Everything you need to know
After thirty years of using chemistry far more than most of you, I think it's fair to say that the following are what you need to know if you're going on in any field besides industrial chemist.
Experiments determine composition
Much of basic chemistry is learning to recognize the elements within a compound. So burning copper makes a blue flame, while burning sodium makes an orange flame. About a third of basic chemistry is taken up by element recognition. Multiple tests are done with bunsen burner safety. Every year someone sets a lab coat on fire. Anything remotely interesting is done in a hood (to remove toxic fumes) by the teacher. But we're missing all of this joy.
If you really want to know what we're missing, here's a video of every lab we'd do (variations) if we had a full set up. The trouble is that his salts really give clear colors. Mine always were contaminated by other lab groups so I'd get weird colors.
Stoichiometry is the art of counting up all the elements on one side of the equation and making sure the same number of molecules live on the other side. It's like counting to make sure all the little kids on the field trip made it on the bus. Not sexy, not exciting, but very necessary.
Converting from molecules to grams
Unless you have an electron microscope and a really small pair of tweezers, we can't work with individual molecules. We have to convert to grams.
We need a way to measure from a single molecule up to something we can hold in our hands. But we need a really big number of molecules. Something like a quintillion millionaires worth of molecules.
So first we need to come up with a way to measure the size of a single element. First they used hydrogen, then oxygen, but there were too many isotopes (variations). So we use carbon 12 (which is almost all carbon, the exception being a bit of carbon 13 and carbon 14.) Carbon 12 is the unit for an atomic unit the same way your thumb is an inch (basically give or take).
Then we need to come up with an atomic unit to gram conversion. We can't do an atom by atom measurement (although x-ray diffraction comes close, think of it like doing a bunsen burner molecule test with x-rays).
So instead we can measure the charge of a bunch of electrons. A mole of electrons by charge is called a Faraday. Notice that I just used a mole to define a mole, which is 6.02214154 x 1023. This was from Scientific American, the preeminent journal. Basically what they do is guessimate well how much a mole of something should be. But, just as if we all used the same funky cup to measure coffee, as long as we all use 6.022 for a mole, then we'll all be fine.
In a nutshell, find the atomic units of whatever you want to convert. Multiple that by 6.022 x 10 and you'll have the amount of grams you need of one molecule to match the amount of grams you need of the other molecule.
Rinse, soak, and repeat.
That's it. Once you can make an equation equal, then convert it to grams, you've mastered basic chemistry. Things like memorizing the periodic table make you cool among a very small group of people. A wider group of people will like it if you memorize the element song, but it's still not that many people.
That's the source code. Now we apply it to the app that is your bodies.
Things Never To Do. You Promised.
How to blow up your house.
NH3 = ammonia
NaOCl = sodium hypochlorite (bleach)
NH3 + NaOCl=
We could now go look at the atomic units of ammonia, then the atomic units of sodium hypochlorite. But that's what anyone besides someone with a lot of time to waste has google for these days. OK,
Nitrogen is 14.007, plus three hydrogens at 1.008. Add together and multiply by Avogadro's number. Or be a normal persona and look up the atomic weight of ammonia.
17.031 grams per mole.
Here's the tricky bit. You might want to mix "equal parts" or about equivalent weight of ammonia and bleach (if you wanted to bleed from your eyes, but we're getting to that). But if you look up the atomic weight of bleach, it's 74.44 grams per mole.
What to they equal?
Start off by understanding that bleach in water is really dilute hydrochloric acid. How fast do you have before hydrochloric acid burns? It depends on the concentration and thickness of the skin. Figure on ten seconds for safety, rinse as soon as possible. In a Quora answer, clearly a mass murderer discusses how long it takes so dissolve a body completely.
So ammonia mixes with the hydrochloric acid to form chloramine. Inhaling the vapors will burn your lungs.
NaOCl + 2HCl → Cl2 + NaCl + H2O
2NH3 + Cl2 → 2NH2Cl
But if you look above you see Cl2, which is chlorine gas.
Chlorine gas is much more toxic, and was first used in the trenches of World War I. (Fritz Haber, hydrogen cyanide (Zyklon B), and Syria).
So your lungs are burning and your eyes are bleeding, but we're not done. Because you wanted to mix equal amounts of ammonia and bleach by eyeballing it, you really screwed up. The excess ammonia mixes with more bleach, forming hydrazine (N2H4).
2NH3 + NaOCl → N2H4 + NaCl + H2O
What does hydrazine do? https://www.youtube.com/watch?v=fhYMh6KTJMQ