danger of sucking back??

[asto5]

in the experiment of adding lithium to distilled water and collecting the hydrogen in an upside down cylinder of water in a bowl of water. is there any danger of sucking back?!

cheers in advance!!

[shammydodger]

There is to a degree. The reaction of lithium with water is exothermic and will warm the solution and the reaction vessel (presumably a boiling tube?) There is no danger as long as the reaction is ongoing, so that hydrogen is being formed. It is best to halt the collection of the gas prior to the reaction ceasing and get the delivery tube out of the water.

It has to be said that any suck back should be of minimal consequence, as the temperatures involved (provided a sensible quantity of lithium is used) will be such that the dynamics ought not to be spectacular.