Polypropylene volumetric flask, 250 ml

A polypropylene volumetric flask of 250 ml is a vessel with a single calibration mark on the neck, intended for preparing a solution of defined concentration. Here the plastic replaces glass wherever the risk of breakage is real and the solution is aqueous. A general-purpose laboratory product from the Laboratory accessories category.

Work with a volumetric flask follows a fixed order: the weighed portion or the aliquot of stock solution goes into the flask, is dissolved in a smaller amount of solvent, and is only then made up to the mark. That way the final volume of the whole solution is known, which is exactly what a concentration calculation requires. A single mark gives better accuracy than a graduation across the whole height, because it is calibrated for one specific volume. A capacity of 250 ml serves series of dilutions and the preparation of stock solutions for further work.

Volumetric ware is calibrated at a stated temperature, usually 20 °C, and the manufacturer gives it together with the tolerance; the solution is therefore made up once the temperature has equalised, not straight after dissolving, which can release heat. A volumetric flask is never heated or dried at raised temperature, because that changes its calibration. The meniscus is set with its lower edge on the mark, with the eye level with it. Polypropylene tolerates acids, alkalis and autoclaving under the conditions the manufacturer states, yet with strong oxidisers and some organic solvents glass is the better choice.

• Name and variant: volumetric flask with a single calibration mark
• Capacity: 250 ml
• Material: polypropylene (PP)

Why does the flask have only one mark?

Because it is calibrated for one volume and is at its most accurate at that single point. Measuring other volumes with the same flask makes no sense; that is what a measuring cylinder is for.

Can a PP flask be autoclaved?

Yes, under the conditions stated by the manufacturer of the item. Repeated thermal cycles can affect the geometry of the plastic, so a flask that has been autoclaved is checked from time to time.

Can a solution be heated in a volumetric flask?

No. Heating and drying at raised temperature change the volume of the vessel and with it the calibration. Where dissolving releases heat, the temperature is left to equalise before the flask is made up to the mark.