How To Do Titration Calculations

A titration is a technique used to work out the concentration of an unknown solution based on its chemical reaction with a solution of known concentration. The process usually involves adding the known solution (the titrant) to a known quantity of the unknown solution (the analyte) until the reaction is complete. To calculate the concentration of the analyte, you measure the volume of titrant used.

1. Prepare the Concentrations

Place the analyte in an Erlenmeyer flask (a conical flat-bottomed laboratory flask with a narrow neck). Place the titrant in a burette (a graduated glass tube with a tap at one end).

2. Mix the Concentrations

Add the titrant to the analyte until the endpoint is reached. This is often indicated by a color change, for example by adding a few drop of phenolphthalein, a commonly used acid‑base indicator, which changes from pink in alkali to colorless in acid.

3. Calculate the Molarity

Use the titration formula. If the titrant and analyte have a 1:1 mole ratio, the formula is molarity (M) of the acid x volume (V) of the acid = molarity (M) of the base x volume (V) of the base. (Molarity is the concentration of a solution expressed as the number of moles of solute per litre of solution.)

If the ratio is not 1:1, use a modified version of the formula. For example, if 35 ml of 1.25 M hydrochloric acid (HCI) is needed to titrate a 25 ml solution of sodium hydroxide (NaOH) to the equivalence point, you can work out the concentration of NaOH using the 1:1 ratio formula, because hydrochloric acid and sodium hydroxide have a 1:1 mole ratio (one mole of HCl reacts with one mole of NaOH).

Multiply the molarity of the acid by the volume of the acid (1.25 x 35). Then take this answer (43.75) and divide it by the volume of the base (25). The answer is 1.75 M, which is the molarity of the base.