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 ).