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Chemistry
11 Dec 2025
190
4 pages
Maya A @maya.ah
This practical shows you how to synthesise aspirin from scratch and test whether you've made it properly. It's... Show more
Ever wondered how aspirin actually works? Aspirin is an ester that blocks pain signals and reduces inflammation, which is why it helps with headaches and can even reduce heart attack risk. However, it can cause stomach bleeding in some people.
The reaction combines salicylic acid with ethanoic anhydride using sulfuric acid as a catalyst. This produces aspirin plus ethanoic acid as a byproduct. The reaction mechanism is called nucleophilic addition-elimination - sounds fancy, but it's just one molecule attacking another and kicking out a leaving group.
Why use ethanoic anhydride instead of ethanoyl chloride? It's much safer! Ethanoic anhydride is cheaper, less corrosive, reacts less violently with water, and won't produce toxic HCl fumes that could harm you.
Top Tip Remember that this synthesis creates a medicine from simple chemicals - it shows how powerful organic chemistry can be in real life!
You'll start by weighing 2g of salicylic acid into a round-bottom flask and setting up a reflux apparatus. The flask sits in hot water (not directly on the flame), with cold water flowing through the condenser from bottom to top.
Add 5cm³ of ethanoic anhydride and 5 drops of concentrated sulfuric acid as your catalyst. Always work in a fume cupboard when handling the sulfuric acid - it's seriously corrosive stuff!
The reflux process is crucial here. Heat gently with a half-open Bunsen burner and watch for colour changes - if your mixture starts changing colour, lift it out and swirl it quickly. The condenser ensures any evaporated reactants cool down and return to your mixture rather than escaping.
After 10 minutes of gentle heating (once everything's dissolved), you'll quench the reaction by adding distilled water and cooling in an ice bath. This causes your aspirin to crystallise out as the temperature drops.
Safety Alert Always turn on the water before lighting the Bunsen burner, and keep that gas valve only half open!
Filtration using a Büchner funnel and vacuum pump removes your crude aspirin crystals. Make sure the filter paper fits perfectly - no gaps around the edges! Moisten it first with ethanol or water so it sticks properly.
The recrystallisation step is where the magic happens. Add just enough ethanol to dissolve your crystals when heated , then cool it down slowly. Pure aspirin dissolves in hot ethanol but crystallises out when cold, while impurities either stay dissolved or don't dissolve at all.
Keep the temperature below 75°C during recrystallisation - ethanol boils at 78°C, so you don't want it evaporating away! Use a watch glass to cover your beaker and minimise losses.
Filter your purified crystals again, then weigh them to calculate your yield. Cover with cling film (pierce some holes) and dry in a desiccator to remove any remaining water.
Key Point Recrystallisation works because aspirin's solubility changes dramatically with temperature, but impurities don't behave the same way!
You'll test your aspirin's purity using two methods melting point determination and thin layer chromatography (TLC). Pure aspirin should melt at exactly 136°C - any impurities will lower this temperature and make it melt over a wider range.
Unreacted salicylic acid is the most common impurity you'll find. If your melting point is too low or covers too wide a range, you know your sample isn't pure enough.
The main safety hazards include corrosive ethanoic anhydride and sulfuric acid, harmful salicylic acid, and flammable ethanol. Always work in a fume cupboard and wear appropriate safety equipment.
Your yield probably won't be 100% - that's completely normal! Some product always gets lost during filtration, washing, and transfer steps. The important thing is getting pure crystals that melt at the right temperature.
Reality Check Professional chemists rarely get perfect yields either - this practical teaches you real-world synthesis skills, not just theory!
Our AI Companion is a student-focused AI tool that offers more than just answers. Built on millions of Knowunity resources, it provides relevant information, personalised study plans, quizzes, and content directly in the chat, adapting to your individual learning journey.
You can download the app from Google Play Store and Apple App Store.
That's right! Enjoy free access to study content, connect with fellow students, and get instant help – all at your fingertips.
5
Smart Tools NEW
Transform this note into: ✓ 50+ Practice Questions ✓ Interactive Flashcards ✓ Full Mock Exam ✓ Essay Outlines
Explore comprehensive AQA A-Level Chemistry tests covering functional groups, transition metals, and ion tests. This resource includes detailed observations and reactions for various chemical tests, ideal for exam preparation and revision. Perfect for students seeking to enhance their understanding of laboratory techniques and chemical nomenclature.
ChemistryExplore the detailed process of mass spectrometry, including ionization methods like Electron Impact and Electrospray, acceleration of ions, and detection techniques. This summary covers key concepts such as mass spectrum, ionization energy, and molecular fragmentation, providing a comprehensive overview for students studying analytical chemistry.
ChemistryExplore the fundamentals of infrared spectroscopy, a key analytical technique in organic chemistry. This summary covers functional groups, bond vibrations, and the significance of infrared spectra in identifying compounds. Ideal for A-level students studying organic analysis. Understand how vibrational frequencies relate to molecular structure and the implications for global warming.
