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Acids are widely considered to be the scariest chemical compounds of all, but bases can be just as powerful. Most powerful of all are a special class of pH scale-defying bases called superbases!

Hosted by: Hank Green
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Hank: This episode is about the most basic things in the world. But I don’t mean, like, simple things, like "ugh, she's so basic" — we’re talking chemically basic, like the opposite of an acid.

If a substance is basic, it’s said to have a high affinity for hydrogen, meaning that it’s great at bonding with hydrogen ions. Just like with super-strong acids, there’s a whole class of bases that are especially strong, called superbases. we have this idea that acids are the most scary of all chemical compounds, but bases can be just as dangerous. And just last year, researchers in Australia managed to create the strongest superbase ever discovered — a compound called ortho-diethynylbenzene dianion.

There are a few characteristics that most bases have: they usually taste bitter and feel kinda slippery, like soap. That’s actually a common use for bases — making soap. Bases like sodium hydroxide, or lye, are combined with fatty acids in vegetable oil or animal fat to produce sodium salts, which help water lift grease away from your skin. So when sodium hydroxide feels slippery to you, it's actually the sodium hydroxide doing chemistry with the oils in your skin to form a kind of soap. But I can’t really recommend washing your hands with very basic substances. Because it burns. Like, a lot. Strong bases can burn just as badly as strong acids.

The most common way to measure the strength of a base is the pH scale, which typically runs from 0 to 14. The scale works by describing how a substance behaves when it’s mixed with water.

See in pure water, a few of the molecules in water split up into positively-charged hydrogen ions and negatively-charged hydroxide ions. If the solution has a pH of 7, it means that there are an equal number of these hydrogen and hydroxide ions. They’re balanced out. But when a compound is higher on the pH scale — and therefore more basic — that means it’s more likely to bond with the hydrogen ions, shifting the balance so there are more hydroxide ions.

One step up on the pH scale means that there are a tenth the hydrogen ions in the solution. So something with a pH of 8 would leave 1 hydrogen ion for every 10 hydroxide ions. And a more extreme base — say, a drain cleaner with a pH of 14 — would leave only 1 hydrogen ion for every 10 million hydroxide ions. You could technically have a pH even higher. A really high concentration of sodium hydroxide in water can have a pH of 15, which means there’s only 1 hydrogen for every 100 million hydroxide ions.

But something strange happens with compounds that have an even higher affinity for hydrogen ions. Because if the base is much stronger, it’s actually capable of completely reacting with water, ripping hydrogen ions right off the water molecules in a process known as deprotonation. And substances that can do that are considered superbases.

Once a base is strong enough to deprotonate water, the pH scale doesn’t really work anymore. But you can measure its strength based on its proton affinity: the amount of energy that’s released as it bonds with hydrogen. The higher the proton affinity, the stronger the base.

So for example, sodium hydroxide releases about 250 kilocalories of energy for every mole, which is about six hundred billion trillion molecules. Whereas the record-breaking ortho-diethynylbenzene dianion has a proton affinity of 440 kilocalories per mole. It’s hard to picture what that actually means, but put it this way: There’s a compound called benzene that’s known to be especially stable.

It’s basically just six carbons in a ring, with one hydrogen bonded to each carbon. But ortho-diethynylbenzene dianion is so basic that it can even pull the hydrogen ions off of benzene.

Researchers are still looking for practical uses for ortho-diethynylbenzene dianion. But already we have plenty of uses for other superbases. Take sodium hydride, for example — a superbase that’s just sodium bonded to a hydrogen. Since superbases quickly react with water, sodium hydride can be used as a drying agent, to dry chemicals in the lab.

Sodium hydride has also been proposed as a way to store hydrogen so the hydrogen can be used as fuel. The sodium hydride could be combined with water to produce sodium hydroxide and hydrogen gas.

And since they’re so good at removing hydrogens, superbases can also be used in certain condensation and polymerization reactions, where smaller molecules are linked into bigger ones. So even though superbases are great at ripping some molecules apart, you can use that strength to put other molecules together.

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