Can you tell the chemical preparation of soap for class 11th chemistry project?

Answer 1

Objective: To prepare soap by alkaline hydrolysis (saponification) of natural fats and test

some of the chemical properties and cleansing power of soap relative to detergent.

Introduction

Soaps are the sodium and potassium salts of long chain fatty acids that are generally

made by saponification (alkaline hydrolysis) of natural fats, such as animal fats or palm oil.

Prior to World War II, most soap was prepared in the home by boiling animal fat with lye

(commercial sodium hydroxide). Soap is not particularly good for cleaning in hard water (water

with high concentrations of Ca2+, Mg2+ and/or Fe3+ ions) because it forms insoluble complexes

with divalent (or trivalent) cations. Organic sulfonic acid and phosphoric acid salts, commonly

known as detergents, were found to be much more effective cleaning agents because they do not

readily form insoluble complexes with the ions in hard water. Modern cleansers labeled "soft

soap" are, in fact, detergents rather than soap. Check the labels for ingredients of some cleansers

you have around the home, including shampoo.

The phosphate detergents caused environmental problems in waterways, not because they

are toxic, but because they are nutrients and resulted in an overabundance of plant growth, or

algal blooms. Consequently phosphate detergents have been replaced with other alternatives.

Today there are a wide variety of synthetic detergents available for various purposes. Some

representative detergents and a soap are shown below.

In this experiment you will prepare soap from a fat and determine some of its properties

relative to a detergent. See the chemical equation for saponification on the next page.

Materials and Reagents

Shortening, lard or coconut oil, 30% NaOH solution, 95% ethanol, 400 mL beaker, 125

mL Erlenmeyer flask, ice, universal pH paper, 1 % detergent (sodium dodecylsulfate) solution,

1% calcium chloride solution, filter paper, filtration apparatus, used pump oil.

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Small watch glass

for ice

Erlenmeyer

flask with boiling

fat/NaOH/EtOH

Beaker for

hot water

.

.

+

CH2O

CHO

CH2O

C(O)(CH2)16CH3

C(O)(CH2)16CH3

C(O)(CH2)16CH3

Tristearin

(a triacylglycerol)

CH2OH

CHOH

CH2OH

Sodium Stearate Glycerol

(a soap)

CH3(CH2)16COO-Na+ + NaOH 3

Procedure

Part A. Preparation of Soap.

1. Add about 150 mL water to a 400 mL beaker and heat the water with your burner to

about 85EC. You will need to mount a clamp above the beaker to hold the Erlenmeyer

flask (see below) upright in the water bath.

2. Add about 3 g (approx. a level, not heaping teaspoon) of shortening, coconut oil, or lard

to a small beaker and dissolve it in 25 mL of 95% ethanol. Do not use too much fat or

you will need more ethanol to dissolve it.

CAUTION!! SODIUM HYDROXIDE SOLUTION IS VERY CAUSTIC. AVOID

GETTING IT ON YOUR SKIN OR CLOTHING. WASH IT OFF IMMEDIATELY

WITH PLENTY OF WATER.

3. When the fat is completely dissolved, pour

the solution into a 125 mL Erlenmeyer flask

and add 15 mL of 30% NaOH solution. Swirl

the flask to mix the solution and add a few (3

to 5) boiling chips (Boilezer) to the flask.

4. Place the flask containing the fat solution in

the water bath and fasten it with a clamp to

hold it upright in the water bath. Place a

small watch glass over the mouth of the flask

to minimize evaporation of the alcohol. Place

an ice cube in the watch glass to more

effectively condense the alcohol.

5. Allow the the fat-alcoholic NaOH solution to boil for at least 30 min. [Note: do not boil

the water in the water bath]. If you observe undissolved fat in the flask, add a little

more ethanol to the flask and stir to dissolve the fat. Do not allow the hot water bath to

get too hot, keep it just hot enough to have controlled boiling of the fat solution.

6. While the saponification proceeds, prepare a salt solution by completely dissolving 20 g

NaCl in 100 mL deionized water in a 250 mL beaker. After the salt completely

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dissolves, transfer about half of this salt solution to another beaker and place both

beakers of salt solution on ice to cool them.

7. After 30 min, test the fat solution to see if saponification is complete by placing a few

drops of the solution in a test tube of deionized water. If you see fat droplets float to the

top, the saponification is not complete and allow it to boil for an additional 10 min.

8. When saponification is complete, carefully pour the hot reaction mixture into one beaker

of salt solution and stir for a minute or two. Place the mixture on ice to cool it before

filtering.

9. Set up a suction filtration apparatus with a Buchner funnel and filter paper (see Appendix

I for a diagram of the vacuum filtration apparatus). Filter the mixture from step 8, and

wash the soap (remaining in the Buchner funnel) twice with ice cold salt water (from the

second beaker). Draw air through the soap for a few minutes to remove most of the

water.

10. Remove the soap cake from the Buchner funnel and save it for the following tests.

Part B. Comparison of the Properties of Soap with Detergent.

B-1. Alkalinity

1. Prepare a 1% soap solution by dissolving about 0.5 g of the soap you just made in 50 mL

of deionized water. It may help to heat the water to get the soap to dissolve completely.

2. Use a glass stirring rod to place a drop of the soap solution on a piece of universal pH

paper to determine whether the solution is alkaline, neutral or acid. Record your

observation on the Report Sheet.

3. Add about 5 mL of detergent (e.g., sodium laurylsulfate) solution to a beaker or test tube.

You will compare this solution with your soap solution for the remaining tests.

4. Test the detergent solution to see if it is alkaline, neutral or acidic by placing one drop of

the detergent solution on a strip of pH paper. Record your observation on the Report

Sheet.

B-2. Lathering Power

1. Add about 2 mL of deionized water to four large test tubes.

2. Add an equal amount of soap solution to one test tube of water and shake vigorously by

placing a stopper in the tube. This should give a permanent lather that lasts for at least 30

sec. If the lather doesn't last, add another 10 drops of soap solution and shake vigorously.

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3. Add an equal amount of detergent solution to another test tube of water and shake

vigorously. This should give a permanent lather. If not, add another 10 drops and shake

vigorously. Record the results on the report sheet.

4. Add 2 mL of 1% Ca2+ solution to each of the two remaining test tubes of water.

5. Add an equal amount of soap solution to one of the tubes containing Ca2+ ion and shake

vigorously. Notice whether this solution forms a permanent lather and note whether

there is any floculent precipitate in the tube. Does the precipitate float or sink?

6. Add an equal amount of detergent solution to the other tube containing Ca2+ ion and

shake vigorously to get a permanent lather. Does the lathering power of the detergent

differ from the soap when Ca2+ is present? Is there any precipitate in this solution?

Record the results on the report sheet.

B-3. Cleansing Power

1. Place a drop of used pump oil on four separate thin strips of filter paper. Make sure the

strips of filter paper will fit in the test tubes used in part B-2.

2. Place one filter paper with oil spot in the tube containing soap in water. Place another in

the tube containing detergent and water. Place a third strip in the tube containing soap in

Ca2+ solution. Place the fourth strip of oily paper in the tube containing detergent and

Ca2+ solution. Shake each one well and make sure the filter paper is immersed in the

solution.

3. After 2 min remove the filter paper and rinse with tap water. Did the oil get washed out

of the filter paper strip? You can discard the solutions in the sink. Throw the paper

strips in the trash can. Compare the cleaning power of soap vs detergent on the Report

Sheet.