How does washing soda help soften hard water?
Answer and explanation
Correct answer: By removing calcium and magnesium ions
The governing concept is precipitation of hardness-causing ions. Hard water contains dissolved calcium and magnesium ions, which interfere with soap and produce scum. Washing soda, sodium carbonate (Na2CO3), reacts with these ions to form insoluble carbonates such as calcium carbonate and magnesium carbonate. The precipitates can be removed, reducing hardness. Hence option A is correct; gas formation, acidification and chlorine removal do not explain softening.
Frequently asked questions
What is the correct answer to this question?
By removing calcium and magnesium ions
Why is this the correct answer?
The governing concept is precipitation of hardness-causing ions. Hard water contains dissolved calcium and magnesium ions, which interfere with soap and produce scum. Washing soda, sodium carbonate (Na2CO3), reacts with these ions to form insoluble carbonates such as calcium carbonate and magnesium carbonate. The precipitates can be removed, reducing hardness. Hence option A is correct; gas formation, acidification and chlorine removal do not explain softening.
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.
