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Britain & the wider world: 1745 -1901
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Chemistry
9 Dec 2025
282
1 page
Mariya Akbar @mariyaakbar_x
Amount of substance is one of the most practical topics in A-level chemistry - it's literally about counting... Show more
The mole is chemistry's way of counting particles - think of it like a dozen, but instead of 12, it's 6.02 × 10²³ particles (that's Avogadro's constant). This massive number lets us work with atoms and molecules in manageable quantities.
Two key formulas will sort most of your calculations moles = mass ÷ Mr (where Mr is relative molecular mass) and moles = concentration × volume. These connect the microscopic world of atoms to the macroscopic measurements you can actually make in the lab.
Percentage yield tells you how efficient your reaction was - it's actual yield divided by theoretical yield, times 100. Atom economy is different - it measures how many atoms from your reactants actually end up in your desired product, helping you spot wasteful reactions.
The ideal gas equation PV = nRT connects pressure, volume, moles, and temperature for gases. Remember your units pressure in pascals, volume in m³ or dm³, and temperature in Kelvin.
Quick tip Always check your units match the formula - most mistakes come from mixing up dm³ and cm³!
Relative atomic mass (Ar) and relative molecular mass (Mr) compare atoms and molecules to 1/12 of a carbon-12 atom. These give you the numbers you need for the periodic table and your mole calculations.
Empirical formulas show the simplest ratio of atoms, whilst molecular formulas show the actual numbers. To find molecular formula from empirical calculate the empirical formula's Mr, divide the actual Mr by this, then multiply all subscripts by your answer.
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.
12
Smart Tools NEW
Transform this note into: ✓ 50+ Practice Questions ✓ Interactive Flashcards ✓ Full Mock Exam ✓ Essay Outlines
Explore key concepts in chemical calculations including moles, percentage yield, atom economy, and the Avogadro constant. This summary provides essential formulas and examples for Year 10/11 students in triple science, helping you understand how to calculate mass, molar mass (Mr), and the limiting reactant in chemical reactions.
ChemistryExplore the key concepts of amount of substance in A-Level Chemistry, including mole calculations, theoretical and actual yield, empirical and molecular formulas, and concentration. This summary provides essential formulas and steps for calculating moles, yields, and molarity, ensuring a comprehensive understanding of the topic. Ideal for students preparing for exams.
ChemistryDive into key concepts of A-Level Chemistry with this comprehensive summary. Explore balancing equations, mole calculations, covalent and ionic bonding, intermolecular forces, and atom economy. Perfect for exam preparation, this resource covers essential topics like Avogadro's number, percent yield, and empirical formulas, ensuring a solid foundation for your studies.
ChemistryExplore the fundamental concepts of atomic structure, isotopes, ions, and chemical formulas in this comprehensive study note. Understand the significance of isotopes, how to calculate relative atomic mass, and the formation of ions. Ideal for A-level chemistry students preparing for exams. Key topics include isotopes, ionic charges, balancing equations, and the periodic table.
ChemistryExplore the fundamentals of molarity and concentration in solutions with this detailed guide. Learn how to calculate the concentration of various solutions using molar mass and the number of moles. This resource covers key concepts such as aqueous solutions, mole calculations, and the relationship between moles, volume, and concentration. Ideal for A Level AQA Chemistry students.
ChemistryExplore the fundamentals of organic chemistry, including IUPAC nomenclature, functional groups, and reaction mechanisms. This summary covers the naming of hydrocarbons, the significance of molecular formulas, and the classification of organic compounds into homologous series. Ideal for A-level chemistry students seeking a comprehensive overview.
ChemistryApp 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
Mariya Akbar
@mariyaakbar_x
Amount of substance is one of the most practical topics in A-level chemistry - it's literally about counting atoms and molecules! Once you master these calculations, you'll be able to predict exactly how much product you'll get from any reaction.
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The mole is chemistry's way of counting particles - think of it like a dozen, but instead of 12, it's 6.02 × 10²³ particles (that's Avogadro's constant). This massive number lets us work with atoms and molecules in manageable quantities.
Two key formulas will sort most of your calculations: moles = mass ÷ Mr (where Mr is relative molecular mass) and moles = concentration × volume. These connect the microscopic world of atoms to the macroscopic measurements you can actually make in the lab.
Percentage yield tells you how efficient your reaction was - it's actual yield divided by theoretical yield, times 100. Atom economy is different - it measures how many atoms from your reactants actually end up in your desired product, helping you spot wasteful reactions.
The ideal gas equation PV = nRT connects pressure, volume, moles, and temperature for gases. Remember your units: pressure in pascals, volume in m³ or dm³, and temperature in Kelvin.
Quick tip: Always check your units match the formula - most mistakes come from mixing up dm³ and cm³!
Relative atomic mass (Ar) and relative molecular mass (Mr) compare atoms and molecules to 1/12 of a carbon-12 atom. These give you the numbers you need for the periodic table and your mole calculations.
Empirical formulas show the simplest ratio of atoms, whilst molecular formulas show the actual numbers. To find molecular formula from empirical: calculate the empirical formula's Mr, divide the actual Mr by this, then multiply all subscripts by your answer.
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.
12
Smart Tools NEW
Transform this note into: ✓ 50+ Practice Questions ✓ Interactive Flashcards ✓ Full Mock Exam ✓ Essay Outlines
Explore key concepts in chemical calculations including moles, percentage yield, atom economy, and the Avogadro constant. This summary provides essential formulas and examples for Year 10/11 students in triple science, helping you understand how to calculate mass, molar mass (Mr), and the limiting reactant in chemical reactions.
ChemistryExplore the key concepts of amount of substance in A-Level Chemistry, including mole calculations, theoretical and actual yield, empirical and molecular formulas, and concentration. This summary provides essential formulas and steps for calculating moles, yields, and molarity, ensuring a comprehensive understanding of the topic. Ideal for students preparing for exams.
ChemistryDive into key concepts of A-Level Chemistry with this comprehensive summary. Explore balancing equations, mole calculations, covalent and ionic bonding, intermolecular forces, and atom economy. Perfect for exam preparation, this resource covers essential topics like Avogadro's number, percent yield, and empirical formulas, ensuring a solid foundation for your studies.
ChemistryExplore the fundamental concepts of atomic structure, isotopes, ions, and chemical formulas in this comprehensive study note. Understand the significance of isotopes, how to calculate relative atomic mass, and the formation of ions. Ideal for A-level chemistry students preparing for exams. Key topics include isotopes, ionic charges, balancing equations, and the periodic table.
ChemistryExplore the fundamentals of molarity and concentration in solutions with this detailed guide. Learn how to calculate the concentration of various solutions using molar mass and the number of moles. This resource covers key concepts such as aqueous solutions, mole calculations, and the relationship between moles, volume, and concentration. Ideal for A Level AQA Chemistry students.
ChemistryExplore the fundamentals of organic chemistry, including IUPAC nomenclature, functional groups, and reaction mechanisms. This summary covers the naming of hydrocarbons, the significance of molecular formulas, and the classification of organic compounds into homologous series. Ideal for A-level chemistry students seeking a comprehensive overview.
ChemistryApp 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
Sociology