Step-by-step ICSE solutions and marking scheme for Study of Compounds: Hydrogen Chloride from Selina Concise Chemistry (Class 10) - Chapter 8 and 5 generated practice problem sets.

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Chemistry Chapter 8 1 Textbook + 5 Generated Exercises 8 - 10 Marks in ICSE Board Exam

Study of Compounds: Hydrogen Chloride — Solved Textbook & 5 Practice Sets

Prescribed Reference Textbook: Selina Concise Chemistry (Class 10) - Chapter 8

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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 8 - Section Review Q.3 Selina Concise Chemistry (Class 10) - Chapter 8 - Review Exercise 8

3 Marks Allotted

In the study of Study of Compounds: Hydrogen Chloride: (i) Give a balanced chemical equation or reaction mechanism illustrating Laboratory Preparation of HCl Gas. (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 "Laboratory Preparation of HCl Gas" 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

Reactants: Sodium chloride (NaCl) and Concentrated Sulphuric Acid (H₂SO₄). Temperature maintained BELOW 200°C: NaCl + conc. H₂SO₄ (<200°C) → NaHSO₄ + HCl↑. Reasons: (1) Fuel is sav...

1 Mark

Step 2: Mandatory Technical Criteria

Ensure the definition contains mandatory keywords: Temperature < 200°C, Formation of sodium hydrogen sulphate (NaHSO4), Dried over concentrated H2SO4.

1 Mark

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

💡 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

Explain the procedural method or practical demonstration used to verify "Fountain Experiment & Inverted Funnel Arrangement". State the working apparatus/setup and key precautions.

Step-by-Step Marking Breakdown

Step 1: State the Formula / Conceptual Principle

State the fundamental principle governing Fountain Experiment & Inverted Funnel Arrangement.

1 Mark

Step 2: Mathematical / Procedural Deduction

Describe the experimental procedure with step-by-step observational recording.

1 Mark

Step 3: Concluding Result & Interpretation

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

1 Mark

Final Answer: Verified procedural conclusion for Fountain Experiment & Inverted Funnel Arrangement (Units: Procedural steps)

💡 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 "Laboratory Preparation of HCl Gas" and "Fountain Experiment & Inverted Funnel Arrangement" 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: Laboratory Preparation of HCl Gas focuses on Temperature < 200°C, whereas Fountain Experiment & Inverted Funnel Arrangement emphasizes Extreme solubility in water.

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 Compounds: Hydrogen Chloride":
(i) State the fundamental law or rule governing "Laboratory Preparation of HCl Gas". [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 Temperature < 200°C with related quantities. The correct understanding requires strict application of Fountain Experiment & Inverted Funnel Arrangement.

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 Compounds: Hydrogen Chloride": An experiment is performed under non-ideal conditions involving "Laboratory Preparation of HCl Gas" and "Fountain Experiment & Inverted Funnel Arrangement".
(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: Temperature < 200°C, Formation of sodium hydrogen sulphate (NaHSO4), Dried over concentrated H2SO4, Quicklime CaO is basic and cannot be used.

2 Marks

Part (c): Correction Protocol & Mathematical Remedy

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

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: Laboratory Preparation of HCl Gas

1 Mark in Chemical Observation / Balanced Equation

"Temperature < 200°C"

📘 Technical Definition & Detailed Description:

In ICSE Class 10 Chemistry (Study of Compounds: Hydrogen Chloride), "Temperature < 200°C" 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 "Temperature < 200°C" 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 Laboratory Preparation of HCl Gas, ensure "Temperature < 200°C" is explicitly stated in the balanced explanation."

Mandatory Keyword #2 Process & Mechanism Chapter Concept: Laboratory Preparation of HCl Gas

1 Mark in Chemical Observation / Balanced Equation

"Formation of sodium hydrogen sulphate (NaHSO4)"

📘 Technical Definition & Detailed Description:

In ICSE Class 10 Chemistry (Study of Compounds: Hydrogen Chloride), "Formation of sodium hydrogen sulphate (NaHSO4)" 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 "Formation of sodium hydrogen sulphate (NaHSO4)" 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 Laboratory Preparation of HCl Gas, ensure "Formation of sodium hydrogen sulphate (NaHSO4)" is explicitly stated in the balanced explanation."

Mandatory Keyword #3 Core Definition Chapter Concept: Laboratory Preparation of HCl Gas

1 Mark in Chemical Observation / Balanced Equation

"Dried over concentrated H2SO4"

📘 Technical Definition & Detailed Description:

In ICSE Class 10 Chemistry (Study of Compounds: Hydrogen Chloride), "Dried over concentrated H2SO4" 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 "Dried over concentrated H2SO4" 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 Laboratory Preparation of HCl Gas, ensure "Dried over concentrated H2SO4" is explicitly stated in the balanced explanation."

Mandatory Keyword #4 Core Definition Chapter Concept: Laboratory Preparation of HCl Gas

1 Mark in Chemical Observation / Balanced Equation

"Quicklime CaO is basic and cannot be used"

📘 Technical Definition & Detailed Description:

In ICSE Class 10 Chemistry (Study of Compounds: Hydrogen Chloride), "Quicklime CaO is basic and cannot be used" 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 "Quicklime CaO is basic and cannot be used" 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 Laboratory Preparation of HCl Gas, ensure "Quicklime CaO is basic and cannot be used" is explicitly stated in the balanced explanation."

Mandatory Keyword #5 Core Definition Chapter Concept: Fountain Experiment & Inverted Funnel Arrangement

1 Mark in Chemical Observation / Balanced Equation

"Extreme solubility in water"

📘 Technical Definition & Detailed Description:

In ICSE Class 10 Chemistry (Study of Compounds: Hydrogen Chloride), "Extreme solubility in water" 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 "Extreme solubility in water" 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 Fountain Experiment & Inverted Funnel Arrangement, ensure "Extreme solubility in water" is explicitly stated in the balanced explanation."

Mandatory Keyword #6 Core Definition Chapter Concept: Fountain Experiment & Inverted Funnel Arrangement

1 Mark in Chemical Observation / Balanced Equation

"Red fountain with blue litmus"

📘 Technical Definition & Detailed Description:

In ICSE Class 10 Chemistry (Study of Compounds: Hydrogen Chloride), "Red fountain with blue litmus" 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 "Red fountain with blue litmus" 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 Fountain Experiment & Inverted Funnel Arrangement, ensure "Red fountain with blue litmus" is explicitly stated in the balanced explanation."

Mandatory Keyword #7 Core Definition Chapter Concept: Fountain Experiment & Inverted Funnel Arrangement

1 Mark in Chemical Observation / Balanced Equation

"Inverted funnel prevents back-suction"

📘 Technical Definition & Detailed Description:

In ICSE Class 10 Chemistry (Study of Compounds: Hydrogen Chloride), "Inverted funnel prevents back-suction" 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 "Inverted funnel prevents back-suction" 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 Fountain Experiment & Inverted Funnel Arrangement, ensure "Inverted funnel prevents back-suction" is explicitly stated in the balanced explanation."

Mandatory Keyword #8 Core Definition Chapter Concept: Fountain Experiment & Inverted Funnel Arrangement

1 Mark in Chemical Observation / Balanced Equation

"Large surface area for absorption"

📘 Technical Definition & Detailed Description:

In ICSE Class 10 Chemistry (Study of Compounds: Hydrogen Chloride), "Large surface area for absorption" 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 "Large surface area for absorption" 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 Fountain Experiment & Inverted Funnel Arrangement, ensure "Large surface area for absorption" 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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