Class 10 Science Case Study Worksheet Chapter 1 Chemical Reactions and Equations

VEDANT WORKSHEET SERIES - ACADEMIC YEAR 2026-27

CLASS X | SCIENCE
CHAPTER 1: CHEMICAL REACTIONS AND EQUATIONS (CASE STUDY BASED)

Time Allowed: 1 Hour
Maximum Marks: 20

GENERAL INSTRUCTIONS:

All questions are compulsory.
Read each case study carefully and answer the questions that follow.
Use balanced chemical equations wherever required.
Maintain proper steps and clarity in answers.

SECTION A: CASE STUDY QUESTIONS (4 × 5 = 20 Marks)

Case Study 1: Rusting of Iron (Oxidation Reaction)

Rohit observed that an iron gate near the seashore developed a reddish-brown layer after a few months. This layer is called rust and forms due to the reaction of iron with oxygen and moisture present in the air. Rusting is a slow process but leads to the weakening of iron structures. It is an example of oxidation. Preventive methods include painting, galvanization, and oiling.

Q1. What is rust chemically? (1 mark)
Q2. Write the balanced chemical equation for rusting of iron. (1 mark)
Q3. Why is rusting considered an oxidation reaction? Explain. (2 marks)

Case Study 2: Electrolysis of Water (Decomposition Reaction)

In a laboratory experiment, water is decomposed into hydrogen and oxygen gases by passing electric current through it. This process is known as electrolysis. The gases are collected separately in a ratio of 2:1 by volume. This reaction requires energy in the form of electricity and is thus classified as an endothermic reaction.

Q1. Name the type of chemical reaction involved. (1 mark)
Q2. Write the balanced chemical equation for the reaction. (1 mark)
Q3. Why is this reaction considered endothermic? Explain. (2 marks)

Case Study 3: Reaction of Zinc with Copper Sulphate (Displacement Reaction)

A student dipped a zinc strip into a blue solution of copper sulphate. After some time, the blue colour faded and a reddish-brown deposit formed on the zinc strip. This happens because zinc is more reactive than copper and displaces it from its compound.

Q1. Identify the type of reaction. (1 mark)
Q2. Write the balanced chemical equation. (1 mark)
Q3. What evidence shows that a chemical reaction has occurred? Explain. (2 marks)

Case Study 4: Formation of Precipitate (Double Displacement Reaction)

When aqueous solutions of silver nitrate and sodium chloride are mixed, a white insoluble substance is formed immediately. This solid settles down and is called a precipitate. The reaction involves exchange of ions between the compounds.

Q1. Name the type of reaction taking place. (1 mark)
Q2. Write the balanced chemical equation. (1 mark)
Q3. What is a precipitation reaction? Explain with reference to this case. (2 marks)

Case Study 5: Combustion of Fuel (Exothermic Reaction)

When methane burns in oxygen, it produces carbon dioxide, water, and a large amount of heat. This reaction is widely used as a source of energy in homes and industries. Combustion reactions release energy and are classified as exothermic reactions.

Q1. What type of reaction is combustion of methane? (1 mark)
Q2. Write the balanced chemical equation for the reaction. (1 mark)
Q3. Why is this reaction called exothermic? Explain. (2 marks)

ANSWANSWER KEY WITH MARKING SCHEME

CLASS X | SCIENCE
CHAPTER 1: CHEMICAL REACTIONS AND EQUATIONS

Case Study 1: Rusting of Iron

Q1. What is rust chemically? (1 mark)
Answer: Rust is hydrated iron(III) oxide, Fe2O3·xH2O.
Marking:

Correct chemical name/formula → 1 mark

Q2. Balanced chemical equation for rusting (1 mark)
Answer:
4Fe + 3O2 + xH2O → 2Fe2O3·xH2O
Marking:

Correct balanced equation → 1 mark

Q3. Why is rusting an oxidation reaction? (2 marks)
Answer:
Rusting is oxidation because iron reacts with oxygen and loses electrons to form iron oxide. Addition of oxygen is oxidation.
Marking:

Mentions addition of oxygen / loss of electrons → 1 mark
Correct explanation → 1 mark

Case Study 2: Electrolysis of Water

Q1. Type of reaction (1 mark)
Answer: Decomposition reaction
Marking:

Correct answer → 1 mark

Q2. Balanced chemical equation (1 mark)
Answer:
2H2O → 2H2 + O2
Marking:

Correct balanced equation → 1 mark

Q3. Why is it endothermic? (2 marks)
Answer:
The reaction requires electrical energy to break water molecules into hydrogen and oxygen, so heat/energy is absorbed.
Marking:

Mentions absorption of energy → 1 mark
Correct explanation → 1 mark

Case Study 3: Zinc and Copper Sulphate

Q1. Type of reaction (1 mark)
Answer: Displacement reaction
Marking:

Correct answer → 1 mark

Q2. Balanced chemical equation (1 mark)
Answer:
Zn + CuSO4 → ZnSO4 + Cu
Marking:

Correct balanced equation → 1 mark

Q3. Evidence of chemical reaction (2 marks)
Answer:

Change in colour (blue solution becomes colourless/light)
Formation of reddish-brown copper deposit
Marking:
Any one correct observation → 1 mark
Second correct observation with explanation → 1 mark

Case Study 4: Precipitation Reaction

Q1. Type of reaction (1 mark)
Answer: Double displacement reaction
Marking:

Correct answer → 1 mark

Q2. Balanced chemical equation (1 mark)
Answer:
AgNO3 + NaCl → AgCl (↓) + NaNO3
Marking:

Correct balanced equation → 1 mark

Q3. What is precipitation reaction? (2 marks)
Answer:
A precipitation reaction is one in which two aqueous solutions react to form an insoluble solid (precipitate). Here, AgCl is the white precipitate formed.
Marking:

Correct definition → 1 mark
Reference to given reaction → 1 mark

Case Study 5: Combustion of Methane

Q1. Type of reaction (1 mark)
Answer: Exothermic (combustion) reaction
Marking:

Correct answer → 1 mark

Q2. Balanced chemical equation (1 mark)
Answer:
CH4 + 2O2 → CO2 + 2H2O
Marking:

Correct balanced equation → 1 mark

Q3. Why is it exothermic? (2 marks)
Answer:
The reaction releases heat energy during combustion, which is why it is used as a fuel.
Marking:

Mentions release of heat → 1 mark
Correct explanation/application → 1 mark

TOTAL MARKING GUIDELINES (CBSE STANDARD)

Stepwise marking to be followed
Chemical equations must be balanced for full marks
Minor spelling mistakes ignored if concept is correct
Logical explanation required for 2-mark questions

ER KEY WITH MARKING SCHEME