Metal Straw in Pop Can eli5


Okay so my girlfriend and I just noticed that when we put a metal straw into a pop can of ginger ale, the pop begins to fizz again and only up through the straw. Can anyone explain?

In: 7

the metal straw acts as a catalyst, causing the ginger ale to undergo a chemical reaction that produces carbon dioxide gas. the gas bubbles become trapped in the liquid and rise up through the straw.

*Probably* what’s happening is this:

There’s carbon dioxide dissolved in the soda. It wants to be out of the soda. But it turns out that it’s very hard for a gas to just decide to leave a liquid; it’s much, much easier to join a pre-existing bubble or just escape through the top. And it’s hard to form a bubble in the middle of a liquid; it’s easier to form it on a surface – a rough surface.

The inside of the can is very smooth, but the surface of the straw is not. So when you insert the straw, lots and lots of bubbles form on its surface and rapidly grow larger.

Unless your straw is made of platinum or palladium, it is not a catalyst and no chemical reaction is occurring.

The carbon dioxide in the drink will form a bubble more easily if it has something to form around or on. Some kind of imperfection. If you drop a spoon of sugar into carbonated drinks or champagne, you get loads of tiny bubbles suddenly. If you pour the drink into a glass you’ll see that they form on the inside of the glass and once one comes off the glass and starts rising to the top, a new bubble will form in the same place as the last. It’s because there is a tiny imperfection in the smoothness of the glass. You can actually make glasses smooth enough now so that there are very few bubble formed, which is not what you want for champagne, so even high end champagne glasses aren’t made like this.

Now for the straw. I suspect when you put the straw in, it’s surface has lots of tiny imperfections/scratches on it, suddenly allowing more bubbles to form quickly. When you took a sip it allowed the surface tension to break and fluid up the straw. When you stopped sucking, on the imperfections within the straw, bubbles formed. Since there is not much space, they will expand up and out the straw