Flask, Conical (Clear Glass)

Quick Answer: A clear glass conical flask is a flat-based, cone-shaped glass flask with a narrow cylindrical neck, used for titrations, mixing and holding solutions. The transparent wall lets students watch colour changes and dissolving solids, while the sloping sides keep the liquid in when it is swirled.

Reading Colour Changes Through a Clear Glass Wall

The conical flask is the vessel in which most school titrations finish. Its flat base stands on a white tile beneath the burette, the sloping sides turn the liquid back on itself when the flask is swirled by hand, and the narrow neck catches splashes that an open beaker would lose. In a clear glass conical flask the end point colour, such as the first permanent pink of phenolphthalein or the orange of methyl orange, can be judged against the tile without any tint from the glass.

The title names clear glass but not the glass composition. In laboratory catalogues a clear glass listing is often the ordinary soda-lime alternative to borosilicate, and soda-lime glass expands roughly three times as much as borosilicate when heated, which makes it less tolerant of sudden temperature change. That matters little for titration, mixing and room-temperature reactions, but the glass type should be confirmed before the flask is used for boiling or placed on a hot plate.

Where heating is part of the practical, the separately listed Erlenmeyer conical flask is the listing to compare. Graduation marks on conical flasks, where present, are approximate filling guides rather than measuring marks; volumes that count should come from a pipette, burette or measuring cylinder.

Care & Handling

• Swirl with the wrist while holding the neck, rather than shaking the flask up and down, so liquid is not thrown out.
• Set a warm flask on a heat-resistant mat and let it cool before washing; cold water on hot glass is a common cause of cracks.
• Remove titration residues promptly, especially permanganate stains, which clear far more easily while fresh.
• Discard any flask with a chipped rim or a star crack in the base, where stress concentrates during handling.

Specifications

Applications

• Titrating hydrochloric acid with sodium hydroxide solution, the flask standing on a white tile below the burette
• Iodine-thiosulfate and permanganate titrations, where a clear wall helps students judge a faint end point
• Rate of reaction practicals with sodium thiosulfate and acid, in which students watch a pencil cross beneath the flask disappear
• Dissolving weighed solids and mixing solutions before they are transferred to a volumetric flask

Why Choose LabEquip

Schools running class titrations need many identical flasks, and a clear body makes the end point easier for beginners to see. LabEquip supplies conical flasks within its chemistry lab equipment range; send the capacities and quantities for your practical sets through the contact page.

Frequently Asked Questions

Why use a conical flask instead of a beaker for titration?

The sloping sides and narrow neck let you swirl the solution vigorously without losing any, and drops from the burette land in a small target area. A beaker’s straight sides and wide top make splashing and loss more likely when it is swirled.

Is a clear glass conical flask suitable for heating?

Gentle warming over a gauze is usually acceptable, but ordinary soda-lime glass is more likely to crack than borosilicate if it is heated quickly or cooled suddenly. Confirm the glass type before boiling liquids in it or using a hot plate.

Can I measure volumes with the marks on a conical flask?

Treat any marks as rough filling guides only. In a titration the volume that matters is read from the burette and the aliquot is delivered by pipette, so the flask itself does not need to be accurate.

Why do I need a white tile under the flask?

A white background makes the first faint, lasting colour change easier to see, particularly with phenolphthalein, where the end point is a very pale pink. A sheet of white paper does the same job.

How do I remove brown stains left by potassium permanganate?

The brown deposit is manganese dioxide. A little acidified hydrogen peroxide or a dilute oxalic acid solution dissolves it; rinse thoroughly with tap water and then distilled water, and wear gloves and eye protection while cleaning.

Should the flask be rinsed with the solution before a titration?

No. Rinse the conical flask with distilled water only. The amount of reactant is fixed by the pipette, and rinsing with the solution would leave extra reactant behind, whereas water left in the flask does not change the number of moles present.

Last Updated: September 2026