About Lesson
Introduction to Changes:
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Our daily lives are filled with various changes, such as dissolving sugar in water or forming curd from milk.
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Simple actions like cutting paper or stretching rubber bands also represent changes occurring around us.
Observation Exercise:
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List ten changes observed in surroundings to understand different types of changes and their significance.
5.1 Physical Changes:
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Definition and Examples: Physical changes alter the appearance or state of a substance without forming new substances.
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Examples include cutting paper, melting wax, or changing the state of water.
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Activity 5.1 (Cutting Paper):
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Cut paper squares into smaller pieces and try to rearrange them to resemble the original shape.
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Outcome: While the paper’s shape changes, its properties remain the same, illustrating a physical change.
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5.2 Chemical Change:
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Definition and Examples: Chemical changes result in the formation of entirely new substances with different properties.
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Examples include rusting of iron, burning coal, or digestion of food.
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Activity 5.6 (Burning Magnesium Ribbon):
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Burn a magnesium ribbon, which transforms into magnesium oxide, showcasing the formation of a new substance.
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Outcome: Magnesium ribbon transforms into magnesium oxide, demonstrating a chemical change.
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5.3 Rusting of Iron:
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Explanation and Prevention: Rusting occurs when iron reacts with oxygen and water to form rust.
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Preventive measures include painting, galvanization, or creating protective shields.
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Activity 5.9 (Rust Resistance of Stainless Steel):
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Explore rust resistance by examining stainless steel, which doesn’t rust easily due to its composition.
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Outcome: Stainless steel remains rust-free, demonstrating its resistance to rusting.
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5.4 Crystallisation:
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Obtaining Pure Substances: Crystallization is used to obtain pure substances from their solutions.
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Large crystals of pure substances can be obtained by controlling the cooling and evaporation of a solution.
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Activity 5.8 (Preparing Copper Sulfate Crystals):
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Dissolve copper sulfate powder in water, allow it to cool, and observe the formation of crystals over time.
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Outcome: Crystals of copper sulfate form, demonstrating the process of crystallization and its application in obtaining pure substances.
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