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5 Dec 2025
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Understanding Chemical Analysis: Flame Tests, Gas Tests, and Identifying Cations and Anions
lily richards
@lily.richards
1 / 3
Purity, Formulations and Gas Tests
Pure substances contain only one type of compound or element and have fixed melting and boiling points. Water always boils at exactly 100°C when it's pure. If you mix in impurities, substances will melt and boil over a range of temperatures instead.
Formulations are mixtures made using specific recipes with precise amounts of different components. Think paint, medicines, cleaning products - each ingredient has a particular job to do. The exact proportions matter because each component contributes different properties.
Testing for gases is surprisingly straightforward. Chlorine bleaches damp blue litmus paper white . Oxygen will relight a glowing splint, making it burst back into flame.
Quick Tip: Always do gas tests in a fume cupboard or well-ventilated area for safety!
More Gas Tests and Anion Detection
Hydrogen makes a distinctive squeaky pop sound when you put a burning splint into it. Carbon dioxide turns lime water cloudy - this is your go-to test for CO₂.
Anion tests (negative ions) follow clear patterns. For carbonates, add dilute HCl and bubble any gas produced through lime water. If it goes cloudy, you've got a carbonate because it's producing CO₂.
Sulfate testing needs two steps. First, add dilute HCl to remove interfering ions. Then add barium chloride - a white precipitate of barium sulfate confirms sulfates are present.
Halide ions (chlorine, bromine, iodine) also need dilute nitric acid first, then silver nitrate. You'll get different coloured precipitates: white for chloride, cream for bromide, and yellow for iodide.
Remember: Always add acid first in anion tests to remove interfering substances!
Cation Tests - Flame Tests and Metal Hydroxides
Flame tests are brilliant for identifying metal ions through their characteristic colours. Clean your nichrome wire with dilute HCl first, then dip it in your sample and hold it in the blue part of the Bunsen flame.
Each metal gives a distinctive colour: lithium burns crimson, sodium bright yellow, potassium lilac, calcium orange-red, and copper green. These colours are like fingerprints for metals.
Metal hydroxide tests use sodium hydroxide solution to create coloured precipitates. Copper gives blue, iron(II) gives green, iron(III) gives brown, while calcium and magnesium both give white precipitates.
The clever bit with aluminium is that it initially forms a white precipitate, but if you add excess sodium hydroxide, it redissolves to form a colourless solution. This unique behaviour helps distinguish it from other metals.
Pro Tip: Learn the flame test colours using memory tricks - "Little Suzy Plays Carefully Outside" for Lithium-crimson, Sodium-yellow, Potassium-lilac, Calcium-orange, Copper-green!
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Basil
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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
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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
Understanding Chemical Analysis: Flame Tests, Gas Tests, and Identifying Cations and Anions
lily richards
@lily.richards
Chemical analysis is all about figuring out what's actually in different substances - whether they're pure, what they're made of, and how much of each component is present. You'll use loads of practical tests to identify mystery substances, which is... Show more
Purity, Formulations and Gas Tests
Pure substances contain only one type of compound or element and have fixed melting and boiling points. Water always boils at exactly 100°C when it's pure. If you mix in impurities, substances will melt and boil over a range of temperatures instead.
Formulations are mixtures made using specific recipes with precise amounts of different components. Think paint, medicines, cleaning products - each ingredient has a particular job to do. The exact proportions matter because each component contributes different properties.
Testing for gases is surprisingly straightforward. Chlorine bleaches damp blue litmus paper white . Oxygen will relight a glowing splint, making it burst back into flame.
Quick Tip: Always do gas tests in a fume cupboard or well-ventilated area for safety!
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More Gas Tests and Anion Detection
Hydrogen makes a distinctive squeaky pop sound when you put a burning splint into it. Carbon dioxide turns lime water cloudy - this is your go-to test for CO₂.
Anion tests (negative ions) follow clear patterns. For carbonates, add dilute HCl and bubble any gas produced through lime water. If it goes cloudy, you've got a carbonate because it's producing CO₂.
Sulfate testing needs two steps. First, add dilute HCl to remove interfering ions. Then add barium chloride - a white precipitate of barium sulfate confirms sulfates are present.
Halide ions (chlorine, bromine, iodine) also need dilute nitric acid first, then silver nitrate. You'll get different coloured precipitates: white for chloride, cream for bromide, and yellow for iodide.
Remember: Always add acid first in anion tests to remove interfering substances!
Sign up to see the contentIt's free!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Cation Tests - Flame Tests and Metal Hydroxides
Flame tests are brilliant for identifying metal ions through their characteristic colours. Clean your nichrome wire with dilute HCl first, then dip it in your sample and hold it in the blue part of the Bunsen flame.
Each metal gives a distinctive colour: lithium burns crimson, sodium bright yellow, potassium lilac, calcium orange-red, and copper green. These colours are like fingerprints for metals.
Metal hydroxide tests use sodium hydroxide solution to create coloured precipitates. Copper gives blue, iron(II) gives green, iron(III) gives brown, while calcium and magnesium both give white precipitates.
The clever bit with aluminium is that it initially forms a white precipitate, but if you add excess sodium hydroxide, it redissolves to form a colourless solution. This unique behaviour helps distinguish it from other metals.
Pro Tip: Learn the flame test colours using memory tricks - "Little Suzy Plays Carefully Outside" for Lithium-crimson, Sodium-yellow, Potassium-lilac, Calcium-orange, Copper-green!
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?
You can download the app from Google Play Store and Apple App Store.
Is Knowunity really free of charge?
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Students love us — and so will you.
4.9/5
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4.8/5
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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
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