AQA · Chemistry · 8462
GCSE Chemistry (AQA): Limiting Reactants
Topic 3 — Quantitative Chemistry. Generated from the caption track of Cognito's lesson video "GCSE Chemistry - Limiting Reactants & Balanced Equations (2027/28 exams)"; each card deep-links to the moment in the video it came from. Lesson 3.06 of Cognito's AQA GCSE Combined Science (Trilogy) and Chemistry course (Higher tier), filed under AQA Chemistry 8462. Teaching by Cognito — https://cognitoedu.org/coursesubtopic/c2-gcse-aqa-h-c_3.06.
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In the balanced equation for sodium burning in air, the mole ratio of sodium to sodium oxide simplifies to ?.
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2:1
What does it mean for a reactant to be in excess?
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There is more of it than needed, so some is left over once the limiting reactant is used up.
When a substance is burned in air, which reactant is assumed to be in excess?
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Oxygen — there is plenty of it in the air, so the other substance is the limiting reactant.
What is a limiting reactant?
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The reactant that is completely used up in a reaction, limiting how much product can be formed.
What are the products when hydrochloric acid reacts with calcium carbonate?
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Calcium chloride, water and carbon dioxide.
How do you calculate mass from moles and Mr?
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mass = moles × Mr.
What does combustion mean in chemistry?
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Reacting with oxygen (burning in air).
Why does adding more of a reactant in excess produce no extra product?
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There is no limiting reactant left for it to react with, so the reaction cannot continue.
What is the first step in a mass-of-product calculation?
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Write out the equation for the reaction and balance it.
What is the equation for the number of moles of a substance from its mass?
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moles = mass ÷ Mr.
What is the Mr of sodium oxide, Na2O?
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62 — (2 × 23) + 16.
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