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Britain & the wider world: 1745 -1901
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4
0
Tara Vidal
02/12/2025
Chemistry
Quantitive Chemistry
499
•
2 Dec 2025
•
Tara Vidal
@taravidal_jrny
Chemistry calculations might seem intimidating, but they're actually just straightforward... Show more
Understanding relative atomic mass is your starting point for all chemistry calculations. It's simply the average mass of an element's isotopes, weighted by how common each isotope is in nature. Don't worry about memorising actual masses - you'll always get these from the periodic table.
The relative formula mass (Mr) works exactly the same way, but for compounds instead of single elements. Just add up all the relative atomic masses of every atom in the formula. Here's the crucial bit: ignore any big numbers at the front of formulas when calculating Mr.
Your most important formula to remember is: Number of moles = Mass (g) ÷ Mr or Ar. Think of it as the "moles triangle" - cover what you want to find, and the triangle shows you what to do with the other two values.
Key Tip: Neither relative atomic mass nor relative formula mass have units - they're just numbers you can read straight from your data sheet.
Reacting masses calculations become simple when you think in moles first. The golden rule: if one mole reacts, one mole gets produced. Work out the moles of what you know, then convert back to mass for your answer.
Watch out for limiting reactants - these are the chemicals that get completely used up and stop the reaction. Any excess reactants just sit there doing nothing, so you can ignore them in your calculations.
Concentration tells you how much stuff is dissolved in a solution. You'll use two different units: g/dm³ and mol/dm³ . The formulas are concentration = mass ÷ volume and concentration = moles ÷ volume respectively.
Percentage yield compares what you actually got with what you theoretically could have got: (actual yield ÷ theoretical yield) × 100. It's always under 100% because reactions are never perfect in real life.
Remember: If your percentage yield is over 100%, you've definitely made a mistake somewhere!
Atom economy measures how much of your starting materials actually becomes useful product. It's calculated as: (Mr of desired product ÷ Mr of all products) × 100. High atom economy means less waste, which saves money and helps the environment.
Companies love reactions with high atom economy because they're not throwing away expensive raw materials. It's all about sustainability and keeping costs down in industrial processes.
For gas volume calculations, there's a brilliantly simple formula: Volume (dm³) = moles × 24. This only works at room temperature and pressure, but that's usually what exam questions assume anyway.
When you're calculating masses using concentration in mol/dm³, work in two steps: first find moles using concentration × volume, then convert to mass using moles × Mr.
Pro Tip: Always check your units match up - if concentration is in mol/dm³, make sure volume is in dm³, not cm³!
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.
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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
Tara Vidal
@taravidal_jrny
Chemistry calculations might seem intimidating, but they're actually just straightforward maths problems with atoms and molecules. Once you master a few key formulas and understand what relative masses and moles really mean, you'll breeze through these questions in your exams.
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Understanding relative atomic mass is your starting point for all chemistry calculations. It's simply the average mass of an element's isotopes, weighted by how common each isotope is in nature. Don't worry about memorising actual masses - you'll always get these from the periodic table.
The relative formula mass (Mr) works exactly the same way, but for compounds instead of single elements. Just add up all the relative atomic masses of every atom in the formula. Here's the crucial bit: ignore any big numbers at the front of formulas when calculating Mr.
Your most important formula to remember is: Number of moles = Mass (g) ÷ Mr or Ar. Think of it as the "moles triangle" - cover what you want to find, and the triangle shows you what to do with the other two values.
Key Tip: Neither relative atomic mass nor relative formula mass have units - they're just numbers you can read straight from your data sheet.
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Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Reacting masses calculations become simple when you think in moles first. The golden rule: if one mole reacts, one mole gets produced. Work out the moles of what you know, then convert back to mass for your answer.
Watch out for limiting reactants - these are the chemicals that get completely used up and stop the reaction. Any excess reactants just sit there doing nothing, so you can ignore them in your calculations.
Concentration tells you how much stuff is dissolved in a solution. You'll use two different units: g/dm³ and mol/dm³ . The formulas are concentration = mass ÷ volume and concentration = moles ÷ volume respectively.
Percentage yield compares what you actually got with what you theoretically could have got: (actual yield ÷ theoretical yield) × 100. It's always under 100% because reactions are never perfect in real life.
Remember: If your percentage yield is over 100%, you've definitely made a mistake somewhere!
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Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Atom economy measures how much of your starting materials actually becomes useful product. It's calculated as: (Mr of desired product ÷ Mr of all products) × 100. High atom economy means less waste, which saves money and helps the environment.
Companies love reactions with high atom economy because they're not throwing away expensive raw materials. It's all about sustainability and keeping costs down in industrial processes.
For gas volume calculations, there's a brilliantly simple formula: Volume (dm³) = moles × 24. This only works at room temperature and pressure, but that's usually what exam questions assume anyway.
When you're calculating masses using concentration in mol/dm³, work in two steps: first find moles using concentration × volume, then convert to mass using moles × Mr.
Pro Tip: Always check your units match up - if concentration is in mol/dm³, make sure volume is in dm³, not cm³!
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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Explore essential chemistry calculations involving moles, mass, concentration, and volume. This summary covers key concepts such as molar mass, stoichiometry, and mole conversions, providing a clear understanding of how to calculate the amounts of substances in chemical reactions. Ideal for students preparing for exams or needing a quick reference.
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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
Sociology