Round-bottom flask
A round-bottom flask is a glass ball with a long neck.
What is it for?
Its round shape spreads heat evenly, so chemists use it to boil liquids and to make new substances.
How to use it
It cannot stand up on its own, so it sits in a cork ring or is held by a clamp on a stand.
🥽 Safety tip: Always clamp it firmly before heating it, and only fill it about half full.
Fun fact from Fizzy: A round shape is stronger than a flat one, so these flasks are also used when air is sucked out of them.
A closer look
A round-bottom flask has no flat side, so heat reaches every part of the glass in the same way. That stops hot spots forming, which is why it is the favourite flask for long, gentle boiling.
It is often heated in a heating mantle, a soft bowl-shaped heater that hugs the round glass, or in a pan of warm water. Chemists can also fit a tube called a condenser on top, which cools the steam back into liquid so nothing boils away.
Where you would see one
You will find round-bottom flasks mostly in university and company labs, where chemists make new medicines, dyes and plastics. They come in sizes from a few millilitres to many litres.