Deeper into Jeopardy! XXXVIII: Chemical Element Pairs – $400

Heading back science-wise, this time it’s chemistry for us, with not just one, but TWO elements per clue. What a wild ride it’ll be!

Jeopardy! category: CHEMICAL ELEMENT PAIRS (10-2-2015)

$400 clue: The 2 that are the components of rust

Correct response

The gist: Specifically, red rust. There are other types out there, like green rust (from the reaction of iron and chlorides), but what most of us think of when we think of rust is produced by the redox reaction of iron and oxygen. Specifically, rust forms when iron loses electrons and bonds with oxygen atoms, forming the compound with the scientific name of iron(III) oxide, or the chemical formula Fe2O3. You’ve probably heard that it’s not a good idea to let things made of iron (or steel, an alloy of iron and carbon) stay wet for too long. That’s because the process of rusting requires three ingreidents: iron, water, and carbon dioxide. When water comes in contact with iron, it mixes with carbon dioxide in the air to create carbonic acid (although the process can work with any acid), a weak acid that is very good at moving electrons around (it’s an electrolyte, like in your sports drink). The acidity causes some of the water to break down into its component elements, hydrogen and oxygen. The water also causes some of the iron atoms to dissolve, freeing it from its stable form and causing it to bond with the oxygen atoms that have been freed up from the water molecules, forming rust. Since rust doesn’t hold together very well, it soon flakes off, exposing more of the iron to the water and acid, causing more rust to form, until all of the iron has “rusted away.” Other substances, like salt (either in salt water or on snowy roads) are even better electrolytes than water and can speed up the rusting process – that’s why cars that spend a lot of time driving in the snow can quickly develop rusty undercarriages.

A rusty iron chain San Francisco Bay, sped along by the Pacific’s salty water

The clue: Straightforward. What makes rust?

In Jeopardy!: “Iron” and “rust” are together in seven clues in the J!Archive together, and surprisingly only three of them are about rust. Three are about haemoglobin, the iron-containing protein in red blood cells that binds with oxygen and carries it to the rest of the body. Turns out iron and oxygen share a couple things! That remaining clue is about acetylene, a gas that’s used in iron welding when burned alongside oxygen.

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