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Chemistry > Soap > Flashcards

Soap Flashcards

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1
Q

Why is the reaction refluxed at the beginning?

A

Allow time for reaction to reach completion

Prevents loss of volatile components/materials

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2
Q

What is in the pear shaped flask in reflux?

A

Vegetable oil [lard], sodium hydroxide and ethanol

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3
Q

Why is vegetable oil used in reflux?

A

It contains lard which has the natural occurring ester glyceryl tristearate

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4
Q

Why is it refluxed for 20-30 minutes?

A

Allow suff time for reaction to take place

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5
Q

What type of reaction occurs in stage one/reflux?

A

Saponification

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6
Q

What substance was removed by distillation in stage two

A

Ethanol

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7
Q

Explain the function of brine is stage 3

A

Precipitates soap - soap is insoluble in brine

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8
Q

Why was it necessary to wash the soap throughly in stage 4?

A

Remove sodium hydroxide

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9
Q

How should the student have washed the soap in stage 4?

A

Ice-cold water

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10
Q

Give the name of the co-product of the reaction and where is it located at the end of the process?

A

Propane-1,2,3-triol

In the filtrate

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11
Q

Calculate the max yield in grams of soap that would have been obtained

A

Find moles of one fat and multiply by three

Then multiply by mr of soap

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12
Q

What happened to the liquid in the flask during reflux?

A

Hot vapour rose and liquid evaporated. It enters condenser and turns to liquid and returns to flask

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13
Q

How did refluxing the mixture help bring the reaction to completion?

A

It allowed enough time

Provides activation energy

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14
Q

Write the IUPAC name for glycerol?

A

Propane-1,2,3-triol

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15
Q

What was the purpose of the ethanol?

A

Solvent

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16
Q

Describe with the aid of a labelled diagram, how the ethanol was removed after the reflux stage

A

At 78 degrees Celsius, heat reaction mix and ethanol evaporated - condenser and enters test tube

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17
Q

How was the soap isolated from the other substances left in the reaction mixture

A

Added to brine

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18
Q

After isolating the soap from other substances, how was it purified and dried?

A

Purified - put in cold water

Dried - put in oven

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19
Q

Calculate the percentage yield of soap

A

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

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20
Q

Why is it desirable to remove the ethanol after reflux?

A

Easier to extract soap as some soap might be disolved in ethanol

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21
Q

Describe how a pure sample of soap was obtained from the reaction mixture?

A

Pour into brine, wash with ice cold water

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22
Q

What is the second product of the reaction?

A

Glycerol

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23
Q

At the end of the experiment, what is the location of the second product of the reaction?

A

In the filtrate

24
Q

At the end of the experiment, what is the location of the excess sodium hydroxide?

A

In the flitrate

25
Q

What would you observe, upon shaking, if a little of the soap prepared is added to a test tube containing deionised water?

A

Form lather

26
Q

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?

A

Form no lather

27
Q

Why is it refluxed for 20-30 minutes?

A

Allow sufficient time for reaction to take place and to bring to completion

28
Q

How is reflux carried out?

A

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

29
Q

Equation for preparation of soap

A

C3H5(C17H35COO)3 + 3NaOH = C3H5(OH)3 + 3C17H35COONa

30
Q

What was the purpose of ethanol?

A

Solvent - Dissolve lard

31
Q

Why is excess NaOH used in first stage?

A

Ensures that hydrolysis reaction takes place completely

32
Q

What is the difference between animal and vegetable fats?

A

Animal - less hydrogen and therefore solid, Veg = more, therefore liquid

33
Q

Name the ester present in lard

A

Glyceryl tristearate

34
Q

What is the purpose of the anti-bumping granules

A

Help bring about smoother boiling and prevent flask from shaking

35
Q

What substance coats the flask during refluxing?

A

Fat that has not been hydrolysed

36
Q

What action should be taken to get rid of the substance that coats the flask during refluxing?

A

Swirl flask gently

37
Q

Why better to use water bath than bunsen burner?

A

Mixture boils gently

38
Q

What substance is removed in distillation?

A

Ethanol

39
Q

What is brine?

A

Its a solution of salt in water that is saturated

40
Q

Why is mixture added to brine?

A

Soap will precipitate as soap does not dissolve in brine - insoluble

41
Q

Why should you use the minimum amount of hot water to dissolve residue in pear shaped flask?

A

To maximise amount of soap precipitated

42
Q

How is soap removed from brine?

A

Filtration using Buchner Funnel and Vacuum pump

43
Q

What substance is found in filtrate?

A

Glycerol, Ethanol and excess NaOH

44
Q

How do you ensure soap is free from sodium hydroxide?

A

Wash soap with salt solution/ice cold water

45
Q

What is the test for soap?

A

Add soap to test tube of deionised (Soft) water - forms lather

46
Q

How is cleansing action of soap explained?

A

Non polar part of soap dissolves non polar oil and grease from skin

47
Q

Name a by-product of the reaction

A

Glycerol

48
Q

Why did glycerol not distill over with the ethanol?

A

Higher boiling point than ethanol

49
Q

Why did the glycerol stay dissolved when added to brine?

A

It is soluble in brine

50
Q

IUPAC name for glycerol?

A

alcohol propane -1,2,3-triol

51
Q

What is glycerol molecular formula?

A

C3H5(OH)3

52
Q

Give the structural formula for glycerol

A

CH2 - OH
CH - OH
CH2 - OH

53
Q

Uses for glycerol

A

Food industry - sweetener

Moisturizer creams - keeps skin smooth

54
Q

What is the name given to the soap?

A

Sodium Stearate

55
Q

How is the soap isolated from all the other substances left in the reaction mixture after removal of ethanol

A

Dissolve residue in hot water
Reaction mixture is added to brine
Precipitated soap is obtained by filtration
Wash with ice water

56
Q

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

A

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

Chemistry (15 decks)

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