CBSE Class 9 Science Chapter 2: Is Matter Around Us Pure NCERT Solutions

Solution: A pure substance is defined as a material that is composed of only one type of particle. This means that all the constituent particles within the substance possess the same chemical nature. Pure substances can be further categorized into two main types: elements and compounds.

Solution:

Here are the key differences between homogeneous and heterogeneous mixtures:

• Homogeneous Mixture: This type of mixture has a uniform composition throughout its entire volume. The components are evenly distributed, and you cannot distinguish between them visually. Examples include salt dissolved in water, sugar dissolved in water, copper sulphate dissolved in water, alloys like brass, and air.
• Heterogeneous Mixture: This type of mixture has a non-uniform composition. The components are not evenly distributed, and different parts of the mixture may have different properties or compositions. Examples include a mixture of sodium chloride and iron filings, salt and sulphur mixed together, oil and water, chalk powder in water, and wheat flour in water.

Solution:

The primary distinction between homogeneous and heterogeneous mixtures lies in the uniformity of their composition:

Homogeneous Mixtures: These mixtures exhibit a uniform composition and properties throughout. The components are completely blended, making them indistinguishable even under a microscope. Examples include:

• Mixtures of salt in water, sugar in water, or copper sulphate in water.
• Iodine dissolved in alcohol.
• Alloys, which are solid solutions of metals or metals and non-metals (e.g., brass, steel).
• Air, which is a uniform mixture of gases.

Heterogeneous Mixtures: These mixtures have a non-uniform composition, meaning the composition and properties vary from one part of the mixture to another. The components are often visibly distinct. Examples include:

• Mixtures of sodium chloride and iron filings, where the iron filings can be separated magnetically.
• Mixtures of salt and sulphur, where both components retain their individual properties.
• Oil and water, which do not mix and form distinct layers.
• Chalk powder or wheat flour suspended in water, where the particles are visible and eventually settle.
• Milk and water, where the fat globules in milk are not uniformly distributed at a molecular level.

Solution:

Sol, solution, and suspension are all types of mixtures, but they differ significantly in their composition, particle size, and properties:

Solution: A solution is a homogeneous mixture where the solute particles are dissolved completely and spread uniformly throughout the solvent. The particle size is extremely small (typically less than 1 nanometer), making them invisible to the naked eye and unable to scatter light. Therefore, solutions do not exhibit the Tyndall effect. Examples include salt in water, sugar in water, and alloys.

Sol: A sol is a type of heterogeneous mixture where the solute particles are dispersed throughout the solvent but are larger than those in a true solution (typically between 1 nanometer and 1 micrometer). These particles are usually too small to be seen with the naked eye but are large enough to scatter light, causing the mixture to exhibit the Tyndall effect. Examples include milk of magnesia, mud, and milk itself.

Suspension: A suspension is also a heterogeneous mixture characterized by larger dispersed particles (typically greater than 1 micrometer). These particles are often visible to the naked eye and remain suspended in the medium. They tend to settle down over time if left undisturbed. Suspensions also exhibit the Tyndall effect because the larger particles scatter light. Examples include chalk powder in water and wheat flour in water.