Step-by-step ICSE solutions and marking scheme for Mole Concept and Stoichiometry from Selina Concise Chemistry (Class 10) - Chapter 5 and 5 generated practice problem sets.

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Chemistry Chapter 5 1 Textbook + 5 Generated Exercises 12 - 14 Marks in ICSE Board Exam

Mole Concept and Stoichiometry — Solved Textbook & 5 Practice Sets

Prescribed Reference Textbook: Selina Concise Chemistry (Class 10) - Chapter 5

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📘 Prescribed Textbook Solved Exercise (Selina Concise Chemistry (Class 10))

Primary Curriculum Benchmark

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

Textbook Exercise 5 - Section Review Q.3 Selina Concise Chemistry (Class 10) - Chapter 5 - Review Exercise 5

3 Marks Allotted

In the study of Mole Concept and Stoichiometry: (i) Give a balanced chemical equation or reaction mechanism illustrating Gay-Lussac’s Law & Avogadro’s Hypothesis. (ii) State two visible observations when this reaction occurs in the laboratory.

Step-by-Step ICSE Evaluator Marking Key

Step 1: Write Balanced Chemical Equation

Write the complete chemical equation with correct molecular formulas, balancing coefficients, and state symbols (s, l, g, aq).

1 Mark

Step 2: Detail First Characteristic Observation

State the primary sensory observation (e.g. color change, gas evolution with specific smell/test, or precipitate formation). Do not simply state the chemical name of the product formed.

1 Mark

Step 3: Detail Second Observation and Chemical Inference

State the second distinguishing property or test verifying the chemical reaction has reached completion.

1 Mark

Final Verified Answer: Balanced equation and distinct physical observations confirmed (Key Units: State symbols (s, l, g, aq))

💡 Examiner Directive: In ICSE Chemistry, an "observation" must describe what is physically seen, smelled, or heard, NOT just naming the compound formed.

🎯 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 "Gay-Lussac’s Law & Avogadro’s Hypothesis" in the context of ICSE Class 10 Chemistry. State its primary characteristic or SI unit/standard symbol.

Step-by-Step Marking Breakdown

Step 1: Precise Technical Definition

Gay-Lussac’s Law: When gases react, they do so in volumes which bear a simple whole number ratio to one another and to the volume of gaseous products, measured under identical temp...

1 Mark

Step 2: Mandatory Technical Criteria

Ensure the definition contains mandatory keywords: Simple whole number ratio of volumes, Avogadro’s number 6.022 × 10²³, Molar volume = 22.4 dm³ at STP.

1 Mark

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

💡 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 "Fundamental Mole Relationships" has standard parameters. Using the relation Moles (n) = Given Mass (w) / Molar Mass (M) = Volume of Gas at STP / 22.4 L = Number of Particles / N_A, 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: Moles (n) = Given Mass (w) / Molar Mass (M) = Volume of Gas at STP / 22.4 L = Number of Particles / N_A. Define each symbol clearly.

Formula: Moles (n) = Given Mass (w) / Molar Mass (M) = Volume of Gas at STP / 22.4 L = Number of Particles / N_A

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 Moles (n) = Given Mass (w) / Molar Mass (M) = Volume of Gas at STP / 22.4 L = Number of Particles / N_A (Units: mol)

💡 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 "Gay-Lussac’s Law & Avogadro’s Hypothesis" and "Empirical vs Molecular Formula" 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: Gay-Lussac’s Law & Avogadro’s Hypothesis focuses on Simple whole number ratio of volumes, whereas Empirical vs Molecular Formula emphasizes Simplest whole number ratio.

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 "Mole Concept and Stoichiometry":
(i) State the fundamental law or rule governing "Gay-Lussac’s Law & Avogadro’s Hypothesis". [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 Simple whole number ratio of volumes with related quantities. The correct understanding requires strict application of Empirical vs Molecular Formula.

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 "Mole Concept and Stoichiometry": An experiment is performed under non-ideal conditions involving "Gay-Lussac’s Law & Avogadro’s Hypothesis" and "Empirical vs Molecular Formula".
(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: Simple whole number ratio of volumes, Avogadro’s number 6.022 × 10²³, Molar volume = 22.4 dm³ at STP, Relative Molecular Mass = 2 × Vapour Density.

