Chemical calculations might seem intimidating, but they're actually just about...
Chemistry326 views·Updated 31 Aug 2026·2 pagesMaster Chemistry Triple GCSE: Chemical Calculations with Mass
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Conservation of Mass and Apparent Mass Changes
Here's something that might blow your mind: atoms can never be created or destroyed during chemical reactions - they just get shuffled around like pieces in a jigsaw puzzle! This is called the conservation of mass, and it means the total mass before a reaction should equal the total mass after.
But wait - sometimes your scales might tell a different story. If you're doing a reaction and the mass seems to decrease, don't panic! This usually happens when one of your reactants is a gas that escapes into the air.
Take sodium reacting with chlorine gas to make salt (sodium chloride). Your sodium starts off light, but the final salt weighs more because invisible chlorine atoms from the air have joined the party. It's like watching a dance where invisible partners suddenly become visible!
Key Tip: If mass appears to change, look for gases entering or leaving the reaction - they're the usual suspects!
2
of 2
Excess and Limiting Reactants
Imagine making sandwiches with 10 slices of bread but only 3 slices of cheese - you'll run out of cheese first! Chemical reactions work exactly the same way. The limiting reactant is like your cheese - it runs out first and stops the whole reaction. The excess reactant is your leftover bread.
To figure out which is which, you need to play detective with a simple 5-step process. Start by writing your balanced symbol equation, then pick one reactant and use the equation's ratio to calculate how much of the other reactant you actually need.
The magic happens when you compare what you need versus what you've got. If you need 5g but have 8g, that reactant is in excess. The one that doesn't have enough becomes your limiting reactant - and that's what determines how much product you'll make.
Remember: The limiting reactant is like the bottleneck in your reaction - it controls everything!
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Chemistry326 views·Updated 31 Aug 2026·2 pagesMaster Chemistry Triple GCSE: Chemical Calculations with Mass
I
isaac@isaac_pcpe
Chemical calculations might seem intimidating, but they're actually just about keeping track of atoms and making sure everything adds up correctly. Understanding how mass works in reactions and identifying which chemicals run out first are essential skills that'll pop up...
1
of 2
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Conservation of Mass and Apparent Mass Changes
Here's something that might blow your mind: atoms can never be created or destroyed during chemical reactions - they just get shuffled around like pieces in a jigsaw puzzle! This is called the conservation of mass, and it means the total mass before a reaction should equal the total mass after.
But wait - sometimes your scales might tell a different story. If you're doing a reaction and the mass seems to decrease, don't panic! This usually happens when one of your reactants is a gas that escapes into the air.
Take sodium reacting with chlorine gas to make salt (sodium chloride). Your sodium starts off light, but the final salt weighs more because invisible chlorine atoms from the air have joined the party. It's like watching a dance where invisible partners suddenly become visible!
Key Tip: If mass appears to change, look for gases entering or leaving the reaction - they're the usual suspects!
2
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Excess and Limiting Reactants
Imagine making sandwiches with 10 slices of bread but only 3 slices of cheese - you'll run out of cheese first! Chemical reactions work exactly the same way. The limiting reactant is like your cheese - it runs out first and stops the whole reaction. The excess reactant is your leftover bread.
To figure out which is which, you need to play detective with a simple 5-step process. Start by writing your balanced symbol equation, then pick one reactant and use the equation's ratio to calculate how much of the other reactant you actually need.
The magic happens when you compare what you need versus what you've got. If you need 5g but have 8g, that reactant is in excess. The one that doesn't have enough becomes your limiting reactant - and that's what determines how much product you'll make.
Remember: The limiting reactant is like the bottleneck in your reaction - it controls everything!
We thought you’d never ask...
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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ChemistryA-level OCR A Chemistry summary sheets
Everything from snaprevise for OCR chemistry a-level
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Explore the fundamentals of redox reactions, including oxidation states, definitions of oxidation and reduction, and the roles of oxidizing and reducing agents. This summary covers key rules for determining oxidation states, the concept of disproportionation, and practical applications in chemical equations. Ideal for A-Level Chemistry students preparing for exams.
126,371320
ChemistryEssential Chemistry Practicals
Explore key AQA GCSE Chemistry practicals, including flame tests, titration, and gas identification. This resource covers essential techniques for analyzing ions, making salts, and understanding reaction kinetics. Perfect for students preparing for exams and practical assessments.
1011,991902
ChemistryAcids, Bases & Salts Overview
Explore the essential concepts of acids, bases, and salts, including acid-base reactions, neutralization processes, and methods for making soluble salts. This summary covers key definitions, pH levels, and indicators, providing a comprehensive understanding for GCSE students. Ideal for exam preparation and quick revision.
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Students love us — and so will you.
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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 SiOS user
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Samantha KlichAndroid user
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AnnaiOS user