LAB 1 UV

Question 1

How does aspirin work?

Answer 1

inhibiting COX in the stimulating the synthesis of prostanoids. a reduction in this would lead to a reduction in pain.

Question 2

why does aspirin help prevent heart attacks?

Answer 2

as prostanoids are involved in the clotting mechanism and so help prevent the formation of blood clots.

Question 3

what is the purpose of this experiment?

Answer 3

to determine the percentage purity of a batch of Aspirin API bt UV and back titration against a blank.

Question 4

what does API stand for?

Answer 4

active pharmaceutical ingredient

Question 5

what does the UV principle rely on?

Answer 5

comparing the absorbance of known concentration standards to the absorbance of test solutions.

Question 6

what percentage purity is the reference aspirin?

Answer 6

100%

Question 7

what is a blank titre?

Answer 7

the differnce between the blank and each aspirin titration represents the volume of sodium hydroxide solution that was required to hydrolyse the asprirn

Question 8

define concentration

Answer 8

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’).

Question 9

define dilution

Answer 9

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.

Question 10

what is the main API of aspirin?

Answer 10

acetylsalicylic acid

Question 11

why do we determine the % purity of a drug?

Answer 11

for safety, a known concentration is given

Question 12

what is the BP limits for the % purity of aspirin?

Answer 12

99.5-101%

Question 13

what is a titratable group in the aspirin molecule?

Answer 13

carboxylic acid , with a base we can see how much is present at the start

Question 14

what can be hydrolyzed in the aspirin molecule?

Answer 14

ester geoup, once hydrolised the bond breaks and some of the NaOH that we titrate changes the % purity- cannot do front titration

Question 15

how do you do a back titration?

Answer 15

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.

Question 16

how does UV spectroscopy work?

Answer 16

by exploiting the functional group to determine how much of a substance is there

Question 17

what does acetylsalicylic acid hydrolysis to?

Answer 17

salicylic acid

Question 18

how do you add the last few drops to the graduated cylinder?

Answer 18

using a pasture pipette

Question 19

why do you dilute the stock solution 20 fold?

Answer 19

too concentrated

Question 20

what material is the cuvette made from? and why?

Answer 20

quartz as it wont absorb UV light

Question 21

what kind of a graph do you expect to obtain

Answer 21

linear

Question 22

what info are we intrested in from the back titration?

Answer 22

the difference between the standard and blank

Question 23

what is the differnce between the back and the blank?

Answer 23

API is in back ,no differnce otherwise

Question 24

when do you add the indicator?

Answer 24

few drops at the end , so it won’t react with chemicals before that

Question 25

why do we heat the conical flasks?

Answer 25

to ensure reaction to completion

-crystals will dissolve and no more of the ester will formed only salicylic acid as a left over salt

Question 26

what indicator did you use in the back titration?

Answer 26

phenolphthalein