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Updated Mar 19, 2026
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GCSE AQA Chemistry Combined Science Paper 2 (Topics C6-C10) Mindmaps
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Measuring Reaction Rates
You can easily measure how fast chemical reactions happen by tracking changes over time. Reaction rate simply means how quickly reactants turn into products, and there are three main ways to measure this.
For reactions that produce a precipitate (solid particles), like mixing sodium thiosulfate with hydrochloric acid, you time how long it takes for a black cross underneath your flask to disappear. Higher concentrations make reactions go faster - it's that simple!
When reactions produce gas (like magnesium with HCl), you can measure the volume of gas released using a syringe, or track the mass lost on a balance as gas escapes. The steeper your graph, the faster your reaction.
Remember: Temperature, concentration, and pressure all affect reaction rates - increase any of these and your reaction speeds up!
Crude Oil and Hydrocarbons
Crude oil is basically ancient plankton that's been cooking underground for millions of years - and it's the source of most modern transport fuels. It's a mixture of hydrocarbons (compounds containing only hydrogen and carbon atoms).
Alkanes are the simplest hydrocarbons with the formula CnH2n+2. Think methane (CH4) or ethane (C2H6) - they only have single bonds between atoms. Shorter hydrocarbon chains are more useful because they're more flammable and easier to vaporise.
Fractional distillation separates crude oil into useful products like petrol, diesel, and kerosene. Cracking breaks long, less useful hydrocarbon chains into shorter, more valuable ones using high temperatures and catalysts.
When hydrocarbons burn completely, they produce carbon dioxide and water. Incomplete combustion (not enough oxygen) produces dangerous carbon monoxide instead - that's why proper ventilation matters!
Key point: Shorter hydrocarbon chains = lower boiling points, more flammable, and more useful as fuels.
Chromatography and Chemical Tests
Chromatography is your go-to method for separating and identifying mixtures - it's like giving different substances a race up paper! You place a drop of your mixture on chromatography paper, then let a solvent travel up and carry the substances at different speeds.
Calculate Rf values using: distance travelled by substance ÷ distance travelled by solvent. Pure substances produce single spots, whilst mixtures create multiple spots. This helps you identify unknown substances by comparing Rf values.
Gas tests are dead useful for identification. Hydrogen burns with a squeaky pop, oxygen relights a glowing splint, carbon dioxide turns limewater cloudy, and chlorine bleaches damp indicator paper white.
Understanding whether something is a pure substance, compound, or mixture is crucial. Elements contain one type of atom, compounds have different elements chemically joined, and mixtures contain substances that aren't chemically bonded.
Pro tip: Always use pencil to draw your starting line in chromatography - ink would interfere with your results!
Earth's Atmosphere and Climate Change
Earth's atmosphere has changed dramatically over billions of years, and human activity is now the main driver of change. Originally, our atmosphere was mostly carbon dioxide with no oxygen - quite different from today's 78% nitrogen and 21% oxygen!
Photosynthesis by early plants and algae produced the oxygen we breathe today, whilst also removing carbon dioxide from the atmosphere. This allowed complex life to evolve and created the atmosphere we depend on.
The greenhouse effect occurs when gases like carbon dioxide, methane, and water vapour absorb heat radiation from Earth's surface. More greenhouse gases from burning fossil fuels and deforestation means more heat gets trapped, causing global warming.
Climate change consequences include melting ice caps, rising sea levels, and more extreme weather. Your carbon footprint measures the greenhouse gases released throughout your lifetime - reducing this through renewable energy and efficient processes helps tackle the problem.
Reality check: While the science is clear, reducing emissions requires global cooperation and changes to how we live and work.
Water Treatment and Earth's Resources
Making potable water (safe drinking water) involves multiple treatment stages that remove dangers and improve taste. Water gets screened, filtered through sand and gravel beds, then disinfected with chlorine or UV light to kill harmful microbes.
Sewage treatment uses both physical and biological processes. Screening removes large objects, sedimentation settles heavy particles, and anaerobic digestion by bacteria breaks down organic matter. The treated water can then be safely returned to rivers.
Finite resources like fossil fuels and metal ores will eventually run out, making recycling and sustainability increasingly important. Life cycle assessments (LCA) help evaluate the environmental impact of products from creation to disposal.
Alternative water sources include desalination (removing salt from seawater using reverse osmosis) and better water conservation. These technologies require significant energy but become essential as freshwater becomes scarcer.
Think ahead: Sustainable resource use isn't just environmental - it's about ensuring future generations have what they need to thrive.
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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
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
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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 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
GCSE AQA Chemistry Combined Science Paper 2 (Topics C6-C10) Mindmaps
Dae !
@dailydae_aojb
Ever wondered how scientists measure chemical reactions, what makes up the air we breathe, or where our fuel comes from? This summary covers the key chemistry concepts you need to master - from reaction rates and chromatography to atmospheric changes... Show more
Measuring Reaction Rates
You can easily measure how fast chemical reactions happen by tracking changes over time. Reaction rate simply means how quickly reactants turn into products, and there are three main ways to measure this.
