Titrations, stoichiometry and end-point evidence

Titrations, stoichiometry and end-point evidence

A titration uses a solution of known concentration to determine an unknown concentration or amount through a balanced reaction. First write the balanced equation and identify the mole ratio. Convert measured volume to dm³, calculate moles of the known solution using n = cV, use the coefficient ratio, then calculate the required concentration or volume. An indicator end point signals a visible colour change near the equivalence point, but the two are not identical concepts. Good technique includes rinsing apparatus with appropriate solution, reading the meniscus at eye level, repeating concordant titres and recording units.

Work it through

25.0 cm³ of 0.100 mol dm⁻³ HCl contains n = 0.100 × 0.0250 = 0.00250 mol HCl. For HCl + NaOH → NaCl + H₂O, the ratio is 1:1, so 0.00250 mol NaOH is required. If the NaOH is also 0.100 mol dm⁻³, V = n/c = 0.00250/0.100 = 0.0250 dm³ = 25.0 cm³.

Mastery target

Plan or complete a simple acid-base titration calculation with a balanced equation, mole ratio, volume conversion, evidence of precision and a sensible final unit.