Class 10th Science: Short Answers: Chemical Reactions and Equation | Acid, Bases and Salts | Our Environment | Life Processes | Control and Coordination | Old CBSE Board Exam Pattern

By Vandita Tiwari

Chemical Reactions and Equations (12 questions)

  1. Write a balanced chemical equation for the reaction between zinc and dilute sulphuric acid. Identify the type of reaction.
  2. Explain why iron articles are painted.
  3. What is a displacement reaction? Give one example with equation.
  4. Balance the following:
    Na + H₂O → NaOH + H₂
  5. Define corrosion. How can it be prevented?
  6. Write the balanced equation for the decomposition of lead nitrate on heating. Mention the type of reaction.
  7. Differentiate between a chemical change and a physical change with examples.
  8. Why is respiration considered an exothermic reaction?
  9. Write the balanced chemical equation for the reaction of calcium oxide with water.
  10. Give two examples of redox reactions.
  11. What is precipitation reaction? Give one example.
  12. Write a balanced equation for the reaction between aluminium and iron(III) oxide. State its use.

Acids, Bases and Salts (12 questions)

  1. Why does dry HCl gas not change the colour of dry litmus paper?
  2. Write the chemical equation for the reaction of sodium carbonate with hydrochloric acid.
  3. Explain why an aqueous solution of an acid conducts electricity.
  4. State the chemical name of bleaching powder. How is it prepared?
  5. Why does tooth enamel get damaged when the pH of the mouth is lower than 5.5?
  6. How is baking soda prepared? Write its chemical equation.
  7. What is a neutralisation reaction? Give an example.
  8. Why is Plaster of Paris stored in a moisture-proof container?
  9. Name the acid present in ant sting and give its chemical formula.
  10. Give one use each of:
    (i) Bleaching powder
    (ii) Baking soda
    (iii) Washing soda
  11. Write the balanced chemical equation for the preparation of washing soda from baking soda.
  12. What is the pH range of an acidic solution?

Our Environment (12 questions)

  1. Define biodegradable substances with examples.
  2. Why is energy flow in an ecosystem unidirectional?
  3. State two differences between a food chain and a food web.
  4. Name two non-biodegradable pollutants of the environment.
  5. What is ozone? How is it formed in the upper atmosphere?
  6. What is biomagnification? Give an example.
  7. Give two ways in which biodegradable substances affect the environment.
  8. What is meant by “biological magnification”?
  9. State two methods of proper disposal of domestic waste.
  10. Why are some substances biodegradable and others non-biodegradable?
  11. Why is ozone layer depletion a cause of concern?
  12. How do decomposers help in maintaining the fertility of soil?

Life Processes (12 questions)

  1. Define autotrophic nutrition. Give an example.
  2. Why is the small intestine in herbivores longer than in carnivores?
  3. What is the role of the diaphragm in the process of breathing?
  4. What is translocation? Which tissue is involved in it?
  5. Write the equation for photosynthesis.
  6. State two differences between aerobic and anaerobic respiration.
  7. Name the enzyme present in saliva. State its function.
  8. Why is transportation of materials necessary in plants and animals?
  9. Explain the process of excretion in human beings.
  10. Name the organ in plants which helps in the removal of gaseous waste.
  11. Why do veins have valves?
  12. Define double circulation.

Control and Coordination (12 questions)

  1. Name the chemical messenger in animals and its function.
  2. What are plant hormones? Name two.
  3. Explain the function of the cerebellum in the human brain.
  4. State one difference between tropic and nastic movements.
  5. What is phototropism? Give an example.
  6. Name the part of the brain which controls voluntary actions.
  7. What are reflex actions? State their significance.
  8. Name the hormone responsible for lowering the blood sugar level in humans.
  9. What are the functions of auxins in plants?
  10. Why is the flow of information in a reflex arc from receptor to effector shown in a single direction?
  11. Give one example of chemotropism in plants.
  12. Name two plant hormones and mention their functions.

Answers

Chemical Reactions and Equations:

  1. Zn + H₂SO₄ → ZnSO₄ + H₂↑ (Displacement)
  2. To prevent rusting by cutting off moisture and oxygen.
  3. One element replaces another: Zn + CuSO₄ → ZnSO₄ + Cu
  4. 2Na + 2H₂O → 2NaOH + H₂
  5. Gradual eating away of metals by atmospheric gases; prevent by painting, galvanising.
  6. 2Pb(NO₃)₂ → 2PbO + 4NO₂ + O₂ (Thermal decomposition)
  7. Chemical change forms new substance, physical change doesn’t.
  8. Energy is released during breakdown of glucose.
  9. CaO + H₂O → Ca(OH)₂
  10. Zn + CuSO₄ → ZnSO₄ + Cu; Fe₂O₃ + 2Al → Al₂O₃ + 2Fe
  11. Reaction producing insoluble solid: AgNO₃ + NaCl → AgCl↓ + NaNO₃
  12. Fe₂O₃ + 2Al → 2Fe + Al₂O₃; used in welding railway tracks.

Acids, Bases and Salts:
13. No H⁺ ions in dry state.
14. Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂
15. Due to presence of mobile ions.
16. CaOCl₂; prepared by Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O
17. Acid reacts with enamel causing decay.
18. NaCl + H₂O + CO₂ + NH₃ → NaHCO₃ + NH₄Cl
19. Acid + Base → Salt + Water; HCl + NaOH → NaCl + H₂O
20. To prevent reaction with moisture forming gypsum.
21. Methanoic acid (HCOOH)
22. (i) Disinfectant (ii) Baking cakes (iii) Softening water
23. 2NaHCO₃ → Na₂CO₃ + CO₂ + H₂O
24. Less than 7.

Our Environment:
25. Broken down by microbes, e.g., paper, wood.
26. Energy lost as heat at each step; not reused by previous level.
27. Chain – linear; web – interconnected.
28. Plastic, DDT.
29. O₃; formed when UV rays split O₂ and atoms combine with O₂.
30. Increase of toxic substances in higher trophic levels; e.g., DDT.
31. Cause foul smell, breed germs.
32. Same as Q30.
33. Composting, segregation.
34. Based on chemical structure; complex non-biodegradable not easily broken.
35. Allows more UV rays, causing skin cancer, eye damage.
36. Decomposers release nutrients back to soil.

Life Processes:
37. Making food from inorganic sources; e.g., green plants.
38. Plant matter harder to digest.
39. Contracts to increase thoracic volume during inhalation.
40. Transport of food from leaves; phloem.
41. 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
42. Aerobic uses O₂, more energy; anaerobic no O₂, less energy.
43. Salivary amylase; breaks starch to sugar.
44. To supply nutrients, remove waste.
45. Kidneys filter blood, form urine excreted via urethra.
46. Stomata.
47. Prevent backflow of blood.
48. Blood passes heart twice in one cycle.

Control and Coordination:
49. Hormones; chemical messengers controlling activities.
50. Chemicals controlling plant growth; auxins, gibberellins.
51. Maintains posture, balance.
52. Tropic – directional, nastic – non-directional.
53. Growth towards light; shoot bending towards sun.
54. Cerebrum.
55. Involuntary quick response; for protection.
56. Insulin.
57. Promote cell elongation, root initiation.
58. Due to one-way nerve impulse conduction.
59. Growth of pollen tube towards ovule.
60. Auxin – cell elongation; Cytokinin – cell division.

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