Colour by Design Flashcards
(6 cards)
describe the structure of a dye molecule
in terms of the chromophore
the chromophore is the part of a molecule
responsible for the characteristic colour
In a dye, the chromophore is the extended
conjugated pi system.
This system decreases the gap between the
ground state and excited state of electrons
within it, so these electrons absorb visible light
when they move to the excited state, and
reflect/transmit the complementary colour
recall the stationary and mobile phase
in GLC
mobile phase: inert gas, such as nitrogen or argon
stationary phase: high boiling point liquid held on a finely divided inert porous solid
describe how GLC is carried out
- stationary phase is packed in a long thin tube, coiled in an oven
- sample is injected into the carrier gas just before it enters the glc column
- components may dissolve in the stationary phase or stay as gases
- detector senses the time taken for each component to emerge from the column
(retention time) - components with higher affinity for the stationary phase have longer retention times
- area under curve is proportional to the amount of each component
- components can be isolated as they emerge and identified by mass spectrometry
whats retention time?
Retention time = time taken for a component to emerge from the column
describe the
procedure for
the Fehling’s
test
Mix Fehling’s A and Fehling’s B to form a dark blue solution
* Add test sample and warm gently in a water bath
aldehyde - brick red
ketone - no change because ketones cannot be oxidised
describe procedure for Tollens test:
put 2cm of 0.1 moldm-3 silver nitrate sol in a test tube
add a few drops of dilute sodium hydroxide solution - a light brown precipitate forms
add drops of dilute ammonia until brown disappears
place test tube in a hot water bath and add 10 drops of aldehyde or ketone
aldehyde - silver mirror on walls of test tube
ketone - nothing
