Round-bottom flasks

A single-neck flask is the standard for distillation, rotary evaporation and collecting fractions, for example the round-bottom flask, 500 ml, NS 29/32. A second neck lets you add a dropping funnel, gas inlet or thermometer while a condenser sits on the centre neck, as on the two-neck flask, 500 ml, NS 29/32 centre and NS 14/23 side neck. Three necks are the usual choice for synthesis with an overhead stirrer, condenser and addition funnel at once, such as the three-neck flask, 1000 ml, with side necks angled at 20°.

The joint must match the rest of your apparatus. NS 29/32 is the most common size for flasks of 250 ml and up, as on the round-bottom flask, 1000 ml, NS 29/32. Smaller flasks often have NS 24/29 or NS 19/26, for example the 250 ml flask, NS 24/29 or the 100 ml flask, NS 19/26. On multi-neck flasks the side necks are often smaller than the centre neck, or the same size, as on the three-neck flask, 500 ml, all necks NS 29/32. Adapters are in distillation heads, adapters and columns.

Choose a flask about twice the volume of your liquid. For distillation and rotary evaporation, fill it to no more than half, so the liquid has room to boil without bumping into the condenser. That means a 1000 ml flask for roughly 500 ml of solution. For reactions, leave space for foaming, gas formation and additions during the run. A flask that is too large, on the other hand, loses heat and leaves residue spread thinly over the wall. For light-sensitive compounds, there are amber flasks, such as the amber round-bottom flask, 500 ml, NS 29/32.

The safest way is a heating mantle sized to the flask volume: it surrounds the round bottom evenly and avoids hot spots. A heating mantle for a 500 ml flask does not fit a 1000 ml flask properly, so match the size. Oil or water baths also give even heat and let you stir with a magnetic stirrer underneath. Never put a round-bottom flask directly on a flat hotplate: contact is too small and the glass heats unevenly. Clamp the flask at the neck and add boiling stones or a stir bar to prevent bumping. Questions about a setup? sales@luminixhealth.com.

A round-bottom flask is the heating flask of a distillation or a reflux. The curved wall takes the heat, and the ground neck connects to a still head or a condenser. The joint size, not only the volume, has to match the rest of the set.

A beaker is an open working vessel: easy to pour, poor as a measure. An Erlenmeyer flask has a flat base and a conical wall so a liquid can be swirled without climbing out. A round-bottom flask is for heating under a condenser, because the heat meets a curved wall and the joint at the neck connects to the rest of the glassware. Borosilicate is the glass that survives the temperature change. These forms are listed under ISO laboratory glassware.

This shelf belongs to Beakers & flasks, inside Labware. Luminix Health distributes this range for laboratory use.

The neighbouring shelves are Beakers, Erlenmeyer flasks, Reaction vessels & jacketed vessels, Flat-bottom flasks, Flasks (other) and Beaker & flask accessories. The category above this shelf is Beakers & flasks.

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