Soaps help remove dirt and impurities through their hydrophobic and hydrophilic ends that attach to oil and water molecules and rinse off every impurity. Nowadays, we have so many different soaps available in the market. However, the basic constituents of all the soaps are the same. Whether soaps are acidic or basic is a common question among curious minds. So, Are soaps acidic or basic? Soaps are basic salt. Soaps are formed by the combination of strong bases and weak acids i.e. long-chain fatty acids. The salts formed by the reaction between weak acids and strong bases are alkaline. Thus, soaps are basic as mostly they are sodium or potassium salts of carboxylic acids. The pH of soaps lies between 9 and 10 on the pH scale, further confirming their basic nature. Keep reading to know more about the basicity of soaps and what soaps are made up of.
Why is Soap Basic?
Soaps are the sodium or potassium salts of fatty acids prepared using a process known as Saponification. In this process, the triglycerides derived from fat or oil are treated with strong bases such as NaOH, KOH, etc. resulting in the formation of soaps and glycerol. The fatty acids are a combination of carboxylic acids which are actually weak acids as they do not ionize completely in water and thus, have a low concentration of hydrogen ions in the solution. On the other hand, the bases used to prepare soaps i.e. NaOH, KOH, etc. are strong bases as they dissociate completely in an aqueous solution to produce plenty of hydroxide ions. To understand the nature of salt, you will have to look at its basic components, viz. • Weak Acid + Strong Base = Basic Salt i.e. pH > 7 • Strong Acid + Weak Base = Acidic Salt i.e. pH < 7 • Strong Acid + Strong Base = Neutral Salt i.e. pH = 7 • Weak Acid + Weak Base = Neutral Salt i.e. pH = 7 The chemical equation of the saponification reaction for the preparation of soaps is given below:
As per the concept of salt formation, a salt formed by the combination of a weak acid and a strong base is always a basic salt. Hence, soaps are basic salts having a pH greater than 7.
pH of Soap
The pH stands for the potential of hydrogen. It is the measure of its alkalinity or acidity. The pH scale ranges from 0 to 14, on which acids always have pH below 7, bases have a pH above 7, and neutral solutions have a pH equal to 7.
Most of the soaps used have a basic pH, usually 9 to 10. However, certain soaps may have a pH higher or lower than this. Below is the list of pH ranges and how will they affect the cleansing and lather forming power of soaps:
Why is Soap not Acidic or Neutral?
Looking at the above table, you realize why soap should not be acidic or neutral. The basic pH of soap is responsible for its cleansing and lather forming properties. As the pH of the soap decreases, these properties also decrease alongside. Thus, the soap can no longer serve its basic purpose of cleaning. Now, let us look at the chemical aspect of this fact. For this, we will have to understand the basic concept of acid-base reactions: • Strong base combined with weak acid gives an alkaline solution due to more number of hydroxide ions available in the solution i.e. H+ < OH-. • Weak base combined with strong acid gives an acidic solution due to more number of hydrogen ions available in the solution i.e. H+ > OH-. • Weak base combined with weak acid or strong base combined with strong acid gives a neutral solution owing to the equal number of hydrogen and hydroxide ions in the solution i.e. H+ = OH-. We already discussed that the soaps are the salts formed as a combination of weak acids and strong bases, with pH above 7, and are, therefore, basic.
Why is Soap Solution Basic?
As mentioned above, the solutions with a pH of more than 7 are said to be basic. The nature of a solution can also be determined based on what kinds of ions are present in that. The presence of hydrogen ions makes a solution acidic while hydroxide ions make a solution basic. Now, let us look at the dissociation equation of soap when it is dissolved in water.
The hydroxide ions formed as a product in the solution indicate the basic nature of this solution. Now, let us look at this reaction closely. When molecules dissociate in water, they form RCOO– ions and Na+ ions while the water molecule itself ionizes into H+ and OH– ions. The RCOO– ions are the conjugate base of a weak carboxylic acid and, therefore, react with the hydrogen ions released by Water, resulting in the formation of RCOOH. Now, we are left with Na+ ions and OH– ions. Amongst these, the sodium ions are weak conjugate acid of a strong base i.e. NaOH and hence, are incapable of participating in the further reaction. Therefore, the OH– ions formed due to the ionization of water molecules are left in large numbers. These OH– ions raise the pH of the solution, making it basic in nature.
What is Soap Made up of?
The basic ingredients of any soap include three things plant oils or animal fat, water, and a strong alkali. However, with the increasing demand of the consumers, various ingredients are now being added to produce different kinds of soaps such as anti-septic soaps, herbal soaps, baby soaps, skincare soaps, etc. A few examples of the other ingredients added to the soaps, to make them suitable for different uses, are essential oils, herbs, flowers, colorants, antiseptic chemicals, aroma oils, etc.
Is Liquid/Hand Soap Basic?
As discussed in the previous sections, the basic components of any type of soap remain the same i.e. acids derived from animal fats or plant oils, Water, and a base. The bases used in the saponification reaction for the preparation of soaps are potassium hydroxide or sodium hydroxide. Both of these alkalis are quite strong in nature resulting in the formation of a basic salt. Also, in the above section, we described how the alkalinity of soap is related to its cleansing and lather forming ability. Hence, any soap, irrespective of its appearance or proposed use is basic in nature. Talking about the liquid and hand soaps, the liquid soaps are usually potassium salts of long-chain carboxylic acids while the hand soaps are sodium salt of long-chain carboxylic acids. Hence, both of these soaps are basic in nature.
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Types of Soap
A few different types of soaps are listed below: • Glycerine soap: Usually, glycerine is formed as a byproduct of saponification reaction which is removed at later stages to be used in other cosmetic products. For making glycerine soap, the byproduct is left in the solution which is heated for a long duration. • Transparent soap: These are prepared using the hot process method by adding alcohol to the soap mixture. Some manufacturers also use sugar solutions in place of alcohol. • Liquid soap: The preparation technique is slightly different from usual soap manufacturing. Here, potassium hydroxide is used instead of sodium hydroxide. Also, more amount of water is used. • Medicated soap: These are manufactured by adding anti-septic or disinfectant liquids to the soap mixture. • Beauty soap: These are manufactured by adding different types of essential oils, aroma oils, or beauty products to the soap mixture. Apart from these, there are other varieties of soaps also available in the market such as baby soap, toilet soap, laundry soap, kitchen soap, etc. Check out the interesting video on how soaps are made.
Conclusion
Soaps are manufactured through the saponification process by using basic ingredients viz. animal fat or plant oil, Water, and a strong base. Soaps are formed as a combination of a weak acid and strong base and resultantly, they are basic salts having pH between 9 and 10. The OH– ions present in the aqueous solution of soap are responsible for its basicity. The pH of soap directly impacts its cleansing and lather forming capacity. These properties usually enhance with the increasing pH. However, the pH range between 8 and 10 is considered suitable for the skin.
