Although there are many types of flasks used in chemistry, the most common is probably the Erlenmeyer flask. Erlenmeyer flasks have narrow openings, a conical shape and a wide flat bottom.
Due to the shape, Erlenmeyer flasks are good reaction and storage vessels. They may be used for swirling liquids safely without spilling and are commonly used in titrations. They also work well for heating liquids since the conical shape allows vapors to condense on the upper section of the flask, reducing solvent loss. The narrow opening may be stoppered for chemical storage and is shaped appropriately to supports funnels during filtering processes.
Erlenmeyer flasks come in various sizes with varying graduations. Like beakers, they are not well suited for precise volumetric measurement as their graduations are only accurate to about 5 - 10% of their marked values.
Filter Flasks (Büchner Flasks)
Filter flasks are essentially Erlenmeyer flasks with a small vacuum port incorporated into the neck of the flask. The vacuum port allows mixtures to be filtered quickly.
A special funnel (Büchner funnel) is fitted with filter paper and placed in the top of the flask. A vacuum pump attached to the side port draws air from the flask and allows atmospheric pressure to quickly push the liquid portion of a mixture through the paper. The solid portion collected on the filter paper is called 'filter cake' and the liquid portion that flows into the flask is called 'filtrate'.
Florence Flasks (Boiling Flasks)
Florence Flasks have a wide spherical body and long narrow neck. They may have a flat or rounded bottom.
Florence flasks are used strictly as reaction vessels. While they are rated for containing particular volumes of liquids, they are not graduated.
Their shape makes them safe for swirling reactants during a reaction and allow for uniform heating of liquids. Frequently, they are used when one wants to capture the vapors/gases produced during a process as in distillation.
Florence flasks are sometimes modified by the addition of side ports that allow the addition of reactants during a process.
Volumetric Flasks (Measuring Flasks)
Volumetric flasks are similar in shape to Florence flasks with a large pear-shaped bottom, flat base, and long narrow neck with a single graduation mark. They are used exclusively for the preparation of solutions.
Volumetric flasks come in a a variety of sizes, but each is precisely calibrated to contain only a single volume of solution. Common sizes are 1000mL, 500mL, 250mL, 100mL and 50mL. The narrow neck provides a higher level of precision than can be accomplished in other types of glassware of similar volume. The marking on the neck indicates the volume of liquid contained when filled up to that point. Volumetric flasks are typically accurate to 1% of their total volume.
Because temperature changes cause alter the structure of glass by causing it to expand or contract, volumetric flasks are never used for heating. The narrow opening allows the flask to be stoppered for mixing or short term storage.