Is Matter Around Us Pure? - Practice Test, Class 9 Science - Class 9 MCQ

A saturated solution can dissolve a particular amount of solute at a given temperature and for further addition we need to increase or decrease the temperature.

Particle Size of Solute in True
The particle size of solute in a true solution refers to the size of individual particles or molecules that are dispersed uniformly in the solvent. These particles are extremely small and cannot be seen with the naked eye. The particle size is typically measured in meters (m) or nanometers (nm).
Order of Particle Size:
The order of the particle size of solute in a true solution is determined by the size range in which the particles fall. To determine the correct answer, we need to compare the given options.
A: 10-6 m
B: 10-7 m
C: 10-8 m
D: 10-9 m
The correct answer is D: 10-9 m. The particle size of solute in a true solution is in the nanometer range, which is typically between 1 to 100 nanometers. Therefore, the particle size is of the order of 10-9 m.
Explanation:
- True solutions are homogeneous mixtures where the solute particles are evenly distributed at the molecular level.
- The particles in a true solution are small and do not settle down due to gravity.
- The solute particles are individual molecules or ions that are smaller than 1 nanometer in size.
- The particle size of solute in a true solution is in the nanometer range, which is 10-9 meters.
- This tiny particle size allows the solute particles to be evenly dispersed throughout the solvent.
- The small particle size also contributes to the stability and transparency of true solutions.
Conclusion:
The particle size of solute in a true solution is of the order of 10-9 meters. This extremely small size allows for the uniform dispersion of solute particles throughout the solvent, resulting in a stable and transparent solution.

Properties of Carbon Dioxide:
- Carbon dioxide (CO2) is a colorless and odorless gas.
- It is denser than air and slightly soluble in water.
- CO2 is non-flammable and non-toxic in small concentrations.
- It does not support combustion or burn.
- CO2 is a greenhouse gas, contributing to global warming and climate change.
- It is formed when carbon (C) burns in the presence of oxygen (O2).
- The molecular formula of carbon dioxide is CO2, consisting of one carbon atom bonded to two oxygen atoms.
- The molecular weight of CO2 is approximately 44 grams per mole.
- Carbon dioxide is a stable compound and does not readily react with other substances under normal conditions.
- It is commonly used in various industries and applications such as carbonation of beverages, fire extinguishers, and as a coolant in refrigeration systems.
Therefore, the properties of carbon dioxide are totally different from both carbon and oxygen.

Substances that cannot be separated from sand by sublimation:


A: NaCl (sodium chloride)
- Sodium chloride cannot be separated from sand by sublimation because it does not undergo sublimation.
- Instead, sodium chloride undergoes a process called dissociation when heated, where it breaks down into its constituent elements (sodium and chlorine).
B: NH₄Cl (ammonium chloride)
- Ammonium chloride can be separated from sand by sublimation.
- When heated, ammonium chloride undergoes sublimation, converting from a solid to a gas without passing through the liquid phase. The gaseous ammonium chloride can be collected and separated from the sand.
C: Camphor
- Camphor can be separated from sand by sublimation.
- When heated, camphor undergoes sublimation, converting from a solid to a gas without passing through the liquid phase. The gaseous camphor can be collected and separated from the sand.
D: Iodine
- Iodine can be separated from sand by sublimation.
- When heated, iodine undergoes sublimation, converting from a solid to a gas without passing through the liquid phase. The gaseous iodine can be collected and separated from the sand.
Therefore, the substance that cannot be separated from sand by sublimation is NaCl (sodium chloride).

Separation of Alcohol and Water:
To separate a mixture of alcohol and water, different techniques can be used. One of the most common methods is fractional distillation.
Fractional Distillation:
Fractional distillation is a process that separates two or more liquids with different boiling points. In the case of alcohol and water, alcohol has a lower boiling point compared to water. This difference in boiling points allows for their separation through fractional distillation. Here's how it works:
1. Heating: The mixture of alcohol and water is heated in a distillation apparatus.
2. Vaporization: As the mixture is heated, the alcohol with the lower boiling point starts to vaporize first.
3. Condensation: The vapor rises through the fractionating column, which contains several trays or packed material. The rising vapor comes in contact with the cooler surfaces of the column and starts to condense.
4. Collection: The condensed alcohol vapor is collected as a liquid in a separate container.
5. Separation: The remaining water in the distillation apparatus is left behind and can be collected separately.
Other Methods:
While fractional distillation is the most effective method for separating alcohol and water, there are other techniques that can also be used, although they may not be as efficient:
1. Simple Distillation: This method is similar to fractional distillation but does not have a fractionating column. It is suitable when the mixture has a large difference in boiling points.
2. Separating Funnel: This method is applicable when the alcohol and water form two immiscible layers, such as when alcohol and water are mixed with an organic solvent. The layers can be separated based on their density using a separating funnel.
3. Sublimation: Sublimation is the process of converting a solid directly into a vapor without going through the liquid phase. While it is not commonly used for separating alcohol and water, it can be used if the mixture contains a solid form of alcohol that readily sublimes.
Conclusion:
In conclusion, the most effective method for separating a mixture of alcohol and water is fractional distillation. This process takes advantage of the difference in boiling points between the two components to separate them. Other methods such as simple distillation, separating funnel, and sublimation can also be used depending on the specific characteristics of the mixture.

