Ever wondered how chemists know exactly how much of something...
Chemistry225 views·Updated 24 Aug 2026·3 pagesComprehensive AQA Quantitative Chemistry Revision Notes
Millie@millie_rains
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1
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Chemical Groups and Their Properties
Group 1 metals get more reactive as you go down the periodic table because it becomes easier for larger atoms to lose their outer electron. These metals have lower melting and boiling points as their relative atomic mass (RAM) increases.
When Group 1 metals meet water, they create metal hydroxides and hydrogen gas. Heat them with chlorine gas, and you'll get metal chlorides instead.
Group 7 elements (halogens) work the opposite way - they become less reactive going down the group because larger atoms find it harder to gain electrons. Their melting and boiling points increase with RAM though.
Key Insight: Group 0 (noble gases) have higher boiling points as RAM increases due to stronger intermolecular forces from more electrons.
Bond breaking always requires energy (endothermic), while bond making always releases energy (exothermic). The limiting reactant determines how much product you can make - it's directly proportional to your final amount.
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Essential Definitions and Concepts
Avogadro's constant (6.02 × 10²³) tells you exactly how many particles are in one mole of any substance. Think of it as chemistry's magic number that connects the microscopic world to measurable amounts.
Concentration measures how much substance you've packed into a given volume of solution. The conservation of mass principle is beautifully simple - no atoms disappear or appear from nowhere, so your reactants' mass always equals your products' mass.
The limiting reactant is like the ingredient that runs out first when you're cooking - it completely controls how much product you can make. Other reactants are added in excess, but they can't do anything once the limiting one is gone.
Remember: Relative formula mass equals the mass of one mole of that substance in grams - this connection makes calculations much easier.
Relative formula mass is just the sum of all the relative atomic masses in a compound, giving you a direct link between molecular scale and laboratory scale.
3
of 3
Quantitative Chemistry in Practice
Conservation of mass means balanced equations aren't just neat - they're essential. No atoms vanish or appear during reactions, making the mass of reactants equal the mass of products every single time.
Sometimes you'll notice mass changes during experiments, but don't panic. If mass increases, a gas was a reactant. If mass decreases, a gas was produced and escaped. The relative formula mass of reactants always equals the relative formula mass of products.
Moles are chemistry's counting unit, measured as mass divided by Mr (or Ar for elements). One mole's mass in grams equals its relative formula mass, thanks to Avogadro's constant.
Pro Tip: The limiting reactant determines your product amount - master this concept and you'll ace stoichiometry problems.
Understanding concentration (mass per volume in g/dm³) lets you work with solutions effectively. Remember, the limiting reactant principle means the amount of this reactant directly equals the amount of product you can make.
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Chemistry225 views·Updated 24 Aug 2026·3 pagesComprehensive AQA Quantitative Chemistry Revision Notes
Millie@millie_rains
Ever wondered how chemists know exactly how much of something they've made in a reaction? Quantitative chemistry is all about the maths behind chemical reactions - from calculating masses to understanding why some reactions stop before others. It's the toolkit...
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Chemical Groups and Their Properties
Group 1 metals get more reactive as you go down the periodic table because it becomes easier for larger atoms to lose their outer electron. These metals have lower melting and boiling points as their relative atomic mass (RAM) increases.
When Group 1 metals meet water, they create metal hydroxides and hydrogen gas. Heat them with chlorine gas, and you'll get metal chlorides instead.
Group 7 elements (halogens) work the opposite way - they become less reactive going down the group because larger atoms find it harder to gain electrons. Their melting and boiling points increase with RAM though.
Key Insight: Group 0 (noble gases) have higher boiling points as RAM increases due to stronger intermolecular forces from more electrons.
Bond breaking always requires energy (endothermic), while bond making always releases energy (exothermic). The limiting reactant determines how much product you can make - it's directly proportional to your final amount.
2
of 3Sign up to see the content. It's free!
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Essential Definitions and Concepts
Avogadro's constant (6.02 × 10²³) tells you exactly how many particles are in one mole of any substance. Think of it as chemistry's magic number that connects the microscopic world to measurable amounts.
Concentration measures how much substance you've packed into a given volume of solution. The conservation of mass principle is beautifully simple - no atoms disappear or appear from nowhere, so your reactants' mass always equals your products' mass.
The limiting reactant is like the ingredient that runs out first when you're cooking - it completely controls how much product you can make. Other reactants are added in excess, but they can't do anything once the limiting one is gone.
Remember: Relative formula mass equals the mass of one mole of that substance in grams - this connection makes calculations much easier.
Relative formula mass is just the sum of all the relative atomic masses in a compound, giving you a direct link between molecular scale and laboratory scale.
3
of 3Sign up to see the content. It's free!
- Access to all documents
- Improve your grades
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By signing up you accept Terms of Service and Privacy Policy
Quantitative Chemistry in Practice
Conservation of mass means balanced equations aren't just neat - they're essential. No atoms vanish or appear during reactions, making the mass of reactants equal the mass of products every single time.
Sometimes you'll notice mass changes during experiments, but don't panic. If mass increases, a gas was a reactant. If mass decreases, a gas was produced and escaped. The relative formula mass of reactants always equals the relative formula mass of products.
Moles are chemistry's counting unit, measured as mass divided by Mr (or Ar for elements). One mole's mass in grams equals its relative formula mass, thanks to Avogadro's constant.
Pro Tip: The limiting reactant determines your product amount - master this concept and you'll ace stoichiometry problems.
Understanding concentration (mass per volume in g/dm³) lets you work with solutions effectively. Remember, the limiting reactant principle means the amount of this reactant directly equals the amount of product you can make.
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.
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