Maths
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Chemistry
English Language
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Responding to change (a2 only)
Infection and response
Homeostasis and response
Energy transfers (a2 only)
Cell biology
Organisms respond to changes in their internal and external environments (a-level only)
Biological molecules
Organisation
Substance exchange
Bioenergetics
Genetic information & variation
Inheritance, variation and evolution
Genetics & ecosystems (a2 only)
Ecology
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1l the quest for political stability: germany, 1871-1991
Britain & the wider world: 1745 -1901
The cold war
Inter-war germany
Medieval period: 1066 -1509
2d religious conflict and the church in england, c1529-c1570
2o democracy and nazism: germany, 1918-1945
1f industrialisation and the people: britain, c1783-1885
1c the tudors: england, 1485-1603
2m wars and welfare: britain in transition, 1906-1957
World war two & the holocaust
2n revolution and dictatorship: russia, 1917-1953
2s the making of modern britain, 1951-2007
World war one
Britain: 1509 -1745
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11
4
Zainab
28/11/2025
Chemistry
GCSE Quantitative Chemistry Active Recall
1,078
•
28 Nov 2025
•
Zainab
@zainab_02839
Quantitative chemistry is all about the maths behind chemical reactions... Show more
Ever wondered why chemists are obsessed with measuring everything? The law of conservation of mass explains it perfectly - no atoms disappear during reactions, so reactants always equal products in mass.
When doing reactions, you'll often have a limiting reactant (the one that runs out first) and others in excess (leftovers). Think of it like making sandwiches - if you've got 10 slices of bread but only 3 slices of ham, the ham limits how many you can make!
Relative formula mass (Mr) is just adding up all the atomic masses in a compound. For CH₄: carbon (12) + four hydrogens (4 × 1) = 16. Percentage by mass tells you what fraction of a compound is made up of each element using: (total Ar of element ÷ Mr of compound) × 100.
Quick Tip: Always double-check your Mr calculations - they're the foundation for everything else in quantitative chemistry!
Moles are chemistry's way of counting particles - like saying "a dozen" but for atoms and molecules. One mole contains Avogadro's constant (6.02 × 10²³) particles, which is an absolutely massive number!
The key equation you'll use constantly is: number of moles = mass ÷ Mr. Once you've got moles sorted, concentration becomes straightforward. You can measure it in g/dm³ (mass ÷ volume) or mol/dm³ (moles ÷ volume).
For gas volume calculations, remember that one mole of any gas occupies 24 dm³ at room temperature and pressure. So volume = moles × 24. Converting units is dead simple: divide by 1000 to go bigger (cm³ to dm³), multiply by 1000 to go smaller.
Memory Aid: Think of moles as chemistry's universal currency - everything converts through moles!
Titration calculations follow a reliable pattern that'll save you in exams. Write the balanced equation, work out the mole ratio, create a table with known values, then calculate what's missing. It's methodical, so take it step by step.
Atom economy measures how much of your starting materials actually becomes useful product. The formula is: (Mr of desired product ÷ Mr of all reactants) × 100. High atom economy means less waste and better sustainability.
Percentage yield compares what you actually get versus the theoretical maximum: (actual yield ÷ theoretical yield) × 100. You'll never hit 100% because reactions are messy - some reactants don't react, side reactions occur, or you lose product during handling.
When choosing industrial methods, consider percentage yield, raw material costs, environmental impact, and reaction rate. It's all about finding the best balance for real-world applications.
Exam Success: Low yields aren't always bad - sometimes the benefits outweigh the drawbacks in industrial processes!
Real chemistry isn't like textbook equations - there's always something that stops you getting perfect results! Side reactions can steal your reactants to make unwanted products instead of what you're after.
You'll also lose some product during the process itself. Maybe some stays stuck in your beaker, or if you're making a gas, some might escape before you can collect it. These practical limitations explain why percentage yields are always less than 100%.
Understanding these limitations makes you a better chemist. Instead of being frustrated by "imperfect" results, you'll know exactly why they happen and how to minimise losses in future experiments.
Real Chemistry: Even professional chemists rarely achieve theoretical yields - it's about optimising, not perfecting!
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.
App 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
Zainab
@zainab_02839
Quantitative chemistry is all about the maths behind chemical reactions - and it's easier than you think! You'll learn how to calculate masses, concentrations, and work out exactly how much product you can make from any reaction.
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Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Ever wondered why chemists are obsessed with measuring everything? The law of conservation of mass explains it perfectly - no atoms disappear during reactions, so reactants always equal products in mass.
When doing reactions, you'll often have a limiting reactant (the one that runs out first) and others in excess (leftovers). Think of it like making sandwiches - if you've got 10 slices of bread but only 3 slices of ham, the ham limits how many you can make!
Relative formula mass (Mr) is just adding up all the atomic masses in a compound. For CH₄: carbon (12) + four hydrogens (4 × 1) = 16. Percentage by mass tells you what fraction of a compound is made up of each element using: (total Ar of element ÷ Mr of compound) × 100.
Quick Tip: Always double-check your Mr calculations - they're the foundation for everything else in quantitative chemistry!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Moles are chemistry's way of counting particles - like saying "a dozen" but for atoms and molecules. One mole contains Avogadro's constant (6.02 × 10²³) particles, which is an absolutely massive number!
The key equation you'll use constantly is: number of moles = mass ÷ Mr. Once you've got moles sorted, concentration becomes straightforward. You can measure it in g/dm³ (mass ÷ volume) or mol/dm³ (moles ÷ volume).
For gas volume calculations, remember that one mole of any gas occupies 24 dm³ at room temperature and pressure. So volume = moles × 24. Converting units is dead simple: divide by 1000 to go bigger (cm³ to dm³), multiply by 1000 to go smaller.
Memory Aid: Think of moles as chemistry's universal currency - everything converts through moles!
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Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Titration calculations follow a reliable pattern that'll save you in exams. Write the balanced equation, work out the mole ratio, create a table with known values, then calculate what's missing. It's methodical, so take it step by step.
Atom economy measures how much of your starting materials actually becomes useful product. The formula is: (Mr of desired product ÷ Mr of all reactants) × 100. High atom economy means less waste and better sustainability.
Percentage yield compares what you actually get versus the theoretical maximum: (actual yield ÷ theoretical yield) × 100. You'll never hit 100% because reactions are messy - some reactants don't react, side reactions occur, or you lose product during handling.
When choosing industrial methods, consider percentage yield, raw material costs, environmental impact, and reaction rate. It's all about finding the best balance for real-world applications.
Exam Success: Low yields aren't always bad - sometimes the benefits outweigh the drawbacks in industrial processes!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Real chemistry isn't like textbook equations - there's always something that stops you getting perfect results! Side reactions can steal your reactants to make unwanted products instead of what you're after.
You'll also lose some product during the process itself. Maybe some stays stuck in your beaker, or if you're making a gas, some might escape before you can collect it. These practical limitations explain why percentage yields are always less than 100%.
Understanding these limitations makes you a better chemist. Instead of being frustrated by "imperfect" results, you'll know exactly why they happen and how to minimise losses in future experiments.
Real Chemistry: Even professional chemists rarely achieve theoretical yields - it's about optimising, not perfecting!
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.
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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
