Quantitative chemistry is all about the maths behind chemical reactions...
Chemistry747 views·Updated Jun 8, 2026·2 pagesAQA Chemistry Topic 3: Mastering Quantitative Chemistry
tay@taylb
1
of 2
Chemical Formulae and the Mole Concept
Writing chemical formulae is like balancing a budget - the charges must always cancel out to zero. Group numbers tell you an element's charge , and don't forget about polyatomic ions like hydroxide (OH⁻) and nitrate (NO₃⁻).
The mole is chemistry's way of counting particles - one mole contains 6.022 × 10²³ particles (Avogadro's number). Think of it like a dozen, but much bigger! You'll use the formula N = n × Nₐ to convert between moles and actual particle numbers.
Relative atomic mass (Ar) is the number at the top of each element on the periodic table, whilst relative formula mass (Mr) is the total mass of all atoms in a compound. For H₂O: Mr = 16 + (1×2) = 18 g/mol.
Key Formula Triangle: Remember Mass = Moles × Mr. Cover what you want to find, and the triangle shows you the calculation!
The conservation of mass means atoms can't disappear - whatever goes into a reaction must come out, just rearranged differently.
2
of 2
Calculations and Practical Applications
Reacting masses follow a simple four-step process: calculate moles of known substance, find the ratio from the balanced equation, work out moles of unknown substance, then calculate its mass. It's like following a recipe - the equation tells you the proportions.
Limiting reactants determine how much product you can actually make. Calculate moles of each reactant, see which runs out first, and that's your limiting factor. Think of it like making sandwiches - if you have 10 slices of bread but only 3 slices of cheese, cheese limits how many you can make.
Percentage yield compares what you actually get versus what you should theoretically get. It's rarely 100% because reactions aren't perfect - some product gets left behind or side reactions occur.
Titration Tip: Always write the balanced equation first, identify the mole ratio, then work through the formula step by step.
Atom economy measures how efficiently a reaction uses its starting materials - higher percentages mean less waste and better environmental impact.
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Chemistry747 views·Updated Jun 8, 2026·2 pagesAQA Chemistry Topic 3: Mastering Quantitative Chemistry
tay@taylb
Quantitative chemistry is all about the maths behind chemical reactions - calculating masses, moles, and concentrations. It's essentially the toolkit you need to predict how much of each substance you'll need or produce in any chemical reaction.
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Chemical Formulae and the Mole Concept
Writing chemical formulae is like balancing a budget - the charges must always cancel out to zero. Group numbers tell you an element's charge , and don't forget about polyatomic ions like hydroxide (OH⁻) and nitrate (NO₃⁻).
The mole is chemistry's way of counting particles - one mole contains 6.022 × 10²³ particles (Avogadro's number). Think of it like a dozen, but much bigger! You'll use the formula N = n × Nₐ to convert between moles and actual particle numbers.
Relative atomic mass (Ar) is the number at the top of each element on the periodic table, whilst relative formula mass (Mr) is the total mass of all atoms in a compound. For H₂O: Mr = 16 + (1×2) = 18 g/mol.
Key Formula Triangle: Remember Mass = Moles × Mr. Cover what you want to find, and the triangle shows you the calculation!
The conservation of mass means atoms can't disappear - whatever goes into a reaction must come out, just rearranged differently.
2
of 2Sign up to see the content. It's free!
- Access to all documents
- Improve your grades
- Join milions of students
Calculations and Practical Applications
Reacting masses follow a simple four-step process: calculate moles of known substance, find the ratio from the balanced equation, work out moles of unknown substance, then calculate its mass. It's like following a recipe - the equation tells you the proportions.
Limiting reactants determine how much product you can actually make. Calculate moles of each reactant, see which runs out first, and that's your limiting factor. Think of it like making sandwiches - if you have 10 slices of bread but only 3 slices of cheese, cheese limits how many you can make.
Percentage yield compares what you actually get versus what you should theoretically get. It's rarely 100% because reactions aren't perfect - some product gets left behind or side reactions occur.
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