Flashcards in The Oxidation Of Phenylmerhanol To Benzoic Acid Deck (47):
Identify the two chemicals added that allow separation of the benzoic acid from the other substances after the oxidation was complete
Na2SO3 (Sodium Sulfite)
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
How would recrystallisation have affected the melting point range?
Melting point is raised and becomes narrower too
What affects the melting point range of benzoic acid in this experiment?
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
What is the appearance of phenylmethanol at room temp?
Structure of phenylmethanol
Benzene + CH2OH
What is the phenylmethanol also known as?
Why was excess potassium permanganate used in this reaction?
Oxidising agent - will oxidise phenylmethanol to benzoic acid
What is the purpose of sodium carbonate?
Provide alkaline conditions
Why are alkaline conditions prefered?
Rate of reaction is greatest
Balanced equation for preparation of benzoic acid
3C6H5CH2OH + 4KMnO4 - 3C6H5COOH + 4MnO2 +H20 + 4KOH
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)
Identify brown precipitate
Brown residue of MnO2
Identify source of almond smell
Formation of benzaldehyde
Draw structure of benzaldehyde
Benzene + CHO
How is the benzaldehyde present in mixture?
Phenylmethanol oxidised by potassium perm to Benzaldehyde
Why is reaction flask cooled under running water?
Benzoic acid is only slightly soluble in cold water, causes benzoic acid to be precipitated out ???
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⁺)
How do you know enough HCL is added?
Until no fizzing is apparent
What is the intermediate compound formed?
What is the structure of the intermediate compound?
Benzene + C double bond O, O-Na+
What is the purpose of adding sodium sulfite?
Reducing agent - Reduces Mn4+ ions that are insoluble to Mn2+ ions which are soluble
What is observed when sodium sulfite is added?
Brown - Colourless
What are the changes in oxidation number of manganese during reaction?
Mn+7 - Mn+4 - Mn+2 = +7 - +4 - +2
Why is the flask placed in ice?
Benzoic acid has a low solubility in cold water, therefore this helps maximise yield of crystals
How were crystals seperated from mixture?
Suction - filtration with Buchner flask, Buchner funnel and filter paper
Why is it preferable to use Suction - Filtration?
Speeds up filtration process and also helps dry crystals
How could the crystals have been dried?
Placing filter paper with crystals on clock glass and allowing to dry overnight
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
What is the overall colour change that occurs in the reaction vessel as phenylmethanol is converted to benzoic acid
Purple - brown - colourless
Name the transition metal reagent used?
Explain the colour change of purple-brown-colourless by reference to the transition metal reagent used?
Mn+7 - Mn+4 - Mn+2
What are the bonds that are broken in phenylmethanol?
What are the bonds that are formed in benzoic acid?
Why is the conical flask rinsed with the filtrate from the Buchner flask?
To get rid of any remaining crystals
In the recrystallisation of benzoic acid, what is collected at hot filtration?
In the recrystallisation of benzoic acid, what is collected at filtration?
Purified Benzoic acid
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
Describe how benzoic acid is dried
Place filter paper with crystals on clock glass and put them in an oven at a low temperature.
Give one common use of benzoic acid
food preservative / disinfectant
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)
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)
How could you have ensured that the recrystallisation was complete
let solution cool fully (efficiently) / cool in ice-water
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.
What reaction occurred when the sodium sulfite was added?
A reduction reaction (Mn4+ reduced to Mn2+).