Step-by-step ICSE solutions and marking scheme for Study of Gas Laws from Selina Concise Chemistry (Class 9) - Chapter 7 and 5 generated practice problem sets.

Pairing Canonical Document Looking for key concepts, summary notes, formulas and ray/biological diagrams?

📘 Open Chapter Notes (class9_chemistry_study_of_gas_laws.html) →

Chemistry Chapter 7 1 Textbook + 5 Generated Exercises 12 Marks in Class 9 Exams

Study of Gas Laws — Solved Textbook & 5 Practice Sets

Prescribed Reference Textbook: Selina Concise Chemistry (Class 9) - Chapter 7

Canonical Link: https://icse.smartindia.pro/class9_chemistry_solved_exercise_study_of_gas_laws.html

Prerendered HTML Page: class9_chemistry_solved_exercise_study_of_gas_laws.html

📘 Prescribed Textbook Solved Exercise (Selina Concise Chemistry (Class 9))

Primary Curriculum Benchmark

Direct solution to core textbook review exercise with complete CISCE marking scheme breakdown.

Selina Exercise 7A - Q10 Selina Concise Chemistry Class 9

3 Marks Allotted

A given mass of gas occupies 500 cm³ at 27°C and 750 mm Hg pressure. What volume will it occupy at STP (0°C and 760 mm Hg)?

Step-by-Step ICSE Evaluator Marking Key

Step 1: Identify given values in Kelvin

P1 = 750 mm, V1 = 500 cm³, T1 = 27 + 273 = 300 K; P2 = 760 mm, T2 = 273 K, V2 = ?

1 Mark

Step 2: Apply combined gas equation

V2 = (P1 × V1 × T2) / (P2 × T1) = (750 × 500 × 273) / (760 × 300) = 102375000 / 228000 = 449.01 cm³.

2 Marks

Final Verified Answer: Volume at STP = 449.01 cm³. (Key Units: cm³)

🎯 5 Generated Practice Exercises with Step-Marking

CISCE Syllabus Graded Set

Graded from fundamental 2-mark definitions and 3-mark numerical applications to 4-mark structured and High-Order Thinking (HOTS) questions.

Generated Practice Set 1 - Core Concept (2 Marks) Difficulty: Easy

2 Marks Total

Define "Boyle’s Law & Charles’ Law" in the context of ICSE Class 9 Chemistry. State its primary characteristic or SI unit/standard symbol.

Step-by-Step Marking Breakdown

Step 1: Precise Technical Definition

Boyle’s Law: Volume of a dry gas is inversely proportional to its pressure at constant temperature (PV = constant). Charles’ Law: Volume is directly proportional to absolute temper...

1 Mark

Step 2: Mandatory Technical Criteria

Ensure the definition contains mandatory keywords: PV = constant at constant T, V/T = constant at constant P, Absolute zero is -273°C (0 K).

1 Mark

Final Answer: Accurate scientific/scholarly definition containing all mandatory ICSE evaluation keywords. (Units: atm / mm Hg)

💡 Examiner Directive: Avoid colloquial explanations. Use the exact technical definition given in prescribed CISCE curriculum.

Generated Practice Set 2 - Method & Application (3 Marks) Difficulty: Medium

3 Marks Total

A system governed by "Combined Gas Equation" has standard parameters. Using the relation (P1 · V1) / T1 = (P2 · V2) / T2, calculate the required variable when other quantities are doubled. State the formula and show step-by-step substitution.

Step-by-Step Marking Breakdown

Step 1: State the Formula / Conceptual Principle

Write the primary governing equation: (P1 · V1) / T1 = (P2 · V2) / T2. Define each symbol clearly.

Formula: (P1 · V1) / T1 = (P2 · V2) / T2

1 Mark

Step 2: Mathematical / Procedural Deduction

Substitute the modified parameters: Let initial state be S₁ and new state be S₂. Set up the ratio S₂ / S₁ and simplify algebraically.

1 Mark

Step 3: Concluding Result & Interpretation

Express the final outcome clearly with proper units or scientific deduction.

1 Mark

Final Answer: Result derived directly from (P1 · V1) / T1 = (P2 · V2) / T2 (Units: atm / mm Hg)

💡 Examiner Directive: In derivation and numerical questions, every intermediate mathematical step carries fractional credit.

