Acid–base titrations
Introduced| English | Meaning |
|---|---|
| titration/taɪˈtreɪʃn/ | A method of finding an unknown concentration by measuring the volume needed to react with a solution of known concentration. |
| burette/bjʊəˈret/ | A graduated tube with a tap used to deliver accurately measured volumes of liquid. |
| pipette/pɪˈpet/ | pipette |
| end point/end pɔɪnt/ | The observed signal used to stop a titration, such as an indicator's colour change, which should be close to equivalence. |
| titre/ˈtɪtə/ | titre |
Measuring exactly how much
- How do you find the exact concentration of an acid or alkali? With a precise technique called a titration 滴定.
- It finds exactly when an acid and alkali have neutralised each other.
In a titration, the piece of apparatus that delivers an exact, measured volume is the:
Difficulty 1/5 · 100 coins + a small bonus on first completion today
The burette delivers a precise, variable volume.
The apparatus
- A burette 滴定管 delivers an exact, measured volume of one solution.
- A pipette 移液管 measures a fixed volume of the other into a flask.
A titration finds the exact volume of one solution that reacts with another
Acid–base titrations
pH jumps at the equivalence point
Track the pH as base is added — it leaps through neutral at the equivalence point.
The end point of a titration is shown by:
Difficulty 1/5 · 100 coins + a small bonus on first completion today
The indicator changes colour at neutralisation.
The volume of solution added from the burette is called the ______.
Difficulty 1/5 · 100 coins + a small bonus on first completion today
The titre is read from the burette.
The end point 终点
- An indicator changes colour at the end point — when neutralisation is complete.
- You record the volume of solution added from the burette (the titre 滴定量).
Solution is run from the burette into the flask until the indicator changes colour
How many moles are in 20 cm³ of acid of concentration 0.5 mol/dm³? (moles = conc × volume in dm³)
Difficulty 2/5 · 140 coins + a small bonus on first completion today
0.5 × (20 ÷ 1000) = 0.01 mol.
If 0.01 mol of alkali is in 25 cm³, what is its concentration (mol/dm³)?
Difficulty 2/5 · 140 coins + a small bonus on first completion today
0.01 ÷ (25 ÷ 1000) = 0.4 mol/dm³.
Using the result
- From the volumes and one known concentration, you calculate the unknown concentration.
- Use moles = concentration × volume and the equation's mole ratio.
Worked example. 25 cm³ of alkali is neutralised by 20 cm³ of acid of concentration 0.5 mol/dm³ (1:1 ratio). Moles of acid = 0.5 × (20 ÷ 1000) = 0.01 mol. So moles of alkali = 0.01, and its concentration = 0.01 ÷ (25 ÷ 1000) = 0.4 mol/dm³.
You've got it
- a titration finds an unknown concentration by neutralising acid with alkali
- a burette delivers a measured volume; an indicator marks the end point
- calculate using moles = concentration × volume and the mole ratio