Cleaning Agents

 

Soap

 
  • Soaps are sodium or potassium fatty acid salts.
  • Soaps are produced from the neutralisation reaction between fatty acids and alkalis.
  • Fatty acids are long-chain carboxylic acids.
  • Sources of fatty acids can be obtained from natural esters in animal fats or vegetable oils.
  • The general formula for soap is \(RCOO−Na^+\) or \(RCOO−K^+\).
  • R is an alkyl group containing at least 8 carbon atoms.
  • However, this alkyl group usually contains 12 to 20 carbon atoms.
  • R consists of saturated or unsaturated hydrocarbons.
 

Examples of soaps

 

Sodium laurate, \(CH_3(CH_2)_{10}COONa\)

 
Fatty acid Source

Lauric acid

\(CH_3(CH_2)_{10}COOH\)

Coconut oil
 

Sodium palmitate, \(CH_3(CH_2)_{14}COONa\)

 
Fatty acid Source

Palmitic acid

\(CH_3(CH_2)_{14}COOH\)

Palm oil
 

Detergent

 
  • The production of detergents began during the second world war owing to the lack of animal fats and vegetable oils.
  • Detergents are non-soap cleaning agents.
  • Detergents are sodium salts of sulphonic acids.
  • Two types of sulphonic acids used to make detergents are alkyl sulphonic acid and alkylbenzene sulphonic acid.
  • Detergents are usually made from synthetic sources, such as petroleum fractions.
 
Alkyl sulphonic acid Alkylbenzene sulphonic acid
 

Preparation of Soap

 
  • Soaps can be prepared from natural sources through hydrolysis of oils or fats in sodium hydroxide, \(NaOH\) or potassium hydroxide, \(KOH\) solutions.
  • This reaction is called saponification, which is the process of hydrolysis of oils or fats by alkalis.
  • Oils or fats react with concentrated alkalis to produce glycerol and fatty acid salts, which is soap.
  • Oils and fats are natural esters known as triglycerides.
 
General equation of saponification reaction
Oil/Fat + Concentrated alkali → Soap + Glycerol
 

Preparation of Detergents

 
  • Detergents are usually made from petroleum fractions and sulphuric acid, \(H_2SO_4\).
  • They are produced through two processes which are:
    • Sulphonation
    • Neutralisation
 

Preparation of Sodium Alkylbenzene Sulphonate

 
(i) Sulphonation of alkylbenzene
Alkylbenzene reacts with concentrated sulphuric acid, \(H_2SO_4\) to form alkylbenzene sulphonic acid.

 

(ii) Neutralisation
Alkylbenzene sulphonic acid will be neutralised by sodium hydroxide, NaOH solution to produce alkylbenzene sulphonate salt, which is detergent.
 

Preparation of Sodium Alkyl Sulphate

 
(i) Sulphonation of alcohol
Long chain alcohol reacts with concentrated sulphuric acid, \(H_2SO_4\) to form alkyl sulphonic acid.

 

(ii) Neutralisation
Alkyl sulphonic acid will be neutralised by sodium hydroxide, NaOH solution to produce sodium alkyl sulphate, which is detergent.
 

Cleansing Action of Soap and Detergent

 
  • Basically, the cleansing action of soap and detergent is the same.
  • Soaps and detergents act as emulsifying agents because soap and detergent molecules are soluble in oil or grease and water.
  • When soap or detergent is dissolved in water, soap or detergent molecules dissolve to form:
    • sodium ion, \(Na^+\) or potassium ion, \(K^+\).
    • soap anion or detergent anion.
 
Examples of equations for ionisation for soap anion and detergent anion
Soap \(\xrightarrow[]{Water}\) Soap anion + Sodium ion
Detergent \(\xrightarrow[]{Water}\) Detergent anion + Sodium ion

 

Structural formula for soap anion and detergent anion
 
  • The structures of soap anion and detergent anion consist of two parts, namely:
    • hydrophilic part that is soluble in water.
    • hydrophobic part that is soluble in oil or grease.
  • Both of these properties make soap and detergent effective cleaning agents.
 
