Master Class 10 Science Ch 1: PYQ-Based Worksheet & Solutions

Unlocking Success: Why PYQ-Based Worksheets are Essential for Class 10 Science?

As dedicated CBSE educators, we understand the constant endeavour to equip our students with the best resources for academic excellence. For Class 10 Science, a strong foundation in core concepts is paramount, and Chapter 01, "Chemical Reactions and Equations," is undeniably one of the most fundamental. To truly master this chapter and excel in board examinations, mere rote learning isn't enough. Students need to apply their knowledge, understand question patterns, and develop effective problem-solving strategies.

This is precisely where Previous Year Question (PYQ) based worksheets become invaluable. PYQs offer a crystal-clear window into the minds of examiners, revealing recurring themes, common pitfalls, and the expected depth of understanding. By integrating PYQs into your teaching methodology, you're not just preparing students for an exam; you're teaching them how to think like an examiner.

At TeachCBSE.com, we are committed to providing you with actionable resources that make your job easier and more effective. This blog post presents a meticulously curated, Worksheet for Class 10 Science Chapter 01 [PYQ based], complete with detailed solutions, designed to be a cornerstone of your teaching toolkit.

Chapter 1: Chemical Reactions and Equations - Key Concepts to Reinforce

Before diving into the worksheet, let's quickly recap why Chapter 1 is so crucial and what key concepts students often find challenging:

• Balancing Chemical Equations: A foundational skill, often tested directly or indirectly.
• Types of Chemical Reactions: Combination, Decomposition, Displacement, Double Displacement, Oxidation, and Reduction (Redox) reactions – understanding their definitions, examples, and identifying them.
• Exothermic and Endothermic Reactions: Distinguishing between processes that release or absorb heat.
• Corrosion and Rancidity: Understanding their causes, effects, and preventive measures.
• Practical Applications: Connecting theoretical knowledge to real-world phenomena.

Our Worksheet for Class 10 Science Chapter 01 [PYQ based] specifically targets these areas, ensuring a holistic review and practice experience.

TeachCBSE.com's Exclusive Worksheet for Class 10 Science Chapter 01 (PYQ Based)

This 30-mark worksheet is designed to be completed in approximately 60 minutes, simulating exam conditions. It covers a range of question types as per the latest CBSE pattern, including MCQs, Assertion-Reason, Short Answer, Long Answer, and a Case-Based question. Each question is followed by a comprehensive answer, making it an ideal self-assessment or classroom discussion tool.

Worksheet: Chemical Reactions and Equations (Chapter 01)

Class: X | Subject: Science | Chapter: 01 – Chemical Reactions and Equations

Time: 60 Minutes | Max. Marks: 30

Instructions:

1. All questions are compulsory.
2. Marks for each question are indicated against it.
3. Attempt all parts of a question together.

Section A: Multiple Choice Questions (1 Mark Each)

Q1. Which of the following statements about the given reaction are correct? (PYQ 2020)

3Fe(s) + 4H₂O(g) → Fe₃O₄(s) + 4H₂(g)

(i) Iron metal is reacting as reducing agent.
(ii) Water is acting as oxidizing agent.
(iii) Iron metal is getting reduced.
(iv) Water is getting reduced.

(a) (i), (ii) and (iii)
(b) (iii) and (iv)
(c) (i), (ii) and (iv)
(d) (ii) and (iv)

Answer: (c) (i), (ii) and (iv)
Explanation: In this reaction, Iron (Fe) is gaining oxygen and forming Fe₃O₄, so it is getting oxidized and acts as a reducing agent. Water (H₂O) is losing oxygen and forming H₂, so it is getting reduced and acts as an oxidizing agent. Therefore, (i), (ii) and (iv) are correct.

Q2. A solution of a substance 'X' is used for whitewashing. What is the substance 'X'? Write the reaction of the substance 'X' with water. (PYQ 2018)

(a) Calcium carbonate, CaCO₃ + H₂O → Ca(OH)₂
(b) Calcium oxide, CaO + H₂O → Ca(OH)₂
(c) Calcium hydroxide, Ca(OH)₂ + H₂O → Ca(OH)₂
(d) Sodium hydroxide, NaOH + H₂O → NaOH(aq)

Answer: (b) Calcium oxide, CaO + H₂O → Ca(OH)₂
Explanation: The substance 'X' is Calcium oxide (quicklime). It reacts vigorously with water to form calcium hydroxide (slaked lime), which is used for whitewashing. The reaction is exothermic.

Q3. Which of the following is an endothermic process?

