HOTS Questions: Is Matter Around Us Pure - Class 9 MCQ

1. Starch solution

Explanation: A colloidal solution consists of tiny particles suspended in a continuous medium. The particle size in a colloid is between that of a true solution and a suspension, meaning the particles do not settle out upon standing.

• Starch solution is a colloid because the starch particles are small enough to remain suspended in water without settling.
• Copper sulphate solution is a true solution, not a colloid.
• Chalk powder in water is a suspension, as the chalk particles settle down when left undisturbed.
• Kerosene oil and water form an immiscible liquid mixture, not a colloid.

Thus, starch solution is the correct example of a colloidal solution.

Topic in NCERT: WHAT IS A COLLOIDAL SOLUTION?

Line in NCERT: "The mixture obtained by group D in activity 2.2 is called a colloid or a colloidal solution."

Physical Changes:
A physical change is a change in the state or form of matter without any change in the chemical composition or identity of the substance. In other words, the substance remains the same before and after the change.
Examples of Physical Changes:
A. Burning of a Natural Gas:
- This is a clear example of a combustion reaction. Natural gas comprehends methane gas. When methane reacts with oxygen in the atmosphere it produces water and carbon dioxide.
B. Rusting of iron:
- This is a chemical change, not a physical change. Rusting occurs when iron reacts with oxygen in the presence of moisture, forming iron (III) oxide (rust).
C. Freezing of water:
- This is a physical change. When water is cooled below its freezing point, it undergoes a phase change from a liquid to a solid, forming ice. The chemical composition of water (H2O) remains the same.
D. Digestion of food:
- This is a chemical change, not a physical change. Digestion involves the breakdown of complex food molecules into simpler substances through various chemical reactions in the digestive system.
Conclusion:
The freezing of water is the only example mentioned that represents a physical change. The other options involve chemical changes.

Topic in NCERT: Physical and Chemical Changes

Line in NCERT: "The interconversion of states is a physical change because these changes occur without a change in composition and no change in the chemical nature of the substance."

To determine the solubility of each compound at 293 K, we can compare their solubility product constants (Ksp). The higher the Ksp value, the greater the solubility of the compound.
The Ksp values for the given compounds are:
A: KNO3 - 37.0
B: NaCl - 36.0
C: KCl - 74.5
D: NH4Cl - 52.0
From the given options, compound D (NH4Cl) has the highest Ksp value of 52.0. Therefore, NH4Cl has the highest solubility at 293 K among the given compounds.
Key Points:
- Solubility can be determined by comparing the solubility product constants (Ksp) of compounds.
- The higher the Ksp value, the greater the solubility of the compound.
- Compound D (NH4Cl) has the highest Ksp value of 52.0 among the given options.
- Therefore, NH4Cl has the highest solubility at 293 K.

Topic in NCERT: Solubility of Salts at Different Temperatures

Line in NCERT: "Find the solubility of each salt at 293 K. Which salt has the highest solubility at this temperature?"

Yes, homogenous mixture have a variable composition as the constituents are present in any ratio such as 1:2 or 1:3 etc

Topic in NCERT: TYPES OF MIXTURES

Line in NCERT: "this shows that a homogeneous mixture can have a variable composition."

Mass of common salt (solute) = 40g
Mass of water (soluted) = 320g
Mass of solution = 320 + 40 = 360g
Concentration of solution = M(mass of solute) / mass of solution = 40/360 x 100 = 11.11%

Topic in NCERT: Mass by mass percentage of a solution

Line in NCERT: "Example 2.1 A solution contains 40 g of common salt in 320 g of water. Calculate the concentration in terms of mass by mass percentage of the solution."

The particles of suspension:
- Can be seen with the naked eye. Suspensions are heterogeneous mixtures in which solid particles are dispersed in a liquid or gas. These particles are usually large enough to be visible to the naked eye.
- Cannot be seen with a powerful microscope. While the particles in a suspension may not be visible under a powerful microscope, they can still be seen without the aid of any magnification.
- Cannot be seen with an electron microscope. Electron microscopes are capable of magnifying objects to a much higher degree than light microscopes, but even they may not be able to visualize the particles in a suspension due to their size and distribution.
- Are larger than the particles in a solution. In contrast to solutions, where the solute particles are evenly distributed and too small to be seen, the particles in a suspension are larger and can settle over time due to gravity.
- Can be separated by filtration or settling. Since the particles in a suspension are larger and more visible, they can be separated from the liquid or gas phase through processes such as filtration or allowing them to settle and then decanting the liquid above.

