July 03, 2020, 07:32:27 AM
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Topic: Back titration of Aspirin  (Read 276 times)

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Offline AvocadosConstant

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Back titration of Aspirin
« on: March 29, 2020, 11:21:00 PM »
Hello,
For a chemistry assignment, I have to complete a back titration of an aspirin tablet to find the amount of acetylsalicylic acid. I weighed one tablet, crushed it and placed it into a volumetric flask with 250mL of NaOH. I then pipetted 25mL of this solution and titrated it against HCL. I am anticipating that I will get a mass of acetylsalicylic acid that x10 smaller than the actual amount. But by using 25mL of the 250mL solution, is this an acceptable method or will the results be off?

Much appreciated.

Online chenbeier

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Re: Back titration of Aspirin
« Reply #1 on: March 30, 2020, 03:59:41 AM »
The method is ok, but probably the amount of NaOH is to much. You didn't tell the concentration of NaOH.

Offline AvocadosConstant

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Re: Back titration of Aspirin
« Reply #2 on: March 30, 2020, 06:30:09 PM »
I had [HCl]=0.11M and [NaOH]=0.113M, and when I titrated 25mL of the NaOH and aspirin solution I got 20.82mL of HCl. I am just confused about how to do the calculations for the amount of acetylsalicylic acid.

Online chenbeier

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Re: Back titration of Aspirin
« Reply #3 on: March 31, 2020, 05:35:16 AM »
The NaOH neutralized the acetylsalicylic acid. The remaining NaOH was titrated. With the  consumption 20.82 ml and the molarities you can calculate the amount of NaOH in mol. You also know how much 25 ml 0.113 M correspond. The Differenz is the amount what react with the Acetylacetic acid.

Offline AvocadosConstant

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Re: Back titration of Aspirin
« Reply #4 on: March 31, 2020, 07:58:09 PM »
I have attempted to calculate the amount of aspirin, however I know i have done something wrong given that I got around 4 grams. The tablet itself weighed 1g.
I appreciate any feedback, means a lot.

Offline AWK

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Re: Back titration of Aspirin
« Reply #5 on: April 01, 2020, 01:40:27 AM »
Quote
I had [HCl]=0.11M and [NaOH]=0.113M
You have previously given different concentrations of HCl and NaOH
AWK

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