Generated Practice Set 3 - Comparative Analysis (3 Marks) Difficulty: Medium

3 Marks Total

Differentiate between "Boyle’s Law & Charles’ Law" and "Boyle’s Law & Charles’ Law" on the basis of: (i) Fundamental definition/mechanism, (ii) Key working condition or formula, (iii) Real-world practical example or application.

Step-by-Step Marking Breakdown

Point 1: Conceptual Difference

Contrast the primary mechanisms: Boyle’s Law & Charles’ Law focuses on PV = constant at constant T, whereas Boyle’s Law & Charles’ Law emphasizes PV = constant at constant T.

1 Mark

Point 2: Quantitative / Operational Difference

Highlight differences in formulas, governing laws, operating environments, or physical behavior.

1 Mark

Point 3: Exemplary Differentiation

Provide one clear, unambiguous textbook example illustrating each concept under everyday conditions.

1 Mark

Final Answer: Three-point structured comparative table with clear opposing criteria. (Units: Tabular points)

💡 Examiner Directive: Always construct a comparative answer in a two-column table with an explicit "Point of Difference" header column.

Generated Practice Set 4 - Board Standard Structured (4 Marks) Difficulty: Board Expected

4 Marks Total

A comprehensive ICSE examination question based on "Study of Gas Laws":
(i) State the fundamental law or rule governing "Boyle’s Law & Charles’ Law". [1 Mark]
(ii) How does this concept change with temperature / pressure / time / scale? [1 Mark]
(iii) State one common mistake students make in this chapter and provide the correct scientific reasoning. [2 Marks]

Step-by-Step Marking Breakdown

Part (i): Statement of the Law

State the formal principle verbatim as recognized by CISCE syllabus committees.

1 Mark

Part (ii): Dependency Analysis

Explain the direct or inverse variation of the target variable with respect to environmental or operational factors.

1 Mark

Part (iii): Error Analysis & Correct Resolution

Identify the frequent pitfall: Students often confuse PV = constant at constant T with related quantities. The correct understanding requires strict application of Boyle’s Law & Charles’ Law.

2 Marks

Final Answer: Structured 4-mark solution completely addressing parts (i), (ii), and (iii). (Units: Multi-part breakdown)

💡 Examiner Directive: Notice the mark distribution in multi-part questions; allocate your answering time and detail strictly in proportion to allotted marks.

Generated Practice Set 5 - Higher Order Thinking (HOTS) (4 Marks) Difficulty: Hard

4 Marks Total

A critical scenario-based problem in "Study of Gas Laws": An experiment is performed under non-ideal conditions involving "Boyle’s Law & Charles’ Law" and "Boyle’s Law & Charles’ Law".
(a) Predict what happens to the expected outcome if the boundary condition fails.
(b) Give complete scientific justification.
(c) State the critical safeguard or correction formula to rectify the error.

Step-by-Step Marking Breakdown

Part (a): Prediction of Anomalous Outcome

Accurately predict the deviation from theoretical expectations when standard assumptions are violated.

1 Mark

Part (b): Scientific Justification

Provide a rigorous scientific explanation using first principles and mandatory keywords: PV = constant at constant T, V/T = constant at constant P, Absolute zero is -273°C (0 K), Always convert temperature to Kelvin.

2 Marks

Part (c): Correction Protocol & Mathematical Remedy

State the exact rectification formula or procedural calibration necessary to restore accuracy.

Formula: (P1 · V1) / T1 = (P2 · V2) / T2

1 Mark

Final Answer: Full scenario analysis with anomaly prediction, first-principles justification, and correction method. (Units: HOTS Analytical Reasoning)

💡 Examiner Directive: HOTS questions in ICSE evaluate depth of conceptual understanding. Avoid superficial guessing; reason backward from core laws.

🔑 Mandatory ICSE Examiner Technical Keywords Required in Solutions

Required for Step-Marking Credit

CISCE evaluators check for the explicit usage of mandatory technical terminology when scoring reasoning questions and step derivations. The table below outlines each key term, its technical description, the examiner marking directive, and the exact model answer phrasing expected in ICSE board examination solutions.