Topic in NCERT: WHAT IS A SUSPENSION?

Line in NCERT: "Particles of a suspension are visible to the naked eye."

Statement: Compound is homogeneous and have fixed composition.

Definition of compound:
- A compound is a substance that is composed of two or more elements chemically combined in a fixed ratio.
- It has its own unique set of properties that are different from the properties of its constituent elements.
Explanation:
- A homogeneous mixture is a mixture that has a uniform composition throughout, meaning that the components are evenly distributed.
- A compound is a type of homogeneous mixture because it has a fixed composition.
- The elements in a compound are combined in a specific ratio, which means that the relative amounts of the elements are always the same.
- This fixed composition gives compounds their distinct properties and makes them different from mixtures.
Key points:
- A compound is homogeneous, meaning it has a uniform composition throughout.
- The composition of a compound is fixed, with elements combined in a specific ratio.
- Compounds have distinct properties that are different from the properties of their constituent elements.
Conclusion:
The correct statement is option A: Compound is homogeneous and has a fixed composition.

Topic in NCERT: Compounds

Line in NCERT: "The composition of a compound is the same throughout."

Correct answer is c

   The process by which we can separate the particles of a colloidal solution is called Centrifugation.

Topic in NCERT: WHAT IS A COLLOIDAL SOLUTION?

Line in NCERT: "But, a special technique of separation known as centrifugation can be used to separate the colloidal particles."

Explanation:
When a substance undergoes a physical change, its composition remains the same. This means that the atoms or molecules that make up the substance do not rearrange or combine with other atoms or molecules to form a new substance. Instead, the physical properties of the substance may change, such as its shape, size, density, state (solid, liquid, gas), or phase (melting, freezing, boiling, condensation).
Key points:
- Physical change refers to a change in the physical properties of a substance without any change in its chemical composition.
- In a physical change, the substance may change its state (e.g., from solid to liquid or gas) or undergo a change in physical properties (e.g., color, shape, size), but the composition of the substance remains the same.
- The atoms or molecules that make up the substance do not rearrange or combine with other atoms or molecules to form a new substance.
- Examples of physical changes include melting ice, boiling water, dissolving salt in water, and crushing a can.

Topic in NCERT: Physical and Chemical Changes

Line in NCERT: "The interconversion of states is a physical change because these changes occur without a change in composition and no change in the chemical nature of the substance."

Separating Kerosene Oil and Water

To separate kerosene oil and water, you can use the following methods:
1. Separating Funnel:
- A separating funnel is a glassware commonly used in laboratories to separate immiscible liquids (liquids that do not mix together).
- You can pour the mixture of kerosene oil and water into the separating funnel and allow it to stand until the two liquids separate into distinct layers based on their densities.
- Carefully open the stopcock at the bottom of the funnel and collect the kerosene oil in a separate container.
2. Distillation:
- Distillation is a process that involves heating a mixture to separate its components based on their boiling points.
- In this case, the mixture of kerosene oil and water is heated, and the kerosene oil, having a lower boiling point, vaporizes and can be collected separately.
- The water, having a higher boiling point, remains in the distillation flask.
3. Centrifugation:
- Centrifugation is a technique used to separate substances of different densities by spinning them at high speeds.
- By placing the kerosene oil and water mixture in a centrifuge and spinning it, the denser water will move to the bottom, while the less dense kerosene oil will accumulate at the top, allowing for separation.
4. Evaporation:
- Evaporation involves heating a mixture to convert the liquid components into vapor, leaving behind the solid or liquid that does not evaporate.
- In this case, the mixture of kerosene oil and water can be heated to evaporate the kerosene oil, which has a lower boiling point.
- The water will remain in the container while the kerosene oil evaporates and can be collected separately.
In conclusion, kerosene oil and water can be separated by using a separating funnel, distillation, centrifugation, or evaporation, depending on the specific requirements and equipment available.

Topic in NCERT: TYPES OF MIXTURES

Line in NCERT: "Mixtures of sodium chloride and iron filings, salt and sulphur, and oil and water are examples of heterogeneous mixtures."