Chemistry
Chapter 7
Board Weightage: 12 Marks in Class 9 Exams
Study of Gas Laws
Prescribed Textbook: Selina Concise Chemistry (Class 9) - Chapter 7
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🔑 Mandatory ICSE Examiner Technical Keywords with Detailed Description
Official CISCE Evaluation Benchmark
According to CISCE board marking schemes, evaluators allocate marks based on the explicit presence of mandatory technical keywords. General or colloquial explanations fail to secure full marks. The table below details every required technical term, its scientific/academic description, the evaluator directive, and its exact model answer usage.
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.
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 Exam):
"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.
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 Exam):
"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.
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 Exam):
"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.
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 Exam):
"During the reaction in Boyle’s Law & Charles’ Law, ensure "Always convert temperature to Kelvin" is explicitly stated in the balanced explanation."
Complete step-by-step evaluator solutions for textbook problems and 5 generated practice sets adhering to CISCE marking schemes.
📘 Textbook Problem: Selina Exercise 7A - Q10
Selina Concise Chemistry Class 9
3 Marks Total
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 Marking Breakdown
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 Answer: Volume at STP = 449.01 cm³.
(Units: cm³)
🎯 Generated Set: Generated Practice Set 1 - Core Concept (2 Marks)
ICSE Class 9 Exam Blueprint - Chapter 7
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 Tip: Avoid colloquial explanations. Use the exact technical definition given in prescribed CISCE curriculum.
🎯 Generated Set: Generated Practice Set 2 - Method & Application (3 Marks)
ICSE Question Bank & Specimen Framework - Chemistry
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 Tip: In derivation and numerical questions, every intermediate mathematical step carries fractional credit.
🎯 Generated Set: Generated Practice Set 3 - Comparative Analysis (3 Marks)
ICSE Exemplar Practice Paper - Chemistry
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 Tip: Always construct a comparative answer in a two-column table with an explicit "Point of Difference" header column.
🎯 Generated Set: Generated Practice Set 4 - Board Standard Structured (4 Marks)
ICSE Board Marking Blueprint - Class 9
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 Tip: Notice the mark distribution in multi-part questions; allocate your answering time and detail strictly in proportion to allotted marks.
🎯 Generated Set: Generated Practice Set 5 - Higher Order Thinking (HOTS) (4 Marks)
ICSE High-Achiever Challenge Series - Class 9
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 Tip: HOTS questions in ICSE evaluate depth of conceptual understanding. Avoid superficial guessing; reason backward from core laws.