They're used to make foods,

soaps and detergents,

fertilizers,

explosives,

dyes,

plastics,

pesticides,

even paper.

Our stomachs are very acidic.

Our blood is slightly basic.

Our proteins are made up of amino acids,

and the letters in our genetic code,

those As, Ts, Cs, and Gs,

are all bases.

You were probably taught

how acids and bases behave

on the molecular level.

You were probably never taught

that a long time ago,

like ancient Greek ago,

before anyone knew about atoms or molecules,

acids and bases were defined

by how they behaved.

Acids tasted sour and corroded metal.

Bases felt slippery

and could somehow counteract acids.

When molecules dissolved in water interact,

they are exchanging two main currencies

with their surroundings:

protons, also known as hydrogen ions,

and electrons.

Depending on how a molecule is composed or shaped,

it may be willing to donate or accept

either protons or electrons

with some other community member.

And some molecules are far more aggressive than others

when it comes to donating or accepting either currency.

Remember that protons are positively charged

and electrons are negatively charged.

So, if a molecule is willing to give up a proton,

that's not too different

from it being willing to accept an electron --

either way it's becoming more negatively charged.

Other molecules are willing to accept a proton

or give up an electron.

These are becoming more positively charged.

Some substances are so aggressive

about donating their protons

that when they get a chance,

all of the molecules in a sample

will dump a proton,

sometimes more than one,

to the surrounding water molecules.

We call these strong acids.

Meanwhile, some compounds are so ready

to accept a proton

that they won't wait around,

they'll just rip one off water,

which usually has two protons

but is generous enough to hang out with just one.

We call these strong bases.

Other acids and bases are not so strong.

They may donate just a few of their protons to water

or accept just a few protons from water,

but most of their molecules stay exactly the same.

If left alone in water,

they'll reach some equilibrium point

where maybe only one out of a hundred

or one out of ten thousand of their molecules

has exchanged currency with water.

As you might guess,

we label these acids and bases weak,

but in the common sense of the word,

they're not weak.

The vinegar in your salad dressing

that you can smell from across the room,

that is a weak acid.

The ammonia you spray on glass

for a streak-free shine,

that is a weak base.

So, it doesn't take much to be an active player

in the chemical economy.

Most acid-base chemistry takes place in water,

which can act as either an acid or a base,

accepting deposits and enabling withdrawals

like a 24-hour molecular ATM.

And when a proton-deposit customer,

that's an acid,

and a proton-withdrawal customer,

the base,

shop at the same time,

their net effect on water's account

may cancel out,

and we call this neutralization.

Now, certain molecules can behave

as acids or bases without water,

but that's another story.

Let's end by saluting water

as the resilient and fair banker

for acids and bases.

It's always open for business,

doesn't charge interest,

and will never foreclose on your molecules,

which is more than I can say for [bleep].

Waah-waah.