Soap vs Detergent: The Science Behind the Dirt Removal

Soap and detergent are substances that, when dissolved in water possess the ability to remove dirt from the surfaces such as human body, textiles, and other solid surfaces. Both serve the same purpose which is cleansing; however, they are significantly different.

There are several factors based on which soap and detergents can be differentiated. Some of the major differentiators include composition, structure, uses, and properties.

Soap vs Detergent

Soaps Detergents
Soap is a sodium or potassium salt of a carboxylic acid that is accompanied by a long aliphatic chain Detergents are usually made of sodium or potassium salts of long alkyl chains that end with a sulfonate group
They are produced using natural ingredients (animal fats or vegetable oils) They are produced using synthetic products (petroleum fractions)
They have –COONa group
They have –SO3Na group
Soaps are biodegradable Not all detergents are biodegradable
They do not work well with woolen garments They work well with woolen garments
Soaps form precipitates in acidic water Detergents do not form precipitates in acidic water
They take time to be dissolved in water Detergents take less time to be dissolved in water
Soaps form less lather in hard water Detergents forms lather properly in hard water
We mostly use soaps for washing hands, our bodies, and kitchen utensils Detergents are often used for laundry and cleaning homes
Soaps are cheap Detergents are expensive
Examples of soaps are sodium stearate, sodium palmitate Examples of detergents are sodium lauryl sulphate (SLS) and sodium dodecylbenzene sulphonate (SDS)

Major Differences Between Soap and Detergent

1.     Definition

Soap is a sodium or potassium salt of a carboxylic acid that is attached to a long aliphatic chain whereas detergents are usually made of sodium salts of long alkyl chains that terminate with a sulfonate group.

2.     Composition and Making

Soaps are made by mixing fats and oils with an alkali or base. They have been around for hundreds of years. Initially, they were made using ashes with animal fats. In order to produce superior quality soaps, nowadays, palm, castor, coconut, and olive oils are used in soap making.

On the other hand, detergents are either sodium salt of alkyl hydrogen sulfates or sodium salt of long-chain alkyl benzene sulphonic acids. Like soaps, they contain both ionic groups and nonionic groups. Sulphonate groups or sulfate groups are ionic and long-chain hydrocarbons are the nonionic groups. For example, sodium lauryl sulfate (SLS), sodium dodecylbenzene sulphonate (SDS).

3.     General formula

The general formula of detergents is (R-SO3Na+) and soaps is (R-(C=O)ONa+). An example of both these chemical reagents is given below:

Sodium Maleate


Sodium dodecyl sulphonate (SDS)

4.     Properties

Some of the differentiating properties between soaps and detergents are here:

  • Detergents are made from synthetic products whereas soaps are made from natural products.
  • Soaps are biodegradable and hence, they do not add to the pollution. Some detergents may not be biodegradable.
  • Detergents can be used in hard water, whereas soaps cannot be used as they do not form lather in hard water.
  • Soaps cannot be used in an acidic medium whereas detergents can work in the acidic medium. Being the salts of strong acids, detergents do not decompose in the acidic medium.
  • Soaps are not as much soluble in water as detergents.
  • Detergents have stronger cleaning action than soaps.

5.     Examples

Examples of soaps are:

  • Sodium palmitate and
  • Sodium stearate
  • Sodium maleate, etc

Examples of detergents are:

  • Deoxycholic acid
  • Sodium Lauryl Sulfate (SLS)
  • Sodium dodecyl sulphonate (SDS)
  • Lauric acid diethanolamine
  • Sodium lauryl sulfate, etc

6.     Disadvantages

Disadvantages of soaps:

  • Soaps do not form enough lather in hard water. Calcium, magnesium, or iron ions present in hard water precipitate out and thus, limit soap’s cleansing effect.
  • Some soaps are unsuitable for fabrics such as silks, wool, and other natural fibers. This is because the alkalis in them damage the fiber.
  • Soaps cannot be used for cleaning if the water is slightly acidic as they are converted to carboxylic acid in the acid media.

Disadvantages of detergents:

  • Some of the detergents may be non-biodegradable. This means it could add to our earth’s pollution.
  • Detergents produce stable foams in river waters and thus, become a danger to aquatic/marine life.
  • They tend to inhibit the oxidation of organic substances present in wastewaters because they form envelopes around them.

Mechanism of action of soap and detergent

Soaps and detergents are made from long molecules containing essentially two parts. The head of the molecule is attracted to water (hydrophilic) and the tail is attracted to grease and dirt (hydrophobic). When the detergent or soap molecules meet grease on clothes, the tails are drawn into the grease, but the heads still sit in the water.

The attractive forces between the head groups and the water are so strong that the grease is lifted away from the surface. The blob of grease is now surrounded by detergent molecules and is broken into smaller pieces that are washed away by the water.

Key Takeaway(s)

Soap vs Detergent - The Science Behind the Dirt Removal - Difference table

Concepts Berg

What are the two main disadvantages of soap over detergent?

  • Soaps do not work well in acidic and saline media whereas detergents work well.
  • Detergents have stronger cleansing action than soaps.

What is the difference between soap and sanitizer?

Washing skin with soap will result in the removal of soils, germs, and dirt. While sanitizers kill most germs effectively, they will not remove soil and dirt from the skin.

Is detergent bad for your skin?

The use of a laundry detergent on your skin may cause itchiness and rashes.

Why do detergents perform better in hard water?

Detergents have an extra substance in it called sodium zeolite-A, which takes up the calcium and magnesium ions out of hard water. This means they first soften the water and then perform the cleaning action.

What is the difference between fabric softener and laundry detergent?

Laundry detergent is formulated to clean fabrics by removing dirt, stains, oil, sweat, and other debris. Whereas, fabric softener is designed to reinforce, protect, and soften your clothes, keeping them in good condition throughout multiple items of washing.

Who invented liquid soap?

William Shepphard invented liquid soap in 1865.

References books

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