Test for hydrogen gas?

The question that my teacher posed was why does the glowing wooden splinter need to be placed at the mouth of the test tube (and not the base or anywhere else) when testing for the presence of Hydrogen. I know that a 'pop' sound can be heard. Can someone explain this in detail?

Answer:
Firstly, Hydrogen is lighter than air, so when you turn the tube the correct way, it will escape rapidly upwards... so putting the splint at the bottom of the tube won't do anything as the hydrogen will have already gone from there!

Also, the tiny explosion that creates the pop sound is dependant on oxygen... The exlposion actually combines the hydrogen with oxygen to create water... If the splint is only surrounded by hydrogen, there can be no explosion... So the mouth of the test tube is better as it is open to the air (which has plenty of oxygen).

hope this helps!
Hydrogen is a flammable gas, so when the glowing splinter pops, it is reacting to Hydogen molecules.
Hydrogen needs Oxygen to burn.
Hydrogen gas is less dense than air so it wants to travel up and that is why you only need to place the ember at the mouth. Hydrogen, like you know is very combustable so when it is in the proximity of the ember it wants to explode. And it does at which point lots and lots of heat are released which causes the surrounding air mixture of hydrogen, watervapor and air to expand rapidly and shoot out of the test tube. Ergo the pop.
yeah POP is a sound that happens when a match(fire) is near hydogen. when u place a match near a tube with hydrogen u hear a POP and the match is turned off..!
Hydrogen gas floats (Reason: Hydrogen gas is the second lightest element, air is a mixture of elements that are heavier than hydrogen gas [except helium]), this explains why the splinter is placed at the mouth of the test tube.

Hydrogen gas is flammable, the pop sound created is the chemical reaction between hydrogen, oxygen and the fire on the burning splint.

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