astudent was in a hurry to carry out this determination and took some shortcuts
ID: 796716 • Letter: A
Question
astudent was in a hurry to carry out this determination and took some shortcuts in doing the a colorimetric determination of aspirin in commercialpreparation experment . explain whether each of the following changes wouldlead to high or low results or no changes and why
1-in the preparing the ASA solution for the beers law plot,the student added 10 ml of 1 M NaOH solution but omitted heating the reaction mixture
2- because all the 250 ml volumetric flasks were dirty,the stdent diluted the stock solution of sodium salicylate in clean 100 ml volumetric flask
3- when analyzing the commercial aspirin tablet, the solution was cloudy after it had been acidified. however, the student went ahead and analyzed it.
Explanation / Answer
sounds like an absorbance experiment in a quant. anal. class.
(1), Heating in base may help the solubility of the compound or affect a chemical change on whatever ASA is (acetyl salicylate?) Heating in base is also a good way to break esters into the corresponding acid and alcohol. my guess is the absorbance readings would be lower (unless the ASA that didn't break down has a higher absorbtivity than the product)
(2) If a 100 mL volumetric flask is used instead, it would affect the final concentration (assuming the same amount of stock salicylate was used). if you apply M(1)V(1) = M(2)V(2) and change the stock added, you can arrive to the same concentration called for from the 250 mL volumetric flask (though you'll only have 100 mL of the correct solution, not 250 mL). if the same amound of stock is added, the stock will be less dilute and the absorbance will be higher than expected (250/100)x more to be exact.
(3)if the solution was cloudy, taht means that all the analyte was not dissolved. it could be the binder in the tablet is insoluble, or perhaps the aspirin was not fully dissolved. hard to tell. regardless, if using Absorbance to test concentrations of aspirin, you would have either a lower reading by UV, or possibly erratic readings from interference by the particulates left in solution.
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