Chemistry
Chapter 3
Board Weightage: 14 Marks in Class 9 Exams
Water
Prescribed Textbook: Selina Concise Chemistry (Class 9) - Chapter 3
Canonical Link:
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📖 Syllabus Scope & Overview
Water as a universal solvent, solutions, suspensions and colloids, solubility and solubility curves, hydrated substances, efflorescence, deliquescence, hygroscopy, and hard vs soft water removal.
💡 Core Concepts & Curriculum Outline
Master the fundamental theoretical framework and syllabus scope approved by CISCE.
Efflorescence, Deliquescence & Hygroscopy
Efflorescent crystals lose water of crystallization when exposed to dry air (e.g., Washing Soda Na2CO3·10H2O). Deliquescent substances absorb moisture from air and dissolve in it to form a solution (e.g., anhydrous CaCl2, NaOH). Hygroscopic substances absorb moisture without liquefying (e.g., concentrated H2SO4).
Temporary vs Permanent Hardness of Water
Temporary hardness is caused by hydrogencarbonates of calcium and magnesium [Ca(HCO3)2, Mg(HCO3)2] and is removed by simple boiling. Permanent hardness is caused by sulphates and chlorides of Ca and Mg, removed using washing soda or ion-exchange resins.
🔑 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: Efflorescence, Deliquescence & Hygroscopy
1 Mark in Chemical Observation / Balanced Equation
"Loses water of crystallization"
📘 Technical Definition & Detailed Description:
In ICSE Class 9 Chemistry (Water), "Loses water of crystallization" denotes a critical reaction condition, bonding mechanism, stoichiometric rule, or analytical observation required by CISCE.
Examiners award marks specifically when "Loses water of crystallization" 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 Efflorescence, Deliquescence & Hygroscopy, ensure "Loses water of crystallization" is explicitly stated in the balanced explanation."
Mandatory Keyword #2
Core Definition
Chapter Concept: Efflorescence, Deliquescence & Hygroscopy
1 Mark in Chemical Observation / Balanced Equation
"Absorbs moisture and dissolves"
📘 Technical Definition & Detailed Description:
In ICSE Class 9 Chemistry (Water), "Absorbs moisture and dissolves" denotes a critical reaction condition, bonding mechanism, stoichiometric rule, or analytical observation required by CISCE.
Examiners award marks specifically when "Absorbs moisture and dissolves" 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 Efflorescence, Deliquescence & Hygroscopy, ensure "Absorbs moisture and dissolves" is explicitly stated in the balanced explanation."
Mandatory Keyword #3
Core Definition
Chapter Concept: Efflorescence, Deliquescence & Hygroscopy
1 Mark in Chemical Observation / Balanced Equation
"Absorbs moisture without dissolving"
📘 Technical Definition & Detailed Description:
In ICSE Class 9 Chemistry (Water), "Absorbs moisture without dissolving" denotes a critical reaction condition, bonding mechanism, stoichiometric rule, or analytical observation required by CISCE.
Examiners award marks specifically when "Absorbs moisture without dissolving" 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 Efflorescence, Deliquescence & Hygroscopy, ensure "Absorbs moisture without dissolving" is explicitly stated in the balanced explanation."
Mandatory Keyword #4
Core Definition
Chapter Concept: Efflorescence, Deliquescence & Hygroscopy
1 Mark in Chemical Observation / Balanced Equation
"Washing soda"
📘 Technical Definition & Detailed Description:
In ICSE Class 9 Chemistry (Water), "Washing soda" denotes a critical reaction condition, bonding mechanism, stoichiometric rule, or analytical observation required by CISCE.
Examiners award marks specifically when "Washing soda" 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 Efflorescence, Deliquescence & Hygroscopy, ensure "Washing soda" is explicitly stated in the balanced explanation."
Mandatory Keyword #5
Core Definition
Chapter Concept: Efflorescence, Deliquescence & Hygroscopy
1 Mark in Chemical Observation / Balanced Equation
"Conc. H2SO4"
📘 Technical Definition & Detailed Description:
In ICSE Class 9 Chemistry (Water), "Conc. H2SO4" denotes a critical reaction condition, bonding mechanism, stoichiometric rule, or analytical observation required by CISCE.
Examiners award marks specifically when "Conc. H2SO4" 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 Efflorescence, Deliquescence & Hygroscopy, ensure "Conc. H2SO4" is explicitly stated in the balanced explanation."
Mandatory Keyword #6
Core Definition
Chapter Concept: Temporary vs Permanent Hardness of Water
1 Mark in Chemical Observation / Balanced Equation
"Bicarbonates cause temporary hardness"
📘 Technical Definition & Detailed Description:
In ICSE Class 9 Chemistry (Water), "Bicarbonates cause temporary hardness" denotes a critical reaction condition, bonding mechanism, stoichiometric rule, or analytical observation required by CISCE.
