Sorting Materials into Groups (NCERT Ch. 4)

• Sort objects/materials based on properties: appearance, hardness, solubility, floating/sinking, transparency.
• Understand that the same material can be used to make different objects, and one object can be made of different materials.
• Classify materials as soluble/insoluble in water and transparent/translucent/opaque.

1. Appearance — colour, shine (lustre), texture.
2. Hardness — hard materials resist being scratched/pressed (e.g. stone); soft materials can be compressed/scratched easily (e.g. sponge, cotton).
3. Solubility — a material that dissolves completely in water is soluble (e.g. sugar, salt); one that does not is insoluble (e.g. sand, chalk powder).
4. Floating and sinking depends on the material of the object, roughly linked to density.
5. Transparency: transparent (see clearly through, e.g. glass), translucent (see partially, e.g. butter paper), opaque (cannot see through, e.g. wood).

Classify salt, sand, and sugar by solubility in water.

Salt: soluble (dissolves completely)
Sugar: soluble (dissolves completely)
Sand: insoluble (settles at the bottom, does not dissolve)

• Confusing "mixing" with "dissolving" — sand mixed in water is still insoluble, just suspended temporarily.
• Assuming heavier objects always sink — it actually depends on the material and shape (e.g. a steel ship floats due to shape).
• Mixing up translucent and transparent.

• Is chalk soluble or insoluble in water?
• Give an example of a translucent material.

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