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Materials Around Us - Grouping and Sorting of Materials

Grade 6CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Classification: The process of grouping objects based on similarities and differences in their properties. It makes the study of a large number of objects easier and more systematic.

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Lustre: Materials like metals (e.g., Iron, Copper, Gold) that shine are said to have lustre. Those that do not shine are non-lustrous.

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Hardness: Materials that can be compressed or scratched easily are called soft (e.g., cotton, sponge), while materials that are difficult to compress are called hard (e.g., iron, stone).

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Solubility: Substances that completely disappear or dissolve in water (H2OH_2O) are called soluble (e.g., salt, sugar). Substances that do not mix with water even after stirring are called insoluble (e.g., sand, sawdust).

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Transparency: Materials through which objects can be seen clearly are called transparent (e.g., glass, water). Materials through which objects cannot be seen are called opaque (e.g., wood, cardboard). Materials through which objects can be seen but not clearly are called translucent (e.g., oiled paper).

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Density and Buoyancy: Objects with a density ρ\rho less than that of water (1 g/cm31 \text{ g/cm}^3) will float, while objects with a density greater than water will sink.

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Miscibility: Liquids that mix completely with each other are called miscible (e.g., vinegar and water), while liquids that form a separate layer are called immiscible (e.g., oil and water).

📐Formulae

Density (ρ)=Mass (m)Volume (V)\text{Density } (\rho) = \frac{\text{Mass } (m)}{\text{Volume } (V)}

Relative Density=ρsubstanceρwater\text{Relative Density} = \frac{\rho_{\text{substance}}}{\rho_{\text{water}}}

Concentration=Mass of SoluteMass of Solution×100\text{Concentration} = \frac{\text{Mass of Solute}}{\text{Mass of Solution}} \times 100

💡Examples

Problem 1:

Why does a piece of iron sink in water while a piece of wood floats?

Solution:

Iron sinks because its density ρiron\rho_{\text{iron}} is greater than the density of water ρH2O\rho_{H_2O}. Wood floats because its density ρwood\rho_{\text{wood}} is less than the density of water.

Explanation:

Density determines the buoyancy of an object. If ρobject>ρliquid\rho_{\text{object}} > \rho_{\text{liquid}}, the object sinks. If ρobject<ρliquid\rho_{\text{object}} < \rho_{\text{liquid}}, it floats.

Problem 2:

Classify the following as Soluble or Insoluble in H2OH_2O: (a) Sugar, (b) Chalk Powder, (c) Cooking Oil, (d) Glucose.

Solution:

(a) Soluble, (b) Insoluble, (c) Insoluble (Immiscible), (d) Soluble.

Explanation:

Sugar and glucose molecules interact with H2OH_2O to dissolve. Chalk powder and oil do not form a homogenous mixture with water.

Problem 3:

If an object has a mass m=50 gm = 50\text{ g} and a volume V=100 cm3V = 100\text{ cm}^3, will it float or sink in water? (Assume ρwater=1 g/cm3\rho_{\text{water}} = 1\text{ g/cm}^3)

Solution:

The density ρ=50 g100 cm3=0.5 g/cm3\rho = \frac{50\text{ g}}{100\text{ cm}^3} = 0.5\text{ g/cm}^3. Since 0.5 g/cm3<1 g/cm30.5\text{ g/cm}^3 < 1\text{ g/cm}^3, the object will float.

Explanation:

By calculating density using the formula ρ=mV\rho = \frac{m}{V}, we compare it to the density of the medium to determine buoyancy.