Step Explanation
1
  • Adding soap or detergent into water will reduce the surface tension of water.
  • This increases the water’s ability to wet the surface of the cloth.
2
  • Soap or detergent will ionise in water to produce free moving soap anions or detergent anions.
3
  • The hydrophilic parts of soap anions or detergent anions dissolve in water.
  • The hydrophobic parts dissolve in grease.
4
  • Movement of water during scrubbing and agitation causes grease to pull away from the surface of the cloth.
5
  • The hydrophilic parts of soap anions or detergent anions surround the grease.
  • Grease floats to the surface of the water.
6
  • Grease will break into small droplets.
  • The small droplets will not reattach to the surface of the cloth due to the repulsion of negative charges of the hydrophilic parts on the surface of the grease.
  • The droplets are suspended in water, forming an emulsion.
  • Rinsing with water causes the surface of the cloth to become clean because the grease droplets are left in the water.

 

Cleansing Action of Soap and Detergent

 

Grease broken into droplets of emulsion
 

Comparison of Cleansing Action of Soap and Detergent

 
  • Water containing calcium ions, \(Ca^{2+}\) and magnesium ions, \(Mg^{2+}\) is called hard water.
  • Soap anions combine with the cations to form insoluble salts called scum.
  • The formation of scum causes wastage of soap because more soap will be needed for the cleansing action.
  • Detergent anions also combine with the cations to form soluble salts in water.
  • Therefore, the effectiveness of the detergent’s cleansing action is not affected by hard water.
 
Aspect Soap Detergent
Effectiveness in soft water Effective Effective
Effectiveness in hard water Less effective More effective
Formation of scum Forms scum in hard water Does not form scum in hard water
Effectiveness in acidic water Not effective due to the formation of insoluble organic acid Effective because the organic acid formed is soluble
 

Additives in Detergent

 
Function Example
Biological enzyme
To remove protein stains, such as blood, milk and sugar. Amylase, protease, cellulase and lipase
Whitening agent
To change dirt to colourless substance. Sodium perborate and Sodium hypochlorite
Optical whitener
To make clothes become whiter and brighter. Fluorescent dyes
Water softener and builder
To enhance the effectiveness of the detergent by softening the water. Sodium tripolyphosphate
Foam control agent
To control the foam formed by the detergent. Alkyl monoethanolamide
Anti suspension agent
To prevent the removed dirt from redepositing to the clothes. Sodium carboxylmethyl-cellulose
Fragrances
To enhance the fragrance of the detergent and fabric. Jasmine and lavender
Drying agent
To ensure that the detergent powder is always dry in its container. Sodium sulphate and sodium silicate

Cleaning Agents

 

Soap

 
  • Soaps are sodium or potassium fatty acid salts.
  • Soaps are produced from the neutralisation reaction between fatty acids and alkalis.
  • Fatty acids are long-chain carboxylic acids.
  • Sources of fatty acids can be obtained from natural esters in animal fats or vegetable oils.
  • The general formula for soap is \(RCOO−Na^+\) or \(RCOO−K^+\).
  • R is an alkyl group containing at least 8 carbon atoms.
  • However, this alkyl group usually contains 12 to 20 carbon atoms.
  • R consists of saturated or unsaturated hydrocarbons.
 

Examples of soaps

 

Sodium laurate, \(CH_3(CH_2)_{10}COONa\)

 
Fatty acid Source

Lauric acid

\(CH_3(CH_2)_{10}COOH\)

Coconut oil
 

Sodium palmitate, \(CH_3(CH_2)_{14}COONa\)

 
Fatty acid Source

Palmitic acid

\(CH_3(CH_2)_{14}COOH\)

Palm oil
 

Detergent

 
  • The production of detergents began during the second world war owing to the lack of animal fats and vegetable oils.
  • Detergents are non-soap cleaning agents.
  • Detergents are sodium salts of sulphonic acids.
  • Two types of sulphonic acids used to make detergents are alkyl sulphonic acid and alkylbenzene sulphonic acid.
  • Detergents are usually made from synthetic sources, such as petroleum fractions.
 
Alkyl sulphonic acid Alkylbenzene sulphonic acid
 

Preparation of Soap

 
  • Soaps can be prepared from natural sources through hydrolysis of oils or fats in sodium hydroxide, \(NaOH\) or potassium hydroxide, \(KOH\) solutions.
  • This reaction is called saponification, which is the process of hydrolysis of oils or fats by alkalis.
  • Oils or fats react with concentrated alkalis to produce glycerol and fatty acid salts, which is soap.
  • Oils and fats are natural esters known as triglycerides.
 
