Volumetric Solutions: mol/L, Normality and the Titration Factor

Nominal concentration and lot value are different

A label such as 0.1 mol/L defines a nominal target. Actual concentration, a correction factor or measurement uncertainty may be reported separately for the relevant lot. These are different concepts: tolerance is an acceptance interval, while uncertainty concerns the information associated with a measured value.

Where the titration factor is defined as actual concentration divided by nominal concentration, actual concentration is the nominal value multiplied by the factor. Confirm the definition and validity of the factor in the product documentation and laboratory procedure.

mol/L and N are not always equal

Molarity expresses amount of substance per volume. Normality depends on the equivalence relationship for a specified reaction. A 0.1 mol/L solution therefore cannot universally be assumed to be 0.1 N; check the reaction and its stoichiometry.

When both units appear on a label, establish which definition the method uses. Entering only a numerical concentration into an instrument without checking units and reaction coefficients can create a systematic error.

Catalogue solutions can serve different roles

Hydrochloric acid, sodium hydroxide, sulfuric or acetic acid, thiosulfate and EDTA solutions belong to different titration systems. The role of sodium carbonate, sodium chloride, calcium chloride or magnesium sulfate solutions also depends on the method. They are not all interchangeable titrants for one analysis.

Documentation and use checks

• Verify the exact code, concentration and units.
• Record the lot factor, certificate date and uncertainty where provided.
• Assess storage, opening and any restandardisation need under the applicable procedure.
• Do not assume similarly named solutions are equivalent without knowing the method and reaction.
• Include pack size and minimum remaining shelf life in your quotation request.