10.) Walt blows up a douchebag's car
When: Season 1, Episode 4
("Cancer Man")
After the twin psychological duresses of terminal cancer and slinging meth begin to sink in, Walt entertains himself by inserting a moist sponge into an obnoxious man's car engine. This is more automotive shenanigans than chemistry, but Bryan Cranston sells Walt as a haunted man toying with his dark side.

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9.) Walt saves his life by building electrochemical cells
When: Season 2, Episode 9
("Four Days Out")
When the RV's battery dies in the middle of nowhere, Walt and Jesse must build something to start the engine. On the verge of fatal dehydration, Walt constructs salvation out of found materials.

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8.) Jesse's lab cleanliness speech
When: Season 4, Episode 10 ("Salud")
When the cartels force Jesse to travel south of the border to cook up his patented Blue Sky methamphetamine, the surly young meth chef is confronted by a group of dubious Mexican chemists. After they doubt his credentials, Jesse shoots back by demanding better workplace standards.

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7.) Walt and Jesse synthesize thermite from Etch A Sketches
When: Season 1, Episode 7
("A No-Rough-Stuff-Type Deal")
To steal a barrel of methylamine from a guarded warehouse, Jesse and Walt crack open a few Etch A Sketches, purloin the aluminum powder inside, and whip up a batch of thermite to burn through security. I'm assuming Bruce Wayne is a major stockholder in the Ohio Art Company, as Batman always seems to have plenty of unsuspicious thermite lying around.

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6.) Walt serves Tuco a ricin burrito
When: Season 2, Episode 2 ("Grilled")
When Walt and Jesse realize that they've hitched their apple cart to mentally unstable drug kingpin Tuco Salamanca, Walt synthesizes ricin from castor beans, laces it with a batch of meth, and offers it to the meth-happy Tuco. After Tuco complains that the ricin meth stinks like "head cheese," Walt adds it as a garnish to his burrito. This plan goes about as well as you'd expect.

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5.) Walt blows up Tuco's HQ with fulminated Mercury
When: Season 1, Episode 6
("Crazy Handful of Nothin'")
The burrito wasn't the first time Walter used chemistry to tussle with Tuco. Several episodes earlier, the drug lord had robbed Jesse, so Walt cooks up some Mercury Fulminate for a hostage situation. The depiction of the explosive was embellished for the episode, but it's one of the first times we see Walt go into 100% bugfuck "Heisenberg mode."

4.) Walt poisons a child using plant toxins
When: Season 4, Episode 12 ("Face-Off")
There were a few shockers in the Season 4 finale, but the revelation that Walt poisoned innocent little kid Brock to break Gus Fring's spell on Jesse was a jaw-dropper. After using Lily of the Valley to put Brock in the hospital, Walt's officially past redemption. Here's a play-by-play of his actions.

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3.) Walt murders a drug dealer with phosphine gas
When: Season 1, Episode 1 ("Pilot")
During the very first episode, drug dealers force Walt into revealing his recipe for meth. Rather than give up his secrets and die in the desert, he intentionally creates phosphine gas to kill his captors.

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2.) Disposing of bodies in hydrofluoric acid
When: Several times, namely Season 1, Episode 2 ("The Cat's In The Bag")
Whenever the protagonists on Breaking Bad need to dispose of a corpse, they usually shove the dead person in a barrel of hydrofluoric acid. The first time Jesse tries this, he fails miserably. To quote Walt, "Hydrofluoric acid won't eat through plastic. It will, however, dissolve metal, rock, glass, ceramic. So there's that."

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1.) Heisenberg's impromptu chemistry lesson
When: Season 2, Episode 10 ("Over")
"Over" is a spectacular episode, as it shows Walt trying to balance his family obligations with his increasingly dominant Heisenberg persona. In the episode's final scene, he meets a novice meth chef in a home supply store. At first, Walt gives the confused cook some avuncular tips straight out of high school chemistry class. But after a moment of reflection, Walt metamorphoses into Heisenberg, and he utters the grimiest five words of the entire series. TV on the Radio makes this scene.

BONUS: Apropos of nothing, Gale Boetticher's full karaoke video! Thanks, SkippityMonster!