(Cₐ × Vₐ) ÷ a = (C_b × V_b) ÷ b — fill in every field except the one you want; the empty field is solved for.
Reaction (acid : base):
Acid concentration (Cₐ) = 0.0428 M
- Rearrange:
Cₐ = a × C_b × V_b ÷ (b × Vₐ) - Substitute:
(1) × (0.1 M) × (21.4 mL) ÷ ((2) × (25 mL))=0.0428 M
How it works
At the end point, moles of acid ÷ a = moles of base ÷ b, where a and b are the coefficients in the balanced equation. Since moles = concentration × volume, (Cₐ × Vₐ) ÷ a = (C_b × V_b) ÷ b. Volumes are converted to millilitres and concentrations to mol/L; because both volumes share a unit, you don't need to convert to litres.
Use the mean of concordant titres (within 0.10 cm³). For non-acid–base titrations — redox or precipitation — the same method works if you enter the mole ratio from the balanced equation for that reaction.
Frequently asked questions
- How do I calculate concentration from a titration?
- Find moles of the known solution (C × V), use the mole ratio to get moles of the unknown, then divide by its volume. For 25.0 mL H₂SO₄ neutralised by 21.40 mL of 0.100 M NaOH: moles NaOH = 0.002140, moles H₂SO₄ = 0.001070, so [H₂SO₄] = 0.001070 ÷ 0.0250 = 0.0428 M.
- Why does the mole ratio matter?
- Sulfuric acid releases two H⁺ ions per molecule, so it needs twice as many moles of NaOH. Ignoring the ratio would double the answer's error.
- What are concordant results?
- Titres that agree within 0.10 cm³. Average only those; discard the rough titre and any outliers.
Related
Advertisement