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Flashcards in Soap Deck (56):
1

Why is the reaction refluxed at the beginning?

Allow time for reaction to reach completion
Prevents loss of volatile components/materials

2

What is in the pear shaped flask in reflux?

Vegetable oil [lard], sodium hydroxide and ethanol

3

Why is vegetable oil used in reflux?

It contains lard which has the natural occurring ester glyceryl tristearate

4

Why is it refluxed for 20-30 minutes?

Allow suff time for reaction to take place

5

What type of reaction occurs in stage one/reflux?

Saponification

6

What substance was removed by distillation in stage two

Ethanol

7

Explain the function of brine is stage 3

Precipitates soap - soap is insoluble in brine

8

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

Remove sodium hydroxide

9

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

Ice-cold water

10

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

11

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

12

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

13

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

It allowed enough time
Provides activation energy

14

Write the IUPAC name for glycerol?

Propane-1,2,3-triol

15

What was the purpose of the ethanol?

Solvent

16

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

17

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

Added to brine

18

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

Purified - put in cold water
Dried - put in oven

19

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

20

Why is it desirable to remove the ethanol after reflux?

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

21

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

Pour into brine, wash with ice cold water

22

What is the second product of the reaction?

Glycerol

23

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

In the filtrate

24

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

In the flitrate

25

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

Form lather

26

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

27

Why is it refluxed for 20-30 minutes?

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

28

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

29

Equation for preparation of soap

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

30

What was the purpose of ethanol?

Solvent - Dissolve lard

31

Why is excess NaOH used in first stage?

Ensures that hydrolysis reaction takes place completely

32

What is the difference between animal and vegetable fats?

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

33

Name the ester present in lard

Glyceryl tristearate

34

What is the purpose of the anti-bumping granules

Help bring about smoother boiling and prevent flask from shaking

35

What substance coats the flask during refluxing?

Fat that has not been hydrolysed

36

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

Swirl flask gently

37

Why better to use water bath than bunsen burner?

Mixture boils gently

38

What substance is removed in distillation?

Ethanol

39

What is brine?

Its a solution of salt in water that is saturated

40

Why is mixture added to brine?

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

41

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

To maximise amount of soap precipitated

42

How is soap removed from brine?

Filtration using Buchner Funnel and Vacuum pump

43

What substance is found in filtrate?

Glycerol, Ethanol and excess NaOH

44

How do you ensure soap is free from sodium hydroxide?

Wash soap with salt solution/ice cold water

45

What is the test for soap?

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

46

How is cleansing action of soap explained?

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

47

Name a by-product of the reaction

Glycerol

48

Why did glycerol not distill over with the ethanol?

Higher boiling point than ethanol

49

Why did the glycerol stay dissolved when added to brine?

It is soluble in brine

50

IUPAC name for glycerol?

alcohol propane -1,2,3-triol

51

What is glycerol molecular formula?

C3H5(OH)3

52

Give the structural formula for glycerol

CH2 - OH
CH - OH
CH2 - OH

53

Uses for glycerol

Food industry - sweetener
Moisturizer creams - keeps skin smooth

54

What is the name given to the soap?

Sodium Stearate

55

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

56

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