Detergent

  1. A detergent is a compound, or a mixture of compounds, intended to assist cleaning.
  2. Detergent are usually made from synthetic subtances.
  3. Example of detergents are sodium alkyl sulphate and sodium alkylbenzene sulphonate.


The Structure of a Detergent Molecule

  1. The basic structure of the detergent molecule is similar in nature to a soaps. It will dissolve in water to produce sodium ion (Na+) and detergent ions.
  2. A detergent ion consists of two parts which are known as the hydrophilic part and the hydrophilics part.
  3. The hydrophilic part consist of the sulphate group (-OSO3) or the sulphonate group (-SO3) which is readily dissolves in water but does not dissolve in oil.
  4. The tail is a long hydrocarbon chain which is hydrophobic in nature and does not dissolve in water but dissolves readily in oil.

Cleaning Action of Detergent

  1. Like the ion of soap, detergent ions consist of two parts, the hydrophobic part and the hydrophilic part.
  2. Therefore, detergent can also act as emulsifying agent and wetting agent as soap, in a cleaning action.

Making of Detergent

Preparation of Sodium Alkyl Sulphate

Stage 1: Sulphonation of alcohol

The long chain alcohol is reacted with concentrated sulphuric acid to form alkyl sulphonic acid.

Stage 2: Neutralization

The alkyl sulphonic acid is then neutralised sodium hydroxide solution to produce sodium alkyl sulphate salt, which is detergent .

Preparation of Sodium Alkyl Benzene Sulphonate

Stage 1: Alkylation

The long chain alkene is reacted with benzene to form alkylbenzene.

Stage 2: Sulphonation

Sulphonation of alkylbenzene:
The alkylbenzene is reacted with concentrated sulphuric acid to form
alkylbenzene sulphonic acid.

Stage 3: Neutralization

Neutralisation: 
The alkylbenzene sulphonic acid is then neutralised sodium hidroxide solution to produce
alkylbenzene sulphonate salt, which is detergent.

Effectiveness of Soap And Detergent

Soap

Advantages:

  1. More effective than water.
  2. It is biodegradable, will not pollute the water.

Disadvantages:

Will form scum with hard water. (Hard water is the water which rich in Ca2+ ions and Mg2+ ions)
Not effective in acidic water.

Detergent

Advantages:

  1. More effective than water.
  2. Will not form scum with hard water.
  3. Still effective in acidic water.

Disadvantages:

  1. Not biodegradable (especially those have a lot of branches in the carbon chain.)
  2. Some of the additives like phosphate and chloride will pollute water.

Additive in Detergent

Biological Enzyme

Examples: Amylase, lipase, protease

Function: Break down fat and protein molecules in food stains.

Whitening agent

Examples: Sodium perborate, Sodium hypochlorite
Function: Convert stain to colourless substances

Brighteners

Examples: Fluorescent dye (Blancophor R)
Function: Make fabrics appear brighter.

Builders

Examples: Sodium tripolyphosphate
Function: To soften hard water.

Suspension agent (Anticoagulant)

Examples: Carboxylmethylcellulose
Function: To prevent the dirt particles removed from deposition onto cleaned fibrics.

Foam control agent (Stabiliser)

Examples: Silicone
Function: To prevent the formation of excess bubbles in automatic washing machine.

Fragrance

Function: Add fragrance to fabrics and detergent