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Updated Mar 22, 2026
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Comprehensive AQA A-Level Chemistry Test Bank
J
Jess Wignall
@jesswignall_safr
Chemical Tests and Identification
Functional Group Tests
Need to identify an organic compound? These tests will help you:
- Alcohols: Mix with sulphuric acid and potassium dichromate - a colour change from orange to green confirms it's an alcohol.
- Alkenes: Add bromine water - if it changes from orange to colourless, you've got an alkene.
- Aldehydes: Use Tollens' reagent (a mixture of silver nitrate, sodium hydroxide and ammonia) - a silver mirror forms with aldehydes. Alternatively, Fehling's solution turns from blue to a brick-red precipitate when heated with aldehydes.
- Carboxylic acids: Add sodium hydrogen carbonate - effervescence (bubbling) of CO₂ indicates a carboxylic acid.
Quick Tip: For practical exams, remember that only aldehydes give positive results with both Tollens' reagent and Fehling's solution - ketones don't react with either!
Anion Tests
Identifying negatively charged ions is straightforward with these reactions:
- Carbonate ions: Add dilute HCl - effervescence occurs. The gas produced turns limewater cloudy (confirming it's CO₂).
- Sulphate ions: Add dilute HCl and barium chloride - a white precipitate forms.
- Halide ions (using silver nitrate followed by ammonia):
- Chloride: White precipitate that dissolves in dilute ammonia
- Bromide: Cream precipitate that remains in dilute ammonia but dissolves in concentrated ammonia
- Iodide: Yellow precipitate that doesn't dissolve in ammonia (dilute or concentrated)
Cation Tests
For positively charged ions, look for these reactions:
- Calcium ions: Give a red flame colour; slight white precipitate with NaOH that dissolves in excess water
- Magnesium ions: Form a white precipitate with sodium hydroxide
- Barium ions: Produce a green flame colour; white precipitate with sulphuric acid
- Strontium ions: Show a red flame colour; white precipitate with sulphuric acid
- Ammonium ions: When mixed with NaOH and heated, turn damp red litmus paper blue
Transition Metal Tests
Transition metal compounds produce distinctive colour changes with reagents:
- Iron(II) ions: Form a green precipitate with NaOH or NH₃ (turns rusty brown in air)
- Iron(III) ions: Produce a rusty brown precipitate with NaOH or NH₃
- Copper(II) ions: Form a blue precipitate with NaOH; with excess NH₃, a royal blue solution forms
- Aluminium ions: Create a white precipitate with NaOH that dissolves in excess NaOH
The vanadium oxidation states also show distinctive colours: VO₂⁻ (yellow), VO²⁺ (blue), V³⁺ (green), and V²⁺ (violet).
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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
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Anna
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Best app on earth! no words because it’s too good
Thomas R
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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
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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
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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 Knowunity AI. 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 Knowunity AI. 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
Comprehensive AQA A-Level Chemistry Test Bank
J
Jess Wignall
@jesswignall_safr
Chemistry tests are the detective work of science, helping us identify unknown substances by their reactions. This summary covers the key chemical tests you need to know for identifying functional groups, ions, and transition metal compounds - essential knowledge for... Show more
Chemical Tests and Identification
Functional Group Tests
Need to identify an organic compound? These tests will help you:
- Alcohols: Mix with sulphuric acid and potassium dichromate - a colour change from orange to green confirms it's an alcohol.
- Alkenes: Add bromine water - if it changes from orange to colourless, you've got an alkene.
- Aldehydes: Use Tollens' reagent (a mixture of silver nitrate, sodium hydroxide and ammonia) - a silver mirror forms with aldehydes. Alternatively, Fehling's solution turns from blue to a brick-red precipitate when heated with aldehydes.
- Carboxylic acids: Add sodium hydrogen carbonate - effervescence (bubbling) of CO₂ indicates a carboxylic acid.
Quick Tip: For practical exams, remember that only aldehydes give positive results with both Tollens' reagent and Fehling's solution - ketones don't react with either!
Anion Tests
Identifying negatively charged ions is straightforward with these reactions:
- Carbonate ions: Add dilute HCl - effervescence occurs. The gas produced turns limewater cloudy (confirming it's CO₂).
- Sulphate ions: Add dilute HCl and barium chloride - a white precipitate forms.
- Halide ions (using silver nitrate followed by ammonia):
- Chloride: White precipitate that dissolves in dilute ammonia
- Bromide: Cream precipitate that remains in dilute ammonia but dissolves in concentrated ammonia
- Iodide: Yellow precipitate that doesn't dissolve in ammonia (dilute or concentrated)
Cation Tests
For positively charged ions, look for these reactions:
- Calcium ions: Give a red flame colour; slight white precipitate with NaOH that dissolves in excess water
- Magnesium ions: Form a white precipitate with sodium hydroxide
- Barium ions: Produce a green flame colour; white precipitate with sulphuric acid
- Strontium ions: Show a red flame colour; white precipitate with sulphuric acid
- Ammonium ions: When mixed with NaOH and heated, turn damp red litmus paper blue
Transition Metal Tests
Transition metal compounds produce distinctive colour changes with reagents:
- Iron(II) ions: Form a green precipitate with NaOH or NH₃ (turns rusty brown in air)
- Iron(III) ions: Produce a rusty brown precipitate with NaOH or NH₃
- Copper(II) ions: Form a blue precipitate with NaOH; with excess NH₃, a royal blue solution forms
- Aluminium ions: Create a white precipitate with NaOH that dissolves in excess NaOH
The vanadium oxidation states also show distinctive colours: VO₂⁻ (yellow), VO²⁺ (blue), V³⁺ (green), and V²⁺ (violet).
We thought you’d never ask...
What is the Knowunity AI companion?
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.
Where can I download the Knowunity app?
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Is Knowunity really free of charge?
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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.
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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 Knowunity AI. 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 Knowunity AI. 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