Imp Questions For All Chapters – General Science Class 8
Short Questions
1. What is a chemical change?
- A chemical change is a change where new substances are formed with different properties.
2. Give one example of a chemical change.
- Rusting of iron is a chemical change.
3. What is a physical change?
- A physical change is a change where no new substance is formed and the change can be reversed.
4. Give one example of a physical change.
- Melting of ice is a physical change.
5. What happens when iron rusts?
- Iron reacts with oxygen and water to form iron oxide (rust).
6. What gas is released when baking soda reacts with lemon juice?
- Carbon dioxide (CO₂) gas is released.
7. Which gas is necessary for combustion (burning)?
- Oxygen (O₂) is necessary for combustion.
8. What type of bond is present in water (H₂O)?
- Covalent bond is present in water.
9. What type of bond is present in sodium chloride (NaCl)?
- Ionic bond is present in sodium chloride.
10. What happens when carbon dioxide is passed through lime water?
- Lime water turns milky, indicating the presence of carbon dioxide.
11. Why is photosynthesis a chemical change?
- Because new substances like glucose and oxygen are formed.
12. What happens when iron nails are kept in copper sulphate solution?
- The iron nails get coated with copper, and the solution changes color.
13. What is an ionic bond?
- An ionic bond is formed when one atom transfers electrons to another atom.
14. What is a covalent bond?
- A covalent bond is formed when atoms share electrons.
15. Which element is a good example of covalent bonding?
- Carbon (C) forms strong covalent bonds.
16. What is a reactant?
- A reactant is a substance that takes part in a chemical reaction.
17. What is a product?
- A product is a new substance formed after a chemical reaction.
18. Which chemical reaction occurs in respiration?
- Glucose reacts with oxygen to produce energy, carbon dioxide, and water.
19. What happens when sodium reacts with chlorine?
- They form sodium chloride (NaCl) through ionic bonding.
20. Why does food spoil over time?
- Food spoils due to chemical changes caused by bacteria and oxidation.
Long Questions
1. What are the differences between physical and chemical changes?
- A physical change does not form a new substance and is reversible (e.g., melting ice). A chemical change forms a new substance with different properties and is irreversible (e.g., burning paper).
2. Why is rusting of iron considered a chemical change?
- Rusting happens when iron reacts with oxygen and water to form iron oxide (rust). Since a new substance is created with different properties, it is a chemical change.
3. What happens when baking soda is added to lemon juice?
- When baking soda reacts with citric acid in lemon juice, it produces bubbles of carbon dioxide gas. This is a chemical change because gas is formed, and the reaction cannot be reversed.
4. Why is respiration a chemical change?
- During respiration, glucose reacts with oxygen to produce carbon dioxide, water, and energy. Since new substances are formed and the process cannot be reversed, it is a chemical change.
5. What are ionic and covalent bonds?
- An ionic bond is formed when one atom transfers electrons to another (e.g., NaCl). A covalent bond is formed when two atoms share electrons (e.g., H₂O).
6. What happens when iron nails are placed in copper sulphate solution?
- Iron reacts with copper sulphate, forming iron sulphate and copper deposits on the nail. This changes the color of the solution, proving a chemical reaction has taken place.
7. Why does food spoil over time?
- Food spoils due to chemical reactions caused by bacteria, oxygen, and heat. These reactions change the smell, color, and taste of food, making it unsafe to eat.
8. Why is photosynthesis a chemical change?
- In photosynthesis, plants use carbon dioxide, water, and sunlight to produce glucose and oxygen. Since new substances are formed, it is an irreversible chemical change.
9. What happens when lime water is exposed to carbon dioxide?
- When carbon dioxide passes through lime water, it reacts with calcium hydroxide to form calcium carbonate, making the lime water turn milky. This reaction helps in testing for CO₂ gas.
10. What is the importance of chemical changes in daily life?
- Chemical changes are used in digestion, respiration, cooking, rusting, and burning. They help in energy production, food preservation, and making useful materials like medicines and plastics.
Leave a Reply