· Question 2 Following is a list of mistakes commonly made during recrystallizat

Question

·         Question 2

Following is a list of mistakes commonly made during recrystallizations. Match each of them with their unfortunate results.

Question

Selected Match

don't premoisten the filter paper in a Buchner funnel

E.

weight of crystals will be wrong (inaccurate, higher yield)

rinse crystals with solvent that isn't ice cold

A.

water can be drawn into the evacuated filter flask

to stop a vacuum filtration, turn off the water

B.

crystals may pass through the funnel with the filtrate

vacuum filter a hot solution

C.

solvent will rapidly boil under reduced pressure

forget to remove the boiling chips

D.

crystals will dissolve (lower yield)

Following is a list of mistakes commonly made during recrystallizations. Match each of them with their unfortunate results.

Question

Selected Match

don't premoisten the filter paper in a Buchner funnel

E.

weight of crystals will be wrong (inaccurate, higher yield)

rinse crystals with solvent that isn't ice cold

A.

water can be drawn into the evacuated filter flask

to stop a vacuum filtration, turn off the water

B.

crystals may pass through the funnel with the filtrate

vacuum filter a hot solution

C.

solvent will rapidly boil under reduced pressure

forget to remove the boiling chips

D.

crystals will dissolve (lower yield)

Explanation / Answer

crystals may pass through the funnel with the filtrate

crystals will dissolve (lower yield)

water can be drawn into the evacuated filter flask

solvent will rapidly boil under reduced pressure

weight of crystals will be wrong (inaccurate, higher yield)

Question Match Explanation don't premoisten the filter paper in a Buchner funnel B.

crystals may pass through the funnel with the filtrate

If you premoisten the filter paper, it will sticks to the funnel properly and by proper sticking will not let the air pass through that passage, and hence speed of filtration will increase without some solid getting under it when you do the filtration. rinse crystals with solvent that isn't ice cold D.

crystals will dissolve (lower yield)

Solubility of any compound is high at higher temperature, hence, if solvent is not an ice cold then it will dissolve some amount of crystals and the yield will be less to stop a vacuum filtration, turn off the water A.

water can be drawn into the evacuated filter flask

Due to vacuum created in the fitration flask if flow of water is stoped it will get drawn in to the flask through the opening for vacuume vacuum filter a hot solution C.

solvent will rapidly boil under reduced pressure

Due to creation of vacuum pressure is reduced and hence, sovent will boil under reduced pressure. forget to remove the boiling chips E.

weight of crystals will be wrong (inaccurate, higher yield)

If boiling chips are not removed it will get added to the crystals and hence, weight of crystals will increase geving higher yields.

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