Detergents (2/4)
Detergents
- a substance which helps water to clean things better.
A) Types of Detergents
1) Soapless detergents ( or synthetic detergents ). They are made using ______.
2) Soapy detergents ( or soaps ). They are made from ______or ______.
B) Structure of Detergents
______tail ______head
is ______is ______
( water-______) ( water-______)
( soluble in _____ but not in ______) ( soluble in ______but not in _____ )
1) Structure of Soapless Detergent particle
e.g. CH3(CH2)11-O-SO3- Na+
2) Structure of Soapy Detergent particle
e.g. CH3(CH2)16-COO- Na+
Soapy detergents are usually sodium ( or potassium ) solats of long-chain alkanoic acids. The ionic head of them is always a ______group ( ).
C) Properties of Detergents
Detergent particles can act as a ______agent and ______agent.
Wetting agent / Emulsifying agentThey reduce the ______of water and thus water spread over the surface ( e.g. a piece of cloth ) and wets it more easily. / When detergent is added to an oil-water mixture and shake, the small oil drops in the oil-water mixture do not join together and remain suspended and the mixture is called an ______.
After shaking, oil droplets are formed which are ______. They ______each other and remain ______throughout the water. The oil-water emulsion is stabilized by the detergent.
Cleansing Action of Detergents
1) A detergent enables water to wet the object thoroughly.
2) Hydrophobic tails of detergent anions dissolve in grease.
3) Water molecules attract the hydrophilic heads of detergent anions, lifting up the grease from the surface.
4) By stirring, the grease forms tiny droplets, forming an emulsion.
D) Making Detergents
Soapless Detergent: ______reacts with concentrated sulphuric acid and then with sodium hydroxide.
Soapy Detergent:
Step 1: boil ______with concentrated NaOH/KOH ( ______)
Step 2: conc. NaCl(aq) is added to ______the solubility of soap in water. ( ______of soap )
E) Differences between Soapy Detergents and Soapless Detergents
They behave very differently in hard and soft water.
Hard water is a water containing quite high concentration of dissolved ______and ______.
Soft water is a water containing very low concentration of dissolved ______and ______.
Soapy Detergents / Soapless DetergentsSoft water / Both detergents clean well and they form a lather ( foam and bubbles ) easily
Hard water / They do not form lather. The soaps react with the ____ and _____ ions in the water to form a sticky insoluble substance called ______. Taking sodium stearate as an example of soap, / Same as above.
Acidic solution / Soaps are changed to ______alkanoic acids. Taking sodium stearate as an example of soap, / Same as above
Water softener such as washing soda, sodium carbonate-10-water (Na2CO3 10H2O can be used to remove the hardness and acidity of water. It removes the hardness of water by precipitating Ca2+ and Mg2+ ions as insoluble carbonates.
Washing soda is alkaline. It thus removes any acidity of water at the same time.
F) Problems caused by Detergents
Non-biodegradable detergents are detergents having ______-chain hydrocarbon tail.
Biodegradable detergents are detergents having ______-chain hydrocarbon tail only.
Non-biodegradable detergents / Biodegradable detergentsThe lather from these detergents produced thick ______. The foam would kill water life, damage machines and cause ______pollution. / They can be broken down by ______in water to form harmless chemicals.
However, bacteria use up too much ______in water and water life will ______.
Phosphate from soft softeners in washing powders become ______for algae. As a result, the amount of algae increases rapidly and it is believed to be one cause of ‘______’. When the algae die and rot, they again use up ______in water.
Most detergent solutions have pH values between 5 and 9. Detergents with pH values outside this range may cause ______.
G) Advantages and Limitations
Soapy Detergents
Advantages / Limitations- non-toxic to water life / - doesn’t work well in hard water
- ALL are biodegradable / - cannot be used in acidic solution
- mildly alkaline. It doesn’t cause skin allergy / - slightly soluble in water
Soapless Detergents
Advantages / Limitations- made from petroleum products, not from fats or oils. More animal fats and plant oils can be saved as food. / NIL
- work well in soft water, hard water and acidic solution
- can be ‘tailor-made’ to suit a particular cleaning problem.
**SOME of soapless detergents are non-biodegradable