Washing soda helps remove which ions from hard water?
Answer and explanation
Correct answer: Calcium and magnesium ions
The governing concept is the removal of hardness-producing ions by precipitation. Hard water mainly contains dissolved Ca²⁺ and Mg²⁺ ions. Washing soda, Na₂CO₃, supplies CO₃²⁻ ions, which form sparingly soluble calcium carbonate and magnesium carbonate: Ca²⁺ + CO₃²⁻ → CaCO₃ and Mg²⁺ + CO₃²⁻ → MgCO₃. These precipitates can be separated, so option B is correct; sodium and chloride ions do not cause hardness.
Frequently asked questions
What is the correct answer to this question?
Calcium and magnesium ions
Why is this the correct answer?
The governing concept is the removal of hardness-producing ions by precipitation. Hard water mainly contains dissolved Ca²⁺ and Mg²⁺ ions. Washing soda, Na₂CO₃, supplies CO₃²⁻ ions, which form sparingly soluble calcium carbonate and magnesium carbonate: Ca²⁺ + CO₃²⁻ → CaCO₃ and Mg²⁺ + CO₃²⁻ → MgCO₃. These precipitates can be separated, so option B is correct; sodium and chloride ions do not cause hardness.
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.