For reactions that produce a precipitate (solid particles), like mixing sodium thiosulfate with hydrochloric acid, you time how long it takes for a black cross underneath your flask to disappear. Higher concentrations make reactions go faster - it's that simple!
When reactions produce gas (like magnesium with HCl), you can measure the volume of gas released using a syringe, or track the mass lost on a balance as gas escapes. The steeper your graph, the faster your reaction.
Remember: Temperature, concentration, and pressure all affect reaction rates - increase any of these and your reaction speeds up!
Sign up to see the contentIt's free!
Access to all documents
Improve your grades
Join milions of students
Crude Oil and Hydrocarbons
Crude oil is basically ancient plankton that's been cooking underground for millions of years - and it's the source of most modern transport fuels. It's a mixture of hydrocarbons (compounds containing only hydrogen and carbon atoms).
Alkanes are the simplest hydrocarbons with the formula CnH2n+2. Think methane (CH4) or ethane (C2H6) - they only have single bonds between atoms. Shorter hydrocarbon chains are more useful because they're more flammable and easier to vaporise.
Fractional distillation separates crude oil into useful products like petrol, diesel, and kerosene. Cracking breaks long, less useful hydrocarbon chains into shorter, more valuable ones using high temperatures and catalysts.
When hydrocarbons burn completely, they produce carbon dioxide and water. Incomplete combustion (not enough oxygen) produces dangerous carbon monoxide instead - that's why proper ventilation matters!
Key point: Shorter hydrocarbon chains = lower boiling points, more flammable, and more useful as fuels.
Sign up to see the contentIt's free!
Access to all documents
Improve your grades
Join milions of students
Chromatography and Chemical Tests
Chromatography is your go-to method for separating and identifying mixtures - it's like giving different substances a race up paper! You place a drop of your mixture on chromatography paper, then let a solvent travel up and carry the substances at different speeds.
Calculate Rf values using: distance travelled by substance ÷ distance travelled by solvent. Pure substances produce single spots, whilst mixtures create multiple spots. This helps you identify unknown substances by comparing Rf values.
Gas tests are dead useful for identification. Hydrogen burns with a squeaky pop, oxygen relights a glowing splint, carbon dioxide turns limewater cloudy, and chlorine bleaches damp indicator paper white.
Understanding whether something is a pure substance, compound, or mixture is crucial. Elements contain one type of atom, compounds have different elements chemically joined, and mixtures contain substances that aren't chemically bonded.
Pro tip: Always use pencil to draw your starting line in chromatography - ink would interfere with your results!
Sign up to see the contentIt's free!
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Improve your grades
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Earth's Atmosphere and Climate Change
Earth's atmosphere has changed dramatically over billions of years, and human activity is now the main driver of change. Originally, our atmosphere was mostly carbon dioxide with no oxygen - quite different from today's 78% nitrogen and 21% oxygen!
Photosynthesis by early plants and algae produced the oxygen we breathe today, whilst also removing carbon dioxide from the atmosphere. This allowed complex life to evolve and created the atmosphere we depend on.
The greenhouse effect occurs when gases like carbon dioxide, methane, and water vapour absorb heat radiation from Earth's surface. More greenhouse gases from burning fossil fuels and deforestation means more heat gets trapped, causing global warming.
Climate change consequences include melting ice caps, rising sea levels, and more extreme weather. Your carbon footprint measures the greenhouse gases released throughout your lifetime - reducing this through renewable energy and efficient processes helps tackle the problem.
Reality check: While the science is clear, reducing emissions requires global cooperation and changes to how we live and work.
Sign up to see the contentIt's free!
Access to all documents
Improve your grades
Join milions of students
Water Treatment and Earth's Resources
Making potable water (safe drinking water) involves multiple treatment stages that remove dangers and improve taste. Water gets screened, filtered through sand and gravel beds, then disinfected with chlorine or UV light to kill harmful microbes.
Sewage treatment uses both physical and biological processes. Screening removes large objects, sedimentation settles heavy particles, and anaerobic digestion by bacteria breaks down organic matter. The treated water can then be safely returned to rivers.
Finite resources like fossil fuels and metal ores will eventually run out, making recycling and sustainability increasingly important. Life cycle assessments (LCA) help evaluate the environmental impact of products from creation to disposal.
Alternative water sources include desalination (removing salt from seawater using reverse osmosis) and better water conservation. These technologies require significant energy but become essential as freshwater becomes scarcer.
Think ahead: Sustainable resource use isn't just environmental - it's about ensuring future generations have what they need to thrive.
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?
That's right! Enjoy free access to study content, connect with fellow students, and get instant help – all at your fingertips.
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4.7/5
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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 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