Discounting any ridiculous side-usage for rubber stoppers that may exist, they are simply used to seal glasswear in a temporary manner.
For example, if you want to shake your solution but don't want to get it all over yourself. Or if you want to transport it and minimize risk of spillage.
We generally don't use rubber stoppers much anymore, though. Glass stoppers are considered safer since they will pop out more easily if pressure builds inside the glasswear (which can be VERY dangerous). I would never stopper anything that I am applying heat to or that I expect gas production from, so be careful in your usage.
Glass stoppers are also a little better because you know if your solution isn't reacting with your glasswear, it won't react with the stopper....whereas it may still react with a rubber stopper.
Another advantage is that glass stoppers are easier to remove (try greasing them if they leak air or don't work smoothly). A good example is if you are using a separating funnel you will usually want to shake the funnel and then relieve the pressure by removing the stopper (at very regular intervals). This can be a pain with a rubber stopper as they require more force, which can also lead to accidents. Again, glass stoppers make this much easier.
Cork stoppers are used similarly.
The easy answer is, "to cap test tubes and flasks." The real answer is, rubber stoppers are used in the lab because the rubber in them is unaffected by most chemicals - and unlike the glass stoppers that used to be standard in laboratories, they don't get stuck in the container.
To keep things in flasks. Glass is less reactive than rubber, and some corrosive chemicals will eat right through the rubber!
Stoppers placed in the mouths of flasks and test tubes prevent spillage and evaporation.
Either to prevent things from getting in OR getting out (or both).
Size 8.
Because... if it's tightly sealed - during cooling the volume of the solvent will decrease - making the pressure inside lower than outside he flask. This could be enough for the glass to shatter - spilling the contents.
Rubber corks are commonly used in labs with test tubes as a stopper. The rubber corks are used on flask as well. The function of the rubber cork is to keep the contents in the container.
Its reduces evaporation, and something else i dont know! :)
to plug your bunghole, which is the hole in the side of a barrel or on top of a flask. AKA rubber cork.
volumetric flask
Normally cork or rubber is used as a stopper in a flask.
An Iodine Flask is essential an Erlenmeyer Flask with a stopper used for the wet chemical analysis "Iodine Determination" . This analysis is typically performed on fatty acids, oils and shellac varnishes.
Size 8.
Because... if it's tightly sealed - during cooling the volume of the solvent will decrease - making the pressure inside lower than outside he flask. This could be enough for the glass to shatter - spilling the contents.
Because - even though the vacuum between the layers of the flask is almost perfect, the junction between the flask and its stopper creates a 'weak spot' where a small amount of heat can escape over time.
The thermal insulation used round the container holding the food. This is normally an evacuated, mirrored, double walled glass flask with an insulated stopper.
The Erlenmeyer flask was named after its creator Emil Erlenmeyer, who was a German chemist. It is a flat bottomed cone-shaped container that has a tapered neck so that a person can hold it, put a stopper on it or attach a clamp with it. This flask is used to measure, mix, and store liquid.
The flask has a double wall, with no air between the two walls (vacuum)- conduction. The walls are highly reflective silver- radiation. the flask has a small beck that is closed by a stopper or cap-convection.
to prevent leaking of substances on the flask. also to maintain the accuracy of measurement of the beam (plug in the beam). it is used in the distillation process
It prevents heat transfer by convection as it prevents contact between the surrounding air and air inside the flask. It prevents heat transfer by conduction as it is a poor conductor of heat.
The vacuum between the two layers cannot conduct heat.The silvering on the inside reflects heat back to the contents.The stopper prevents heat loss by convection.The stopper is made of poor thermal conductors.