[squealer]

Hi, I have a reaction that generates hydrogen so I need to flush the container with nitrogen. The question is which of the following is better safety-wise ?

1) top of boiling flask open and regular flushing with nitrogen

2) top of boiling flask goes to a gas washing tube, so that air cannot get in. I flush once initially the closed setup with nitrogen to get the air out. Then the reaction starts taking place. The mixture of nitrogen and hydrogen in the bottle (and a little bit of air) escapes through the wash tube. When the reaction is done, I flush once more with nitrogen.

In 1 there is oxygen present at all times, in 2 I'll have mostly hydrogen in the container and a bit of oxygen that didn't flush out initially.

   

[Doc Oc]

If it's a small scale reaction you could probably just put a septum over the reaction and stick a nitrogen balloon in it.  Larger scale reactions (gram scale or more) will require more consideration than that.

[squealer]

If it's a small scale reaction you could probably just put a septum over the reaction and stick a nitrogen balloon in it.  Larger scale reactions (gram scale or more) will require more consideration than that.

Well the reaction solution is about 1000 - 2000 ml , so it's not exactly small scale.