General equation of saponification reaction
Oil/Fat + Concentrated alkali → Soap + Glycerol
 

Preparation of Detergents

 
  • Detergents are usually made from petroleum fractions and sulphuric acid, \(H_2SO_4\).
  • They are produced through two processes which are:
    • Sulphonation
    • Neutralisation
 

Preparation of Sodium Alkylbenzene Sulphonate

 
(i) Sulphonation of alkylbenzene
Alkylbenzene reacts with concentrated sulphuric acid, \(H_2SO_4\) to form alkylbenzene sulphonic acid.

 

(ii) Neutralisation
Alkylbenzene sulphonic acid will be neutralised by sodium hydroxide, NaOH solution to produce alkylbenzene sulphonate salt, which is detergent.
 

Preparation of Sodium Alkyl Sulphate

 
(i) Sulphonation of alcohol
Long chain alcohol reacts with concentrated sulphuric acid, \(H_2SO_4\) to form alkyl sulphonic acid.

 

(ii) Neutralisation
Alkyl sulphonic acid will be neutralised by sodium hydroxide, NaOH solution to produce sodium alkyl sulphate, which is detergent.
 

Cleansing Action of Soap and Detergent

 
  • Basically, the cleansing action of soap and detergent is the same.
  • Soaps and detergents act as emulsifying agents because soap and detergent molecules are soluble in oil or grease and water.
  • When soap or detergent is dissolved in water, soap or detergent molecules dissolve to form:
    • sodium ion, \(Na^+\) or potassium ion, \(K^+\).
    • soap anion or detergent anion.
 
Examples of equations for ionisation for soap anion and detergent anion
Soap \(\xrightarrow[]{Water}\) Soap anion + Sodium ion
Detergent \(\xrightarrow[]{Water}\) Detergent anion + Sodium ion

 

Structural formula for soap anion and detergent anion
 
  • The structures of soap anion and detergent anion consist of two parts, namely:
    • hydrophilic part that is soluble in water.
    • hydrophobic part that is soluble in oil or grease.
  • Both of these properties make soap and detergent effective cleaning agents.
 
Step Explanation
1
  • Adding soap or detergent into water will reduce the surface tension of water.
  • This increases the water’s ability to wet the surface of the cloth.
2
  • Soap or detergent will ionise in water to produce free moving soap anions or detergent anions.
3
  • The hydrophilic parts of soap anions or detergent anions dissolve in water.
  • The hydrophobic parts dissolve in grease.
4
  • Movement of water during scrubbing and agitation causes grease to pull away from the surface of the cloth.
5
  • The hydrophilic parts of soap anions or detergent anions surround the grease.
  • Grease floats to the surface of the water.
6
  • Grease will break into small droplets.
  • The small droplets will not reattach to the surface of the cloth due to the repulsion of negative charges of the hydrophilic parts on the surface of the grease.
  • The droplets are suspended in water, forming an emulsion.
  • Rinsing with water causes the surface of the cloth to become clean because the grease droplets are left in the water.

 

Cleansing Action of Soap and Detergent

 

Grease broken into droplets of emulsion
 

Comparison of Cleansing Action of Soap and Detergent

 
  • Water containing calcium ions, \(Ca^{2+}\) and magnesium ions, \(Mg^{2+}\) is called hard water.
  • Soap anions combine with the cations to form insoluble salts called scum.
  • The formation of scum causes wastage of soap because more soap will be needed for the cleansing action.
  • Detergent anions also combine with the cations to form soluble salts in water.
  • Therefore, the effectiveness of the detergent’s cleansing action is not affected by hard water.
 
Aspect Soap Detergent
Effectiveness in soft water Effective Effective
Effectiveness in hard water Less effective More effective
Formation of scum Forms scum in hard water Does not form scum in hard water
Effectiveness in acidic water Not effective due to the formation of insoluble organic acid Effective because the organic acid formed is soluble
 

Additives in Detergent

 
Function Example
Biological enzyme
To remove protein stains, such as blood, milk and sugar. Amylase, protease, cellulase and lipase
Whitening agent
To change dirt to colourless substance. Sodium perborate and Sodium hypochlorite
Optical whitener
To make clothes become whiter and brighter. Fluorescent dyes
Water softener and builder
To enhance the effectiveness of the detergent by softening the water. Sodium tripolyphosphate
Foam control agent
To control the foam formed by the detergent. Alkyl monoethanolamide
Anti suspension agent
To prevent the removed dirt from redepositing to the clothes. Sodium carboxylmethyl-cellulose
Fragrances
To enhance the fragrance of the detergent and fabric. Jasmine and lavender
Drying agent
To ensure that the detergent powder is always dry in its container. Sodium sulphate and sodium silicate