Explanation:
Chemical changes involve the formation of new substances with different chemical properties. They typically result in the breaking and forming of chemical bonds. On the other hand, physical changes do not involve the formation of new substances and only alter the physical properties of a substance, such as its shape, size, or state of matter.
Now, let's analyze the given options:
A: Rusting of iron
- Rusting of iron involves a chemical reaction with oxygen in the presence of moisture, resulting in the formation of iron oxide (rust). This is a chemical change as new substances are formed.
B: Cooking of food
- Cooking of food is a chemical change as it involves the application of heat, which causes various chemical reactions such as denaturation of proteins, caramelization of sugars, and Maillard reactions. These reactions result in the formation of new compounds and changes in the taste, texture, and aroma of the food.
C: Freezing of water
- Freezing of water is a physical change. It involves the conversion of liquid water into solid ice, but no new substances are formed. The water molecules simply arrange themselves in a more ordered structure.
D: Digestion of food
- Digestion of food is a complex process involving various chemical reactions. Enzymes and digestive juices break down the food into smaller molecules that can be absorbed by the body. This is a chemical change as new substances are formed during the digestion process.
Therefore, the correct answer is C: Freezing of water, as it is a physical change rather than a chemical change.

A true solution is a homogeneous mixture.
A true solution is a type of mixture where the solute particles are evenly distributed throughout the solvent. It is characterized by the following properties:
Homogeneous Mixture:
- A true solution is a homogeneous mixture because the solute particles are uniformly dispersed in the solvent.
- The composition of the solution is the same throughout, and there is no visible separation of the components.
- The solute particles are at the molecular or ionic level and are dispersed at the molecular level in the solvent particles.
- Examples of true solutions include saltwater, sugar dissolved in water, and air.
Characteristics of a True
- Homogeneity: The solution appears uniform throughout, with no visible particles or separation.
- Transparency: True solutions are usually transparent or clear, allowing light to pass through without scattering.
- Particle Size: The solute particles in a true solution are very small, usually less than 1 nanometer in diameter.
- Stability: The solute particles remain dispersed in the solvent due to the balanced forces between the solute and solvent particles.
- No Settling: Unlike suspensions or colloids, true solutions do not settle over time.
Summary:
- A true solution is a homogeneous mixture where the solute particles are uniformly dispersed in the solvent.
- It is characterized by its homogeneity, transparency, small particle size, stability, and lack of settling.
- Examples of true solutions include saltwater, sugar dissolved in water, and air.
- True solutions play a crucial role in various fields, including chemistry, biology, and medicine.

Fractional Crystallization
Fractional crystallization is a separation technique commonly used in chemistry to separate two or more substances based on their different solubilities. It relies on the principle that different substances have different solubilities at different temperatures.
Process of Fractional Crystallization
1. Dissolving: The mixture of substances is dissolved in a suitable solvent, usually a liquid.
2. Heating: The solution is heated to increase the solubility of the substances. This allows all the substances to dissolve completely.
3. Cooling: The solution is slowly cooled down, causing the solubility of the substances to decrease. As a result, crystals of one of the substances start to form.
4. Separation: The formed crystals are carefully separated from the remaining liquid. This can be done by filtration or decantation.
5. Recovery: The separated crystals are then dried to remove any remaining solvent.
Application of Fractional Crystallization
Fractional crystallization is commonly used to separate two solids. This is because solids tend to have different solubilities in a given solvent, allowing for the selective crystallization of one substance while leaving the other behind in the solution. It is particularly useful when the substances have significantly different melting points or boiling points.
Therefore, the correct answer is A: Two solids.

