How It Works: The Endpoint Tells You the Exact Ratio
Part of Titrations (HT) — GCSE Chemistry
This how it works covers How It Works: The Endpoint Tells You the Exact Ratio within Titrations (HT) for GCSE Chemistry. Revise Titrations (HT) in Quantitative Chemistry for GCSE Chemistry with 22 exam-style questions and 20 flashcards. This topic appears regularly enough that it should still be part of a steady revision cycle. It is section 3 of 13 in this topic. Use this how it works to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 3 of 13
Practice
22 questions
Recall
20 flashcards
⚙️ How It Works: The Endpoint Tells You the Exact Ratio
The key idea behind titration is that neutralisation happens in a fixed mole ratio. For hydrochloric acid reacting with sodium hydroxide, the ratio is exactly 1:1. For sulfuric acid and sodium hydroxide, it is 1:2. The balanced equation tells you this ratio.
When you add acid from the burette to alkali in the conical flask, the acid is neutralising the alkali molecule by molecule. At the equivalence point (also called the endpoint), every mole of acid has been matched by exactly the right number of moles of alkali. At this moment, the solution changes pH sharply — and the indicator detects this sharp change by changing colour.
Because the volume of alkali in the flask is fixed (measured by the pipette), and the concentration of acid in the burette is known, measuring the exact volume of acid added (the titre) gives you all the information you need. You can then calculate: n(acid) = c × V, then use the mole ratio to find n(alkali), then use c = n ÷ V to find the unknown concentration of alkali.
Concordant results (repeats within 0.10 cm³ of each other) confirm the endpoint was found accurately each time, removing the effect of random errors.