Unit 16 Franklin`s Famous Kite Experiment Lecturer : Fan Liyan.
Experiment 16
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Transcript of Experiment 16
Experiment 16Soap and detergents
Pre-laboratory questions:
1. Differentiate fats from oils.2. Write an equation showing the
saponification of fats and oils with NaOH.
3. Draw the complete structures, showing all bonds , for stearic acid and sodium stearate.
4. Draw structures of some syndets.
Answers to the questions:
1. Fats Oils
Tend to be solid or semi-solid at
room temperature
Tend to be liquid at room temperature
Usually come from animal
sources
Usually come from plant
sourcesMore saturated Less saturated
2.
3. Structure of stearic acid
Structure of sodium stearate
4. Structure of some syndets
Objectives:
To observe the preparation of soap. To compare syndets and prepared
soap.
Results and
discussions
Preparation of soap:
Observation: When we mixed the lard & the NaOH in
35ml of 1:1 ethanol-water. The lard was insoluble in the mixture.
When heated for 2 minutes the lard dissolved
When heated for 5 minutes the solution became viscous
We stopped heating when we reached 18 minutes the solution became very thick. (homogeneous mixture)
After mixing a salt solution with the soap mixture the soap from a homogeneous mixture it became little pieces.
Mixed lard and NaOH solution
2 minutes 5 minutes
18 minutes
Finished product
SOAP USED:SYNDET LIQUID SOAP
WINGS SURF
Data: Oil
Prepared: Syndet: Liquid: Distilled water:
MiscibleOil is
emulsified
MiscibleOil is
emulsified
Immiscible
Oil is not emulsifie
d
Immiscible
Oil is not emulsifie
dTap Water:
Prepared: Syndet: Liquid: Distilled water:
No precipitat
e
No precipitat
e
No precipitat
e
No precipitat
e
pictures
OIL
TAP WATER
Discussion:
Soaps are soluble both in water and oil. The carboxylate end of the long-chain
molecule is ionic and therefore hydrophilic, or attracted to water.
The long hydrocarbon portion of the molecule, however is non-polar and hydrophobic, or water avoiding, and therefore more soluble in oils.
Since the liquid soap wasn’t soluble in oil. We can conclude that it isn’t effective in removing oils from the dishes.
There was no precipitate formed when we placed the soap in the tap water. This indicates that the tap water doesn’t contain soluble sodium carboxylates .
Data: CaCl2
Prepared: Syndet: Liquid:
No precipitate formed
No precipitate formed
No precipitate formed
MgCl3
Prepared: Syndet: Liquid: precipitate
formed No precipitate
formedNo precipitate
formed
FeCl2
Prepared: Syndet: Liquid:No precipitate
formed Precipitate
formedPrecipitate
formed
Discussion:
Soaps have some drawbacks In hard water, w/c contains Ca2+,
Mg2+, Fe3+, SO42-, and HCO3
-, soluble sodium carboxylates are converted into insoluble metal salts (precipitate), leaving the familiar ring of scum around bathtubs and the gray tinge on white clothes.
Data:
Litmus paper test:
Prepared: Syndet:Blue Blue
Phenolphthalein solution:
Prepared: Syndet:Colorless to Pink Colorless to Pink
Picture
Discussion:
Since the color of the paper is blue this means that the soaps are basic.
Soap is made from sodium hydroxide and fats. The presence of sodium hydroxide makes it
basic
Litmus Paper Test:
Phenolphthalein test:Phenolphthalein turns pink when the solution is basic
With this it is proven that the prepared soap and the syndet are both basic which is one of the qualities of a soap.
Post-laboratory questions:
1. Explain why you poured the hydrolyzed fat mixture into a concentrated solution to precipitate the soap.
2. Why is the hydrolysis of a fat called saponification.
3. Describe the cleansing action of soap.4. Assuming a soap to be pure sodium
stearate, give an equation.1. That shows why its solutions are alkaline2. For its reactions with Mg+2 in hard water3. For its reaction with hydrochloric acid
answers
1. Because in mixing the NaOH solution to the lard both soap and glycerol is produced.
GLYCEROL- interferes with testing so we need to take the glycerol out to take it out we add the salt solution which has a salting out effect thereby removing glycerol. Additionally, we wash the soap with cold water to remove the remaining glycerol and salt.
2. The hydrolysis of fat is called saponification after the Latin word sapo, “soap”. This reaction then results to the formation of soap. Soap is a mixture of carboxylate salts of fatty acids derived from the fatty acids of the triacylglycerols contained in the fat or oil.
3. The cleansing action of both soaps and detergents results from their ability to emulsify or disperse water-insoluble materials (dirt, oil, grease, etc.) and hold them in suspension in water. This ability comes from the molecular structure of soaps and detergents. When a soap or detergent is added to water that contains oil or other water-insoluble materials, the soap or detergent molecules surround the oil droplets. The oil or grease is “dissolved” in the alkyl groups of the soap molecules while the ionic end allows the micelle to dissolve in water. As a result, the oil droplets are dispersed throughout the water (this is referred to as emulsification ) and can be rinsed away
a.CH3(CH2)16COONa + HCl CH3(CH2)16COOH +NaCl
b.
c.
Conclusion
Soaps are prepared through the process of saponification. Soaps are basic, soluble in both water and oil, but creates precipitate in hard water (contains Ca2+, Mg2+, Fe3+, SO4
2-, and HCO3
-, soluble sodium carboxylates ).