Flask, Boiling, Flat Bottom

Quick Answer: A flat bottom flask is a round-bodied glass boiling flask with a flattened base, so it stands upright on a bench, gauze or hot plate without a support ring. It is used for heating liquids, preparing solutions and generating gases in simple set-ups.

A Boiling Flask That Stands on Its Own

This flask combines the round body of a boiling flask with a base flattened enough to stand on. That makes it convenient in school laboratories: it can sit on a gauze over a tripod, on a bench mat while a bung is fitted, or on a hot plate, without the clamps and cork rings a round-based flask needs.

It is the generating flask in many classic gas preparations. Fitted with a two-hole bung carrying a thistle funnel and a delivery tube, it produces hydrogen from zinc and dilute sulfuric acid, or carbon dioxide from marble chips and dilute hydrochloric acid, with acid added through the funnel as needed. It is equally at home boiling water in heat experiments or dissolving solids with warming.

The flattened base is also its limitation. A flat glass surface is weaker under a pressure difference than a sphere and heats less evenly, so the flask should not be used under vacuum or for heating to dryness. For reduced-pressure distillation or long, strong heating, a round bottom flask is the right choice. Capacity and glass type are not given in the listing.

Applications

• Gas generation with a thistle funnel and delivery tube for hydrogen or carbon dioxide
• Heating water or solutions over a tripod and gauze
• Dissolving solids with gentle warming when preparing solutions
• Simple distillation demonstrations at atmospheric pressure, with the flask clamped at the neck

Specifications

Care & Handling

• Always put the flask on a wire gauze when using a burner; a direct flame on the flat base causes hot spots and cracks.
• Clamp the neck as well when a bung, funnel and tubing are fitted, as the loaded flask can topple.
• Never connect this flask to a vacuum pump.
• Cool the flask gradually on a heat-resistant mat, not on a cold, wet bench.

Why Choose LabEquip

Schools set up flat-based flasks for gas preparations and heating practicals where a self-standing vessel keeps the apparatus simple. LabEquip lists it in the chemistry lab equipment range; send the capacities you need through the contact page.

Frequently Asked Questions

What is the difference between a flat bottom and a round bottom flask?

A flat bottom flask stands on its own and suits simple heating and gas preparation. A round bottom flask needs a clamp or cork ring but heats more evenly and withstands vacuum and prolonged strong heating better.

Can a flat-based flask be used for vacuum distillation?

No. The flat base is weaker than a curved surface under a pressure difference and could implode. Use a round-based flask for any work under reduced pressure.

Why does a thistle funnel have to dip below the liquid?

If the lower end of the funnel is above the liquid, the gas produced escapes up through the funnel instead of the delivery tube. Keeping it below the surface forms a seal while still letting acid be added.

Can the flask be heated on a hot plate?

Yes, the flat base sits well on a hot plate. Heat gradually and do not let the flask boil dry, since the base can crack when it overheats without liquid in it.

How much liquid should be put in for boiling?

Fill it no more than about half full and add a few anti-bumping granules before heating. This leaves room for boiling and reduces the chance of sudden, violent boiling.

Can it be used instead of a conical flask in titrations?

It can hold the solution, but a conical flask is preferred because its sloping sides let the liquid be swirled vigorously without splashing out. The rounded shoulder of a boiling flask spills more easily when swirled.

Last Updated: September 2026