"Soft water" has been treated to replace the polyvalent metal cations with sodium and potassium ions. Why are the problems of scale and bathtub ring not associated with soft water?
...and/or...
What mineral(s) would be sources of the calcium in hard water?
2007-10-28 09:21:52 · 2 answers · asked by JitterBug589 3 in Science & Mathematics ➔ Chemistry
Scale is due to the insoluble compounds calcium carbonate and magnesium carbonate which are formed when the corresponding soluble hydrogencarbonates are heated in aqueous solution. As sodium and potassium carbonate are soluble, you do not get scale when you heat soft water.
Scum (bathtub ring) is due to the insoluble compound formed when calcium (or magnesium) ions combine with the anions in soap (e.g. stearate). Sodium and potassium stearate are soluble so you do not get scum with soft water.
2007-10-28 09:28:46 · answer #1 · answered by Chemmunicator 5 · 0⤊ 0⤋
Soaps are sodium salts of long-chain fatty acids,such as sodium stearate. Calcium and magnesium ions form insoluble stearate salts. These ARE scale and ring-around-the-bathtub. Because our hypothetical soap is already water-soluble sodium stearate, there is no precipitate. Ground water percolates through rock formations such as "insoluble" calcium carbonate. This is limestone or marble. Ca++ winds up in the water.
2007-10-28 09:31:30 · answer #2 · answered by steve_geo1 7 · 0⤊ 0⤋