Soaps and Detergents - Preparation, Difference, Examples, FAQs

Soaps and detergents are used everywhere in our daily lives for ourselves, our homes, and our environment to be clean and hygienic. From waking up from bed to going to bed, we use these chemical compounds one way or another—starting from washing our hands with soaps to washing our clothes using detergents. Whereas they are ubiquitous in our daily lives, many among us take for granted the science behind cleaning agents and their impacts on our lives. The paper will present the soaps and detergents, their constitution, properties, and how they are applied in everyday life.

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This Story also Contains

1. Understanding Soaps and Detergents
2. Types and Features
3. Synthetic Detergents
4. Applications in Real Life and Consequences
5. Some Solved Examples
6. Conclusion

Probably the most interesting thing about soaps and detergents is their ability to adapt to various situations or environments. On the mild extreme are balanced-pH formulae in baby shampoos, while on the opposite extreme are heavy-duty grease-cutting detergents used industrially—so cleaning agents are formulated to suit their users' needs. In personal care, soaps and detergents will become very instrumental in maintaining hygiene and containment from various diseases. Probably one of the most practical measures to help prevent the spread of infectious diseases is washing one's hands as frequently as possible with soap and clean water—something the COVID-19 pandemic made very clear.

Understanding Soaps and Detergents

Soaps and detergents are amphipathic molecules, meaning they have both hydrophilic and hydrophobic regions of the molecule. This unique characteristic gives them the capability of cleaning surfaces as well as lifting grease and dirt. Soaps are obtained by the reaction of fatty acids with an alkali metal; detergents on the other hand are tailor-made synthetic chemical compounds that mimic the soaps' cleaning action. They may or may not contain a soapy element.

Sodium or potassium salts of higher fatty acids such as lauric acid(C₁₁H₂₃COOH), palmitic acid(C₁₅H₃₁COOH), etc. are called soaps. Sodium salts of fatty acids are known as hard soaps and potassium salts of fatty acids are soft soaps. Shaving creams and liquid soaps are soft whereas others are hard. Soaps are generally obtained by the hydrolysis of oils and fats with aqueous alkali. The process is called the saponification of oils and fats. Fats and oils are triesters of higher acids and glycerol. Hard soaps are prepared from cheap oils fats and sodium hydroxide. They contain free alkali and are used for washing purposes. Soft soaps are prepared from good oils and potassium hydroxide. They do not contain free alkalis and are used as toilet soaps, shaving creams, and shampoos. Transparent soaps are prepared by dissolving the soap in ethanol and then evaporating the excess solvent. Medicated soaps are soft soaps and are prepared by adding some antiseptics like Dettol, salons, etc. In some soaps, deodorants are added. Toilet soaps are prepared by using better grades of fats and oils and care is taken to remove the excess alkali. Colors and perfumes are added to make them attractive. Shaving soaps contain glycerol to prevent rapid drying. A gum called rosin is added while preparing these soaps. It forms sodium rosinate which leathers well. Laundry soaps contain fillers like sodium resonate, sodium silicate, borax, and sodium carbonate.

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Why do soaps not work in hard water?

Hard water contains calcium and magnesium ions. These ions form insoluble calcium and magnesium soaps respectively when sodium or potassium soaps are dissolved in hard water.

$2 \mathrm{C}_{17} \mathrm{H}_{35} \mathrm{COONa}+\mathrm{CaCl}_2 \rightarrow 2 \mathrm{NaCl}+\left(\mathrm{C}_{17} \mathrm{H}_{35} \mathrm{COO}\right)_2 \mathrm{Ca}$
Soap Insoluble calcium stearate(Soap)

These insoluble soaps separate as scum in water and are useless as a cleansing agent. In fact, these are hindrances to good washing because the precipitate adheres onto the fibre of the cloth as a gummy mass. Hair washed with hard water looks dull because of this sticky precipitate. Dye does not absorb evenly on cloth washed with soap using hard water, because of this gummy mass.

Types and Features

Soaps and detergents can also be classified into several classes based on their chemical makeup and properties. Anionic detergents, like sodium lauryl sulfate, exhibit good cleaning ability and find use in laundry detergents and shampoos. The cationic detergents find major use mostly as fabric softeners and disinfectants. Non-ionic detergents do not contain charged heads and find main application in dishwashing liquids and personal care products.

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Synthetic Detergents

Clearly, synthetic detergents are an advance in cleaning. Some of them are very strong substitutes for traditional soaps. Synthetic detergents are chemical compound designed to work like a soap but will overcome some of the shortcomings of the latter, especially in hard water. They have equal cleaning action for household purposes, just the same as for industrial cleaning, because, unlike soap that forms insoluble compounds with hard water minerals, they do not lose their washing power.

The paper shall be on composition, types, and real-life applications that make synthetic detergents important for a myriad of purposes. We will start with an overview of synthetic detergents—what they are chemically and how they are different from soaps. Thereafter, we shall start classifying the various kinds of synthetic detergents by type, showing their various properties and applications. The last section makes some inferences about the usages of these synthetic detergents in relation to everyday life: their use in washing clothes and dishwasher use, and quantification of associated environmental impact in view of an increasingly sustainable compound formulation trend. By the end of this paper, the reader shall have clarity on what these synthetic detergents are and what their critical roles in modern cleaning practices have become.

