# Finding mass of acetyl salicylic acid in aspirin tablet

• annnoyyying
In summary: Your help was greatly appreciated.In summary, an incorrect calculation resulted in an incorrect answer to the titration.
annnoyyying

## Homework Statement

25 cm3 of 1M NaOH added to an aspirin tablet. 25cm3 of distilled water also added. Mixture heated for 10 mins. Hydrolysed solution and washings transferred to a 250 cm3 conical flask and made up to the mark (250cm3).
25 cm3 of the hydrolysed solution is titrated against 0.1M HCl. The average titration is 12.13 cm3 HCl required to reach end point.
1 mol acetyl salicylic acid reacts with 2 mols NaOH
1 mol NaOH reacts with 1 mol HCL
Mr(ASA) = 180.15 g/mol

theory:
excess NaOH is added to neutralise the acid in the tablet. the hydrolysed solution is titrated against HCl, the number of moles HCl used proportional to the moles of remaining NaOH.

n=C*V/1000

## The Attempt at a Solution

a) number of moles of NaOH originally added to the aspirin tablet is:
25*1/1000=0.025 mols

b) number of moles of NaOH remaining in 250 cm3 hydrolysed solution(not used to hydrolyse ASA):
=number of moles of HCl used to titrate against 25cm3 hydrolysed solution *10
=(12.13*0.1/1000)*10 =0.01213 mols

c) number of moles of NaOH used to hydrolyse the ASA
= a) - b)
=0.025-0.01213
=0.01287 mols

d) number of moles of acetyl salicylic acid hydrolysed by NaOH:
=number of moles of NaOH used to hydrolyse ASA/2
= 0.01287/2 = 0.00644mols

e) mass of ASA in the tablet:
=0.00644*180.15
=1.6g

however, the mass of ASA should be 300mg (as on the packet)...
There must be something wrong with my calculation.

What was the indicator used in the titration?

It should be 1.16g, not 1.6g, but it doesn't change much. Nothing strikes me as being obviously wrong, and the only thing I have doubts about would change the result to even worse.

Borek said:
What was the indicator used in the titration?

It should be 1.16g, not 1.6g, but it doesn't change much. Nothing strikes me as being obviously wrong, and the only thing I have doubts about would change the result to even worse.

Ah yes it is 1.16g, typo.
I have discussed with my lab partner and now I know what has gone wrong (4.5 tablets were actually used instead of just 1) which solves my problem.
But thank you very much for taking the effort to check my working.

## What is the purpose of finding the mass of acetyl salicylic acid in aspirin tablet?

The purpose of finding the mass of acetyl salicylic acid in aspirin tablet is to determine the amount of active ingredient present in each tablet. This information is important for quality control and dosage calculations.

## How is the mass of acetyl salicylic acid in aspirin tablet determined?

The mass of acetyl salicylic acid in aspirin tablet is determined by weighing the tablet using a sensitive balance. The tablet is crushed and dissolved in a solvent, and then the solution is filtered to remove any impurities. The remaining pure solution is then dried and the mass of acetyl salicylic acid is calculated based on the weight of the solution.

## What is the chemical composition of acetyl salicylic acid?

Acetyl salicylic acid, also known as aspirin, has a chemical formula of C9H8O4. It is composed of nine carbon atoms, eight hydrogen atoms, and four oxygen atoms. It is a white, crystalline solid at room temperature.

## Why is it important to accurately determine the mass of acetyl salicylic acid in aspirin tablet?

Accurately determining the mass of acetyl salicylic acid in aspirin tablet ensures that each tablet contains the correct amount of active ingredient. This is important for ensuring the effectiveness and safety of the medication.

## Can the mass of acetyl salicylic acid in aspirin tablet vary between different brands?

Yes, the mass of acetyl salicylic acid in aspirin tablet can vary between different brands. This is because different brands may use different manufacturing processes and may have different concentrations of active ingredient in their tablets. It is important to check the label and follow the recommended dosage instructions for each brand of aspirin.

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