Cleansing Substance- SOAP

Introduction

Cleansing agents are chemical substances used to remove grease and dirt. There are two types of cleansing agents, which is soap and detergent. What actually is soap? I think most of the people will able to answer it. Soap is  an organic compound that is used with water for washing or cleaning purpose, which is made from the compound of natural fats or oils and with any type of strong alkali, and basically having perfume and colouring added.  Soaps are mainly used as surfactants for washing, bathing, and cleaning, yet they are also used in textile spinning and are important components of lubricants.

History of Soap

Although no one really knows when soap was discovered, there are various legends surrounding its beginning. According to Roman legend, soap was named after Mount Sapo, an ancient site of animal sacrifices. After an animal sacrifice, rain would wash animal fat and ash that collected under the ceremonial altars down to the banks of the Tiber River. Women washing clothes in the river noticed that if they washed their clothes in certain parts of the river after a heavy rain their clothes were much cleaner. Thus the emergence of the first soap – or at least the first use of soap.

Composition

Soaps are sodium or potassium salts of long chain fatty acids with 12 to 18 carbon atoms per molecules. All soaps are obtained from the reaction between fats or oils and with strong alkali. Hence, what differ between one soap and another is the type of the fats and oils and type of strong alkali use. Hence, let’s examine the composition of fats, oils and alkalis

1.   Fats and Oils
Fats and oils that involve in the process of soapmaking are naturally occurring esters    formed from propan-1,2,3-triol (known as glycerol) and long chain carboxylic acid (known as fatty acid). Naturally occurring esters normally consist of one molecule of glycerol and three molecules of fatty acid. The reaction between glycerol and fatty acid to form fats/oil is also known as esterification as glycerol is a type of alcohol that contains three hydroxyl group per molecule while fatty acid is a type of carboxylic acid consisting of a hydrocarbon chain and a terminal carboxyl group. As a result of the reaction, it will produce an ester, which is the fat or oil. Fat or oil, the product of the esterification, is also known as triglycerides. The reaction between glycerol and fatty acid as shown below:

Glycerol + Fatty Acids à Fats/Oils + Water

Fats and oils that used in the production of soaps are mainly from animals or plants. In animals, the fats are in solid state at room temperature while in plants; the fats are in the form of liquid at room temperature which we usually known as oil. What differentiate between animal fats and plants oils is in terms of molecular structure. The molecular structure of animal fats consists of carbon-carbon(C-C) single bond while of plant oils it consists of C-C double bond. Due to the C-C single bond in the structure, animal fats are also known as saturated fats, where all the carbon atoms in the structure hold on with hydrogen atoms and no more hydrogen atoms can be added in. In contrast, in the molecular structure of plant oil, it consists of C-C double bond where the carbon atoms can still hold more hydrogen atoms. Hence, plant oils are unsaturated fats. Tallow, for example, rendered beef fat, is the most available triglyceride from animals. Its saponified product is called sodium tallowate. Typical vegetable oils used in soap making are palm oil, coconut oil, olive oil, and laurel oil. Each species offers quite different fatty acid content and, hence, results in soaps of distinct feel. 

Example of unsaturated fats  

   

Example of saturated fats (tallow) 

2.   Alkali
An alkali is a soluble salt of an alkali metal like sodium or potassium. In previous days, the alkalis that used to produce soap were obtained from the ashes of plants. However, for nowadays, the alkalis are produced commercially. Today, the alkali is defined as a substance that chemically is a base (oppose of an acid) in which it will react and neutralizes acid.
The kind of soap product is affected by the type of alkali used. The common alkalis used in production of soap are sodium hydroxide (NaOH), also known as caustic soda; and potassium hydroxide (KOH), also known as caustic potash. Sodium soaps, prepared from sodium hydroxide, are firm, whereas potassium soaps, derived from potassium hydroxide, are softer or often liquid.

Chemistry of Soap

For all soaps, the basic structure is almost all the same, which are consisting a long hydrocarbon chain which act as hydrophobic ‘tail’ (water-fearing) and a hydrophilic (waterloving) anionic "head":

Structure of Soap Molecule

General formula of hydrocarbon ‘tail’ in soap:

CH ₃ CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ COO ⁻ or CH ₃ (CH ₂ ) _n COO ⁻

The length of the hydrocarbon chain ("n") depends on the type of fat or oil but normally is quite long. The anionic charge on the carboxylate head is usually balanced by either a positively charged potassium (K ⁺) or sodium (Na ⁺) cation. How is the soap being produced? It is actually formed as the result of reaction between sodium or potassium hydroxide with animal fats or vegetable oils. This process is what we known as saponification. During this process, animal fats or vegetable oils are boiled with sodium or potassium hydroxide, which will result in the production of three molecules of soap for every molecule of glycerol. The reaction is as shown below:

Similar to synthetic detergents, soaps are "surface active" substances (surfactants ) and hence make water better at cleaning surfaces. Although water is a good general solvent, however, unfortunately it is also a substance with very high surface tension. Due to this reason, water molecules generally prefer to stay together rather than to wet other surfaces. Therefore, surfactants work by reducing the surface tension of water, allowing the water molecules to better wet the surface and thus increase water's ability to dissolve dirty, oily stains.

