Listen to a conversation between two students in a chemistry class.

Marie: Huh! This isn’t working.

Peter: What isn’t?

M: This reaction. I’m supposed to get hydrogen gas, but I don’t seem to be getting anything except air.

P: How are you supposed to tell?

M: Well, hydrogen gas should explode when I hold this burning splint up to the test tube- but… nothing happens, see?

P: Hmm. Very unimpressive. How do you do this experiment, again?

M: Well, I put some hydrochloric acid into this test tube here. And then I add a piece of zinc metal to it. A reaction takes place and hydrogen gas is produced- it says- which should come out of the glass tubing, over here, and go into this other test tube. But it doesn’t.

P: Nothing happens?

M: Well, something happens. The zinc bubbles and bounces around- the acid does something to it. Some gas must be coming off, I guess, but it isn’t flammable. It doesn’t burn at all.

P: Is there any way else to identify hydrogen?

M: Not that I ‘ve learned. It’s completely colorless and tasteless, I know- it just burns very dramatically.

P: Huh. Well, I dunno. Shall we run through your experiment again together and see how it goes?

M: Sure, if you don’t mind- that would be great! I’m sure I’m doing everything right, I’ve gone through it twice now, but I still get nothing, nada.

P: OK. Lessee…. We need what? Clean test tubes? Two of ‘em? Here we are. And… a rubber stopper with ten centimeters or so of glass tubing through it… right…uh…here. That’s it?

M: Yep. And a graduated cylinder and the Bunsen burner. And the zinc and the acid.

P: All right: let’s do this first- let’s take the zinc and the HCl from different sources- from, uh, those reagent bottles on that lab table over there. Maybe your bottles are contaminated or mislabeled or something.

M: Oh, good idea. Trust me to use the wrong reagents.

P: Just a sec…. here we are… OK, now you run the experiment like you think you should, and I’ll watch what you do.

M: Well, first I clamp this test tube onto its stand…like this… and put in about five milliliters of the hydrochloric acid….

P: “About” five milliliters?! Isn’t this a scientific laboratory?

M: All right, all right. Exactly five milliliters of HCl…like this….

P: OK. Mmm… and….

M: Then I take a little piece of zinc metal with these tweezers, like this, and-

P: Are they all the same size?

M: Yeah, they seem to be. It looks like they’re pressed out of some kind of machine in standard bits.

P: And add “one”?

M: Yeah, one. Like this. And see?- it starts to bubble!

P: Sure does!

M: So I slap the stopper into the top of the test tube real quick, like- unh!- this….

P: Mmm….

M: And then, I hold the other test tube under the other end of the glass tubing, here…like this, and…uh, wait until I think I’ve collected enough hydrogen gas to ignite, I guess. Is the Bunsen burner going?

P: Yes, it’s burning- and you also need a splint, right? Here’s one. Hey! Just a minute- how in heck are you going to collect any gas like that?!

M: Like what?

P: Like that- holding the test tube under the mouth of the tubing

M: What? Am I spilling it or something?

P: No, no- you’re losing it entirely! Hydrogen is lighter than air, Marie. It’s floating UP.

M: Huh?

P: It’s floating up. It’s rising from the tube mouth. It’s not falling into your container. Hold it above the tube!

M: Ack! How stupid! I am so stupid. I’m never gonna pass this course. OK, OK- now…light that for me, will you?

P: Right…here you go.

M: And…. POW! Wow, did you see that?

P: And we’ve got lift off! And you’ve got hydrogen. Congratulations.

M: Yeah. (sighs) Thanks, Peter. Now all I gotta do is write this experiment up.

P: No problem. So, what’s your next experiment?

M: Uh, something about sodium and water.

P: Oh no!