Explanation:
To determine which substance does not sublime, we need to understand the process of sublimation. Sublimation is the phase transition in which a solid directly converts into a gas without passing through the liquid state. The substance that does not undergo sublimation will either melt or decompose when heated.
Substances:
A:

Camphor

- Camphor is known to sublime when heated. It directly converts from a solid to a gas without melting.
B:

Charcoal

- Charcoal does not sublime. Instead, it undergoes a process called combustion, in which it reacts with oxygen to produce carbon dioxide and other byproducts.
C:

Naphthalene

- Naphthalene is a compound that readily undergoes sublimation. It can transform from a solid to a gas without melting.
D:

Iodine

- Iodine is another substance that sublimes when heated. It bypasses the liquid state and directly changes from a solid to a gas.
Conclusion:
Based on the information provided, the substance that does not sublime is Charcoal (Option B). Unlike the other options, charcoal undergoes combustion rather than sublimation when heated.

The given mixture of mercury and copper is an example of a liquid and solid mixture. Here is a detailed explanation:
1. Introduction:
- The question asks about the mixture of mercury and copper.
- We need to determine the state of each component in the mixture.
2. Mercury:
- Mercury is a liquid at room temperature.
- It has a low melting point of -38.83°C and a boiling point of 356.73°C.
- Therefore, mercury is a liquid component in the mixture.
3. Copper:
- Copper is a solid at room temperature.
- It has a melting point of 1084.62°C and a boiling point of 2562°C.
- Therefore, copper is a solid component in the mixture.
4. Mixture of Mercury and Copper:
- Since mercury is a liquid and copper is a solid, their combination forms a liquid and solid mixture.
- The liquid mercury will act as a solvent, while the solid copper will act as a solute.
- The copper particles will be dispersed in the liquid mercury, forming a heterogeneous mixture.
5. Answer:
- Based on the above analysis, the correct answer is option B: Liquid and solid.
In conclusion, the mixture of mercury and copper is an example of a liquid and solid mixture, where the liquid mercury acts as a solvent and the solid copper acts as a solute.

To determine which property does not describe a compound, let's analyze each option:
A: It is a pure substance.
- Compounds are pure substances because they consist of a fixed ratio of different elements.
B: It is mixed in any proportion by mass.
- This property does not describe a compound because compounds have a fixed composition, meaning they are made up of specific elements in a specific ratio.
C: It cannot be separated into constituents by physical means.
- Compounds cannot be separated into their constituent elements by physical means. They can only be broken down into their elements through chemical reactions.
D: It is composed of two or more elements.
- This property describes compounds. Compounds are made up of two or more different elements chemically bonded together.
Therefore, the property that does not describe a compound is B: It is mixed in any proportion by mass.

To determine which of the following is not a mixture, we need to understand the definition of a mixture. A mixture is a substance that consists of two or more different substances that are not chemically combined.
Let's analyze each option:
A: Blood
Blood is a mixture because it contains various components such as red blood cells, white blood cells, platelets, and plasma.
B: Silver coins
Silver coins are not a mixture as they are made of pure silver. Therefore, they consist of only one substance.
C: Saliva
Saliva is a mixture as it contains water, enzymes, electrolytes, mucus, and other substances.
D: Plutonium
Plutonium is not a mixture as it is an element with the atomic number 94. It consists of only one type of atom.
Therefore, the correct answer is D: Plutonium because it is not a mixture.

This process is generally used for those mixtures, where the difference in the boiling points of the two liquids is less than 15 K. Acetone boils at 330 K while methyl alcohol at 338 K, therefore, these two liquids are separated by the fractional distillation process. This is similar to the ordinary distillation method with the only exception that a fractionating column is introduced in between the distillation flask and the condenser.

The process of separation of the components of a liquid mixture at their respective boiling points in the form of vapours and the subsequent condensation of these vapours is called fractional distillation.

Suspension is heterogeneous mixture which contains solid particles for sedimentation the particle usually be larger than 1 micrometre and will eventually settle and the particles may be visible to naked eyes.

Components retain their properties in a Mixture.

Explanation:

A mixture refers to a combination of two or more substances that are physically combined but not chemically bonded. In a mixture, the components retain their individual properties, and they can be separated by physical means. Here are some key points to support this answer:

• Definition of a mixture: A mixture is a combination of two or more substances that are not chemically joined and can be separated by physical means.


• Physical properties: Each component of a mixture retains its own physical properties such as color, shape, size, density, boiling point, and melting point.


• No chemical reaction: In a mixture, the components do not undergo any chemical reaction or change in their chemical composition.


