LAB 1 UV Flashcards
How does aspirin work?
inhibiting COX in the stimulating the synthesis of prostanoids. a reduction in this would lead to a reduction in pain.
why does aspirin help prevent heart attacks?
as prostanoids are involved in the clotting mechanism and so help prevent the formation of blood clots.
what is the purpose of this experiment?
to determine the percentage purity of a batch of Aspirin API bt UV and back titration against a blank.
what does API stand for?
active pharmaceutical ingredient
what does the UV principle rely on?
comparing the absorbance of known concentration standards to the absorbance of test solutions.
what percentage purity is the reference aspirin?
100%
what is a blank titre?
the differnce between the blank and each aspirin titration represents the volume of sodium hydroxide solution that was required to hydrolyse the asprirn
define concentration
describes the proportion of one substance contained within a known quantity of another substance. This can be used to describe solids, but is most commonly used for solutions of a substance (the ‘solute’) is dissolved in another (the ‘solvent’).
define dilution
is the reduction of the concentration by adding more of the solvent. In the case of a solution, adding more solvent increases the overall volume of the solution, whilst the quantity of the solute remains unchanged. Therefore, the concentration of the solute decreases.
what is the main API of aspirin?
acetylsalicylic acid
why do we determine the % purity of a drug?
for safety, a known concentration is given
what is the BP limits for the % purity of aspirin?
99.5-101%
what is a titratable group in the aspirin molecule?
carboxylic acid , with a base we can see how much is present at the start
what can be hydrolyzed in the aspirin molecule?
ester geoup, once hydrolised the bond breaks and some of the NaOH that we titrate changes the % purity- cannot do front titration
how do you do a back titration?
with an excess,
but known amount of NaOH so that the ester is completely hydrolyzed and we lose an acetyl group,
and we are just left with the salt which we titrate with a strong acid to find the ammount remaining.
how does UV spectroscopy work?
by exploiting the functional group to determine how much of a substance is there
what does acetylsalicylic acid hydrolysis to?
salicylic acid
how do you add the last few drops to the graduated cylinder?
using a pasture pipette
why do you dilute the stock solution 20 fold?
too concentrated
what material is the cuvette made from? and why?
quartz as it wont absorb UV light
what kind of a graph do you expect to obtain
linear
what info are we intrested in from the back titration?
the difference between the standard and blank
what is the differnce between the back and the blank?
API is in back ,no differnce otherwise
when do you add the indicator?
few drops at the end , so it won’t react with chemicals before that
why do we heat the conical flasks?
to ensure reaction to completion
-crystals will dissolve and no more of the ester will formed only salicylic acid as a left over salt
what indicator did you use in the back titration?
phenolphthalein
