On heating baking soda, the remaining solid solution turns red litmus blue. What is the identity of the remaining solid?
Answer and explanation
Correct answer: Sodium carbonate
Baking soda is sodium hydrogen carbonate, NaHCO₃. On heating, it decomposes according to 2NaHCO₃ → Na₂CO₃ + CO₂ + H₂O. The solid residue is therefore sodium carbonate, Na₂CO₃. Its aqueous solution is basic because carbonate ions hydrolyse water to produce hydroxide ions, so it turns red litmus blue. Sodium chloride is neutral, while the other choices do not match this decomposition.
Frequently asked questions
What is the correct answer to this question?
Sodium carbonate
Why is this the correct answer?
Baking soda is sodium hydrogen carbonate, NaHCO₃. On heating, it decomposes according to 2NaHCO₃ → Na₂CO₃ + CO₂ + H₂O. The solid residue is therefore sodium carbonate, Na₂CO₃. Its aqueous solution is basic because carbonate ions hydrolyse water to produce hydroxide ions, so it turns red litmus blue. Sodium chloride is neutral, while the other choices do not match this decomposition.
Which subject and chapter does this question cover?
This is a Class 10 Science question. Chapter: Chemical Substances – Nature and Behaviour. Topic: Acids, Bases, and Salts.
