A-Level AQA Titration Calculations: Formula and Examples

This AQA A-level chemistry titration calculator finds the unknown concentration of an acid or base from the measured titre, the known solution concentration, and the balanced equation’s mole ratio. Enter volumes in mL, concentrations in mol/L, and the coefficients for the known and unknown reactants; it returns the unknown concentration in mol/L.

Formula

At the equivalence point, reacting amounts follow the coefficients in the balanced equation. The calculator uses:

c_u = c_k × (V_k / 1000) × (ν_u / ν_k) ÷ (V_t / 1000)

• c_u is the unknown solution concentration, in mol/L.
• c_k is the known solution concentration, in mol/L.
• V_k is the volume of known solution used, in mL.
• V_t is the titre, the volume of unknown solution delivered, in mL.
• ν_k and ν_u are the balanced-equation coefficients for the known and unknown reactants.

The factor 1000 converts each volume from mL to L before calculating amount in moles. The coefficient ratio is essential when the reaction is not 1:1. The calculator assumes the entered titre is the volume of unknown solution that reacts with the entered known-solution volume.

Worked Example

Using the calculator’s defaults, 25 mL of 0.100 mol/L known solution reacts with a 24.8 mL titre of unknown solution. Both coefficients are 1.

1. Convert the volumes: 25 mL / 1000 = 0.025 L and 24.8 mL / 1000 = 0.0248 L.
2. Find the known reactant amount: 0.100 mol/L × 0.025 L = 0.00250000 mol.
3. Apply the coefficient ratio: 0.00250000 mol × (1 / 1) = 0.00250000 mol of unknown reactant at equivalence.
4. Divide by the unknown solution volume: 0.00250000 mol / 0.0248 L = 0.10080645 mol/L.

To four decimal places, the unknown concentration is 0.1008 mol/L. The unrounded value is approximately 0.10080645 mol/L; the calculator displays the concentration to four decimal places.

Assumptions

• The balanced equation correctly represents the reaction, and its coefficients are entered as positive numbers.
• The titre and known-solution volume refer to the reactant volumes that meet at the equivalence point.
• The reaction proceeds quantitatively according to the equation; no side reaction consumes either reactant.
• Volumes are measured in mL and converted to L using / 1000. Concentrations are in mol/L.
• This is study and lab-planning arithmetic, not a substitute for experimental readings or an assessed practical method.

How A-Level Titration Calculations Work

A titration uses a solution of known concentration to determine the concentration of another solution. In an acid–base titration, a measured volume of one solution is added to the other until the reaction reaches its endpoint, commonly indicated by a suitable indicator changing colour. The endpoint is an observable signal used to estimate the equivalence point, where the reactants have combined in the exact ratio in the balanced equation.

AQA A-level questions typically test a chain of linked ideas: convert volume to dm³ (the same volume unit as L), calculate moles with n = cV, apply the reaction ratio, then calculate an unknown concentration or another requested quantity. The calculator combines those steps when the target is the unknown concentration. In written exam working, showing the individual steps makes it easier to identify a unit or ratio error and earn method marks.

For example, hydrochloric acid and sodium hydroxide react in a 1:1 ratio: HCl + NaOH → NaCl + H₂O. Sulfuric acid and sodium hydroxide react in a 1:2 ratio: H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O. If sulfuric acid is the known solution and sodium hydroxide is unknown, enter coefficients 1 for the known acid and 2 for the unknown base. The amount of base at equivalence is twice the amount of acid.

Using the Calculator and Choosing the Ratio

• Balance the reaction first, including the states or ionic form if your question requires it.
• Identify which reactant is the known solution and which is unknown. Enter the known solution’s concentration and the volume of it used.
• Enter the titre for the unknown solution and the coefficients belonging to each reactant. Do not swap the known and unknown coefficients.
• Check the returned concentration’s units and significant figures against the question. Keep extra digits during working, then round at the end as instructed.

Some exam questions provide repeated titres. A rough first run may be a trial, while concordant titres are close results judged using the practical’s stated tolerance. If the question instructs you to average concordant readings, calculate the mean titre before using it; do not automatically average every reading, especially where one result is an obvious rough outlier.

Common Mistakes and Checks

The most frequent error is using a volume in mL directly in n = cV when concentration is in mol/L. Convert mL to L by dividing by 1000. Since both volumes in the calculator are converted in the same way, the conversion factors cancel algebraically in the final concentration ratio, but they are included explicitly to keep the mole calculation correct and clear.

Another common mistake is assuming every neutralisation is 1:1. The equation, not the labels “acid” and “base,” determines the mole ratio. For polyprotic acids or bases with more than one reactive hydroxide ion, use the balanced equation for the actual reaction being tested. A wrong coefficient can produce a neat-looking but systematically incorrect answer.

Do not confuse the endpoint with a perfectly exact equivalence point. Indicator choice, drop size, reading the burette, and overshooting can affect the titre. Read a burette at eye level, record its scale readings to the precision required by the practical, and subtract the initial reading from the final reading to obtain the volume delivered. Follow your lab method, the safety data sheet (SDS) and your supervisor.

What the Result Does—and Does Not—Tell You

The result is the concentration implied by the entered measurements and reaction stoichiometry. It does not correct inaccurate measurements, an unsuitable indicator, contaminated solutions, or a reaction that does not go to completion. A calculator cannot decide whether two titres are sufficiently concordant or whether a particular indicator is appropriate; those decisions depend on the procedure and the chemistry.

Pay attention to precision. A result such as 0.1008 mol/L should not imply greater experimental certainty than the titre and standard-solution concentration support. In calculations, retain digits until the final line; in reporting, use appropriate significant figures and any rounding rule given by the exam question. If a question asks for mass, pH, or percentage composition rather than concentration, continue from the mole amount using the relevant equation instead of treating this calculator’s concentration output as the final answer.

Frequently Asked Questions

How do you calculate concentration from a titration?
Calculate moles of the known reactant using n = cV, with volume in L. Use the balanced equation’s coefficient ratio to find moles of the unknown, then divide by the unknown solution volume in L.

Do I use cm³ or dm³ in AQA titration calculations?
Either can describe a volume, but if concentration is in mol/dm³, convert volume to dm³ before using n = cV. Divide cm³ by 1000; 1 dm³ equals 1000 cm³ and is equivalent to 1 L.

How do I know which mole ratio to use?
Balance the chemical equation and compare the coefficients of the two reacting substances. Use unknown coefficient divided by known coefficient when converting known moles into unknown moles.

Is the titre the same as the endpoint?
No. The titre is the measured volume delivered from a burette. The endpoint is the observed signal, such as an indicator colour change, used to identify when the reaction is close to equivalence.

Should I average all my titration results?
Use the procedure or question’s rule. Usually, a rough trial is not included in the mean, and concordant titres are averaged; do not discard a reading without a stated or justified reason.

Related

• Equivalents From Moles: Calculate and Convert
• Titration Calculations A Level: Formula and Example
• Scientific Calculator for Moles: Formula and Examples

in vk | Known-solution volume | mL | 25 | 0
in ck | Known-solution concentration | mol/L | 0.1 | 0
in vt | Titre of unknown solution | mL | 24.8 | 0
in nk | Known reactant coefficient | - | 1 | 0
in nu | Unknown reactant coefficient | - | 1 | 0
out cu | Unknown concentration | mol/L | ck * (vk / 1000) * (nu / nk) / (vt / 1000) | 4
out nknown | Known reactant amount | mol | ck * (vk / 1000) | 6
out nunknown | Unknown reactant amount at equivalence | mol | nknown * (nu / nk) | 6