Chapter 6 of Class 6 Science Changes Around Us 

 1.Understanding Changes

 - Changes occur all around us. They may happen on their own (natural) or be caused by humans (man-made).

- Examples- include melting ice, folding paper, or burning wood.

 2. Types of Changes

-Reversible Changes: These are changes that can be undone. Examples:

- Melting: Ice melts into water, and water can freeze back into ice.

- Folding: A piece of paper folded can be unfolded.

- Irreversible Changes: These are changes that cannot be undone. Examples:

- Burning: Burning wood turns into ash and cannot return to wood.

- Cutting: Once a paper is cut, it cannot be made whole again.

 3. Physical Changes and Chemical Changes

 - Physical Change: The substance itself doesn’t change, only its form or appearance. Example: Dissolving sugar in water.

 - Chemical Change: New substances are formed. Example: Rusting of iron, where iron reacts with oxygen to form rust.

4.Other Characteristics of Changes

 -*Slow and Fast Changes:

 - Slow Change: Happens over a long period, e.g., rusting of iron.

 - Fast Change: Happens quickly, e.g., bursting of a balloon.

  - *Desirable and Undesirable Changes:

 - Desirable: Changes we want to happen, e.g., cooking food.

 - Undesirable: Changes we do not want, e.g., food spoilage.

 - Periodic and Non-Periodic Changes:

 -Periodic: Changes that repeat after a regular interval, e.g., seasons, day and night.

 - Non-Periodic: Changes that occur at irregular intervals, e.g., earthquakes.

 5. Examples of Daily Changes

 - The chapter provides examples from daily life to help students observe and classify various changes, like stretching a rubber band, inflating a balloon, or cooking.

These notes cover key concepts to help students understand and differentiate between various types of changes in their environment.

 Class 6 Science, Chapter 5: Separation of Substances

# Introduction

In everyday life, we come across mixtures of many substances. This chapter describes why we need to separate substances, how it is done, and some practical examples in which separation is required.

# Topics Covered

1. Need for Separation

 - Purpose of Separation:

- To remove undesirable or harmful substances.

     Useful constituents of a mixture

     To separate different substances for individual use

   - Examples

     Removal of stones from rice or pulses.

     Salt removal from seawater.

2. Types of Mixtures

Heterogeneous Mixtures: The components are not evenly dispersed (such as sand with iron fillings).

Homogeneous Mixtures: The components are evenly distributed (such as saltwater).

3. Methods of Separation

   - Picking by Hand

    - For bulk, visible impurities.

    - Illustration: Stone removal from rice or beans.

  *Threshing

It is used to separate grain stalks in agriculture.

    It entails beating the stalks free of grain.

   *Winnowing

    it separates smaller particles from heavier using wind or air

    Example - Separation of husk from grain

  *Sieving

- Uses a sieve to separate particles of different sizes.

Example: Sieving flour to remove lumps.

Sedimentation, Decantation, and Filtration

Sedimentation; Heavier particles settle at the bottom of a liquid.

Decantation: Pouring out the liquid to leave sediment behind.

Filtration: The separation of solid from liquids using a filter.

Example: Getting water from sand.

 *Evaporation

It is used to get the substance dissolved in the liquid by heating the mixture after which the liquid gets evaporated. 

Example: From seawater, how salt can be obtained.

 *Condensation

 The process in which the vapor is cooled to get converted into liquid form.

 Example: Water droplets condensed on a cold surface.

  *Distillation

    A combination of distillation and condensation. Separates mixtures with different boiling points.

    Example: Purify water.

4. Use of Separation Techniques

- Purifying Drinking Water: Filtering and distillation

- Salt extraction from sea: Evaporation and crystallization

- Grain storage: Winnowing, sieving and drying are done to maintain quality in the process of storage.

5. Solubility and Saturation

   -Soluble substances: Those which dissolve in a solvent (salt in water)

  -Insoluble substances: Those which cannot dissolve (sand in water).

Saturation: Condition at which no further amount of solute can dissolve in a given amount of solvent at a specified temperature.

# Summary

Knowing about the techniques of separation helps us process substances, obtain required constituents, and save resources. These techniques are used practically everywhere in our day-to-day lives, agriculture, and industries.

These notes encompass all the key points and methods of Chapter 5, which aid in gaining a better understanding about separation techniques and their significance.