Imagine you are about to be marooned on a tropical island as part of an outdoor

Question

Imagine you are about to be marooned on a tropical island as part of an outdoor survival course. The island has no fresh water, but it does have an abundant supply of coconuts which you can use for your drinking water. You must use sea water for all washing purposes. You have been given the choice of taking either a bar of soap or 100mL of liquid detergent with you to wash yourself during your 4 weeks of isolation on the island. Will you take the bar of soap or the detergent to keep clean? Explain your choice

Explanation / Answer

Inexpensive common regular commercial soap will not lather or dissolve in seawater (or also "hard water" from calcium) due to high levels of sodium chloride in the water. Similarly, common soap does not work as well as potassium-based soap in hard water where calcium replaces the sodium, making residual insoluble "scum" due to the insolubility of the soap residue. To be an effective cleaning agent, soap must be able to dissolve in water.

In the cleaning process, surface tension must be reduced so water can spread and wet surfaces. Chemicals that are able to do this effectively are called surface active agents, or surfactants. They are said to make water “wetter.”

A detergent is an effective cleaning product because it contains one or more surfactants. Because of their chemical makeup, the surfactants used in detergents can be engineered to perform well under a variety of conditions. Such surfactants are less sensitive than soap to the hardness minerals in water and most will not form a film.

By lowering the surface tension of water, surfactants enable the cleaning solution to wet a surface (for example, clothes, dishes, countertops) more quickly, so soil can be readily loosened and removed (usually with the aid of mechanical action). Surfactants also emulsify oily soils and keep them dispersed and suspended so they do not settle back on the surface. To accomplish their intended jobs effectively, many cleaning products include two or more surfactants.

So, the most obvious choice would be 100ml of liquid detergent. Although its very less in quantity but atleast it will help in cleaning process unlike soap which would only produce scum.

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