Titration need help

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danhas20
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#1
Report Thread starter 7 months ago
#1
Hi I'm stuck on this question and I would appreciate any help.
A student has read on a packet of aspirin that each tablet contains 250 mg of aspirin,
and has decided to find out if this is true.
The systematic name of aspirin is 2-ethanoylhydroxybenzoic acid. Aspirin is a
carboxylic acid and neutralises a cold dilute solution of sodium hydroxide to form a salt.
This reaction is used to form the basis of a titration.
CH3COOC6H4COOH + NaOH → CH3COOC6H4COONa + H2O
aspirin
1. Calculate the relative molecular mass of aspirin (2-ethanoylhydroxybenzoic acid).
(1 mark) Done = 180
The student decides to use this reaction in a titration to determine the mass of
aspirin in each tablet.
She crushes four tablets, transfers them to a 100 cm3 volumetric flask, dissolving
them in a 50:50 mixture of ethanol and distilled water (it is difficult to dissolve aspirin
© Oxford University Press 2015 www.oxfordsecondary.co.uk/acknowledgements
This resource sheet may have been changed from the original 1
OCR Chemistry A
4.2 Acid–base titrations
Stretch and challenge
in pure water). Using a pipette she transfers 25 cm3 of this solution into a conical
flask and titrates it against a 0.1 mol dm−3 standard solution of sodium hydroxide,
using phenolphthalein as an indicator. The average titre is 14.70 cm3
.
2. Calculate the mass of aspirin in each tablet. (4 marks)
I got 0.06615g.
Could someone check please?

I did no. of moles of NaOH used = (14.7 x 25cm3 )/1000 = 0.00147.
Then I think its a 1:1 ratio with the aspirin so im assuming 0.00147 moles aspirin to react with it.
Then to get the mass of aspirin in the conical flask I did 0.00147 x 180 = 0.2646.
Finally because there was 4 tablets I divided by 4 to get 0.06615.

Does this answer look right?
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WhitneyPowel
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#2
Report 7 months ago
#2
(Original post by danhas20)
Hi I'm stuck on this question and I would appreciate any help.
A student has read on a packet of aspirin that each tablet contains 250 mg of aspirin,
and has decided to find out if this is true.
The systematic name of aspirin is 2-ethanoylhydroxybenzoic acid. Aspirin is a
carboxylic acid and neutralises a cold dilute solution of sodium hydroxide to form a salt.
This reaction is used to form the basis of a titration.
CH3COOC6H4COOH + NaOH → CH3COOC6H4COONa + H2O
aspirin
1. Calculate the relative molecular mass of aspirin (2-ethanoylhydroxybenzoic acid).
(1 mark) Done = 180
The student decides to use this reaction in a titration to determine the mass of
aspirin in each tablet.
She crushes four tablets, transfers them to a 100 cm3 volumetric flask, dissolving
them in a 50:50 mixture of ethanol and distilled water (it is difficult to dissolve aspirin
© Oxford University Press 2015 www.oxfordsecondary.co.uk/acknowledgements
This resource sheet may have been changed from the original 1
OCR Chemistry A
4.2 Acid–base titrations
Stretch and challenge
in pure water). Using a pipette she transfers 25 cm3 of this solution into a conical
flask and titrates it against a 0.1 mol dm−3 standard solution of sodium hydroxide,
using phenolphthalein as an indicator. The average titre is 14.70 cm3
.
2. Calculate the mass of aspirin in each tablet. (4 marks)
I got 0.06615g.
Could someone check please?

I did no. of moles of NaOH used = (14.7 x 25cm3 )/1000 = 0.00147.
Then I think its a 1:1 ratio with the aspirin so im assuming 0.00147 moles aspirin to react with it.
Then to get the mass of aspirin in the conical flask I did 0.00147 x 180 = 0.2646.
Finally because there was 4 tablets I divided by 4 to get 0.06615.

Does this answer look right?
from my opinion it looks right. for more questions and answers you can inbox me
1
reply
danhas20
Badges: 12
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#3
Report Thread starter 7 months ago
#3
(Original post by WhitneyPowel)
from my opinion it looks right. for more questions and answers you can inbox me
Thanks, I appreciate you getting back to me.
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