Soap Flashcards
Why is the reaction refluxed at the beginning?
Allow time for reaction to reach completion
Prevents loss of volatile components/materials
What is in the pear shaped flask in reflux?
Vegetable oil [lard], sodium hydroxide and ethanol
Why is vegetable oil used in reflux?
It contains lard which has the natural occurring ester glyceryl tristearate
Why is it refluxed for 20-30 minutes?
Allow suff time for reaction to take place
What type of reaction occurs in stage one/reflux?
Saponification
What substance was removed by distillation in stage two
Ethanol
Explain the function of brine is stage 3
Precipitates soap - soap is insoluble in brine
Why was it necessary to wash the soap throughly in stage 4?
Remove sodium hydroxide
How should the student have washed the soap in stage 4?
Ice-cold water
Give the name of the co-product of the reaction and where is it located at the end of the process?
Propane-1,2,3-triol
In the filtrate
Calculate the max yield in grams of soap that would have been obtained
Find moles of one fat and multiply by three
Then multiply by mr of soap
What happened to the liquid in the flask during reflux?
Hot vapour rose and liquid evaporated. It enters condenser and turns to liquid and returns to flask
How did refluxing the mixture help bring the reaction to completion?
It allowed enough time
Provides activation energy
Write the IUPAC name for glycerol?
Propane-1,2,3-triol
What was the purpose of the ethanol?
Solvent
Describe with the aid of a labelled diagram, how the ethanol was removed after the reflux stage
At 78 degrees Celsius, heat reaction mix and ethanol evaporated - condenser and enters test tube
How was the soap isolated from the other substances left in the reaction mixture
Added to brine
After isolating the soap from other substances, how was it purified and dried?
Purified - put in cold water
Dried - put in oven
Calculate the percentage yield of soap
Find moles of glyceryl tristearate - dividing by mr
do mole hoppin to find of soap
find grams of soap
Put over actual yield given in question and multiply by 100
Why is it desirable to remove the ethanol after reflux?
Easier to extract soap as some soap might be disolved in ethanol
Describe how a pure sample of soap was obtained from the reaction mixture?
Pour into brine, wash with ice cold water
What is the second product of the reaction?
Glycerol
At the end of the experiment, what is the location of the second product of the reaction?
In the filtrate
At the end of the experiment, what is the location of the excess sodium hydroxide?
In the flitrate
What would you observe, upon shaking, if a little of the soap prepared is added to a test tube containing deionised water?
Form lather
What would you observe, upon shaking, if a little of the soap prepared is added to a test tube containing mineral water from a limestone region?
Form no lather
Why is it refluxed for 20-30 minutes?
Allow sufficient time for reaction to take place and to bring to completion
How is reflux carried out?
A liquid is boiled and attached to a vertical condenser, hot vapours rise and enter liebig condenser and cooled back to flask. Liquid is kept at b.p without loss of vapour - NO LOSS OF SOLVENT ETHANOL
Equation for preparation of soap
C3H5(C17H35COO)3 + 3NaOH = C3H5(OH)3 + 3C17H35COONa
What was the purpose of ethanol?
Solvent - Dissolve lard
Why is excess NaOH used in first stage?
Ensures that hydrolysis reaction takes place completely
What is the difference between animal and vegetable fats?
Animal - less hydrogen and therefore solid, Veg = more, therefore liquid
Name the ester present in lard
Glyceryl tristearate
What is the purpose of the anti-bumping granules
Help bring about smoother boiling and prevent flask from shaking
What substance coats the flask during refluxing?
Fat that has not been hydrolysed
What action should be taken to get rid of the substance that coats the flask during refluxing?
Swirl flask gently
Why better to use water bath than bunsen burner?
Mixture boils gently
What substance is removed in distillation?
Ethanol
What is brine?
Its a solution of salt in water that is saturated
Why is mixture added to brine?
Soap will precipitate as soap does not dissolve in brine - insoluble
Why should you use the minimum amount of hot water to dissolve residue in pear shaped flask?
To maximise amount of soap precipitated
How is soap removed from brine?
Filtration using Buchner Funnel and Vacuum pump
What substance is found in filtrate?
Glycerol, Ethanol and excess NaOH
How do you ensure soap is free from sodium hydroxide?
Wash soap with salt solution/ice cold water
What is the test for soap?
Add soap to test tube of deionised (Soft) water - forms lather
How is cleansing action of soap explained?
Non polar part of soap dissolves non polar oil and grease from skin
Name a by-product of the reaction
Glycerol
Why did glycerol not distill over with the ethanol?
Higher boiling point than ethanol
Why did the glycerol stay dissolved when added to brine?
It is soluble in brine
IUPAC name for glycerol?
alcohol propane -1,2,3-triol
What is glycerol molecular formula?
C3H5(OH)3
Give the structural formula for glycerol
CH2 - OH
CH - OH
CH2 - OH
Uses for glycerol
Food industry - sweetener
Moisturizer creams - keeps skin smooth
What is the name given to the soap?
Sodium Stearate
How is the soap isolated from all the other substances left in the reaction mixture after removal of ethanol
Dissolve residue in hot water
Reaction mixture is added to brine
Precipitated soap is obtained by filtration
Wash with ice water
Suggest with reference to its structure, how a soap like sodium stearate can dissolve both non-polar oils and the ionic salts in sweat from skin
C17H35 {hydrocarbon part (end)} is non-polar (hydrophobic) and dissolves oils (non-
–COO–Na+
[Charges required.]
{ionic part (end)} attracted to (dissolves) salts in sweat