Examiners award marks specifically when "Bicarbonates cause temporary hardness" 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 Temporary vs Permanent Hardness of Water, ensure "Bicarbonates cause temporary hardness" is explicitly stated in the balanced explanation."
Mandatory Keyword #7
Core Definition
Chapter Concept: Temporary vs Permanent Hardness of Water
1 Mark in Chemical Observation / Balanced Equation
"Removed by boiling"
📘 Technical Definition & Detailed Description:
In ICSE Class 9 Chemistry (Water), "Removed by boiling" denotes a critical reaction condition, bonding mechanism, stoichiometric rule, or analytical observation required by CISCE.
Examiners award marks specifically when "Removed by boiling" 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 Temporary vs Permanent Hardness of Water, ensure "Removed by boiling" is explicitly stated in the balanced explanation."
Mandatory Keyword #8
Core Definition
Chapter Concept: Temporary vs Permanent Hardness of Water
1 Mark in Chemical Observation / Balanced Equation
"Sulphates and chlorides cause permanent hardness"
📘 Technical Definition & Detailed Description:
In ICSE Class 9 Chemistry (Water), "Sulphates and chlorides cause permanent hardness" denotes a critical reaction condition, bonding mechanism, stoichiometric rule, or analytical observation required by CISCE.
Examiners award marks specifically when "Sulphates and chlorides cause permanent hardness" 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 Temporary vs Permanent Hardness of Water, ensure "Sulphates and chlorides cause permanent hardness" is explicitly stated in the balanced explanation."
Mandatory Keyword #9
Core Definition
Chapter Concept: Temporary vs Permanent Hardness of Water
1 Mark in Chemical Observation / Balanced Equation
"Washing soda removes both"
📘 Technical Definition & Detailed Description:
In ICSE Class 9 Chemistry (Water), "Washing soda removes both" denotes a critical reaction condition, bonding mechanism, stoichiometric rule, or analytical observation required by CISCE.
Examiners award marks specifically when "Washing soda removes both" 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 Temporary vs Permanent Hardness of Water, ensure "Washing soda removes both" 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: Textbook Exercise 3 - Section Review Q.3
Selina Concise Chemistry (Class 9) - Chapter 3 - Review Exercise 3
3 Marks Total
In the study of Water: (i) Give a balanced chemical equation or reaction mechanism illustrating Efflorescence, Deliquescence & Hygroscopy. (ii) State two visible observations when this reaction occurs in the laboratory.
Step-by-Step Marking Breakdown
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 Answer: Balanced equation and distinct physical observations confirmed
(Units: State symbols (s, l, g, aq))
💡 Examiner Tip: In ICSE Chemistry, an "observation" must describe what is physically seen, smelled, or heard, NOT just naming the compound formed.
🎯 Generated Set: Generated Practice Set 1 - Core Concept (2 Marks)
ICSE Class 9 Exam Blueprint - Chapter 3
2 Marks Total
Define "Efflorescence, Deliquescence & Hygroscopy" 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: Efflorescent crystals lose water of crystallization when exposed to dry air (e.g., Washing Soda Na2CO3·10H2O). Deliquescent substances absorb moisture from air and dissolve in it t...
1 Mark
Step 2: Mandatory Technical Criteria: Ensure the definition contains mandatory keywords: Loses water of crystallization, Absorbs moisture and dissolves, Absorbs moisture without dissolving.
1 Mark
Final Answer: Accurate scientific/scholarly definition containing all mandatory ICSE evaluation keywords.
(Units: Theoretical definition)
💡 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
Explain the procedural method or practical demonstration used to verify "Temporary vs Permanent Hardness of Water". 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 Temporary vs Permanent Hardness of Water.
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 Temporary vs Permanent Hardness of Water
(Units: Procedural steps)
💡 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 "Efflorescence, Deliquescence & Hygroscopy" and "Temporary vs Permanent Hardness of Water" 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: Efflorescence, Deliquescence & Hygroscopy focuses on Loses water of crystallization, whereas Temporary vs Permanent Hardness of Water emphasizes Bicarbonates cause temporary hardness.
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 "Water":
(i) State the fundamental law or rule governing "Efflorescence, Deliquescence & Hygroscopy". [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 Loses water of crystallization with related quantities. The correct understanding requires strict application of Temporary vs Permanent Hardness of Water.
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 "Water": An experiment is performed under non-ideal conditions involving "Efflorescence, Deliquescence & Hygroscopy" and "Temporary vs Permanent Hardness of Water".
(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: Loses water of crystallization, Absorbs moisture and dissolves, Absorbs moisture without dissolving, Washing soda.
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 Tip: HOTS questions in ICSE evaluate depth of conceptual understanding. Avoid superficial guessing; reason backward from core laws.