6.3 Analysis

Question 1

How do you find rf value from TLC

Answer 1

Rf value=distance travelled by spot/distance travelled by solvent

Question 2

How do you interpret gas chromatograms in terms of retention Time?

Answer 2

Measured from zero to centre of peak, look up in reference table to identify substance present

Question 3

How do you interpret gas chromatograms in terms of The amount and proportion of the components of a mixture

Answer 3

Area under peak is proportional to relative amount of each substance

Question 4

How do you create a external calibration curve?

Answer 4

1. Create a series of standard solution of different concentration of analyte
2. One by one inject your standard solution into a gas chromatography instrument and record the result
3. Calculate the area under the peak of each response for each standard solution
4. Plus these values on a graph of area vs concentration
5. Join your plot up to create an external calibration curve

Question 5

What is a good idea to do when you’re making a calibration curve?

Answer 5

Run a blank. (A solution containing all solvents and reagents used to make standard solution) subtract the response from each response from standard solution to find a correct peak.

Question 6

How do you identify Alkenes

Answer 6

Reaction with bromine water

Shake test tube

Orange to colourless

Question 7

How do you identify haloalkanes?

Answer 7

React with aqueous silver nitrate in ethanol

Place in water bath

Observe colour precipitate

Question 8

How do you identify phenol?

Answer 8

Weak acidity (dissolve in NaOH) but no reaction with (sodium) carbonates.

Question 9

How do you identify carbonyl compounds

Answer 9

Dissolve 0.2g 2,4-DNP, in 1 cm³ of sulphuric acid, 2 cm³ of water and 5 cm³ of methanol

In a different test tube add five drops of the unknown substance to 2 cm³ of your solution

shake the test tube and watch for a precipitate

Orange

Check crystalline derivative mp and compare to known value

Question 10

How do you test for aldehydes?

Answer 10

2 cm³ of 0.1 silver nitrate solution in a test tube

add five drops of 0.8 sodium hydroxide solution

A light brown precipitative should form

Add drops of dilute ammonia solution until the brown precipitate dissolves completely

place the tube in the hot water bath and a 10 drops aldehyde

wait for a few minutes

Silver mirror form

Question 11

What do you use as the standard for chemical shift measurements?

Answer 11

TMZ, tetramethylesaline, Si(CH3)4,

As low frequency absorption peak

Question 12

How do you identify N-H and O-H on proton NMR?

Answer 12

Run 2 spectre of the molecule one with a little D2O added

Peak will disappear due to proton exchange