How does Soap Work?

The chemical bonding and structures of soap determine the cleansing action of soap on dirt. The ionic “head” (negatively-charged) is soluble in water (hydrophilic) but insoluble in oil. The long hydrocarbon “tail” (neutral) is insoluble in water (hydrophobic) but soluble in water.

When soap is mixed with water, it lowers the surface tension of water and wets the dirty surface. The negatively-charged ‘heads’ of soap dissolve in water (hydrophilic). In contrast, the hydrocarbon “tails” of soap dissolve in the layer of grease (hydrophobic). If the water is agitated slightly, the grease begins to lift off the surface. On further agitation during washing, the greasy dirt is lifted from the surface since the density of grease is less than water. When the water is shaken, the grease will be emulsified when it breaks into smaller droplets. Due to the same charge (negatively-charged), these greasy droplets repel one another. As a result, the grease is suspended in the solution. When the cloth is rinsed with water, the droplets will be carried away. The cleaning process will become more efficient if the water containing the soap is stirred vigorously or the washing is done at a higher temperature. This is because heating and stirring can help to loosen the dirt particles from the material being washed.

Advantages and Disadvantages of Soap

There are a few advantages of soap as cleansing agents. For example, soaps are effective cleansing agents in soft water, which is, water that does not contain magnesium, Mg²⁺ ions and calcium, Ca²⁺ ions. In addition, it does not cause pollution problems to the environment. This is because soaps are organic compound, which is a compound that made from chemicals that found in animals and plants. This means that soaps are biodegradable.

As good as soaps are, they are not perfect. For example, they ineffective in hard water containing Mg²⁺ and Ca²⁺ ions. In hard water, soaps will react with Mg²⁺ and Ca²⁺ ions to form a precipitate called scum, a grey solid that is insoluble in water. It consists of magnesium stearate and calcium stearate. Hence, soaps do not lather in hard water. Thus soaps have been largely replaced in modern cleaning solutions by synthetic detergents that have a sulfonate (R-SO ₃ ⁻⁾ group instead of the carboxylate head (R-COO ⁻ ). Sulfonate detergents tend not to precipitate with calcium or magnesium ions and are generally more soluble in water. Besides, soaps are also ineffective in acidic water. For example, rainwater contains dissolved acids. Hydrogen, H⁺ ions from acids will react with soap ions to produce fatty acid molecules of large molecular size that are insoluble in water.

Make Your Own Soap

In making soap, triglycerides in fat or oils are heated in the presence of a strong alkali base such as sodium hydroxide, producing three molecules of soap for every molecule of glycerol. This process is called saponification.

1.    Gather all the necessary materials. Items needed are safety goggles, rubber gloves, a stainless steel pot, a glass bowl, a glass measuring bowl, a scale, rubber stirring utensils, thermometer (two thermometers if possible, one for the oils and one for the lye), the soap batch recipe, the recipe ingredients, and soap molds.

2.    Fill the glass measuring bowl with the appropriate amount of distilled water, based on the recipe. Important note: the caustic nature of the lye will etch the glass bowl making it appear frosted. The glass bowl will be fine but the look is permanent.

3.    Add the appropriate amount of lye very slowly to create the lye/water solution and stir. The lye and water will react with each other and initially get very hot. Be sure to always add the lye to the water. Adding the water to the lye may cause a bubbling "volcanic" reaction.

4.    Set the lye/water solution safely off to the side so that it may cool a bit.

5.    Weigh the oils and melt them in the stainless steel pot using the stove on medium heat.

6.    When the lye/water solution and oils have reached the same temperature, ideally around 110 °F (43 °C), stir the lye/water solution slowly in to the stainless steel pot of melted oils to create the soap mixture. It is recommended to wear the goggles and rubber gloves here in case of any lye splashes.

7.    Stir the soap mixture thoroughly. Expect to stir continuously for about 15 minutes, until the mixture starts to thicken, like pudding. This is called the "trace" stage. Using an electric stick blender is one way to speed up the stirring and bring the soap mixture to the "trace" stage more quickly.

8.    Once the soap mixture reaches "trace", add the essential oils, other fragrances or herbs, pigments and stir. Again, the "trace" stage can be recognized by the patterns left in the soap mixture as it is stirred. It will resemble a thickening pudding.

9.    Pour the soap mixture into the molds. Be sure that the soap mixture is evenly distributed.

10. Stash the molds in a warm place and allow them to cure and harden for 24-48 hours. Wrapping the molds in a blanket or towel for insulation will keep the soap warm and accelerate the curing process.

11. After the soap has hardened, its water content will still be quite high. Remove the soap from the mold, cut in to bars and allow the bars to cure and dry out for 4-6 weeks.

In conclusion, soap is a substance, water soluble sodium salts of fatty acids, that is used to remove dirt and grime from a surface. The presence of soaps make our life become easier as it act as a cleansing agent for washing, bathing, and cleaning, yet they are also used in textile spinning and are important components of lubricants. In such a high technology era, the soap is even modified and now become more attractive for the user as it has different colour, shapes, sizes and even the smell. Due to this reason, it provides many choices for users when choosing the type of soap to buy.