Chapter 17, Problem 102A

Interpretation Introduction

Interpretation:

The reason for the undesirable presence of Ca and Mg ions in water and measures for their removal are to be written.

Concept introduction:

Water containing salts of calcium and magnesium is known as hard water. Hard water does not lather easily with soap.

Answer to Problem 102A

The presence of Ca and Mg ions in water is undesirable because its K_sp is lower than that of soap so on addition of soap, instead of lather scum is formed. To remove these ions measures like boiling, washing soda method, ion exchange method or chelation method.

Explanation of Solution

Since K_sp of Calcium and magnesium salts is less, the soap will act as a precipitation agent to precipitate the salts resulting in the formation of scum.

Conclusion

Ca and Mg salts can be removed by the usage of various softening methods.