Question

If crystals don’t form after the recrystallization flask is cooled in an ice bath, there is nothing more to do to gain crystals.

True

False

Question 2

What is the recrystallization solvent for triphenylmethanol?

hexanes

ethanol

a hexanes/ethanol mixture

water

Question 3

What is the theoretical yield of the product, triphenylmethanol, if 20.0 mmol of benzophenone is the limiting reagent?

3.140 g

3.644 g

5.207 g

20.0 g

Question 9

When recrystallizing a solid:

hot solvent should be used

the recrystallization flask should be kept on the hotplate once solvent has been added

hot solvent should be added at a rate of about 1 mL per minute until all the solid dissolves

all of the above

Question 10

when the contents of the reaction mixture are in the separatory funnel, will the aqueous layer be on top or bottom?

top

bottom

Answer 1

1) If crystals don’t form after the recrystallization flask is cooled in an ice bath, there is nothing more to do to gain crystals.

This is false because when there are no crystals form even after the cooling process in an ice bath, then we can use a fire polished stirring rod and rub the glass of the beaker. It has been done because the rubbing or scratching will lead small pieces of glass of the rod fall into the beaker and it will work as nuclie for crystal formation.

2) What is the recrystallization solvent for triphenylmethanol?

The answer is "a hexanes/ethanol mixture". Recrystallization is done mainly because to remove impurity and the stated mixture works well. When crystals form, there are some by-products and impurities also formed in this case such as biphenyl.

3) What is the theoretical yield of the product, triphenylmethanol, if 20.0 mmol of benzophenone is the limiting reagent?

Moles of benzophenone (limiting reagent) = 20.00 mmoles = 0.02 moles (given)

Molar mass of Ph3COH = 260.3 g/mol

The theoretical yield can be easily calculated by multiplying moles of benzophenone (limiting reagent) by molar mass of triphenylmethanol,

Theoretical Yield = moles of Ph2CO X molar mass of Ph3COH

Theoretical Yield = 0.02 X 260.03 = 5.207 g of Ph3COH

4) When recrystallizing a solid:

When we recrytallize a solid, the process should be stable. A solvent is the one which dissolve solute easily and it is mainly possible when the solvent is hot. So, first option is correct.

5) when the contents of the reaction mixture are in the separatory funnel, will the aqueous layer be on top or bottom?

We can't say anything without knowing the contents and their densities because density tells us that which content is going to be at bottom or top. Just for example the aqueous solution has the density more than other content then it will at the bottom.