Neutralisation and titration curves
| English | Chinese | Pinyin |
|---|---|---|
| titration | 滴定 | dī dìng |
| neutralisation | 中和 | zhōng hé |
| indicator | 指示剂 | zhǐ shì jì |
| salt | 盐 | yán |
| end point | 终点 | zhōng diǎn |
Following a titration 滴定
- Neutralisation 中和 reacts an acid with an alkali.
- A titration follows the pH as you add one to the other.
- The curve guides which indicator 指示剂 to use.
An indicator is used to find the end point of a titration.
It changes colour at neutralisation.
Neutralisation
- The hydrogen ions from the acid react with the hydroxide ions from the alkali:
- A salt 盐 is also formed, from the rest of the acid and base.
Titration curves have a steep jump near the end point 终点; pick an indicator that changes inside it
Titration curves
pH jumps at the equivalence point
Adding base nudges the pH, then it jumps sharply through pH 7 at the equivalence point.
The ionic equation for neutralisation is:
Hydrogen ions from the acid combine with hydroxide ions from the alkali to make water (plus a salt).
The titration curve
- The curve has a steep, almost vertical jump near the end point.
- Its exact shape depends on whether each reactant is strong or weak.
A titration curve has:
Near the end point the pH changes very rapidly, giving a steep jump on the curve.
For a weak acid with a strong base, the indicator should change colour in the:
The weak-acid/strong-base jump sits at higher pH, so the indicator must change in that range.
Match each titration idea to its meaning.
Each item links the term to its correct meaning.
Choosing an indicator
- Pick an indicator whose colour change falls inside the steep jump.
- For a weak acid with a strong base, you need one that changes in the higher pH range.
A suitable indicator is one whose colour change:
The indicator must change colour within the steep jump so the end point is shown sharply.
You've got it
- neutralisation: $\text{H}^{+} + \text{OH}^{-} \rightarrow \text{H}_2\text{O}$, also forming a salt
- a titration curve has a steep pH jump at the end point (shape depends on strong/weak)
- choose an indicator that changes colour inside the jump (higher pH for weak acid + strong base)