Grade 9 Chemistry
🔴 REVIEW QUESTIONS (MCQs)
1. Encircle the correct answer:
📝 WRITTEN QUESTIONS
2. Give short answer:
(i) Can you write the formula of the carbon dioxide gas that we exhale?
The formula for carbon dioxide is CO₂
(ii) Define the element, Compound, Mixture
Element: A pure substance that cannot be broken down into simpler substances by chemical means. It consists of only one type of atom.
Compound: A substance formed when two or more different elements combine chemically in a fixed ratio.
Mixture: A combination of two or more substances that are physically mixed together but not chemically combined.
(iii) Differentiate between compound and mixture
Compound: Chemically combined, fixed composition, properties different from constituent elements, can only be separated by chemical methods.
Mixture: Physically mixed, variable composition, retains properties of constituents, can be separated by physical methods.
(iv) Differentiate between concentrated and dilute solution
Concentrated Solution: Contains a large amount of solute dissolved in a given amount of solvent.
Dilute Solution: Contains a small amount of solute dissolved in a given amount of solvent.
3. Define the term Allotropes. Explain the allotropes of Carbon
Allotropes: Different physical forms of the same element in which the atoms are arranged differently.
Allotropes of Carbon:
• Diamond: Each carbon atom is bonded to four other carbon atoms in a tetrahedral arrangement. Very hard and used in jewelry and cutting tools.
• Graphite: Carbon atoms are arranged in layers with weak forces between layers. Soft, conducts electricity, used in pencils.
• Fullerenes: Cage-like structures with 60 or more carbon atoms, including buckyballs and carbon nanotubes.
4. What is the difference between Homogeneous and Heterogeneous solution?
Homogeneous Solution: A solution where the solute is completely dissolved and uniformly distributed throughout the solvent. The composition is the same throughout. Example: Salt water, sugar water.
Heterogeneous Solution: A mixture where the components are not uniformly distributed and can be distinguished from each other. Example: Oil and water, sand and water.
5. Differentiate between the Colloids, Suspension
Colloids:
• Particle size: 1-100 nanometers
• Particles don't settle on standing
• Show Tyndall effect (light scattering)
• Cannot be separated by filtration
• Examples: Milk, fog, smoke
Suspension:
• Particle size: Greater than 100 nanometers
• Particles settle on standing
• Do not show Tyndall effect
• Can be separated by filtration
• Examples: Muddy water, chalk in water
6. How can you identify solvent and solute?
Solute: The substance that is dissolved (usually present in smaller amount)
Solvent: The substance that does the dissolving (usually present in larger amount)
Identification: In a solution, the component present in larger quantity is usually the solvent, and the one present in smaller quantity is the solute. For example, in salt water, water is the solvent and salt is the solute.
7. If there are 18 protons in the Argon atom, then what is the atomic number of Argon?
The atomic number equals the number of protons in an atom.
Since Argon has 18 protons, the atomic number of Argon is 18.
8. Describe State of matter with example
Solid: Definite shape and volume, particles closely packed, strong intermolecular forces. Example: Ice, wood, iron
Liquid: Definite volume but no definite shape, takes shape of container, moderate intermolecular forces. Example: Water, oil, mercury
Gas: No definite shape or volume, particles far apart, weak intermolecular forces. Example: Air, oxygen, carbon dioxide
Plasma: Ionized gas with free electrons and ions, found at very high temperatures. Example: Stars, lightning, neon signs
9. Differentiate between the following:
a. Colloids and Suspensions (Already answered in question 5)
b. Elements and Compounds
Elements: Pure substances with only one type of atom, cannot be broken down chemically. Examples: Oxygen (O₂), Gold (Au)
Compounds: Formed by chemical combination of two or more elements in fixed ratios. Examples: Water (H₂O), Salt (NaCl)
c. Concentrated and Dilute solutions (Already answered in question 2)
10. Examine the concept of solubility
Solubility: The maximum amount of solute that can be dissolved in a given amount of solvent at a specific temperature and pressure.
Factors affecting solubility:
• Temperature: Generally, solubility of solids increases with temperature, while gas solubility decreases
• Pressure: Affects gas solubility (Henry's Law)
• Nature of solute and solvent: "Like dissolves like" - polar dissolves polar, non-polar dissolves non-polar
• Particle size: Smaller particles dissolve faster
🧠 THINK TANK
11. Why is a solution considered mixture?
A solution is considered a mixture because:
• It contains two or more substances (solute and solvent)
• The components retain their chemical identity
• The composition can be varied (different concentrations possible)
• The components can be separated by physical methods like evaporation
• No new chemical bonds are formed between solute and solvent
12. How will you test weather given solution is a colloid or a solution?
Tyndall Effect Test:
• Pass a beam of light through the given solution
• If the light beam is visible (scattered), it's a colloid
• If the light beam is not visible (not scattered), it's a true solution
Other tests:
• Filtration: Colloids cannot be filtered through ordinary filter paper
• Brownian motion: Colloidal particles show random motion under microscope
🎨 PROJECT
Create a poster that illustrates the various form of matter in the students everyday environment
Poster Ideas - "Matter Around Us":
SOLIDS in our environment:
• Furniture (chairs, tables, beds)
• Books and stationery
• Rocks, stones, buildings
• Ice cubes, frozen foods
LIQUIDS in our environment:
• Water in bottles, taps, rivers
• Milk, juices, soft drinks
• Oil for cooking
• Rain water
GASES in our environment:
• Air we breathe
• Steam from hot water
• Gas in balloons
• Car exhaust
PLASMA in our environment:
• Lightning during storms
• Neon signs and fluorescent lights
• Fire flames
• The Sun and stars
Design Tips: Use colorful illustrations, label each state clearly, show examples from home, school, and nature!
🔑 KEY POINTS SUMMARY
• Matter has mass and occupies space
• Elements, compounds, and mixtures are different forms of matter
• Solutions, colloids, and suspensions are types of mixtures
• Allotropes are different forms of the same element
• Tyndall effect helps identify colloids
• Atomic number equals number of protons