2 Marks

Part (c): Correction Protocol & Mathematical Remedy

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

Formula: Moles (n) = Given Mass (w) / Molar Mass (M) = Volume of Gas at STP / 22.4 L = Number of Particles / N_A

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 Experimental Precaution Chapter Concept: Gay-Lussac’s Law & Avogadro’s Hypothesis

1 Mark in Chemical Observation / Balanced Equation

"Simple whole number ratio of volumes"

📘 Technical Definition & Detailed Description:

In ICSE Class 10 Chemistry (Mole Concept and Stoichiometry), "Simple whole number ratio of volumes" 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 "Simple whole number ratio of volumes" 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 Gay-Lussac’s Law & Avogadro’s Hypothesis, ensure "Simple whole number ratio of volumes" is explicitly stated in the balanced explanation."

Mandatory Keyword #2 Core Definition Chapter Concept: Gay-Lussac’s Law & Avogadro’s Hypothesis

1 Mark in Chemical Observation / Balanced Equation

"Avogadro’s number 6.022 × 10²³"

📘 Technical Definition & Detailed Description:

In ICSE Class 10 Chemistry (Mole Concept and Stoichiometry), "Avogadro’s number 6.022 × 10²³" 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 "Avogadro’s number 6.022 × 10²³" 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 Gay-Lussac’s Law & Avogadro’s Hypothesis, ensure "Avogadro’s number 6.022 × 10²³" is explicitly stated in the balanced explanation."

Mandatory Keyword #3 Core Definition Chapter Concept: Gay-Lussac’s Law & Avogadro’s Hypothesis

1 Mark in Chemical Observation / Balanced Equation

"Molar volume = 22.4 dm³ at STP"

📘 Technical Definition & Detailed Description:

In ICSE Class 10 Chemistry (Mole Concept and Stoichiometry), "Molar volume = 22.4 dm³ at STP" 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 "Molar volume = 22.4 dm³ at STP" 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 Gay-Lussac’s Law & Avogadro’s Hypothesis, ensure "Molar volume = 22.4 dm³ at STP" is explicitly stated in the balanced explanation."

Mandatory Keyword #4 Core Definition Chapter Concept: Gay-Lussac’s Law & Avogadro’s Hypothesis

1 Mark in Chemical Observation / Balanced Equation

"Relative Molecular Mass = 2 × Vapour Density"

📘 Technical Definition & Detailed Description:

In ICSE Class 10 Chemistry (Mole Concept and Stoichiometry), "Relative Molecular Mass = 2 × Vapour Density" 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 "Relative Molecular Mass = 2 × Vapour Density" 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 Gay-Lussac’s Law & Avogadro’s Hypothesis, ensure "Relative Molecular Mass = 2 × Vapour Density" is explicitly stated in the balanced explanation."

Mandatory Keyword #5 Experimental Precaution Chapter Concept: Empirical vs Molecular Formula

1 Mark in Chemical Observation / Balanced Equation

"Simplest whole number ratio"

📘 Technical Definition & Detailed Description:

In ICSE Class 10 Chemistry (Mole Concept and Stoichiometry), "Simplest whole number ratio" 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 "Simplest whole number ratio" 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 Empirical vs Molecular Formula, ensure "Simplest whole number ratio" is explicitly stated in the balanced explanation."

Mandatory Keyword #6 Core Definition Chapter Concept: Empirical vs Molecular Formula

1 Mark in Chemical Observation / Balanced Equation

"Molecular Mass = 2 × Vapour Density"

📘 Technical Definition & Detailed Description:

In ICSE Class 10 Chemistry (Mole Concept and Stoichiometry), "Molecular Mass = 2 × Vapour Density" 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 "Molecular Mass = 2 × Vapour Density" 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 Empirical vs Molecular Formula, ensure "Molecular Mass = 2 × Vapour Density" is explicitly stated in the balanced explanation."

Mandatory Keyword #7 Core Definition Chapter Concept: Empirical vs Molecular Formula

1 Mark in Chemical Observation / Balanced Equation

"n = Molecular Mass / Empirical Mass"

📘 Technical Definition & Detailed Description:

In ICSE Class 10 Chemistry (Mole Concept and Stoichiometry), "n = Molecular Mass / Empirical Mass" 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 "n = Molecular Mass / Empirical Mass" 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 Empirical vs Molecular Formula, ensure "n = Molecular Mass / Empirical Mass" 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.

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