ChemistryApp Store
Google Play
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
Maya A
@maya.ah
This practical shows you how to synthesise aspirin from scratch and test whether you've made it properly. It's a brilliant example of organic chemistry in action - turning simple starting materials into a medicine you've probably got in your bathroom... Show more
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Improve your grades
Join milions of students
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Ever wondered how aspirin actually works? Aspirin is an ester that blocks pain signals and reduces inflammation, which is why it helps with headaches and can even reduce heart attack risk. However, it can cause stomach bleeding in some people.
The reaction combines salicylic acid with ethanoic anhydride using sulfuric acid as a catalyst. This produces aspirin plus ethanoic acid as a byproduct. The reaction mechanism is called nucleophilic addition-elimination - sounds fancy, but it's just one molecule attacking another and kicking out a leaving group.
Why use ethanoic anhydride instead of ethanoyl chloride? It's much safer! Ethanoic anhydride is cheaper, less corrosive, reacts less violently with water, and won't produce toxic HCl fumes that could harm you.
Top Tip: Remember that this synthesis creates a medicine from simple chemicals - it shows how powerful organic chemistry can be in real life!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
You'll start by weighing 2g of salicylic acid into a round-bottom flask and setting up a reflux apparatus. The flask sits in hot water (not directly on the flame), with cold water flowing through the condenser from bottom to top.
Add 5cm³ of ethanoic anhydride and 5 drops of concentrated sulfuric acid as your catalyst. Always work in a fume cupboard when handling the sulfuric acid - it's seriously corrosive stuff!
The reflux process is crucial here. Heat gently with a half-open Bunsen burner and watch for colour changes - if your mixture starts changing colour, lift it out and swirl it quickly. The condenser ensures any evaporated reactants cool down and return to your mixture rather than escaping.
After 10 minutes of gentle heating (once everything's dissolved), you'll quench the reaction by adding distilled water and cooling in an ice bath. This causes your aspirin to crystallise out as the temperature drops.
Safety Alert: Always turn on the water before lighting the Bunsen burner, and keep that gas valve only half open!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Filtration using a Büchner funnel and vacuum pump removes your crude aspirin crystals. Make sure the filter paper fits perfectly - no gaps around the edges! Moisten it first with ethanol or water so it sticks properly.
The recrystallisation step is where the magic happens. Add just enough ethanol to dissolve your crystals when heated , then cool it down slowly. Pure aspirin dissolves in hot ethanol but crystallises out when cold, while impurities either stay dissolved or don't dissolve at all.
Keep the temperature below 75°C during recrystallisation - ethanol boils at 78°C, so you don't want it evaporating away! Use a watch glass to cover your beaker and minimise losses.
Filter your purified crystals again, then weigh them to calculate your yield. Cover with cling film (pierce some holes) and dry in a desiccator to remove any remaining water.
Key Point: Recrystallisation works because aspirin's solubility changes dramatically with temperature, but impurities don't behave the same way!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
You'll test your aspirin's purity using two methods: melting point determination and thin layer chromatography (TLC). Pure aspirin should melt at exactly 136°C - any impurities will lower this temperature and make it melt over a wider range.
Unreacted salicylic acid is the most common impurity you'll find. If your melting point is too low or covers too wide a range, you know your sample isn't pure enough.
The main safety hazards include corrosive ethanoic anhydride and sulfuric acid, harmful salicylic acid, and flammable ethanol. Always work in a fume cupboard and wear appropriate safety equipment.
Your yield probably won't be 100% - that's completely normal! Some product always gets lost during filtration, washing, and transfer steps. The important thing is getting pure crystals that melt at the right temperature.
Reality Check: Professional chemists rarely get perfect yields either - this practical teaches you real-world synthesis skills, not just theory!
Our AI Companion is a student-focused AI tool that offers more than just answers. Built on millions of Knowunity resources, it provides relevant information, personalised study plans, quizzes, and content directly in the chat, adapting to your individual learning journey.
You can download the app from Google Play Store and Apple App Store.
That's right! Enjoy free access to study content, connect with fellow students, and get instant help – all at your fingertips.
5
Smart Tools NEW
Transform this note into: ✓ 50+ Practice Questions ✓ Interactive Flashcards ✓ Full Mock Exam ✓ Essay Outlines
Explore comprehensive AQA A-Level Chemistry tests covering functional groups, transition metals, and ion tests. This resource includes detailed observations and reactions for various chemical tests, ideal for exam preparation and revision. Perfect for students seeking to enhance their understanding of laboratory techniques and chemical nomenclature.
ChemistryExplore the detailed process of mass spectrometry, including ionization methods like Electron Impact and Electrospray, acceleration of ions, and detection techniques. This summary covers key concepts such as mass spectrum, ionization energy, and molecular fragmentation, providing a comprehensive overview for students studying analytical chemistry.
ChemistryExplore the fundamentals of infrared spectroscopy, a key analytical technique in organic chemistry. This summary covers functional groups, bond vibrations, and the significance of infrared spectra in identifying compounds. Ideal for A-level students studying organic analysis. Understand how vibrational frequencies relate to molecular structure and the implications for global warming.
ChemistryApp Store
Google Play
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
Sociology