2. Give short answer.
(i) Can you write the formula of the carbon dioxide gas that we exhale?
Answer: The chemical formula of carbon dioxide gas that we exhale is CO₂. It is composed of one carbon atom and two oxygen atoms. Carbon dioxide is a colorless, odorless gas that is a product of cellular respiration in humans and animals. It is also a greenhouse gas and is involved in the carbon cycle. It is produced when we breathe out and is essential for plant photosynthesis.
(ii) Define the element, Compound, Mixture.
Answer:
Element: A pure substance consisting of only one type of atom, which cannot be broken down into simpler substances by chemical means (e.g., hydrogen, oxygen, gold). Compound: A pure substance formed when two or more different elements are chemically combined in fixed
proportions (e.g., water, carbon dioxide). Mixture: A combination of two or more substances that are physically combined but not chemically bonded, and can be separated by physical means (e.g., air, saltwater).
(iii) Differentiate between compound and mixture.
Answer:
| Feature | Compound | Mixture |
| Composition | Fixed ratio of elements. | Variable ratio of components. |
| Bonding | Chemically bonded. | Physically combined. |
| Separation | Can only be separated by chemical means. | Can be separated by physical means. |
| Properties | Properties are different from constituent elements. | Properties are similar to constituent substances. |
| Example | Water (H₂O). | Saltwater. |
(iv) Differentiate between concentrated and dilute solution.
Answer:
Concentrated Solution: A solution that contains a large amount of solute dissolved in a given amount of solvent. It has a high solute-to-solvent ratio. Dilute Solution: A solution that contains a small amount of solute dissolved in a given amount of solvent. It has a low solute-to-solvent ratio. The concentration can be increased by adding more solute or evaporating solvent, and decreased by adding more solvent.
3. Define the term Allotropes Explain the allotropes of Carbon.
Answer: Allotropes are different structural forms of the same element in the same physical state. Allotropes have different physical properties but the same chemical properties because they are made of the same element. Allotropes of Carbon:
Diamond: A tetrahedral network of carbon atoms, hardest known natural substance, used in cutting tools. Graphite: Layers of hexagonal carbon rings, soft, slippery, used in pencils and lubricants. Fullerenes: Spherical, tube-like, or cage-like carbon molecules (e.g., C₆₀ Buckminsterfullerene). Graphene: A single layer of graphite, extremely strong and conductive. Carbon Nanotubes: Cylindrical carbon structures with unique properties.
4. What is difference between Homogeneous and heterogeneous solution?
Answer:
| Feature | Homogeneous Solution | Heterogeneous Solution |
| | |
| Composition | Uniform composition throughout. | Non-uniform composition. |
| Phases | Single phase. | Multiple phases. |
| Visibility | Components are not visible. | Components are visible. |
| Separation | Cannot be separated by filtration. | Can be separated by filtration. |
| Example | Saltwater, air. | Sand and water, oil and water. |
5. Differentiate between the colloids, suspension and solution.
Answer:
| Feature | Solution | Colloid | Suspension |
| Particle Size | < 1 nm | 1-1000 nm | > 1000 nm |
| Appearance | Transparent | Translucent | Opaque |
| Visibility | Not visible | Visible under microscope | Visible to naked eye |
| | | |
| Settling | Does not settle | Does not settle | Settles on standing |
| Tyndall Effect | Not shown | Shown | May be shown |
| Example | Saltwater | Milk, fog | Sand in water |
6. If there are 18 protons in the Argon atom, then what is the atomic number of Argon?
Answer: The atomic number of an element is defined as the number of protons in the nucleus of its atom. Since Argon has 18 protons, its atomic number is 18. This determines its position in the periodic table and its chemical identity. In a neutral atom, the number of electrons equals the number of protons, so Argon also has 18 electrons.
7. Describe State of matter with example.
Answer: Matter exists in three primary states:
Solid: Definite shape and volume. Particles are tightly packed and vibrate in fixed positions. Example: Ice, iron, wood. Liquid: Definite volume but no definite shape; takes the shape of the container. Particles are close but can move past each other. Example: Water, oil, alcohol. Gas: No definite shape or volume; fills the container. Particles are far apart and move freely. Example: Oxygen, carbon dioxide, nitrogen.
8. Differentiate between the following.
(a) Colloids and Suspensions (Refer to Question 5)
(b) Elements and Compounds
Answer: Elements are pure substances made of only one type of atom (e.g., H₂, O₂). Compounds are pure substances made of two or more different elements chemically bonded in fixed ratios (e.g., H₂O, CO₂).
(c) Concentrated and Dilute solutions (Refer to Question 2(iv))
9. Examine the concept of solubility.
Answer: Solubility is the maximum amount of a solute that can be dissolved in a given amount of solvent at a specific temperature and pressure to form a saturated solution. It is usually expressed in grams of solute per 100 grams of solvent. Solubility depends on:
Nature of Solute and Solvent: "Like dissolves like" (polar solutes dissolve in polar solvents). Temperature: Solubility of solids generally increases with temperature; solubility of gases decreases with temperature. Pressure: Solubility of gases increases with pressure (Henry's Law). Solubility is a key concept in chemistry, biology, and industry.
