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A. SOAP AND DETERGENT
A sodium or potassium salt of long-chain fatty acid
General formula of soap:
RCOO-Na+ or RCOO-K+
A sodium or potassium salt of alkyl sulphonic
acids or alkylbenzene sulphonic acid
Soap preparation process
• Soap is prepared by hydrolyzing fats or oils under
alkaline condition. This reaction is called
• The process involves boiling fats or oils with
concentrated NaOH or concentrated KOH to
produce glycerol and the salts of fatty acids which
are the soap
Describe how soap can be prepared in laboratory
1. Place 10 g of palm oil in a beaker.
2. Slowly and carefully add 15 cm3 of 6 mol dm-3
concentrated sodium hydroxide solution.
3. Gently heat the mixture, stirring with glass rod until the oil
layer becomes invisible.
4. Add 20 ml of water and 12 g of sodium chloride into the
mixture and stir.
5. Cool the mixture.
6. Filter the mixture.
7. Rinse the solid soap with distrilled water and dry the solid
Why is sodium chloride added to the mixture?
Sodium chloride, NaCl is added to:
• Reduces the solubility of soap in water
• To precipitate the soap produced
Detergent preparation process
• During the preparation of detergent, a long-chain
hydrocarbon obtained from petroleum fraction is
converted into an organic acid through a series of
• The organic acid is then neutralized with sodium
hydroxide, NaOH solution to produce a detergent.
Structure of soap
• Soap consists of sodium/potassium cations and soap
• When a sodium/potassium soap dissolve in water, it
will form soap anions and sodium ion, Na+ or
potassium ion, K+
What is soap anions?
Cleaning action of soap & detergent
• When soap/detergent is
added to water,
dissolve in water to form
free moving anions and
• Soap reduces surface
tension of water
• The hydrophobic
part dissolve in
• The hydrophilic part
attracted to water
• Mechanical agitation
helps the hydrophobic
part pull away the
grease from the
• The grease is broken
up into small droplet
• The droplet does not
coagulate due to the
• The droplets are
suspended in water to
form an emulsion
• When rinsed, the droplet
will be removed
Explain why detergent is more effective in hard water
• Hard water contain calcium ion, Ca2+ and magnesium
• Soap anions react with Ca2+ ion and Mg2+ ion to form
• Scum is insoluble in water
• Detergent does not form scum in hard water
• Detergent is more effective than soap in hard water
5.1 Soap and Detergent
Describe a laboratory experiment to prepare a soap by
using a namely oil and alkali.
State how to verify the product formed is soap.
Terangkan suatu experiment makmal untuk menyediakan
sabun dengan menggunakan minyak dan alkali yang
Nyatakan bagaimana anda mengesahkan hasil yang
terbentuk itu adalah sabun.