These are also called synthetic detergents syndets soapless soaps or just detergents. They have cleansing power as good or better than ordinary soaps can be used for washing even with hard water and do not precipitate in the presence of $\mathrm{Ca}^{2+} / \mathrm{Mg}^{2+}$ or in acidic solution.
A synthetic detergent is the sodium salt of a long-chain alkyl hydrogen sulfate or the sodium salt of a long-chain benzene sulphonic acid. Like soap, they contain both hydrophilic and hydrophobic parts in the molecule.

Detergents are mainly classified into three categories, namely:

1. Anionic Detergents:

Anionic detergents are sodium salts of sulfonated long-chain alcohols or hydrocarbons. Alkyl hydrogen sulfates formed by treating long-chain alcohols with concentrated sulphuric acid are neutralized with alkali to form anionic detergents. Similarly, alkyl benzene sulphonates are obtained by neutralizing alkyl benzene sulphonic acids with alkali.

In anionic detergents, the anionic part of the molecule is involved in the cleansing action. Sodium salts of alkyl benzene sulphonates are an important class of anionic detergents. They are mostly used for household work. Anionic detergents are also used in toothpaste.

2. Cationic detergents:

These are mostly acetates, chlorides, or bromides of quaternary ammonium salts containing one or more long-chain alkyl groups. Being more expensive than the anionic detergents, they find limited use. But these detergents are also used in hair shampoos and hair conditioners. Such detergents, however, possess germicidal properties and are used quite extensively as germicides. Examples are trimethyl stearyl ammonium bromide, cetyl trimethyl ammonium bromide, or N-benzyl quaternary ammonium chlorides.

3. Non-ionic detergents:

They are neutral surface active detergents obtained from long-chain alcohols by treatment with ethylene oxide in the presence of a base. One such detergent is formed when stearic acid reacts with polyethyleneglycol.$\mathrm{CH}_3\left(\mathrm{CH}_2\right)_{16} \mathrm{COOH}+\mathrm{HO}\left(\mathrm{CH}_2 \mathrm{CH}_2 \mathrm{O}\right)_2 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{OH} \xrightarrow{-\mathrm{H}_2 \mathrm{O}} \mathrm{CH}_3\left(\mathrm{CH}_2\right)_{16} \mathrm{COO}\left(\mathrm{CH}_2 \mathrm{CH}_2 \mathrm{O}\right)_3 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{OH}$

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Applications in Real Life and Consequences

Soaps and detergents are in great demand for individual hygiene, disinfection, and cleaning of a person's surroundings. One of the most benevolent practices to arrest infectious diseases like COVID-19 is handwashing, which can be performed with soap and water. Dishwashing liquids will keep the dishes free from food remains and bacteria, and laundry detergents remove stains and odors from clothes.

Extensive application of the soaps and detergents, however, opened an avenue of concern about the effect of the products on the environment. Phosphates are primary components of most traditional detergents and often enhance the eutrophication of the water bodies, resulting in a situation whereby oxygen is greatly reduced, killing the aquatic life. In response to such concerns, eco-friendly and biodegradable alternatives have been invented that include plant-based detergents and soaps manufactured from natural ingredients.

The study of soaps and detergents forms part of the academic curriculum designed to introduce a student to the principles of chemistry, especially the divisions of organic and surface chemistry. This includes the chemical reactions in the preparation of soaps and detergents and various factors that would have an effect on their cleaning effectiveness like pH, water hardness, and temperature.

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Some Solved Examples

Example 1

Question: Which one of the following cannot be used as soap?

1. Stearic acid
2. Oleic acid
3. Palmitic acid
4. Bithional

Solution: Bithional acts as an antiseptic and is not used as soap. Stearic acid, Oleic acid, and Palmitic acid can be used as soaps. Hence, the answer is option 4.

Example 2

Question: Which of the following is used in the reaction called saponification?

1. Strong base
2. Strong acid
3. Hydrogen
4. Nickel

Solution: In the saponification reaction, fat or oil reacts with a strong base (NaOH) to produce soap molecules. Hence, the answer is option 1.

Example 3

Question: Soft soaps are the limitation of the hot process because of their

1. High alkalinity
2. Low alkalinity
3. Low solubility in water
4. High solubility in water

Solution: Soft soaps are more soluble in water, which is a limitation of the hot process. Hence, the answer is option 4.

Example 4

Question: Which one of the following is true about floating soaps?

1. These are made by beating tiny air bubbles before their hardening
2. These are made by dissolving soap in ethanol, then evaporating excess solvent
3. These are made by adding substances of medicinal value like Dettol, etc.
4. The soaps contain glycerol and rosin forming sodium resonate for lather

Solution: Floating soaps are made by beating tiny air bubbles into the soap before it hardens. Hence, the answer is option 1.

Example 5

Question: Transparent soaps are made by dissolving soap in which of the following solvents?

1. Methanol
2. Acetone
3. DMSO
4. Ethanol

Solution: Transparent soaps are made by dissolving the soap in ethanol and then evaporating the excess solvent. Hence, the answer is option 4.

Conclusion

Soaps and detergents have, therefore, become very essential commodities in our everyday life, keeping us clean, and hygienic, and ensuring good health. As we continue to use these chemical compounds, it becomes very necessary to also take into consideration the effects they are having on the environment and try to find more environmentally friendly ways. We learn the science of soaps and detergents to make conscious decisions and help in cleaning and healthy living.

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