Washing soda softens hard water by removing which ions?
Answer and explanation
Correct answer: Calcium and magnesium ions
Hard water contains dissolved calcium ions, Ca²⁺, and magnesium ions, Mg²⁺, which form scum with soap. Washing soda, sodium carbonate (Na₂CO₃), supplies carbonate ions that precipitate these ions as insoluble calcium carbonate and magnesium carbonate. Removing them reduces hardness. Sodium and chloride ions are not the hardness-causing pair, so option A is correct.
Frequently asked questions
What is the correct answer to this question?
Calcium and magnesium ions
Why is this the correct answer?
Hard water contains dissolved calcium ions, Ca²⁺, and magnesium ions, Mg²⁺, which form scum with soap. Washing soda, sodium carbonate (Na₂CO₃), supplies carbonate ions that precipitate these ions as insoluble calcium carbonate and magnesium carbonate. Removing them reduces hardness. Sodium and chloride ions are not the hardness-causing pair, so option A is correct.
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.
