Recrystallization

Question 1

Recrystallization main purpose

Answer 1

to purify

Question 2

What is recrystallization?

Answer 2

You start with solid but we will break it and reform it

Question 3

What happen when we dissolve ?

Answer 3

Breakdown the intermolecular molecules

Question 4

First step in recrystallization

Answer 4

is dissolving (in solvent) not melting

Question 5

The benzoic acids &impurities are stuck together via

Answer 5

intermolecular forces

Question 6

inter vs intra

Answer 6

inter: between, reversible, this is what you dissolve, little energy to break down
intra: inside, irreversible, needs high energy to break down

Question 7

Two parameter to control in recrystallzation:

Answer 7

temp and solvent (like water)

Question 8

Benzoic acid should be soluable in

Answer 8

hot but not in cold.

Question 9

Why should impurities be soluable at both high and low temp?

Answer 9

So it doesn’t precipitate with benzoic acid

Question 10

Precipitation of benzoic will cause ?

Answer 10

reforming of bond.

Question 11

Why do we use room temp to the solution and not cold ?

Answer 11

• The benzoic acid crystal will trap the impurities again.
• To form correct shape of crystals

Question 12

How do we know whether the recrystalixation worked or not ?

Answer 12

Take the mass from the filter paper then substract it from the mass of the filter with the benzoic

Question 13

How do we know the exp was successful?

Answer 13

Calculate the % recovery and the melting point (It should be less than 1)

Question 14

After filtration we should have?

Answer 14

water and impurities in the flask and pure benzoic acid in the filter paper

Question 15

What is the percent recover?

Answer 15

How much benzoic acid was recovered

Question 16

Melting point is represented in a

Answer 16

Range (beginning is when is start to melt and ending is when its fully melted)

Question 17

Heating rate:

Answer 17

how fast you want the test to be

Question 18

The most accurate heating rate is

Answer 18

the lowest heating rate

Question 19

The magnifier technique rely on

Answer 19

our observation

Question 20

What happen when a substance melt?

Answer 20

change of state

Question 21

What determine when a substance reach melting point?

Answer 21

The breakage of between intermolecular molecules

Question 22

melting vs dissolving

Answer 22

Melting breaking down intermolecular forces only (no solvent)
Dissolving breaking down and forming new one when touch with water (need solvent )

Question 23

Melting technique is used when we want to

Answer 23

1 test the purity( our work)
2 to find the nature of an unknown substance and find the range
3 when doing a chemical reaction