6.3.1 - Chromatography and qualitative analysis

Question 1

How can we test for alkene’s ?

Answer 1

Question 2

How can we test for carbonyls ?

Answer 2

Question 3

How can we test for aldehydes ?

Answer 3

Question 4

How can we test for Carboxylic acids ?

Answer 4

Question 5

How can we test for Primary and tertiary alcohols ?

Answer 5

Question 6

How can we test for Haloalkanes ?

Answer 6

Question 7

How can we test for Phenols ?

Answer 7

1. Phenol and Sodium Hydroxide (NaOH):
   
   • Phenol reacts with sodium hydroxide to form sodium phenoxide and water.
2. Phenol and Sodium Metal (Na):
   
   • When phenol reacts with metallic sodium, you’ll get fizzing because hydrogen gas (H2) is released.
3. Phenol and Sodium Carbonate ):
   
   • Phenol does not react with sodium carbonate. This is because phenol is a weak acid, and it’s not strong enough to react with carbonate ions to release carbon dioxide gas

Question 8

What do we use TLC for ?

Answer 8

To separate and identify compounds from a mixture

Question 9

How do we calculate the Rf value

Answer 9

Distance moved by spot / Distance moved by solvent

Question 10

Stationary phase

Answer 10

The paper
Or
Silicon dioxide or aluminium dioxide

Question 11

Mobile phase

Answer 11

The solvent or gas

Question 12

Why do we use a glass lid ?

Answer 12

To prevent the solvent from evaporating

Question 13

Why do we use a pencil to dissolve the line ?

Answer 13

As it will not dissolve the solvent

Question 14

Why would we use a UV light ?

Answer 14

UV lamp used if the spots are colourless and
not visible

Question 15

Why do we make our drops tiny ?

Answer 15

too big a drop will cause different spots to merge

Question 16

How do we carry out a chromatography ?

Answer 16

Question 17

Why do we use gas chromatography ?

Answer 17

To separate mixtures of volatile liquids

Question 18

How does a gas chromatography look like ?

Answer 18

Question 19

What is the mobile phase in gc ?

Answer 19

The gas e.g Helium

Question 20

What is the stationary phase in gc ?

Answer 20

The high boiling point liquid absorbed onto a solid

Question 21

What is the retention time ?

Answer 21

The time taken for a particular compound to travel from the injection of the sample to where it leaves the column to the detector is known.

Question 22

How does the retention time help us ?

Answer 22

Helps to identify a substance.

Question 23

What does the area under the peaks on a chromatogram tell us about?

Answer 23

Peak intergrations (area under each peak) can be used to determine the concentrations of components

Question 24

What can we use GC for ?

Answer 24

Question 25

How can GC be used in art ?

Answer 25

Question 26

What do we use a calibration curve for ?

Answer 26

To measure the concertration of a substance tested via gas chromatography.

Question 27

How do we determine the concentration of a component in a sample ?

Answer 27

So basically, you make a calibration curve using known concentrations of your compound. As in, you would have a compound, you'd have different concentrations, and you would record the area under the curve that it produces. And then when you have your compound in a mixture, we've identified the user retention time, but you know the concentration, you measure the area under it, and then you use that and reference the calibration curve, and you figure out the concentration from the value of the area under the curve that you have been recorded, or you recorded or measured.

Question 28

Factors affecting retention time.

Answer 28

Question 29

Explain the whole process of gas chromatography including how you would identify a compound and its concentration

Answer 29