4.WM Techniques and Procedures

Question 1

How do you calculate Rf value?

Answer 1

distance travelled by spot/distance travelled by solvent

Question 2

If the substance used in TLC is colourless, what could you use to find the solvent position?

Answer 2

Iodine crystals could be placed in jar and would stick to chemicals, staining them.
Fluorescent dye could be added to silica-alumina and can be seen with UV light.

Question 3

If a compound/solvent has moved up far the silica, does that mean it is polar or non-polar? why?

Answer 3

It is less polar as it is not as attracted to the polar silica gel and more attracted to the mobile phase.

Question 4

If a compound/solvent has moved up far the silica, does that mean it is polar or non-polar? why?

Answer 4

It is less polar as it is not as attracted to the polar silica gel and more attracted to the mobile phase.

Question 5

Pros and Cons of TLC:

Answer 5

Pros - effective for small quantities, accurate separation

Cons - doesn’t give info on purity of compound

Question 6

What is distillation used for?

Answer 6

To purify a liquid product/separate mixture with diff. boiling points

Question 7

Name the final stage in the purification of an ester.

Answer 7

Distillation

Question 8

What is heating under reflux used for?

Answer 8

Used in reactions involving volatile (easily evaporated) liquids.

Question 9

what is the use of adding bumping granule to reactants in pear-shaped flask?

Answer 9

granules burst bubbles in the boiling mixture and prevent from boiling over.

Question 10

What does a primary alcohol oxidise into under reflux?

Answer 10

Carboxylic acid

Question 11

What is recrystallisation used for?

Answer 11

used to purify solid crude organic products with a small amount of impurities

Question 12

why is does the initial solvent need to be hot?

Answer 12

to fully dissolve the crystal into the solvent

Question 13

why does the filter paper and filter need to be hot?

Answer 13

to prevent the dissolved crystals to crystalize with the solid impurities

Question 14

Pros and cons of Recrystallisation:

Answer 14

Pros - Low Cost, High purity of the product

Cons - time-consuming, solution must be at high temp

Question 15

what is the test for a phenol?

Answer 15

Compounds with a phenol group will form a blue, violet, purple, green, or red-brown colour upon addition of aqueous ferric chloride.