Benzoic acid experiment

Colourless

Describe appearance of phenylmethanol at room temp

Graduated dropper

name a suitable piece of apparatus to measure accurately 1.5cm3 of phenylmethanol

Purple to brown

How does the appearance of the reaction mixture change when the the phenylmethanol is heated along with potassium manganate solution to which sodium carbonate has been added

Brown solid disappears and benzoic white crystals form

Explain : MnO2 is reduced and crystallization of benzoic acid

Describe what is observed during stages of when Na2SO3 is added and the cooled in ice water. And explain these observations

Place sample crystals in melting point capillary tube on melting point block

Heat slowly while observing the crystals

Record temperature at which melting occurs

Describe how you measured the melting point of a sample of benzoic acid crystals

Benzoic aldehyde

Name the organic compound that gives rise to the smell of almonds during the heating phase

To neutralise any alkali base remaining in the solution

To convert sodium benzoate to benzoic acid

Give two reasons why the solution was acidified with conc. Hydrochloric acid

Dip a rod in solution and touch off moist blue litmus paper

The color should o red

How would you test if enough acid had been added

The sodium sulfite reduces MN+4 to MN+2

What was the purpose of adding sodium sulfite solution

To ensure all benzoic acid crystallises out of solution

Why was the flask placed in ice before filtration?

Air dry overnight

How could the crystals have been dried?

Measure melting point before and after. Purer melting point closer to 122

How could it have been verified that the recrystallised benzoic acid crystals were purer than the original sample

Removal of insoluble impurities

During the recrystallization a hot solution of benzoic acid in water was filtered through a fluted filter paper as shown. State the purpose of this step

Heat filtrate

What steps are carried out to maximise the yield of pure benzoic acid between the first and second filtrations

Wash with ice cold water dry the crystals

What steps are carried out to maximise the yield of pure benzoic acid after the second filtration

It's faster

State one advantage of suction filtration over gravity filtration

Recrystallisation

Name a laboratory technique that could be used to purify impure benzoic acid

Water

Very soluble in hot but less soluble in cold

Students were required to recrystallise the impure benzoic acid. What solvent should they have used for the recystallisation and why is this solvent suitable