Soap

History of Soap Manufacturing

In the past, soaps was made by mixing animal fats with alkaline wood ashes. The wood ashes dissolve in water produce sodium hydroxide and potassium hydroxide. The boiling of animal fats with sodium hydroxide (or potassium hydroxide) produces soap.

Potassium salts produce soft soaps whereas sodium soaps are harder and more widely employed. The quality of soap produced is very dependent on the quality of the materials employed in the reaction. Early attempts at soap production relied on ash, produced by burning various vegetable materials, as a make shift source of alkali.

In Britain early production of soap was usually based on rendered animal fat, such as tallow from beef or mutton. Later, growing imports of oils such as palm, coconut, olive, linseed and cottonseed oils offered a wider choice of raw materials and favoured production of soap in sea-ports such as London and Bristol. Production of soap in Bristol as early as the 12th century has already been referred to.

What is Soap?

Soap are sodium or potassium salts of long-chain fatty acids. The general formula of a soap can be written as:

R is an alkly group usually containing 12 to 18 carbon atoms.

Example of soap, sodium palmitate and potassium stearate.

Soap Preparation Process

Animal fat and vegatables are natural occuring esters.

Soap can be prepares by boiling the animal fats or vegatables oils with concentrated sodium hydroxide. The fats and oils are hydrolyed to produce glycerol and the sodium salts of fatty acids which are soaps.

In general,

Esters + concentrated sodium hydroxide ---> Soap + Glycerol

Alkaline hydrolysis of esters is called saponification.

Example of akaline hydrolysis of animal fat, glycerol tristearate produce sodium stearate(soap) and glycerol.

Properties of Soaps

1- Soaps are slippery.

2- Soaps form lather when shaken with water.

Soaps molecular structure

One soap molecule consists of two parts that is ionic (hydrophilic) part which is soluble in water and hydrocarbon (hydrophobic) chain which is soluble in oils or grease.

Cleansing action

In Soft Water;

Soap reduces the surface tension of water. Therefore, the dirty surface is wetted with water and soap.

During cleaning process, the hydrocarbon part dissolves in grease and the ionic part dissolves in water.

When scrub, the grease is freed from the surface and also break into droplets. These droplets are suspended in water forming an emulsion.

Rinsing washes away these droplets and leaves the surface clean.

Example:

In sodium stearate,

sodium ion is positively charged and stearate ion is negatively charged.

When you apply soap on a surface which has oily dirt, the stearate part embeds itself in the oil as it is attracted to it but repelled by water.

On the other hand, the sodium ion is attracted to water and sticks to it.

When you wash off the soap, the sodium ion gets pulled by the water, it pulls its stearate ion which in turn pulls the oil off.

A diagram of the function of the soap:

Disadvantages of Soaps

As salts of weak acids, they are converted by mineral acids into free fatty acids:
These fatty acids are less soluble than the sodium or potassium salts and form a precipitate.

Because of this, soaps are ineffective in acidic water.

Also, soaps form insoluble salts in hard water, such as water containing magnesium, calcium, or iron. Soaps form scum in hard water. For example:

Effect to Environment

As soaps are made from natural sources.

Soaps are bodegradable .

Do not cause any pollution.