Titration Formula

Titration Formula

A titration involves finding the unknown concentration of one solution by reacting it with a solution of known concentration. The solution of unknown concentration (the analyte) is usually placed in an Erlenmeyer flask, while the solution of known concentration (titrant) is placed in a burette. The titrant is added to the analyte until the endpoint is reached usually determined by a color change. Calculations are then performed to find the unknown concentration of the analyte. Titrations are typically performed on acid/base reactions but are not limited to them.

Macid x Vacid = Mbase x Vbase

Macid = Molarity of the acid

Vacid = Volume of the acid

Mbase = Molarity of the base

Vbase = Volume of the base

If the titrant and analyte have a 1:1 mole ratio, the equation above can be used to determine the unknown concentration, if the ratio is not 1:1 then a modified version should be used.

Titration Formula Questions:

1. Calculate the concentration of a 25 mL NaOH solution if 35 mL of 1.25 M HCl is needed to titrate to the equivalence point.

NaOH + HCl → NaCl + H2O

Answer:

In this equation the mole ratio of NaOH (base) and HCl (acid) is 1:1 as determined by the balanced chemical equation. The equivalence point is where the moles of titrant and analyte in the reaction are equal.

Macid x Vacid = Mbase x Vbase

1.25 x 35 = Mbase x 25

43.75 = Mbase x 25

1.75 = Mbase

2. Calculate the concentration of a 35.24 mL Ca(OH)2 solution if 28.35 mL of 1.21 M HNO3 is needed to titrate to the equivalence point.

Ca(OH)2 + 2HNO3 → Ca(NO3)2 + 2H2O

Answer:

In this equation the mole ratio of acid (HNO3) and base (Ca(OH)2) is 2:1. In this case a modified version of the Macid x Vacid = Mbase x Vbase equation is required.

2 x Macid x Vacid = Mbase x Vbase

2 x 1.21 x 28.35 = Mbase x 35.24

68.61 = Mbase x 35.24

1.95 = Mbase

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