CAPF AC 2022 Q29: Science & Technology – Chemistry
- (a) Sodium salt of acid
- (b) NaHCO3
- (c) CO2
- (d) H2O
Answer: (c) CO2
Explanation
Why bread and cake rise
How to think: something must push the dough up from inside.
Only a gas can do that.
Baking soda releases carbon dioxide when heated, and the gas bubbles make holes in the dough.
The reaction on heating:
2NaHCO3 → Na2CO3 + H2O + CO2.
| Substance | Role |
|---|---|
| NaHCO3 (baking soda) | The source of the gas, not the cause of sponginess itself |
| CO2 | The gas that makes the bread soft and spongy |
| Sodium salt of the acid | Left behind when the acid in baking powder neutralises the soda |
| H2O | A by-product |
Baking powder: it is baking soda mixed with a mild edible acid such as tartaric acid.
The acid removes the bitter taste of sodium carbonate.
Answer: (c) CO2.
Why each option is right or wrong
- (a) Incorrect. The sodium salt is only a leftover product and does not raise the dough.
- (b) Incorrect. NaHCO3 is the baking soda itself; the question asks what it produces.
- (c) CORRECT. Carbon dioxide gas makes the bread rise and become spongy.
- (d) Incorrect. Water is formed too, but it does not puff up the dough.
Key point
Baking soda = sodium hydrogencarbonate, NaHCO3. Baking powder = NaHCO3 + mild edible acid (tartaric acid). Heating or mixing with water releases CO2, which makes bread and cake soft and spongy. Baking soda is also an antacid and is used in soda-acid fire extinguishers.
Remember
Baking soda → CO2 → spongy bread.
Common mistakes
- Marking NaHCO3, the starting material, instead of the gas it gives off.
- Mixing up baking soda (NaHCO3) with washing soda (Na2CO3.10H2O).
- Thinking steam from the water alone makes the bread spongy.
Exam tip
Educated guess: sponginess means holes, and holes need a gas. Among the options the only gas is carbon dioxide.
Sources
- NCERT Class X Science — Acids, Bases and Salts (baking soda)
- NCERT Class VII Science — Acids, Bases and Salts