Changes-Physical and Chemical

In everyday life, we come across both physical and chemical changes. A chemical change is when a substance transforms into a new material with a different composition and properties, while a physical change only affects the appearance or state of a substance without changing its chemical makeup.

• For example, the ripening of a mango or banana involves chemical reactions that change the fruit’s taste, texture, and colour. Enzymes convert starches into sugars, altering the fruit's composition and making it sweeter.
• In contrast, melting ice and boiling water are physical changes. Ice melting into water changes its state from solid to liquid, and boiling turns it into vapour, but the chemical structure of water (H₂O) stays the same.
• Similarly, dissolving salt in water is a physical process where the salt separates into ions but does not change chemically.

Some observations of chemical change

The image shows examples of various chemical changes.

• An apple turns brown, and bread becomes toasted, indicating a colour change.
• Nails rust over time, changing colour and forming rust.
• A matchstick burning demonstrates the release of energy as light and heat.
• Bananas become black as they ripen and decay, showing a colour and texture change.
• A colour change occurs in a chemical solution, indicating a reaction.
• Gas is released and bubbling is visible in a chemical reaction in a flask.

1. Fruit falling from a tree: physical change (movement).
2. Rusting of iron: chemical change (new substance formed).
3. Raining: physical change (change in state: water vapour to liquid).
4. Lighting an electric bulb: physical change (no new substance formed, just energy transformation).
5. Cutting vegetables: physical change (shape change, but still the same material).

1. Aim: To observe and understand the characteristics of a chemical change by adding baking soda to lemon juice.

2. Requirements: lemon juice (in a clean glass), baking soda, a spoon, and clean apparatus for tasting.

3. Procedure

• Pour lemon juice into a clean glass.
• Take two drops of the lemon juice on a spoon and taste it. Note the sourness.
• Add a pinch of baking soda to the glass of lemon juice. Observe what happens:

1. Do you see bubbles forming around the soda particles?
2. Do you hear a faint fizzing sound when you put your ear close to the glass?

• Taste the mixture again. Compare the taste with the original lemon juice.

Observations

• Bubbles form, indicating the release of gas.
• A faint sound is heard due to the reaction.
• The baking soda particles dissolve in the liquid.
• The sour taste of the lemon juice becomes milder.

Conclusion: The change in taste and the formation of bubbles indicate a chemical change. A new substance with different properties is formed, showing that the composition of the original substances has changed.