At nearly 70 °C, sodium bicarbonate shows the property of gradually decomposing, which makes it usable in bakery products. The product of decomposition responsible for this use of sodium bicarbonate is
- (a)Carbon dioxide
- (b)Hydrogen
- (c)Water vapour
- (d)Oxygen
Correct — A, Carbon dioxide. On heating, sodium bicarbonate (baking soda) decomposes: 2NaHCO3 gives Na2CO3 + H2O + CO2. The carbon dioxide gas released is trapped as bubbles in the batter, making cakes and bread rise and become spongy, which is exactly why baking soda is used in bakery products.
- (b)Hydrogen — No hydrogen gas is produced in this decomposition.
- (c)Water vapour — Water is one of the products, but it is the carbon dioxide gas that gets trapped and leavens the dough; water vapour alone does not give the rising, spongy texture.
- (d)Oxygen — No oxygen is released when sodium bicarbonate decomposes.
Sodium bicarbonate undergoes thermal decomposition on gentle heating to give sodium carbonate, water and carbon dioxide. The escaping carbon dioxide is a leavening agent — it forms bubbles that make baked goods light and porous. In baking powder the soda is mixed with a mild edible acid so the leftover sodium carbonate does not leave a bitter taste.
Water vapour is the tempting distractor because it is also a product, but the leavening (rising) effect comes specifically from the carbon dioxide gas.
- Heating baking soda: 2NaHCO3 gives Na2CO3 + H2O + CO2 (from roughly 50 to 100 °C).
- The carbon dioxide gas released makes dough and batter rise and become porous and spongy.
- Baking powder is baking soda plus a mild edible acid (such as tartaric acid), which removes the bitter taste of the sodium carbonate left behind.
- Sodium bicarbonate is also used in antacids and in soda-acid fire extinguishers.
- Choosing water vapour — it is produced, but the carbon dioxide is what leavens the dough.
- Assuming oxygen or hydrogen is released.
Asked as 'which gas from baking soda makes cakes rise' or as the decomposition products of NaHCO3.
No directly related past PYQ was found.
- practice — not a real PYQ
Baking powder is a mixture of baking soda and
- (a)washing soda
- (b)a mild edible acid such as tartaric acid
- (c)common salt
- (d)slaked lime
Answer(b) a mild edible acid such as tartaric acid — it neutralises the bitter sodium carbonate formed.
- practice — not a real PYQ
The chemical formula of baking soda is
- (a)Na2CO3
- (b)NaHCO3
- (c)NaOH
- (d)Na2CO3·10H2O
Answer(b) NaHCO3 — sodium hydrogencarbonate.