Soaps and Detergents - Comprehensive Notes

Soaps

History

Preparation and Composition of Soap

Word equation for saponification:
$Fats \ or \ oils + strong \ base \rightarrow soaps + glycerol \ (sodium \ hydroxide \ or \ Potassium \ hydroxide)$
Preparation and chemical composition.
Byproduct.

Distinguish Between Oils and Fats

Solid at room temperature.
Animal origin.
Less unsaturated (fewer double bonds).

Oils

Liquid at room temperature.
Plant origin.
More unsaturated (more double bonds).

Similarities

Density < 1.
Insoluble in water, but soluble in some organic solvents.
Both are organic substances.

Note: Unsaturated means it contains double bonds.

Glycerol (Glycerin)

Organic compound obtained as a byproduct from saponification reaction.
Properties:
1. Family: alcohol (trialcohol).
2. Functional group: (OH-) group (hydroxyl group).
3. Chemical Formula: $C<em>3H</em>8O_3$
4. Condensed structural formula: $(CH<em>2OH–CHOH-CH</em>2OH)$
5. Uses:
  - Medical applications
  - Skin moisturizer

Fatty Acids

Definition: Organic acids that can be produced from the hydrolysis of fats and oils (reaction with water).
Formula: R - COOH
Functional group: carboxyl group (-COOH).
Properties:
- Used to prepare thickeners for paints and lubricants.
- Used in plastic products.
- Coatings for wood and metals.
- Number of carbon atoms in fatty acids is always even and ranges between 4 and 22.

Esterification Reaction

Word equation:
$Fatty \ acid + alcohol \rightarrow ester (fat \ or \ oil) + water$
*Hydrolysis is the reverse.
Property of esterification: incomplete and reversible.

Triglycerides - Triesters (oils and fats)

General chemical formula:
\text{CH}2\text{-0OC-R} \atop \text{CH-OOC-R} \atop \text{CH}2\text{-0OC-R''}

The Cleaning Action of Soap

Depends on:
- Type of dirt.
- Structure of the soap.

Principle of Detergency

When soap solution comes in contact with the surface to be washed, they should:
1. Wet the surface.
2. Remove the dirt such as oil, dust, soil…
3. Dissolve and get rid of it in water.

Formation of Micelles

Soap $(RCOO^- Na^+)$
Acts as a cleaning agent because it is attracted both to oil and water.
$RCOO^- Na^+$
- R (nonpolar):
  - Insoluble in water
  - Hydrophobic
  - Lipophilic
- $COO^- \ (polar)$
  - Soluble in water
  - Hydrophilic
  - Lipophobic

Definitions:

Hydrophilic: water-loving
Hydrophobic: water-hating = lipophilic
Representation of soap molecule: COO-
The R- part (nonpolar) will accumulate inside, whereas $COO^-$ (polar) stays outside, forming the micelles.

How Does Soap Clean?

When we put a dirty piece of tissue in water containing soap, a larger number of $RCOO^-$ surround the oil with the hydrophobic part dissolving in the oil, while the hydrophilic part is dissolving in water.
When water is added and after shaking, the dirt is detached from the clothes in a spherical shape called micelle.

Key Concepts Review

$Fats + oils \rightarrow soaps + glycerol$
Saponification is a slow reaction; heat is used to accelerate it.

Hard Water vs. Soft Water

Hard Water

High mineral content
$Ca^{2+}, Mg^{2+}$

Soft Water

Low mineral content
Sometimes $Na^+$
Sources of Hard Water: well water
Sources of Soft Water: rain or snow, distilled water

Formation of Scum in Hard Water

Hard water does not give ready lather with soap.
Soaps are sodium salts of higher fatty acids.
They react with Ca and Mg ions present in hard water to form salts and produce a curdy precipitate.
Hence, they are not suitable for washing purposes.

Detergents

What is a Detergent?

A detergent is a synthetic product that is used for cleaning and washing.

Difference Between Soap and Detergent

Soaps come from natural sources, while detergents come from synthetic products.
Soaps are not effective in hard water, while detergents are.

Composition of Detergent

Detergents are composed of surfactants, builders, and additives.
- The action of detergent is mainly due to the surfactant.
- The builders help to improve the action of surfactants.
- The additives are added to respond to the needs of consumers (whitening, odor removal…).

Detergent Structure

Detergents have two ends:
- Hydrophobic end: links with fats and oils
- Hydrophilic end: soluble in water

Surfactants

Surface-active agents are the essential constituents of detergents.
They are classified into three types based upon the nature of their active site:
- Anionic surfactants
- Cationic surfactants
- Non-ionic surfactants
- Amphoteric surfactants

Anionic Surfactants

The active site of anionic surfactants is an anion.
They are mainly used in laundry and dishwashing detergents.

Cationic Surfactants

The active site of cationic surfactants is a cation.
They are mainly used as hair conditioners and softeners.

Non-Ionic Surfactants

The active site of non-ionic surfactants contains many oxygen atoms.
They are mainly used in liquid and dishwashing detergents.

Amphoteric Surfactants

Amphoteric surfactants are used in cosmetics and shampooing products.
Have both positive and negative charges.

Builders

Builders are substances that help improve the action of surfactants.
They provide optimal water quality for the proper functioning of surfactants.

Types of Builders

STPP (Sodium Tripolyphosphate): diminishes water hardness and improves the quality of detergents.
Sodium Hydroxide or Sodium Carbonate: dissolves in water and makes it basic and helps to dissolve fatty substances by changing them into soap.
Potassium or Sodium Silicate: inhibits the corrosion of metals and acts as anti-redeposition agents.

Additives

Bleaches
Antiredeposition agents
Alcohols
Complexing agents
Fluorescent whitening agents
Suds control agents
Enzymes
Colorants
Fragrances
Filters

Detergent Characteristics

Improving the wetting power of water
Emulsifying oils and fats
Decomposing organic and inorganic dirt
Stopping the re-deposition of dirt
Diminishing water hardness
Whitening
Protecting washing machines from corrosion
Guaranteeing an alkaline medium
Giving a pleasant smell and a good touch

Detergent Properties

Efficient for the specific type of cleaning
Safe for the user
Stable during storage
Safe for the environment
Affordable prices

Types of Detergents

Powdered Detergents

Machine-washing of fabrics
Washing delicate fabrics
Machine-dish washing

Liquid Detergents

Used for the same purposes as powdered detergents
Contain small quantities of STPP (less than powdered detergents)
Contain a higher percentage of surfactants

Impact on the Environment

First step: Identifying pollution problems
Second step: Establishing strategies to eliminate or reduce damage resulting from pollution
Using detergents in homes results in the disposal of non-biodegradable products of petroleum origins in water.
In addition, large amounts of phosphates (STPP) that cause eutrophication are disposed of in water every day.

Accumulation of Non-Biodegradable Substances

Non-biodegradable substances are substances that cannot be broken down by microorganisms, heat, or ultraviolet light.
Accumulation of these products causes pollution problems.
Soaps, when disposed of in sewage water, don’t cause pollution problems because they are made of biodegradable substances (natural fatty acids).
Conversely, detergents contain surfactants that are non-biodegradable.

Eutrophication

STPP leads to:
- Production of algae
- Decomposition of algae
- Reduction of the quantity of oxygen
- Deterioration of aquatic life

How to Protect the Environment?

Consumers should:
- Buy biodegradable detergents that contain minimal quantity of phosphates
- Buy detergents in biodegradable packaging such as cardboard or recyclable plastics
- Use detergents that are designed to work at lower temperatures to save energy
- Decrease waste in using detergents