GCSE-ready- Home
- Lessons
- GCSE & IGCSE Chemistry
- Concentration and titrations
Concentration and titrations
🎬 The doodle video for this lesson is coming soon. Subscribe on YouTube to see it first.
A titration measures exactly how much acid reacts with an alkali, so you can work out an unknown concentration. Separate Chemistry, Higher calculations.
Concentration
concentration (g/dm3) = massvolume in dm3
concentration (mol/dm3) = molesvolume in dm3
1 dm3 = 1000 cm3, so divide cm3 by 1000.
concentration (mol/dm3) = molesvolume in dm3
1 dm3 = 1000 cm3, so divide cm3 by 1000.
The titration
Use a pipette to measure a fixed volume of alkali into a flask with an indicator.
Add acid from a burette until the indicator just changes colour (the end point).
Repeat until results are concordant (within 0.10 cm3).
Add acid from a burette until the indicator just changes colour (the end point).
Repeat until results are concordant (within 0.10 cm3).
The calculation
1. Moles of the known solution = concentration × volume (dm3).
2. Use the equation ratio to find moles of the unknown.
3. Concentration = moles ÷ volume (dm3).
Molar gas volume: 1 mole of any gas at room temperature and pressure occupies 24 dm3.
2. Use the equation ratio to find moles of the unknown.
3. Concentration = moles ÷ volume (dm3).
Molar gas volume: 1 mole of any gas at room temperature and pressure occupies 24 dm3.
25.0 cm3 of NaOH is neutralised by 20.0 cm3 of 0.100 mol/dm3 HCl. Find the NaOH concentration.
- Moles HCl = 0.100 × 0.0200 = 0.00200
- Ratio 1 : 1, so moles NaOH = 0.00200
- 0.00200 ÷ 0.0250 = 0.0800 mol/dm3
Answer: 0.0800 mol/dm3
Concentration = moles (or mass) ÷ volume in dm3. In a titration, use the burette until the end point and repeat for concordant results. Moles known → ratio → moles unknown → concentration.
Check you have got it
Answer 6 quick questions with instant marking. If you get one wrong, GCSE-ready shows you why and gives you another go. It is free, and you do not need an account.