The Oxidation Of Phenylmerhanol To Benzoic Acid Flashcards Preview

Chemistry > The Oxidation Of Phenylmerhanol To Benzoic Acid > Flashcards

Flashcards in The Oxidation Of Phenylmerhanol To Benzoic Acid Deck (47):
1

Identify the two chemicals added that allow separation of the benzoic acid from the other substances after the oxidation was complete

HCL
Na2SO3 (Sodium Sulfite)

2

What changes were observed in the reaction vessel on addition of HCL and Sodium Sulfite and as cooling occured

Brown disappears and it becomes colourless, white crystals form

3

How would recrystallisation have affected the melting point range?

Melting point is raised and becomes narrower too

4

What affects the melting point range of benzoic acid in this experiment?

Recrystallisation

5

Calculate percentage yield

Multiply density by volume to get grams
find moles of phenylmethanol and it is equal to benzoic acid
multiply by mr of benzoic acid and get theoretical yield
actual yield / theoretical yield x 100

6

What is the appearance of phenylmethanol at room temp?

Colourless liquid

7

Structure of phenylmethanol

Benzene + CH2OH

8

What is the phenylmethanol also known as?

Benzyl alcohol

9

Why was excess potassium permanganate used in this reaction?

Oxidising agent - will oxidise phenylmethanol to benzoic acid

10

What is the purpose of sodium carbonate?

Provide alkaline conditions

11

Why are alkaline conditions prefered?

Rate of reaction is greatest

12

Balanced equation for preparation of benzoic acid

3C6H5CH2OH + 4KMnO4 - 3C6H5COOH + 4MnO2 +H20 + 4KOH

13

State and explain the colour change when reaction mixture is heated

Changes from purple to brown due to formation of MnO2 (not soluble in water)

14

Identify brown precipitate

Brown residue of MnO2

15

Identify source of almond smell

Formation of benzaldehyde

16

Draw structure of benzaldehyde

Benzene + CHO

17

How is the benzaldehyde present in mixture?

Phenylmethanol oxidised by potassium perm to Benzaldehyde

18

Why is reaction flask cooled under running water?

Benzoic acid is only slightly soluble in cold water, causes benzoic acid to be precipitated out ???

19

Why is HCL added?

Neutralise sodium carbonate
Provides an acidic medium for Mn⁴⁺ ions to be reduced
Mn⁴⁺ + 2e⁻ → Mn²⁺ (in the presence of H⁺)

20

How do you know enough HCL is added?

Until no fizzing is apparent

21

What is the intermediate compound formed?

Sodium Benzonate

22

What is the structure of the intermediate compound?

Benzene + C double bond O, O-Na+

23

What is the purpose of adding sodium sulfite?

Reducing agent - Reduces Mn4+ ions that are insoluble to Mn2+ ions which are soluble

24

What is observed when sodium sulfite is added?

Brown - Colourless

25

What are the changes in oxidation number of manganese during reaction?

Mn+7 - Mn+4 - Mn+2 = +7 - +4 - +2

26

Why is the flask placed in ice?

Benzoic acid has a low solubility in cold water, therefore this helps maximise yield of crystals

27

How were crystals seperated from mixture?

Suction - filtration with Buchner flask, Buchner funnel and filter paper

28

Why is it preferable to use Suction - Filtration?

Speeds up filtration process and also helps dry crystals

29

How could the crystals have been dried?

Placing filter paper with crystals on clock glass and allowing to dry overnight

30

Mention three things you could do to maximise yield of benzoic acid

Putting conical flask of solution in ice (after addition of sodium sulfite)
Use minimum amount of boiling water (solvent)
Use fluted filter paper

31

What is the overall colour change that occurs in the reaction vessel as phenylmethanol is converted to benzoic acid

Purple - brown - colourless

32

Name the transition metal reagent used?

MnO4

33

Explain the colour change of purple-brown-colourless by reference to the transition metal reagent used?

Mn+7 - Mn+4 - Mn+2

34

What are the bonds that are broken in phenylmethanol?

-H
-H

35

What are the bonds that are formed in benzoic acid?

C=O

36

Why is the conical flask rinsed with the filtrate from the Buchner flask?

To get rid of any remaining crystals

37

In the recrystallisation of benzoic acid, what is collected at hot filtration?

Charcoal

38

In the recrystallisation of benzoic acid, what is collected at filtration?

Purified Benzoic acid

39

In the recrystallisation of benzoic acid, how is benzoic acid seperated from salt

Both substances soluble in hot water however benzoic acid much less soluble in cold water so comes out of solution
NaCl much more soluble in cold water so remains in solution

40

Describe how benzoic acid is dried

Place filter paper with crystals on clock glass and put them in an oven at a low temperature.

41

Give one common use of benzoic acid

food preservative / disinfectant

42

Indicate clearly the stage of the recrystallisation process at which insoluble impurities were removed and how it was achieved

filtration of hot solution
remained on filter paper (in funnel)

43

Indicate clearly the stage of the recrystallisation process at which soluble impurities were removed and how it was achieved

filtration of recrystallised benzoic acid
passed through filter paper (funnel)

44

How could you have ensured that the recrystallisation was complete

let solution cool fully (efficiently) / cool in ice-water

45

Why was an excess solution of potassium manganate (VII) used?

To ensure there was a sufficient amount of KMnO4 to oxidise all of
the benzyl alcohol to benzoic acid.

46

What reaction occurred when the sodium sulfite was added?

A reduction reaction (Mn4+ reduced to Mn2+).

47

What is the structure of Benzoic acid?

Benzene ring - C double bond to O and OH