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Engineering Exams RRB-JE CMA (Chemical and Metallurgical Assistant) Technical Abilities 2025 22.04.25 Paper-2 Shift-1 Medium +1 -0.33
Which of the following statements about washing soda (Na2CO3·10H2O) are correct? Statement 1: Washing soda is obtained from sodium hydroxide. Statement 2: It is used to remove permanent hardness of water. Statement 3: Washing soda is a hydrated salt.
Correct Answer: D. Only Statements 2 and 3 are correct.
Explanation: Washing soda, chemically known as sodium carbonate decahydrate (Na2CO3·10H2O), is a hydrated salt containing ten molecules of water of crystallization. It is industrially produced via the Solvay process, where sodium carbonate is obtained by heating sodium hydrogencarbonate rather than being directly derived from sodium hydroxide. A primary application of washing soda is in water treatment, where it effectively eliminates both temporary and permanent hardness by reacting with dissolved calcium and magnesium minerals to form insoluble precipitates. Therefore, Statements 2 and 3 are correct, while Statement 1 is incorrect.
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