When I was in grade 8, we had a science class in a portable. I remember the first class, the teacher gave us 4 chemicals and told us we had to figure out how to make Oxygen and Hydrogen with them. You would know that you had it when you held a glowing flint stick (piece of smoldering wood, actually, no flint) over the test tube. If you had hydrogen you would get a pop. If you had oxygen, it would turn into a blaze.
Before we started he threw in one more comment. "There is no way you can make a bomb with this, so don't even try!"
So we went to work. I was working with my friend Richard, and nothing was working. So, we tried putting all 4 chemicals into the test-tube. As near as I can tell, thinking back on it, we must have got one layer producing hydrogen, and another producing oxygen.
My friend was holding the test tube and he lifted it off the bunsen burner, as I held the flint stick over our test tube for probably the 10th time, but this time there was a difference!
There was a loud bang, and a flash of flame that shot about a foot out the top of the test tube! The bottom of the test tube was gone (we never found any glass, either) and my friend and I both jumped. I think a couple of girls shrieked (might have been a couple of boys, too!)
The moral of the story? Don't tell 13 year olds that something can't be done unless you're really sure it can't!
Fortunately, no one was hurt, but I did learn something. Hydrogen and oxygen are a dangerous mixture!