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What are Chemical Changes?
They are changes in which one or more new substances are formed .
- Chemical changes involve formation of new substances .
- New substances are formed through chemical reactions .
- Chemical reactions can be represented by chemical equations .
- Lime water test is used to detect carbon dioxide .
Activity 5.3: Let us explore
Take two glass tumblers or small transparent bottles. Mark them A and B .
Fill one-fourth of tumbler A with tap water and one-fourth of tumbler B with lime water .
Blow air (exhale) into each tumbler one at a time using separate straws and observe them.
Caution — Do not suck the water or lime water while doing this.
Observations:
| Tumbler | Contents | Observation when air is blown in |
|---|---|---|
| A | Tap water | Bubbles form only; no change in the appearance of water |
| B | Lime water | Bubbles form; lime water turns milky (cloudy) ; white substance (calcium carbonate) settles at the bottom |
In glass tumbler B, a white substance (calcium carbonate) settles at the bottom, indicating that a new substance has formed . Such changes, in which one or more new substances are formed, are called chemical changes . New substances are formed through a process called a chemical reaction .
In this case, carbon dioxide from the air you exhale reacts with lime water (calcium hydroxide) to form calcium carbonate (insoluble white substance) and water:
Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water
(Lime water)
(Insoluble substance)
The turning of lime water milky is also used as a test for carbon dioxide .
