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Pure Substances and Mixtures
Pure substances contain only one type of material - either a single element (like pure gold) or a single compound (like pure water). Mixtures, on the other hand, are combinations of different substances that aren't chemically bonded together - think of sand mixed with water or air (which contains oxygen, nitrogen, and other gases).
Here's a simple way to remember the difference: elements have just one type of atom, compounds have different types of atoms joined together, and mixtures have different substances just sitting next to each other without forming chemical bonds.
Quick Test Tip: Pure substances have sharp, exact melting points, whilst mixtures melt over a range of temperatures - this is a common exam question!
Separation Techniques: The Basics
Scientists use different techniques to separate mixtures, and choosing the right method depends on the properties of the substances involved. Filtration is your go-to method when you need to separate an insoluble solid from a liquid - like removing sand from water or filtering out excess reactants after a chemical reaction.
The key is understanding that filtration only works when one substance doesn't dissolve in the liquid. The liquid passes through the filter paper, but the solid particles are too big to get through.
Crystallisation: Getting Solids from Solutions
Crystallisation lets you recover solid crystals from a solution by carefully evaporating the solvent. You heat the solution in an evaporating basin with a Bunsen burner, and as the water evaporates, the solution becomes more concentrated until solid crystals start forming.
Sometimes you need to be careful not to evaporate all the water at once - especially with compounds like hydrated copper sulphate crystals. Instead, you partially evaporate the solution then leave it in a warm place to finish slowly, preventing the crystals from losing their water molecules.
Simple Distillation: Separating Solvents
Simple distillation works brilliantly when you want to separate a solvent from a dissolved substance that has a much higher boiling point. As you heat the mixture, the solvent evaporates first, travels through the apparatus as vapour, then condenses back into pure liquid in the collection flask.
This technique is perfect for getting pure water from salt water, since water boils at 100°C whilst salt doesn't evaporate at these temperatures.
Fractional Distillation: Separating Liquid Mixtures
When you need to separate different liquids from each other (like ethanol from water), fractional distillation is your best bet. This clever technique uses a column that's hot at the bottom and cool at the top, allowing different liquids to condense at different heights based on their boiling points.
You can collect the separated liquids in two ways: either gather different substances from different parts of the column simultaneously, or gradually increase the temperature to collect substances one by one, starting with the lowest boiling point first.
Real-World Connection: Oil refineries use massive fractional distillation columns to separate crude oil into petrol, diesel, and other useful products!
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Stefan S
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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
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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
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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
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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
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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
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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 Separating Techniques in Chemistry
Ever wondered how scientists separate salt from seawater or how oil refineries get petrol from crude oil? Understanding pure substances, mixtures, and how to separate them is fundamental to chemistry and explains countless processes you see every day.
Pure Substances and Mixtures
Pure substances contain only one type of material - either a single element (like pure gold) or a single compound (like pure water). Mixtures, on the other hand, are combinations of different substances that aren't chemically bonded together - think of sand mixed with water or air (which contains oxygen, nitrogen, and other gases).
Here's a simple way to remember the difference: elements have just one type of atom, compounds have different types of atoms joined together, and mixtures have different substances just sitting next to each other without forming chemical bonds.
Quick Test Tip: Pure substances have sharp, exact melting points, whilst mixtures melt over a range of temperatures - this is a common exam question!
Separation Techniques: The Basics
Scientists use different techniques to separate mixtures, and choosing the right method depends on the properties of the substances involved. Filtration is your go-to method when you need to separate an insoluble solid from a liquid - like removing sand from water or filtering out excess reactants after a chemical reaction.
The key is understanding that filtration only works when one substance doesn't dissolve in the liquid. The liquid passes through the filter paper, but the solid particles are too big to get through.
Crystallisation: Getting Solids from Solutions
Crystallisation lets you recover solid crystals from a solution by carefully evaporating the solvent. You heat the solution in an evaporating basin with a Bunsen burner, and as the water evaporates, the solution becomes more concentrated until solid crystals start forming.
Sometimes you need to be careful not to evaporate all the water at once - especially with compounds like hydrated copper sulphate crystals. Instead, you partially evaporate the solution then leave it in a warm place to finish slowly, preventing the crystals from losing their water molecules.
Simple Distillation: Separating Solvents
Simple distillation works brilliantly when you want to separate a solvent from a dissolved substance that has a much higher boiling point. As you heat the mixture, the solvent evaporates first, travels through the apparatus as vapour, then condenses back into pure liquid in the collection flask.
This technique is perfect for getting pure water from salt water, since water boils at 100°C whilst salt doesn't evaporate at these temperatures.
Fractional Distillation: Separating Liquid Mixtures
When you need to separate different liquids from each other (like ethanol from water), fractional distillation is your best bet. This clever technique uses a column that's hot at the bottom and cool at the top, allowing different liquids to condense at different heights based on their boiling points.
You can collect the separated liquids in two ways: either gather different substances from different parts of the column simultaneously, or gradually increase the temperature to collect substances one by one, starting with the lowest boiling point first.
Real-World Connection: Oil refineries use massive fractional distillation columns to separate crude oil into petrol, diesel, and other useful products!
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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4.8/5
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