question 5 and 6.a and b Pannon (FID) detector s Provide two reasons that meltin

Question

question 5 and 6.a and b

Pannon (FID) detector s Provide two reasons that melting range is observed for a pure compound. 3 points a 6. Describe the effect on resolution (decreased or increased) and on retention ime (shorter or longer) for each of the changes below. (4 points) (a) The column oven temperature is lowered. resolution: retention time: (b) The length of the column is doubled. resolution: retention time: 7. List the advantages and disadvantages of the using a flame ionization detector (FID)

Explanation / Answer

5.   

A pure organic compound usually melts over a range of two degrees or less.

If the melting point of a pure compound is within a degree of the value found a lab handbook it is presumed to be pure.

A sample is impure if it has a melting point range that is lower and/or wider than that the literature value.More impurities increase this effect.

In the organic lab, unless something is wrong with the procedure or the equipment, a substance generally cannot be observed to melt at a higher temperature than its melting point!

Experimental melting points should be always reported as a range, for example, 42-44°.

Size of the molecule. Melting range is also used for the identification and characterisation of a compound.

Force of attraction between the molecules. The force of attraction between the molecules affects the melting range of a compound.

6. a) The column oven temperature is lowered.

   Resolution: Increased

   The retention time : Longer

( Applicable in Gas chromatography)

   b) The length of column doubled.  

Resolution: Increased

The retention time : Longer

(Applicable in  chromatography)

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