Soaps and soapless detergents
HOW ARE SOAPS MADE?
Soaps are made by the process of saponification, which involves the hydrolysis of fats and oils using an alkali; for example, heating animal fat or vegetable oil with concentrated sodium bydroxide (NaOH). The alkali, sodium hydroxide, hydrolyses the ester present in the fat or oil. Soaps are, therefore, the alkali metal (Na, K or Li) salts of fatty acids. The oil or fat would represent the ester formed from the combination of glycerol with a fatty acid. When sodium hydroxide is added, the ester is hydrolysed to form glycerol, and the sodium ion replaces the hydrogen on the acid to form the sodium salt (a soap). E.g., Fat/Oil (ester) + sodium hydroxide ––– glycerol + sodium stearate (soap) A soap molecule is made of two parts: a long, hydrocarbon part and a short, ionic part containing COO-Na+ group. The structure of the soap molecule resembles a tadpole. The long, hydrocarbon chain forms the hydrophobic end which repels or hates water. The ionic part forms the hydrophilic or water-loving end.
WHAT IS THE MAIN DIFFERENCE BETWEEN A SOAP AND A DETERGENT?
The main difference between the two is that soaps are made from plant oils or animal fats reacting with an alkali, while detergents are made from petroleum products reacting with sulphuric acid. Here, crude oil is used instead of animal fats and vegetable oils. In soapless detergents, the hydrophilic end contains a sulphonate ion from the use of the sulphuric acid.
Soaps and detergents are also different in other ways. Soaps are usually biodegradable, since they are made from plant or animal products, while soapless detergents are non-biodegradable products that can end up harming the environment.
WHY IS MORE SOAP USED WHEN WASHING WITH HARD WATER?
Hard water describes water that has dissolved calcium and magnesium salts, usually occurring when water flows over rocks such as limestone. When used with hard water, soap reacts with the calcium and magnesium ions to form insoluble precipitates called scum. The presence of scum is unsightly, as it sticks to clothes. As scum sticks to clothes, the cleaning action of the soap is affected, hence, it results in the use of more soap being used in the washing process.
WHAT ARE THE ADVANTAGES AND DISADVANTAGES OF USING DETERGENTS AND SOAPS?
Detergents can clean effectively, even in acidic mediums, as they are made from the salts of strong acids (e.g., sulphuric acid). They are more soluble in water and have a stronger cleansing action. Unlike soap, less detergent would be needed, as it is not being used up to form scum. The use of detergents would also result in the conserving of natural vegetable oils and animal fats which can serve other purposes. Unfortunately, the fact that they are made from petroleum products will only serve to deplete these non-renewable resources. Soaps have less impact on the environment since they are biodegradable, while detergents can cause more harm to the environment. The phosphate levels in some of these detergents influence the pollution of water bodies as a result of nutrient enrichment. Nowadays, some detergents are made ‘phosphate-free’, which lessens their impact on waterways.
SOAP MAKING IS SIMILAR TO WHICH REACTION OF ESTERS?
Since soap making involves the breaking down of an ester from oil or fat, this would be similar to the hydrolysis reaction of esters. Esters can be hydrolysed (broken down) using acid or alkali to yield the acid (or salt of the acid) and alcohol that formed the ester. Soaps would represent the salt of the acid formed from the hydrolysis reaction. For example, the ester methyl ethanoate can be heated in the presence of acid to form methanol and ethanoic acid. CH 3COOCH3(l) –––– CH3OH (l) + CH3COOH (l) Methyl ethanoate methanol ethanoic acid Francine Taylor-Campbell is an independent contributor. Send comments to kerry-ann. hepburn@gleanerjm.com.