Mandatory Keyword #1 Core Definition Chapter Concept: Boyle’s Law & Charles’ Law

1 Mark in Chemical Observation / Balanced Equation

"PV = constant at constant T"

📘 Technical Definition & Detailed Description:

In ICSE Class 9 Chemistry (Study of Gas Laws), "PV = constant at constant T" denotes a critical reaction condition, bonding mechanism, stoichiometric rule, or analytical observation required by CISCE.

⚠️ CISCE Examiner Directive & Marking Rubric:

Examiners award marks specifically when "PV = constant at constant T" is included alongside balanced chemical equations, observable color changes, or state symbols (s, l, g, aq).

📝 Model Answer Application (Exact Phrasing for Board Solutions):

"During the reaction in Boyle’s Law & Charles’ Law, ensure "PV = constant at constant T" is explicitly stated in the balanced explanation."

Mandatory Keyword #2 Core Definition Chapter Concept: Boyle’s Law & Charles’ Law

1 Mark in Chemical Observation / Balanced Equation

"V/T = constant at constant P"

📘 Technical Definition & Detailed Description:

In ICSE Class 9 Chemistry (Study of Gas Laws), "V/T = constant at constant P" denotes a critical reaction condition, bonding mechanism, stoichiometric rule, or analytical observation required by CISCE.

⚠️ CISCE Examiner Directive & Marking Rubric:

Examiners award marks specifically when "V/T = constant at constant P" is included alongside balanced chemical equations, observable color changes, or state symbols (s, l, g, aq).

📝 Model Answer Application (Exact Phrasing for Board Solutions):

"During the reaction in Boyle’s Law & Charles’ Law, ensure "V/T = constant at constant P" is explicitly stated in the balanced explanation."

Mandatory Keyword #3 Core Definition Chapter Concept: Boyle’s Law & Charles’ Law

1 Mark in Chemical Observation / Balanced Equation

"Absolute zero is -273°C (0 K)"

📘 Technical Definition & Detailed Description:

In ICSE Class 9 Chemistry (Study of Gas Laws), "Absolute zero is -273°C (0 K)" denotes a critical reaction condition, bonding mechanism, stoichiometric rule, or analytical observation required by CISCE.

⚠️ CISCE Examiner Directive & Marking Rubric:

Examiners award marks specifically when "Absolute zero is -273°C (0 K)" is included alongside balanced chemical equations, observable color changes, or state symbols (s, l, g, aq).

📝 Model Answer Application (Exact Phrasing for Board Solutions):

"During the reaction in Boyle’s Law & Charles’ Law, ensure "Absolute zero is -273°C (0 K)" is explicitly stated in the balanced explanation."

Mandatory Keyword #4 Core Definition Chapter Concept: Boyle’s Law & Charles’ Law

1 Mark in Chemical Observation / Balanced Equation

"Always convert temperature to Kelvin"

📘 Technical Definition & Detailed Description:

In ICSE Class 9 Chemistry (Study of Gas Laws), "Always convert temperature to Kelvin" denotes a critical reaction condition, bonding mechanism, stoichiometric rule, or analytical observation required by CISCE.

⚠️ CISCE Examiner Directive & Marking Rubric:

Examiners award marks specifically when "Always convert temperature to Kelvin" is included alongside balanced chemical equations, observable color changes, or state symbols (s, l, g, aq).

📝 Model Answer Application (Exact Phrasing for Board Solutions):

"During the reaction in Boyle’s Law & Charles’ Law, ensure "Always convert temperature to Kelvin" is explicitly stated in the balanced explanation."

⚖️ CISCE Evaluation Directives for Chemistry

Step-Mark Allocation: Every sub-step, formula statement, and intermediate substitution carries independent marks. Writing final answers without formula yields zero in Section B numericals.

Mandatory SI Units: In ICSE Science and Mathematics, omitting SI units or writing incorrect unit exponents causes automatic 1/2 mark deduction per problem.

Examiner Technical Vocabulary: CISCE evaluators look for exact prescribed terms in definitions and reasoning questions. General paraphrasing often loses full credit.

📚 Other Class 9 Chemistry Solved Exercises

Solve Exercises Interactively in the App

Bookmark questions, get real-time AI Mentor hints for tough steps, and test your exam readiness with live timed quizzes.

⚡ Practice in Interactive ICSE Hub