Why is washing soda useful for softening hard water?
Answer and explanation
Correct answer: It helps remove hardness-causing ions
Hard water contains dissolved calcium and magnesium ions. Washing soda, sodium carbonate decahydrate, dissolves to provide carbonate ions. These react with Ca²⁺ and Mg²⁺ to form insoluble carbonates, such as CaCO₃, which can be removed: Ca²⁺ + CO₃²⁻ → CaCO₃(s). Consequently, option A is correct. Washing soda does not soften water by making it acidic, gaseous, or black, so B, C, and D are implausible.
Frequently asked questions
What is the correct answer to this question?
It helps remove hardness-causing ions
Why is this the correct answer?
Hard water contains dissolved calcium and magnesium ions. Washing soda, sodium carbonate decahydrate, dissolves to provide carbonate ions. These react with Ca²⁺ and Mg²⁺ to form insoluble carbonates, such as CaCO₃, which can be removed: Ca²⁺ + CO₃²⁻ → CaCO₃(s). Consequently, option A is correct. Washing soda does not soften water by making it acidic, gaseous, or black, so B, C, and D are implausible.
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.
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