chemistry easy science
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7CHEMISTRY EASY SCIENCE
By ; Nuriman Syakirah409/13138
Definition Preparation Cleansing Action Additives In Detergents
Are synthetic cleansing agents that use chemicals extracted mostly from petroleum instead of fatty acid.Detergents are sodium salts of sulphonic acid that has 12 to 18 carbon atoms per molecule. The types of detergents commonly used today are sodium alkybenzene suplhonates and sodium alkyl sulphates.
There are THREE steps to prepare Sodium alkylbenzene
Step 1 : Alkylation- Alkylation adds the benzene ring to a long chain alkene group to form alkylbenzene.
Step 2 : Sulphonation- The alkybenzene is added with concentrated sulphuric acid to form alkylbenzene sulfonic acid and water.Alkylbenzene + Concentrated Sulphuric Acid → Alkylbenzene sulphonic acid + Water
Step 3 : Neutralisation- The alkybenzene sulphonic acid is neutralised by sodium hydroxide to form a stable salt (Detergent) Alkylbenzene sulphonic acid + Sodium hyroxide → Dodecylbenzene sulphonate + Water
There are TWO steps to prepare Sodium alkyl sulphates
Step 1 : Reacting with concentrated sulphuric acid- The long chain alcohol reacts with concentrated sulphuric acid to form an alkyl sulphuric acid. Alcohol + Sulphuric acid→ Alkyl sulphonic acid + Water
Step 1 : Neutralisation with sodium hydroxide- The alkyl sulphuric acid neutralised by sodium hyroxide to form sodium alkyl sulphate. Alkyl sulphonic acid + Sodium hydroxide → Sodium alkyl sulphate + Water
Cleansing action1. Akylbenzene sulphonates, particularly sodium
dodecylbenzene sulphonate is the most common detergent.
2. When detergent dissolves in water, the molecule ionises into a sodium ion, Na+ and a detergent ion.
3. The detergent ion has a long hydrocarbon chain that is hydrophobic but soluble in grease and ionic end that a hydrophilic and water soluble.
4. Detergents are like soap surfacatants. It lowers the surface tension, improves the wetting ability of water, breaks down grease or oils by emulsifying the grease and oils and suspending them in water
Similarities and Differences of Soap and Detergent
Soaps Detergentso Both are long molecules that when dissolved in water form ions that have an ionic part and a long hydrocarbon part. The ionic part is soluble in water and the hydrocarbon chain is solublle in grease.
o Both are surfactants (able to reduce surface tension of water, to emulsify ioils and grease)
Soaps Detergents• Not effective as cleansing agent in hard and acidic water• Limited in variety of cleansing abilities.• Made from natural fats and oils• Biodegradable• Ionic part carboxylate
• Effective as cleansing agent in hard or acidic water• Can be modified for different cleansing needs• Made from petroleum• Usually not biodegradable• Ionic part sulphate or sulphonate
Additives in detergent and their functions
Phosphate Make hard water soft (Ex : sodium tripolyphosphate, a substance
which is currently ban)
Flourescent whitening agents Enhance fabric appeareance and maintain whiteness or brightness
Fragrances Give pleasant scent to fabrics
Bleach Removes colour stains but does note affect the colour of the
fabric dye.Enzymes Break down complex stains such
as proteins and blood into soluble and easily removable substances
Fabric softening agents Impart softness in fabrics