A2.12 Chromatography And Qualititaive Analysis

Question 1

Chromatography

Answer 1

Used to separate and identify the different components of a mixture

Question 2

TLC

Answer 2

Thin layer chromatography is used mainly to follow progress of a reaction or identify the purity of a product

Question 3

Stationary phase - TLC

Answer 3

Does not move

Is usually a solid

Adsorbs

Question 4

Mobile phase in TLC

Answer 4

Moves over stationary phase and is a liquid

Question 5

TLC plate

Answer 5

Spot a sample onto the base line using capillary tube

Base line is drawn in pencil 1cm up

TLC plate is placed in shallow level of solvent (must be below baseline)

Travels up TLC plate
No of spots = no of parts to mixture

Elongated spots could be due to 2 parts with very similar structures

Question 6

Rf

Answer 6

Distance spot travels
——————————-
Distance to solvent front

Question 7

How far a substance travels in TLC depends on……

Answer 7

1) how strongly the substance adsorbs onto stationary phase

2) how soluble substance is in mobile phase

If it travels far - weakly adsorbed and very soluble

Question 8

GC

Answer 8

Gas chromatography is useful in separating and analysing the amounts of different organic compounds in a mixture

Question 9

Retention time

Answer 9

Time taken for a component of a mixture to reach the detector

Question 10

Stationary phase in GC

Answer 10

Normally a liquid coating a tube or beads in a tube

Question 11

Mobile phase in GC

Answer 11

Inert gas e.g. He or N

Question 12

Retention time depends on…….

Answer 12

How soluble substance is in stationary phase

More soluble = longer retention time

Peaks = components

Question 13

External calibration curve

Answer 13

Obtain several GC of same substance in different concentrations

Plot graph of relative peak area vs conc

Use GC for unknown concentration and use graph

Question 14

Peak furthest to right on NMR

Answer 14

TMS - Si(CH3)4

Reference peak

Lots of equivalent H to give single environment

Question 15

13C NMR

Answer 15

Each peak = 1 environment

Tells us functional group in environment (furthest to left if multiple)

Question 16

1H NMR

Answer 16

Each peak is an environment

Number above peak - no of H in environment

Peak splits into patterns showing how many H in neighbouring environment

Split is n + 1
So if 4 in neighbouring then splits into triplet

Question 17

Solvents in NMR

Answer 17

CDCl3 for polar

CCl4 for non polar

Don’t have H atoms so won’t give peak

Question 18

D

Answer 18

Isotope of hydrogen - 2H (has 1 neutron)

Question 19

D2O in NMR

Answer 19

Confirms presence of OH or NH

Peak will be removed as H is removed and exchanged for D