Test: Is Matter Around Us Pure- Assertion & Reason Type Questions - Class 9 MCQ

To separate a mixture of two or more miscible liquids for which difference in boiling point is less than 25C, fractional distillation process is used. It is a purification technique of separation of two or more miscible liquids. But reason doesnt justify the direction.

In separating funnel technique, immiscible liquids separate out in layers depending on their densities.

Explanation:

• Assertion (A): Impure benzoic acid can be purified by sublimation — This is true. Benzoic acid is one of the compounds that can be purified by sublimation because it sublimes upon heating, which helps to separate impurities that do not sublime.

• Reason (R): Benzoic acid sublimes on heating — This is also true. Benzoic acid transitions directly from a solid to a vapor when heated, skipping the liquid phase.

Since both the assertion and reason are correct, and the reason properly explains why benzoic acid can be purified by sublimation, option 1 is the correct choice.

Due to constant movement of particles colloidal particles do not settle down.

To determine the correct choice, let’s examine the Assertion and Reason:

Assertion (A): True solution exhibits Tyndall effect.

• True solutions do not exhibit the Tyndall effect because the particles in a true solution are too small to scatter light. The Tyndall effect is observed in colloidal solutions, where the particles are of intermediate size to scatter light.

Reason (R): Particles are very large in size.

• The Tyndall effect occurs because particles are of intermediate size, not very large. In colloids, the particles are of intermediate size (in the range of 1 nm to 1 μm) to scatter light, whereas in true solutions, the particles are too small to cause this scattering.

Given this analysis:

• Assertion (A) is false because true solutions do not exhibit the Tyndall effect.
• Reason (R) is also false because it incorrectly describes the size of particles that cause the Tyndall effect.

Thus, the correct answer is: c

Explanation: Both the statements are correct. Sublimation is a process where a substance changes directly from solid to vapour without passing through liquid state. On the other hand, distillation is a process that involves vaporization and condensation. However, the reason does not explain the assertion as both are different processes. Sublimation is a single step process, while distillation is a two-step process.

- Colloidal Solution Definition: A colloidal solution consists of particles that are larger than molecules but too small to settle out or be filtered easily. These particles are dispersed throughout a medium.

- Milk as a Colloid:
- Milk is a colloid known as an emulsion.
- It contains fat globules dispersed in water.
- The particles are large enough to scatter light (Tyndall effect), making milk appear opaque.

- To separate a mixture of sand and salt, use filtration.
- Add water to the mixture, dissolving the salt and leaving sand as a solid.
- Pour the mixture through a filter paper.
- Sand: Trapped by the filter paper as residue.
- Salt Solution: Passes through as filtrate.
- Evaporate the water from the filtrate to recover the salt.
- This method efficiently separates insoluble solids from soluble substances.