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When the air feels "stuffy" and stale in a room, what is usually the reason?


Do you have all you need... for your mountaineering trip? - Mmm... - Rope, axe, and... oxygen? - Are you climbing that high? - I am indeed! I'm heading for the peak of Mount Kilimanjaro. The air is so thin there that I'll need extra oxygen, they say.

Oh, no! The oxygen bottle is almost empty! What'll happen if I don't get enough oxygen? If you don't get enough oxygen you'll get dizzy and may lose consciousness. And with no oxygen at all, you'll survive only a few minutes.

Just like a flame needs oxygen to keep burning, the cells in the your body needs oxygen to extract energy from the food you eat. For every breath you take, some of the oxygen from the air stays inside your body. Sometimes, when there are a lot of people in a room, - it can feel stuffy. - Ouch! Careful! Is that the oxygen running out?

No, actually not. What we feel, is that the amount of carbon dioxide has increased. It's the same thing when we feel out of breath. It's not a lack of oxygen, but a surplus of carbon dioxide, that we feel. But what is oxygen, really?

Oxygen is an element, which means it only contains oxygen atoms. But one oxygen atom can't be alone, when in gas form, they always need to be in pairs. An oxygen gas molecule is written: O-two. Oxygen is eager to react with other substances, and form chemical compounds. Such compounds we call oxides.

Metals like to react with the oxygen in the air -- they oxidize. The metal oxide that appears on the surface is, at room temperature, in solid state. Ordinary water is an oxide that is formed by hydrogen and oxygen. It is in liquid form at room temperature. When oxygen reacts with other non-metals, like sulphur, it forms oxides that are almost always in gas form, at room temperature.

Carbon dioxide, for example, found in the air you exhale. Oxygen is useful for a lot of things: In a hospital, it's used to help those who can't get enough air when breathing on their own. And when producing steel. By blowing oxygen through molten iron, we can regulate the amount of carbon, sulphur and other substances. And when you're welding.

The oxygen allows you to reach such a high temperature, that you can cut through steel... ... and of course - when you are about to climb Kilimanjaro -- which is almost 6000 meters high. But now the bottle is empty. We'll have to produce our own oxygen in the chemistry lab! Fun!

How do you do that? Well, the element oxygen is an ingredient in many different substances. Some of them are willing to let the oxygen go. Hydrogen peroxide for example: H-two-O-two. The oxygen atoms are released two by two, as oxygen gas.

If all the hydrogen peroxide is decomposed, then there's only water left. Can we make it go a bit faster! - Indeed! We add some manganese oxide. - Let me guess! The manganese oxide is a... catalyst!

YES! It makes the chemical reaction faster, without being consumed. But there are more ways to create oxygen. You can use an electrical current to break water molecules into its ingredients: hydrogen and oxygen. The hydrogen gas will form on one side and the oxygen gas on the other.

But how do I know which one is oxygen? Simple. Since oxygen is great at setting things on fire, we can do this: Light a taper and blow it out, so it's just glowing. The gas that ignites it again is oxygen. - Want to try another way to make oxygen? - Sure! Like this!

Take ordinary air - nitrogen and oxygen - and cool it until it transforms to liquid. Then: Heat it a tiny bit, just to make the nitrogen evaporate. - What do you have left? - Oxygen. - Liquid oxygen! - Yep. Ready to refill the bottle. That's it. The bottle is full.

Kilimanjaro, here I come!