(a) Dilution of sulphuric acid
(b) Sublimation of dry ice
(c) Condensation of water vapours
(d) Respiration

Answer: (b) Sublimation of dry ice
Explanation: Sublimation of dry ice (solid CO₂) requires absorption of heat from the surroundings to change from solid to gas, hence it is an endothermic process. Dilution of sulphuric acid, condensation of water vapours, and respiration are all exothermic processes.

Q4. Which of the following methods is suitable for preventing an iron frying pan from rusting? (PYQ 2020)

(a) Applying grease
(b) Applying paint
(c) Applying a coating of zinc
(d) All of the above

Answer: (d) All of the above
Explanation: All the listed methods (greasing, painting, galvanizing with zinc) prevent the iron surface from coming into contact with oxygen and moisture, thereby preventing rusting.

Q5. In the reaction, PbO + C → Pb + CO, which substance is oxidized?

(a) PbO
(b) C
(c) Pb
(d) CO

Answer: (b) C
Explanation: Carbon (C) gains oxygen to form carbon monoxide (CO), hence it is oxidized. Lead oxide (PbO) loses oxygen to form Lead (Pb), hence it is reduced.

Section B: Assertion and Reason Questions (1 Mark Each)

Directions: In the following questions, a statement of Assertion (A) is followed by a statement of Reason (R). Mark the correct choice as:

(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.

Q6. Assertion (A): Decomposition of silver chloride is an endothermic process. (PYQ 2019)

Reason (R): Energy is required for the decomposition reaction.

Answer: (a) Both A and R are true and R is the correct explanation of A.
Explanation: Decomposition reactions generally require energy (heat, light, or electricity) to break down reactants. The decomposition of silver chloride (2AgCl(s) → 2Ag(s) + Cl₂(g)) requires light energy, making it an endothermic process. Thus, the reason correctly explains the assertion.

Q7. Assertion (A): Zinc reacts with sulphuric acid to form zinc sulphate and hydrogen gas.

Reason (R): Zinc is more reactive than hydrogen.

Answer: (a) Both A and R are true and R is the correct explanation of A.
Explanation: Zinc is indeed more reactive than hydrogen and can displace hydrogen from acids, forming zinc sulphate and hydrogen gas (Zn + H₂SO₄ → ZnSO₄ + H₂). The reason correctly explains why the reaction occurs.

Section C: Short Answer Questions (2 Marks Each)

Q8. Why do we store silver chloride in dark coloured bottles? (PYQ 2017)

Answer: Silver chloride (AgCl) is stored in dark coloured bottles because it is sensitive to light. When exposed to light, it undergoes photodecomposition (a type of decomposition reaction) to form silver metal and chlorine gas. This reaction (2AgCl(s) → 2Ag(s) + Cl₂(g)) makes the silver chloride decompose and lose its properties. Dark coloured bottles prevent light from reaching the compound, thus preventing its decomposition.

Q9. What happens when carbon dioxide gas is passed through lime water for a short time and for a long time? Give relevant equations. (PYQ 2016)

Answer:

When CO₂ gas is passed through lime water (calcium hydroxide solution) for a short time, it forms insoluble calcium carbonate, which makes the lime water milky/cloudy.

Ca(OH)₂(aq) + CO₂(g) → CaCO₃(s) + H₂O(l)

If CO₂ gas is passed for a long time, the excess carbon dioxide reacts with the insoluble calcium carbonate and water to form soluble calcium hydrogen carbonate. This makes the milky solution clear again.

CaCO₃(s) + H₂O(l) + CO₂(g) → Ca(HCO₃)₂(aq)

Q10. Identify the type of reaction in the following examples:

(a) A + B → AB
(b) AB + CD → AD + CB

Answer:

(a) A + B → AB represents a Combination Reaction, where two or more reactants combine to form a single product.

(b) AB + CD → AD + CB represents a Double Displacement Reaction, where there is an exchange of ions between two compounds.

Q11. Balance the following chemical equation:

Fe(s) + H₂O(g) → Fe₃O₄(s) + H₂(g)

Answer:

The balanced chemical equation is:

3Fe(s) + 4H₂O(g) → Fe₃O₄(s) + 4H₂(g)

Section D: Long Answer Questions (3 Marks Each)

Q12. Write balanced chemical equations for the following reactions: (PYQ 2019)

(a) Hydrogen sulphide gas reacts with sulphur dioxide gas to form sulphur and water.
(b) Barium chloride reacts with sodium sulphate to form barium sulphate and sodium chloride.

