Class 9 Science - ICSE-CHEMISTRY
Water
The Chapter 'Water' in Class 9 ICSE Chemistry explores water as a universal solvent, its physical and chemical properties, solutions, suspensions, and colloids, and the concept of water of crystallization. Students will learn about saturated and unsaturated solutions, solubility curves, and methods to test for the presence of water. This chapter is fundamental for understanding chemical bonding, solutions in volumetric analysis, and environmental chemistry, regularly carrying about 6 to 8 marks in the ICSE board examination through direct definitions, numerical problems on solubility, and reasoning questions.
Start Learning FreeKey Concepts
Water as a Universal Solvent
Water has a high dielectric constant which weakens the attraction between ions, allowing it to dissolve a large variety of polar and ionic substances.
Solutions, Suspensions, and Colloids
A solution is a homogeneous mixture with particles smaller than 1 nm, a suspension is heterogeneous with visible particles settling down, and a colloid shows the Tyndall effect with intermediate particle sizes.
Solubility
Solubility is the maximum amount of solute in grams that can dissolve in 100 grams of a solvent at a specific temperature to form a saturated solution.
Water of Crystallization
Fixed number of water molecules chemically combined in a definite stoichiometric ratio with the salt in its crystalline state, such as CuSO4.5H2O.
Efflorescence, Deliquescence, and Hygroscopy
Efflorescent substances lose their water of crystallization to the air, deliquescent substances absorb moisture and dissolve in it, and hygroscopic substances absorb moisture without dissolving.
Important Formulas
Board Exam Info
In the ICSE Chemistry Class 9 examination, this chapter typically carries 6 to 8 marks. Questions frequently include numerical problems on solubility percentage, defining terms like deliquescence and efflorescence with examples, explaining the Tyndall effect, and giving balanced equations for the action of heat on hydrated salts.
Frequently Asked Questions
What is the difference between deliquescent and hygroscopic substances?
Deliquescent substances absorb moisture from the atmosphere and dissolve in it to form a solution (e.g., NaOH, CaCl2), whereas hygroscopic substances only absorb moisture from the air without dissolving or forming a solution (e.g., concentrated H2SO4, silica gel).
Why is water called a universal solvent?
Water is called a universal solvent because its polar nature and high dielectric constant enable it to dissolve a wider variety of polar and ionic compounds than any other liquid.
How does temperature affect the solubility of solids in water?
For most solid solutes, solubility increases as temperature increases because the dissolution process is endothermic, though a few exceptions like sodium sulphate show decreased solubility at higher temperatures.
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