3rd Grade ICSE

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Chapter: 08. Some Properties Of Water

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Substances are categorized as either soluble or insoluble based on their ability to dissolve in a solvent, typically water. Soluble substances are those that completely dissolve in a solvent to form a clear solution, where the solute particles are evenly distributed and no longer visible. An example of a soluble substance is sugar, which disappears when stirred into water. In contrast, insoluble substances are those that do not dissolve in a solvent, meaning they remain as separate particles or form a suspension rather than a true solution. Oil is an example of an insoluble substance in water, as it separates and forms distinct layers.

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Whether an object floats or sinks in water is determined by Archimedes’ principle, which relates to the amount of water an object displaces compared to its own weight. If an object displaces less water than its own weight, it will sink to the bottom because it is denser than the water it pushes aside. Conversely, an object will float if it displaces more water than its own weight, indicating it is less dense than the water it displaces. This principle explains why a small coin sinks while a large wooden log floats, as it’s not simply about the size of the object but its density relative to water.

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Several conditions can significantly speed up the process of forming a solution. Firstly, heating the solvent increases the kinetic energy of its particles, allowing them to interact more frequently with the solute and dissolve it faster. Secondly, stirring the solute into the solvent helps to distribute the solute particles more evenly throughout the solvent, accelerating dissolution. Thirdly, using the solute in powdered form or breaking it into smaller pieces increases its surface area, which allows it to dissolve more rapidly. Lastly, increasing the quantity of the solvent can also contribute to a faster solution formation by providing more molecules to interact with the solute.

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Water can change between its solid, liquid, and gaseous forms through various processes. Melting occurs when a solid (like ice) changes into a liquid (water) upon heating. Conversely, solidification (or freezing) is when a liquid (water) turns into a solid (ice) upon cooling. Evaporation is the process where a liquid (water) transforms into a gas (water vapour) when heated. Finally, condensation happens when a gas (water vapour) cools down and changes back into a liquid (water).

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A solution is a homogeneous mixture where one substance fully dissolves into another at a specific temperature. The substance that dissolves is called the solute. The substance in which the solute dissolves is known as the solvent. Together, the solute and solvent form the solution. For example, in lemonade, sugar is the solute because it dissolves, and water is the solvent because it dissolves the sugar, resulting in a sugar-water solution.

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Water exists in three distinct physical forms: solid, liquid, and gas. As a solid, known as ice, water has a fixed shape and size. The liquid form, common water, is wet and fluid; it does not have a fixed shape or size, instead taking on the shape of any container it fills. Water in its gaseous state is called water vapour, which is present all around us, lacks a fixed shape or size, can flow, and expands to fill all available space.

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