a foam (air trapped in a solid).
- Each type matches the dispersed phase and dispersing medium as given for colloids.