Question

Permanent hard water may be softened by passing it through
A.sodium silicate
B. sodium bicarbonate
C. sodium hexametaphosphate
D. sodium phosphate

Answer 1

Answer:

Permanent hard water may be softened by passing it through sodium hexametaphosphate.

Explanation:

• Sodium hexametaphosphate has a trading name, Calgon.

• Its chemical formula is (NaPO3)6.
• It is used to soften the permanent hard water.
• This process involves the treatment of Calgon (Na6P6O18) for a complex anion.  
• This complex anion keeps the Mg²⁺ and Ca²⁺ ions in solution.
• When Calgon is added to the hard water to displace Na ions from the anion of Calgon.
• Ca²+ + Na4P6O182 - from the hard water anion of Calgon goes into the solution.
• [Na₄CaP₆O₁₈] + Ca²⁺ →[Na₂CaPO₁₈]²⁻
• With Mg²⁺:[Na₄CaP₆O₁₈] + Mg²⁺ →[Na₂CaPO₁₈]²⁻

• This results in the abolition of Calcium and Magnesium ions from the hard water.
• As a result, water is softened and sodium ions will be released into the water.  

Hence, Sodium hexametaphosphate is used to soften the permanent hard water.