Stoppers are most often used to plug openings in glassware, usually flasks. Sometimes, a glass rod or thermometer or funnel is held in place with a rubber stopper.

Stoppers come in several sizes, and are made out of many materials. The three most common types of stoppers used in the organic chemistry labs are cork stoppers, rubber stoppers, and glass stoppers. The choice of which type to use depends on the task at hand.

Cork stoppers

Cork stoppers are used mainly to stopper test tubes, and in any applications where the contents might react with a rubber stopper. Cork stoppers are all solid, but if you need to bore a hole through a cork stopper, the stockroom has various cork borers available.

Cork stoppers are available from the stockroom, and there should be a small assortment of sizes in your equipment drawer.

Rubber stoppers

Rubber stoppers are usually used for larger flasks, and for applications where the contents might react with a cork stopper. Solid rubber stoppers are available, as are rubber stoppers with one (or two) pre-drilled holes.

You should have a small assortment of rubber stoppers in your equipment drawer. If you need a stopper for an Erlenmeyer flask , check the side of the flask -- it will sometimes specify the size needed. Otherwise, bring the flask with you to the stockroom to get the correct size.

Glass stoppers

Glass stoppers, like the one shown above, are used to stopper separatory funnels. They are specially ground to a specific size, which will fit the size designated on your separatory funnel. Each separatory funnel should come equipped with a glass stopper -- but if you lose yours, replacement stoppers are available from the stockroom.

Cost:

all stoppers are free