Class 8 Science - ICSE-CHEMISTRY
Water
The chapter 'Water' in Class 8 ICSE Chemistry explores water as a universal solvent, its physical and chemical properties, and its role as a compound. Students will learn about solutions, solubility, and the distinction between unsaturated, saturated, and supersaturated solutions. The chapter also covers the presence of water of crystallization in hydrated salts, the difference between hard and soft water, and methods to remove hardness. This chapter is vital for ICSE board exams as it tests conceptual understanding of solubility curves, chemical formulas of hydrated crystals, and reasoning questions on water pollution and purification.
Start Learning FreeKey Concepts
Universal Solvent
Water is called a universal solvent because it can dissolve a wide variety of substances, both solids and gases, more than any other liquid.
Solubility
Solubility is the maximum amount of a solute that can dissolve in 100 grams of a solvent at a specific temperature to form a saturated solution.
Water of Crystallization
It is the fixed number of water molecules chemically combined in a definite proportion within the crystal lattice of a salt.
Efflorescence
The property of certain hydrated crystals to lose their water of crystallization to the atmosphere when exposed, turning into a powdery substance.
Deliquescence
The property of certain water-soluble substances to absorb moisture from the atmospheric air and dissolve completely in it to form a solution.
Hard and Soft Water
Soft water readily forms lather with soap, while hard water contains dissolved calcium and magnesium salts that prevent easy lather formation.
Important Formulas
Board Exam Info
In ICSE Chemistry (Class 8), this chapter typically carries around 6 to 10 marks. Common question types include defining terms like efflorescence and deliquescence, giving examples of hydrated salts, distinguishing between saturated and unsaturated solutions, and explaining reasons for water hardness and its removal.
Frequently Asked Questions
What is the difference between efflorescence and deliquescence?
Efflorescence is the loss of water of crystallization from hydrated crystals to the air, whereas deliquescence is the absorption of moisture from the air by substances until they dissolve.
Why is water called a universal solvent?
Water is called a universal solvent because its polar nature allows it to dissolve polar and ionic compounds easily, making it capable of dissolving more substances than any other liquid.
Does solubility increase with temperature for all substances?
No, while the solubility of most solid solutes increases with a rise in temperature, the solubility of gases in water generally decreases as temperature increases.
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