Question

In the removal of permanent hardness of water by permutit process, Na\(^+\) ions of permutit are exchanged with which ions of water?

• A. K\(^+\), Ba\(^{2+}\)
• B. Fe\(^{2+}\), K\(^+\)
• C. Ca\(^{2+}\), Mg\(^{2+}\)
• D. Zn\(^{2+}\), Cu\(^{2+}\)

Hint:

Remember the simple fact: Water hardness is caused by Ca\(^{2+}\) and Mg\(^{2+}\) ions.
Therefore, any water softening process must be designed to remove these two specific ions.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
We need to determine the hardness of water in ppm by converting the given amount of MgCl₂ into its CaCO₃ equivalent.

Step 2: Key Formula or Approach:
Calculate the CaCO₃ equivalent using the molar mass ratio and then divide it by the mass of water in kilograms to obtain hardness in ppm.

Step 3: Detailed Explanation:
The water sample contains 19 mg of MgCl₂ in 2 kg of water. Since the molar masses of MgCl₂ and CaCO₃ are 95 and 100 respectively, the equivalent amount of CaCO₃ is \(19\times100/95=20\) mg. Therefore, hardness is \(20/2=10\) mg/kg, which is equal to 10 ppm because 1 mg/kg equals 1 ppm.

Step 4: Final Answer:
The hardness of the water sample is 10 ppm.