Could it be that the more foam a soap or detergent produces, the greater its cleaning power?
Most people think so, because when washing dishes, for example, we get the feeling that if a lot of foam is not being produced, the product is not removing the fat. But is this really true?
Well, in order to arrive at a satisfactory answer, we need to know what produces foam in detergents and soaps. But first, let's just specify a few terms used in this text for clarity.
Detergents include soaps, soaps, synthetic detergents, toothpastes, shampoos, among other compounds. All these products are called detergents because they all have the detergent action, that is, from Latin detoxify, which means “clean”. Thus, soaps are a subgroup of detergents; since every soap is a detergent, but not every detergent is a soap.
In this text, however, for didactic purposes, when we mention the term “detergent”, we will be referring to synthetic detergent and not to detergents in general.
Soaps produce the ability to produce bubbles, which are thin films that retain gases. N
In the case of soap, the foam can, to a certain extent, demonstrate that it is acting in cleaning. Many waters contain some cations, such as calcium (Ca2+(here)), magnesium (Mg2+(here)) and iron (Fe2+(here)), which react with the anions present in the soaps, forming the so-called "hard water”, as insoluble compounds are formed that precipitate out.Hard water prevents the soap from cleaning efficiently, as its action as a grease emulsifier is canceled and it cannot remove grease from surfaces and nor produce foam.
An example that clearly shows this is sea water. It is rich in sodium chloride (NaCl, known as table salt) and calcium and magnesium salts. Therefore, we cannot get foam using soap in seawater.
But bubbles play very little role in removing dirt and grease when it comes to detergents. An advantage of detergents over soaps is that they act efficiently even when used in waters rich in calcium, magnesium and iron salts. Detergents do not react with hard water cations. Therefore, they act effectively regardless of the nature of the water.
In the case of detergents, what will indicate whether it is efficient or not, in removing dirt, is the ability to form micelles, that is, small globules that trap the fat inside. This is achieved by the fact that the detergent structure is a non-polar part; and its tip, polar. This chemical structure of detergents (and not the fact that they form foam) ensures cleanliness.
Since manufacturers know that the vast majority of consumers associate the presence of foam with cleaning efficiency, they add foaming substances to detergents. Even though we are aware that non-foaming products are more easily removed by water; even so, these detergent manufacturers prefer to increase the amount of foam in detergents so as not to lose sales.
However, excess foam can cause damage to the consumer, as it can damage the gears of washing machines, for example. Worst of all, lakes and rivers turn into foam deposits, which causes environmental problems, as the foam layer makes it difficult to oxygenate the water, causing the death of fish and algae; and the detergent present in the foam dissolves the wax layer that waterproofs the feathers of water birds, making it difficult for them to float.
Effects of excess foam on rivers and lakes.
Jennifer Fogaça
Graduated in Chemistry
Source: Brazil School - https://brasilescola.uol.com.br/quimica/relacao-entre-quantidade-espuma-eficiencia-limpeza.htm
