Chapter 3: Atoms and Molecules Case Study Questions | science Class 9 CBSE

ByteNotes

Chapter 3: Atoms and Molecules Case Study Questions | science Class 9 CBSE | ByteNotes.in

Case Study

Passage with linked questions

Case Set

Case Set 1

Case Analysis

Passage

Riya performed an activity to mix barium chloride and sodium sulphate solutions. She carefully weighed the setup before and after mixing and found that the mass remained unchanged.

Question 1: Q1. Which law of chemical combination does this activity demonstrate?

It demonstrates the Law of Conservation of Mass.
The total mass of reactants and products remains the same.
Mass can neither be created nor destroyed in a chemical reaction.

Question 2: Q2. Why was the flask corked during the experiment?

To prevent the escape of gases formed during reaction.
Ensures accurate measurement of total mass.
Maintains a closed system to validate mass conservation.

Question 3: Q3. What conclusion can be drawn from the final mass being unchanged?

The reaction obeys the law of conservation of mass.
No matter was lost or gained during the reaction.
The experiment supports a fundamental principle in chemistry.

ByteNotes

Case Study

Passage with linked questions

Case Set

Case Set 2

Case Analysis

Passage

In a classroom discussion, it was stated that 9 grams of water always yields 1 g of hydrogen and 8 g of oxygen upon decomposition, regardless of its source.

Question 1: Q1. Which chemical law is illustrated here?

This illustrates the Law of Constant Proportions.
A chemical compound always contains elements in a fixed ratio by mass.
It applies to water from any natural or artificial source.

Question 2: Q2. Who proposed this law and how does it apply to ammonia?

Joseph Proust proposed this law.
Ammonia always contains nitrogen and hydrogen in a 14:3 mass ratio.
The source or method of preparation does not change this proportion.

Question 3: Q3. How does this support Dalton’s atomic theory?

Dalton stated atoms combine in fixed ratios to form compounds.
Fixed ratios explain consistent mass proportions.
It confirms that atoms have defined masses.

ByteNotes

Case Study

Passage with linked questions

Case Set

Case Set 3

Case Analysis

Passage

Ravi read that John Dalton proposed the atomic theory and that each element is made up of identical atoms which combine in simple whole-number ratios to form compounds.

Question 1: Q1. Name two postulates of Dalton’s atomic theory.

All matter is made up of tiny indivisible particles called atoms.
Atoms of a given element are identical in mass and properties.
Atoms combine in small whole-number ratios to form compounds.

Question 2: Q2. Which postulate explains the Law of Conservation of Mass?

Atoms are indivisible and cannot be created or destroyed.
This explains why total mass remains unchanged during reactions.
It supports mass conservation in chemical reactions.

Question 3: Q3. Which postulate explains the Law of Constant Proportions?

Atoms combine in fixed, simple ratios by number.
This leads to fixed mass ratios in compounds.
Confirms definite composition of compounds like water or ammonia.

ByteNotes

Case Study

Passage with linked questions

Case Set

Case Set 4

Case Analysis

Passage

Sanya observed a table of atomic masses where hydrogen had 1u, oxygen 16u, and sodium 23u. She learned these are based on the carbon-12 standard.

Question 1: Q1. What is the standard unit for atomic mass?

It is the unified mass (u).
Defined as 1/12th the mass of one carbon-12 atom.
Used to compare relative atomic masses.

Question 2: Q2. Why is relative mass used instead of actual mass?

Atoms are extremely small and their actual mass is hard to measure.
Relative mass simplifies comparison between elements.
It avoids extremely tiny decimal values.

Question 3: Q3. Which two historical units were used before the unified standard?

Initially, 1/16 of an oxygen atom was used.
Later, carbon-12 was universally adopted.
Carbon-12 provides simpler, near-whole-number values.

ByteNotes

Case Study

Passage with linked questions

Case Set

Case Set 5

Case Analysis

Passage

A fruit seller used pieces of a watermelon as a standard unit to weigh other fruits. This analogy helped students understand relative atomic mass.

Question 1: Q1. How is this analogy similar to atomic mass units?

Just like fruit was compared to watermelon pieces, atoms are compared to carbon-12.
Provides a consistent standard for measurement.
Helps express masses relatively instead of absolute terms.

Question 2: Q2. What is meant by ‘relative atomic mass’?

Mass of an atom compared to 1/12th mass of a carbon-12 atom.
It is a ratio, not an actual mass.
Used to determine molecular and formula masses.

Question 3: Q3. Give the atomic mass of oxygen and chlorine from the table.

Oxygen: 16 u.
Chlorine: 35.5 u.
These values are based on the carbon-12 scale.

ByteNotes

Premium Access

Unlock all Case Study sets

You are viewing 5 free case study sets from this chapter. Upgrade to Premium to unlock the remaining 7 sets.

Upgrade to Premium7 questions locked

Chapter sections

Chapter 3: Atoms and Molecules | Case Study Questions

Passage

Question 1: Q1. Which law of chemical combination does this activity demonstrate?

Question 2: Q2. Why was the flask corked during the experiment?

Question 3: Q3. What conclusion can be drawn from the final mass being unchanged?

Passage

Question 1: Q1. Which chemical law is illustrated here?

Question 2: Q2. Who proposed this law and how does it apply to ammonia?

Question 3: Q3. How does this support Dalton’s atomic theory?

Passage

Question 1: Q1. Name two postulates of Dalton’s atomic theory.

Question 2: Q2. Which postulate explains the Law of Conservation of Mass?

Question 3: Q3. Which postulate explains the Law of Constant Proportions?

Passage

Question 1: Q1. What is the standard unit for atomic mass?

Question 2: Q2. Why is relative mass used instead of actual mass?

Question 3: Q3. Which two historical units were used before the unified standard?

Passage

Question 1: Q1. How is this analogy similar to atomic mass units?

Question 2: Q2. What is meant by ‘relative atomic mass’?

Question 3: Q3. Give the atomic mass of oxygen and chlorine from the table.

Unlock all Case Study sets