Answer:

(a) Hydrogen sulphide gas reacts with sulphur dioxide gas to form sulphur and water:
2H₂S(g) + SO₂(g) → 3S(s) + 2H₂O(l)

(b) Barium chloride reacts with sodium sulphate to form barium sulphate and sodium chloride:
BaCl₂(aq) + Na₂SO₄(aq) → BaSO₄(s) + 2NaCl(aq)

Q13. What is a redox reaction? Identify the substance oxidized, reduced, oxidizing agent, and reducing agent in the following reaction: (PYQ 2018)

CuO(s) + H₂(g) → Cu(s) + H₂O(l)

Answer:

A redox reaction is a chemical reaction in which both oxidation and reduction occur simultaneously. Oxidation is the gain of oxygen or loss of hydrogen/electrons, while reduction is the loss of oxygen or gain of hydrogen/electrons.

In the given reaction: CuO(s) + H₂(g) → Cu(s) + H₂O(l)

• Substance oxidized: H₂ (Hydrogen gains oxygen to form H₂O)
• Substance reduced: CuO (Copper oxide loses oxygen to form Cu)
• Oxidizing agent: CuO (It provides oxygen for the oxidation of H₂)
• Reducing agent: H₂ (It removes oxygen from CuO, causing its reduction)

Section E: Case-Based Question (4 Marks)

Q14. A student took a small amount of solid barium hydroxide in a test tube and added solid ammonium chloride to it. He observed a reaction and noted the following: (PYQ 2020 modified)

I. A white precipitate was formed.
II. The mixture in the test tube became cold.
III. The gas evolved had a pungent smell.

(a) Write the balanced chemical equation for the reaction.
(b) What type of reaction is this based on heat change?
(c) Identify the gas evolved and its nature (acidic/basic).
(d) What would happen if the student touched the bottom of the test tube?

Answer:

(a) The balanced chemical equation for the reaction is: Ba(OH)₂(s) + 2NH₄Cl(s) → BaCl₂(aq) + 2NH₃(g) + 2H₂O(l)

(b) Since the mixture in the test tube became cold (absorbed heat from surroundings), this is an Endothermic Reaction.

(c) The gas evolved is Ammonia (NH₃). Ammonia gas has a pungent smell and is basic in nature (it turns red litmus blue).

(d) If the student touched the bottom of the test tube, they would feel it to be cold, confirming the endothermic nature of the reaction.

Section F: Long Answer Question (5 Marks)

Q15. (a) Define oxidation and reduction in terms of gain or loss of oxygen and hydrogen. (PYQ 2019)

(b) Write balanced chemical equations for the following reactions and identify the type of reaction in each case:

(i) Magnesium ribbon is burnt in air.
(ii) Iron nails are dipped in copper sulphate solution.

Answer:

(a) Oxidation: It is a process that involves the gain of oxygen or loss of hydrogen by a substance.
Reduction: It is a process that involves the loss of oxygen or gain of hydrogen by a substance.

(b) Balanced chemical equations and types of reactions:

(i) Magnesium ribbon is burnt in air:
2Mg(s) + O₂(g) → 2MgO(s)
Type of reaction: Combination reaction (as two reactants combine to form a single product) and also a Redox reaction (Mg is oxidized, O₂ is reduced).

(ii) Iron nails are dipped in copper sulphate solution:
Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s)
Type of reaction: Displacement reaction (as a more reactive metal, iron, displaces a less reactive metal, copper, from its salt solution).

How to Effectively Use This Worksheet in Your Classroom

This Worksheet for Class 10 Science Chapter 01 [PYQ based] is more than just a set of questions; it's a strategic learning tool:

1. Pre-Assessment: Use it before starting the chapter to gauge prior knowledge and identify areas needing more focus.
2. Formative Assessment: Administer it after completing the chapter to assess understanding and retention.
3. Revision Tool: Encourage students to solve it independently during revision cycles, especially leading up to unit tests and board exams.
4. Discussion Starter: Use the detailed solutions to facilitate classroom discussions, clarify doubts, and explain common mistakes.
5. Homework Assignment: Assign it as homework to reinforce learning and provide extra practice.

Remember to emphasize the importance of understanding the 'why' behind each answer, not just memorizing the solutions. Encourage students to articulate their thought processes, especially for Assertion-Reason and Case-Based questions.

Conclusion

Preparing students for the CBSE Class 10 Science board exam requires a blend of conceptual clarity, rigorous practice, and strategic exposure to exam-style questions. Our Worksheet for Class 10 Science Chapter 01 [PYQ based] is designed to be a comprehensive, teacher-friendly resource that addresses all these needs. By incorporating this worksheet into your teaching plan, you can significantly boost your students' confidence and performance in Chemical Reactions and Equations.

Explore more such resources and teaching opportunities at TeachCBSE.com!