Class 6 Science Notes Chapter 4 (Sorting Materials into Groups) – Science Book

Detailed Notes with MCQs of Chapter 4: 'Sorting Materials into Groups'. This is a fundamental chapter that helps us understand why things are made of certain materials and how we can classify them. Understanding these basics is crucial, not just for your class exams, but also as foundational knowledge for various government exams.

Chapter 4: Sorting Materials into Groups - Detailed Notes

1. Introduction: Objects and Materials

• Our surroundings are filled with a vast variety of objects (e.g., chair, table, book, pen, clothes, utensils, toys).
• These objects differ in shape, size, colour, and use.
• Objects are made from one or more types of materials.
• Examples:
  • A chair can be made of wood, plastic, or metal.
  • A tumbler can be made of glass, plastic, or metal (like steel or brass).
  • A coin is made of metal.
  • A book is made mainly of paper.
• Sometimes, a single object is made from multiple materials (e.g., a bicycle has metal, rubber, plastic parts). Conversely, the same material can be used to make many different objects (e.g., wood is used for chairs, tables, doors, boats, carts).

2. Why Sorting is Necessary?

• Convenience: Grouping objects helps us locate them easily. Think about arranging books by subject in a library, or spices in a kitchen.
• Study of Properties: Grouping objects based on the materials they are made of allows us to study the common properties of those materials.
• Utility: We choose a material to make an object depending on its properties and the purpose the object is intended for (e.g., we use glass for tumblers because it's transparent and can hold liquids, not cloth).

3. Basis for Sorting: Properties of Materials

We group materials based on similarities or differences in their properties. Key properties discussed are:

• (a) Appearance:

  • Lustre: This refers to the shine of a material.
    • Materials with shine are called lustrous (e.g., metals like gold, silver, iron, copper, aluminium).
    • Materials without shine are non-lustrous or dull (e.g., wood, paper, cardboard, chalk, plastic).
    • Note: Some metals lose their lustre when exposed to air and moisture due to chemical reactions (tarnish or rust), but their freshly cut surface reveals the shine.
  • Hardness: This refers to how easily a material can be compressed or scratched.
    • Hard Materials: Difficult to compress or scratch (e.g., iron, stone, wood, diamond - the hardest natural substance).
    • Soft Materials: Can be compressed or scratched easily (e.g., cotton, sponge, wax, chalk).
  • Texture: How a material feels on touching (e.g., smooth, rough). Glass is smooth, sandpaper is rough.

• (b) Solubility: This refers to the ability of a substance to dissolve in a liquid (usually water is considered).

  • Soluble Substances: Disappear completely when mixed with water, forming a solution (e.g., salt, sugar, vinegar, lemon juice). Water is a good solvent for many substances.
  • Insoluble Substances: Do not dissolve in water even after stirring, and remain separate (e.g., sand, chalk powder, sawdust, oil, stone).
  • Liquids: Some liquids mix well with water (miscible, e.g., vinegar, lemon juice), while others form a separate layer (immiscible, e.g., mustard oil, coconut oil, kerosene).
  • Gases: Some gases dissolve in water (e.g., oxygen, carbon dioxide - crucial for aquatic life), while others are less soluble.

• (c) Float or Sink in Water: This property is related to density (how heavy a material is for its size compared to water).

  • Float: Materials that are lighter than water float on its surface (e.g., wood, dried leaves, plastic ball, oil, wax, ice).
  • Sink: Materials that are heavier than water sink to the bottom (e.g., stone, coin, key, iron nail, sand, sugar, salt - though salt/sugar dissolve, the solid particles initially sink).

• (d) Transparency: This refers to the ability of a material to allow light to pass through it.

  • Transparent Materials: Allow light to pass through completely, so we can see clearly through them (e.g., glass, clear water, air, some plastics like cellophane). Used for windows, spectacles, containers to see contents.
  • Translucent Materials: Allow light to pass through partially, so we can see through them, but not clearly (e.g., butter paper, frosted glass, oily patch on paper, thin muslin cloth). Used where partial visibility or diffused light is needed.
  • Opaque Materials: Do not allow any light to pass through them, so we cannot see through them at all (e.g., wood, metals, cardboard, stone, walls). Used for privacy, blocking light, making containers where contents need not be seen.

4. Summary of Key Concepts

• Objects are made of materials.
• Materials have distinct properties like lustre, hardness, solubility, density (float/sink), and transparency.
• We group materials based on these properties for convenience and study.
• The choice of material for making an object depends on its properties and the required function.

Key Terms for Revision:
Hard, Insoluble, Lustre, Material, Metals, Opaque, Rough, Soluble, Translucent, Transparent.

Multiple Choice Questions (MCQs) for Practice:

1. Which of the following materials typically possesses lustre?
   a) Wood
   b) Plastic
   c) Aluminium
   d) Chalk

2. A substance that dissolves completely in water is called:
   a) Insoluble
   b) Opaque
   c) Soluble
   d) Lustrous

3. Which property allows us to see clearly through glass?
   a) Hardness
   b) Solubility
   c) Transparency
   d) Lustre

4. Identify the opaque material from the following options:
   a) Clear Water
   b) Air
   c) Cardboard
   d) Frosted Glass

5. If you drop a coin and a dried leaf into a bucket of water, what will you observe?
   a) Both will float
   b) Both will sink
   c) The coin will sink, and the leaf will float
   d) The coin will float, and the leaf will sink

6. Vinegar mixes completely with water. Therefore, vinegar is ______ in water.
   a) Insoluble
   b) Immiscible
   c) Miscible
   d) Translucent

7. Which of these is a soft material?
   a) Iron
   b) Stone
   c) Cotton
   d) Glass

8. Butter paper allows light to pass through partially, making objects behind it look blurry. Butter paper is:
   a) Transparent
   b) Opaque
   c) Lustrous
   d) Translucent

9. Grouping materials is useful because:
   a) It makes the materials look better.
   b) It helps in studying their properties systematically.
   c) It changes the properties of the materials.
   d) It makes all materials soluble.

10. Which pair consists of materials that are generally non-lustrous?
    a) Gold and Silver
    b) Iron and Copper
    c) Wood and Plastic
    d) Aluminium and Steel

Answer Key for MCQs:

1. c) Aluminium
2. c) Soluble
3. c) Transparency
4. c) Cardboard
5. c) The coin will sink, and the leaf will float
6. c) Miscible
7. c) Cotton
8. d) Translucent
9. b) It helps in studying their properties systematically.
10. c) Wood and Plastic

Study these notes carefully, focusing on the definitions and examples of each property. Understanding the basis of classification is key. Good luck with your preparation!