Library / Foundations: Chemistry / FCH-14
Foundations: Chemistry
Titration calculation
Concentration of an unknown solution from the volume of a known solution needed to react with it.
- Ref
- FCH-14
- Rev
- v1
- Field
- Foundations: Chemistry
- Result
- cB [mol/dm³]
For the reaction aA + bB, c is concentration in mol/dm³ and V the volume, in any matching unit. The titre is the volume added from the burette at the end point.
Use the amount of the known solution that was needed to react exactly, and the balanced equation, to find the unknown concentration.
Calculator
- Moles of A used2.25 mmol
- Concentration of B3.6 g/dm³ if M = 40
What drives the result
Each variable is moved across its typical range while the others stay at the values above. The longest bar is the key driver.
- Take the average of concordant titres (within 0.10 cm³) before using the formula.
- A 1:2 reaction such as H₂SO₄ with NaOH must have a different a:b ratio.
Chart data as tables
Ranked variables
| Variable | Typical range | Lowest result | Highest result | Swing (mol/dm³) | Local step | Change in result |
|---|---|---|---|---|---|---|
| cA Concentration of A (burette) | 0.001 to 5 mol/dm³ | 9e-4 | 4.5 | 4.499 | +10% | +10 % |
| VB Volume of B (flask) | 1 to 100 cm³ | 0.0225 | 2.25 | 2.228 | +10% | −9.09 % |
| VA Titre (volume of A) | 1 to 100 cm³ | 0.004 | 0.4 | 0.396 | +10% | +10 % |
| b Coefficient of B | 1 to 5 | 0.09 | 0.45 | 0.36 | +10% | +10 % |
| a Coefficient of A | 1 to 5 | 0.018 | 0.09 | 0.072 | +10% | −9.09 % |
Sweep of Titre (volume of A)
| Titre (volume of A) (cm³) | Concentration of B (mol/dm³) |
|---|---|
| 1 | 0.004 |
| 1.778 | 0.007113 |
| 3.162 | 0.01265 |
| 5.623 | 0.02249 |
| 10 | 0.04 |
| 17.78 | 0.07113 |
| 31.62 | 0.1265 |
| 56.23 | 0.2249 |
| 100 | 0.4 |
Sweep one variable
Variables and how each one contributes
Concentration of B
What the equation gives you. Everything else feeds it.
Concentration of A (burette)
Concentration of the known solution. Directly proportional.
Titre (volume of A)
Volume of A needed to reach the end point. Directly proportional.
Volume of B (flask)
Volume of the unknown solution pipetted into the flask. Inversely proportional.
Coefficient of A
Balancing number of A (HCl = 1). Inversely proportional.
Coefficient of B
Balancing number of B (NaOH = 1). Directly proportional.
Worked example with the values above
- Moles of A: 0.1 × 22.5 / 1000 = 0.00225 mol.
- Moles of B: 0.00225 × (1/1) = 0.00225 mol.
- cB = 0.00225 / 0.025 dm³ = 0.09 mol/dm³.
Assumptions and limits
- The reaction goes to completion at the end point.
- The indicator changes at the equivalence point.
Common mistakes
- Ignoring the reaction ratio.
- Using a rough (first) titre in the average.
Statistics and uncertainty
A burette reading is good to ±0.05 cm³, so two readings give ±0.10 cm³; on a 22.5 cm³ titre that is about 0.4%.
Where it is used
- Acid and alkali concentration checks.
- Water and chemical quality control.
Maths you need
- Concentration: mol/dm³
- Mole ratios: balanced equation