Class 6 Notes

Class 6 Science Notes Chapter 4 (Chapter 4) – Examplar Problem Book

Philoid

Philoid

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Examplar Problem
Detailed Notes with MCQs of Chapter 4, 'Sorting Materials into Groups', from your NCERT Science Exemplar book. This is a foundational chapter, and understanding the properties of materials is crucial not just for your class exams but also forms the basis for many questions in government recruitment exams. Pay close attention to the properties used for classification.

Chapter 4: Sorting Materials into Groups - Detailed Notes

1. Introduction: Why Sort?

  • We see a vast variety of objects around us (chairs, clothes, utensils, toys, water, stones, etc.).
  • These objects are made from different materials (wood, plastic, cotton, metal, glass, mud, paper, etc.).
  • Sometimes, an object is made from a single material (e.g., a plastic toy).
  • Sometimes, an object is made from multiple materials (e.g., a bicycle has metal, rubber, plastic parts).
  • Sorting or Grouping helps us:
    • Organize objects for convenience (e.g., keeping all spices together in the kitchen).
    • Study the properties of materials systematically.
    • Understand why certain materials are used for specific purposes.
    • Locate items easily.
  • Grouping is done based on similarities or differences in their properties.

2. What are Materials?

  • The substance or matter from which an object is made is called a material.
  • Examples: Wood, Glass, Plastic, Metals (Iron, Copper, Aluminium, Gold, Silver), Cotton, Silk, Wool, Paper, Leather, Mud, Rock, Sand, Water, Air.

3. Key Properties of Materials (Basis for Sorting)

We group materials based on certain characteristics they possess. The important properties are:

  • (a) Appearance:

    • Lustre: This refers to the shine of a material.
      • Materials with shine are called lustrous. Examples: Metals like Gold, Silver, Iron, Copper, Aluminium (often lose shine when exposed to air/moisture, but shine is visible on freshly cut surfaces or when polished).
      • Materials without shine are called non-lustrous or dull. Examples: Wood, Paper, Plastic, Cotton, Chalk.
    • Some materials might feel rough, while others feel smooth. This is related to texture, another aspect of appearance.

  • (b) Hardness:

    • Hard Materials: Difficult to compress or scratch. Examples: Iron, Steel, Wood, Stone, Diamond (hardest natural substance).
    • Soft Materials: Can be compressed or scratched easily. Examples: Cotton, Sponge, Wax, Chalk, Rubber.

  • (c) Solubility (in Water):

    • Soluble Substances: Substances that completely disappear or dissolve in water. When dissolved, they form a solution. Examples: Salt, Sugar, Vinegar, Lemon Juice, Glycerine, Oxygen gas (essential for aquatic life).
    • Insoluble Substances: Substances that do not dissolve in water, even after stirring. They may sink to the bottom or float on the surface. Examples: Sand, Chalk powder, Sawdust, Oil, Kerosene, Mustard oil, Coconut oil, Nitrogen gas.
    • Liquids & Solubility:
      • Miscible Liquids: Liquids that mix completely with water. Examples: Vinegar, Lemon juice, Alcohol, Glycerine.
      • Immiscible Liquids: Liquids that do not mix with water and form a separate layer. Examples: Mustard oil, Coconut oil, Kerosene, Petrol.

  • (d) Floatation/Sinking (in Water):

    • Objects/Materials that are less dense than water float on it. Examples: Wood (most types), Dried leaves, Plastic ball, Oil, Wax, Ice (though solid water, it's less dense than liquid water).
    • Objects/Materials that are denser than water sink in it. Examples: Stone, Iron nail, Coin, Key, Sand, Sugar, Salt (though soluble, the solid particles initially sink).
    • Note: Density is the key factor, though the term might not be heavily emphasized in Class 6, the concept of 'heavier' or 'lighter' for the same volume is introduced.

  • (e) Transparency: This property relates to how much light can pass through a material.

    • Transparent Materials: Allow light to pass through them completely, so we can see clearly through them. Examples: Glass, Clean Water, Air, Some plastics (like cellophane sheets). Used for making window panes, spectacles, containers to see contents.
    • Translucent Materials: Allow light to pass through partially, so we can see through them, but not clearly (objects appear blurry). Examples: Butter paper, Oiled paper, Frosted glass, Thin muslin cloth, Some plastics. Used where partial light is needed, like bathroom windows.
    • Opaque Materials: Do not allow any light to pass through them. We cannot see through them at all. Examples: Wood, Metals, Cardboard, Brick wall, Stone. Used for making walls, containers to protect contents from light.

4. Importance of Grouping based on Properties:

  • Knowing the properties helps us choose the right material for a specific purpose.
    • Example: We use glass (transparent) for windows, but wood or metal (opaque) for doors.
    • Example: We use metals (hard, strong, often lustrous) for making utensils, tools, and vehicles, but cotton (soft, absorbent) for clothes.
    • Example: Tumblers are made of glass, plastic or metal, not cloth (as cloth cannot hold liquids).

Summary for Quick Revision:

  • Objects are made of materials.
  • Materials are grouped based on properties: Appearance (Lustre), Hardness, Solubility (Soluble/Insoluble, Miscible/Immiscible), Floatation/Sinking, Transparency (Transparent/Translucent/Opaque).
  • Grouping helps in organization, study, and choosing materials for specific uses.

Multiple Choice Questions (MCQs)

Here are 10 MCQs based on Chapter 4 to test your understanding:

  1. Which of the following properties refers to the shine observed on a freshly cut surface of metal?
    (a) Hardness
    (b) Lustre
    (c) Transparency
    (d) Solubility

  2. Which material among the following is generally considered soft?
    (a) Iron
    (b) Stone
    (c) Cotton
    (d) Glass

  3. A substance that disappears completely when mixed with water is called:
    (a) Insoluble
    (b) Opaque
    (c) Soluble
    (d) Lustrous

  4. Which pair of liquids will form a separate layer when mixed, indicating they are immiscible?
    (a) Vinegar and Water
    (b) Lemon Juice and Water
    (c) Coconut Oil and Water
    (d) Alcohol and Water

  5. Materials through which objects can be seen, but not clearly, are known as:
    (a) Transparent
    (b) Opaque
    (c) Lustrous
    (d) Translucent

  6. Wood and cardboard are examples of materials that do not allow light to pass through them. They are classified as:
    (a) Transparent
    (b) Translucent
    (c) Opaque
    (d) Soluble

  7. Which of the following items is most likely to float on water?
    (a) An iron key
    (b) A marble
    (c) A plastic bottle cap
    (d) A steel spoon

  8. The primary reason for sorting materials into groups is:
    (a) To make them look beautiful
    (b) For convenience and to study their properties systematically
    (c) To increase their weight
    (d) To change their colour

  9. Frosted glass is an example of a material that is:
    (a) Transparent
    (b) Translucent
    (c) Opaque
    (d) Soluble

  10. Which of the following materials typically possesses lustre?
    (a) Chalk powder
    (b) A piece of wood
    (c) A copper wire
    (d) A rubber band

Answer Key:

  1. (b)
  2. (c)
  3. (c)
  4. (c)
  5. (d)
  6. (c)
  7. (c)
  8. (b)
  9. (b)
  10. (c)

Study these notes carefully. Understanding these basic properties is essential. Let me know if any part needs further clarification!

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