1. Why do floating bands of different ions go down through the cation resin column during the service cycle?

2. During the down flow service cycle, in what order would bands of sodium, calcium and magnesium ions occur, from top to bottom, in the cation exchange resin bed?

3. During the cocurrent regeneration cycle, in what order would these bands of ions in question No. 2 occur in the resin bed top to bottom?

4. True or False: The exchange capacity of a water softener is directly related to the level of salting used during regeneration.

5. Select the appropriate option at each lettered item below. At high salting levels:

a. Salt efficiency is (high or low).
b. Regeneration is required (more or less) often.
c. Hardness leakage is (less or greater)

6. Select the appropriate options in parentheses: High total dissolved solids in the supply water will tend to block the exchange sites, leaving fewer sites for the exchange of ions. This may require (more or less) frequent regenerations and (higher or lower) salting levels.

7. List three factors that may affect the purity and concentration of the brine in the salt container.

8. True or False: Whenever very low hardness is required in a commercial application, softened water should be used for brine making.

9. Name two regenerants in addition to sodium chloride that can be used for regeneration of cation resins.

10. True or False: Potassium chloride is less efficient at regenerating strong acid cation than sodium chloride.


1. Cation resin has a unique and respective selectivity for different ions. As a result, some ions move faster down the column of resin than others.

2. Calcium, magnesium, sodium

3. Sodium, calcium, magnesium

4. True

5. a. Low
b. Less
c. Less

6. More, higher

7. 1. Impurities in the salt
2. Impurities in the water used to make brine
3. Temperature of the brine solution

8. True

9. Sodium citrate, potassium chloride

10. False. While potassium chloride (KCl) has fewer ions per pound than NaCl due to its higher molecular weight, the solubility of both compounds in water is identical (360 grams/Kg solution), and the higher atomic weight of potassium makes it more preferred by strong acid cation resin than sodium. The net effect is that the regeneration efficiency of KCl and NaCl is about the same.