Which laboratory glassware is commonly used to heat liquids over an open flame?

Flasks are commonly used to heat liquids over an open flame due to their specific design and material properties. They generally have thicker glass than other types of laboratory glassware, which allows them to withstand the thermal stress caused by a direct flame. The shape of flasks, especially round-bottom flasks, allows for even heating of the liquids inside, making them suitable for reactions that require controlled heating.

Additionally, flasks often come with necks that can accommodate stoppers or tubing for gas in or out. This is particularly useful in chemical reactions where gas production or absorption occurs. The use of a flat bottom of certain flasks also allows them to sit stably on a heat source without tipping over.

When considering other types of glassware, test tubes, beakers, and pipettes are not designed for heating over an open flame. Test tubes may be used for small-scale reactions but typically require a test tube holder for heating rather than direct flame exposure. Beakers, while they can withstand heat, are primarily used for mixing and pouring rather than heating over a flame due to their thinner walls. Pipettes are exclusively for transferring liquids and do not have any heating capability inherent to their design.

Therefore, the characteristics of flasks make them the best