|Why can’t we wash with saltwater?
2012.07.06 - 10:00:11 / firstname.lastname@example.org / Translated by: Pedro A. Fanego Sea
Havana, Cuba. – Have you ever wondered why can’t we bathe or wash with saltwater?
Only Chemistry can answer such question.
First, the amount of foam produced by soap depends on the kind of running water that comes from the faucet. Foam is a way to know if water contains a high concentration of certain cations (positive ions).
Admittedly, water can be soft or hard. The former takes much soap to wash. It contains a large quantity of calcium salt or magnesium. The ions released when these salts ionize impede the formation of foam.
Water hardness may be permanent or temporary. The latter is caused by calcium salts and magnesium in the form of bicarbonates. When water is boiled, these salts precipitate and turn into carbonates. On the other hand, the remaining hardness is due to other calcium salts: chlorides and sulfates. Total hardness will come from the sum of temporary and permanent hardness.
In places where water has the right hardness, it is easy to take a foam bath. The products that generate it have 60% of synthetic substances that reduce the water surface tension.
Many of these products for foam baths only contain small detergent quantities. That’s why they are good for relaxing and emitting a pleasant scent, but hardly remove the dirt.
When soap is dipped into the water, foam gradually fades. People must choose between treating their skin properly and bathing with more foam. Products that contain the right quantity of substances with healing properties, or skin protectors, usually produce less foam.
Those who have been at sea without drinking water; know it is hard to take a foam bath. One can’t even wash properly, because soap and seawater are incompatible.
What’s the reason for this? It just depends on the characteristics of soap, a salt of fatty acid and sodium. Once dissolved in water, it dissociates in sodium ions and long chains of fatty acid. The first have a positive electric charge and the second have a negative one.
Fatty acid chains have two parts. One is hydrophobic and, therefore, doesn't combine with water. The other one, with negative charge, is hydrophilic. Salt water contains chloride and sodium ions. The former are negative and the latter are positive. Salt, or sodium chloride, strongly dissociates. Yet, due to the balance between ions, sodium ions decrease the dissociation of soap components.
More sodium implies less dissociated fatty acid. If soap is dissolved in water and the right quantity of salt is added, the dissolved soap will precipitate. Therefore, when saltwater is used, soap cannot produce foam and can hardly remove any dirt. By: Lucia Sanz