• Separation methods: The components of a mixture can be separated using techniques like filtration, distillation, evaporation, and chromatography.


• No fixed ratio: Unlike compounds, mixtures can have varying ratios of components. There is no fixed ratio between the substances in a mixture.

Therefore, the correct answer is B: Mixture.

Gases can be separated from each other by fractional distillation.
Explanation:
Fractional distillation is a process used to separate mixtures of liquids with different boiling points. It is based on the principle that each component of the mixture has a different boiling point, and therefore, they can be separated by heating the mixture and collecting the vapors at different temperatures.
Here is a detailed explanation of fractional distillation as a method for separating gases:
1. Principle: Fractional distillation takes advantage of the fact that different gases have different boiling points. By heating the mixture of gases, each gas will vaporize and condense at its respective boiling point.
2. Setup: The mixture of gases is introduced into a fractional distillation column, which is a tall vertical column with several horizontal trays or plates. The column is equipped with a heat source at the bottom and a condenser at the top.
3. Heating: The mixture of gases is heated at the bottom of the column. As the temperature increases, the gas with the lowest boiling point will start to vaporize and rise up the column.
4. Fractionation: As the vapor rises through the column, it will encounter the cooler plates or trays. At each tray, the vapor will partially condense, with the gas with the highest boiling point condensing first and the gas with the lowest boiling point continuing to rise.
5. Collection: The condensed liquid on each tray is collected and removed from the column. This liquid is enriched in the higher boiling point gases.
6. Final separation: The vapor that reaches the top of the column is condensed by the condenser and collected separately. This vapor is enriched in the gas with the lowest boiling point.
7. Repeating the process: The process of heating, vaporization, partial condensation, and collection is repeated several times in the column to achieve a higher degree of separation.
8. Obtaining pure gases: By collecting the condensed liquids and the final vapor separately, it is possible to obtain individual gases in a more purified form.
Fractional distillation is widely used in industrial processes to separate and purify gases. It is an efficient method for separating gases with different boiling points and plays a crucial role in various industries such as petrochemicals, oil refining, and gas processing.

Non-Metal from the given options:
- Diamond: Diamond is a form of carbon and is classified as a non-metal.
- Gold: Gold is a metal and not a non-metal.
- Silver: Silver is a metal and not a non-metal.
- Platinum: Platinum is a metal and not a non-metal.
Therefore, the non-metal from the given options is Diamond.

Shaving cream is a colloidal solution of gas in liquid.
Colloidal solutions are a type of mixture where the particle size of the dispersed phase is between 1-1000 nanometers. These particles are evenly distributed throughout the solution and do not settle down due to gravity. Shaving cream is a perfect example of a colloidal solution.
Gas in Liquid:
In the case of shaving cream, the dispersed phase is gas, which is usually carbon dioxide. It is trapped within a liquid medium, which is usually water or oil. The gas is dispersed in the liquid to form a stable foam-like structure.
Structure of Shaving Cream:
Shaving cream consists of tiny gas bubbles, which are surrounded by a liquid layer. The gas bubbles act as the dispersed phase, and the liquid layer acts as the continuous phase. This structure gives the shaving cream its characteristic texture and allows it to spread easily on the skin.
Stability of Shaving Cream:
The stability of shaving cream as a colloidal solution is due to the presence of surfactants. Surfactants are compounds that lower the surface tension between two substances, in this case, the gas and liquid phases. They help in the formation and stabilization of the gas bubbles in the liquid.
Conclusion:
Therefore, shaving cream is a colloidal solution of gas in liquid. The gas phase (carbon dioxide) is dispersed in the liquid phase (water or oil) to form a stable foam-like structure.

Explanation:

A pure substance is a substance that is made up of only one type of particle and has a uniform and definite composition. It cannot be separated into other substances by physical means.

Out of the given options, sodium chloride (A) can be termed as a pure substance because:

• It is made up of only one type of particle, which is the ionic compound NaCl.


• It has a uniform and definite composition, with each NaCl unit being identical.


• It cannot be separated into other substances by physical means, such as filtration or distillation.

On the other hand, the other options do not meet the criteria of a pure substance:

• Soft drink (B) is a mixture of various substances, such as water, sugar, flavorings, and carbon dioxide.


• Aerosol (C) is a suspension of solid or liquid particles in a gas. It is also a mixture.


• Soil (D) is a complex mixture of organic matter, minerals, water, and air. It is not a pure substance.

Therefore, the correct answer is A: Sodium chloride.