- [Instructor] What we're going to do in this video
is talk about acidity and in particular,
we're gonna talk about the pH scale.
Now the first question is what does pH stand for
and it turns out that there's some debate
why we have this lowercase p here,
we know why we have the h,
and some people will tell you it stands
for power of hydrogen, the capital h for hydrogen.
Some people will say it's the potential of hydrogen.
Some people will say it's the capacity for hydrogen,
you might say capacity doesn't start with a p
but if you go into Latin, it can.
But what do all of these things mean
and why do we care about hydrogen so much?
Well, it turns out that hydrogen, and in particular,
a hydrogen positive ion, and ion
is just a positively charged molecule,
that a hydrogen ion can play a major role
in how acidic or basic something is.
And so the pH scale, you're gonna see it
go from zero all the way to 14
with of course, seven in the middle,
and something that is towards the left,
something that is less than seven is considered acidic,
and so if you have a pH near zero
that is highly, highly, highly acidic,
while something to the right is considered basic
and something in the middle is considered neutral.
And another term for basic you'll sometimes see
is alkaline, and alkaline actually comes from Arabic
for alkali which was the word that ancient Arab chemists use
for a compound that happens to be very basic
by our modern definition.
But what does it mean to be acidic
and what does it mean to be basic
and once again, how does that connect with hydrogen ions?
Well, it turns out, and I'm not gonna go in depth
in this video, is that things that are acidic
tend to have lots of hydrogen ions
and while things that are basic tend to react,
react with these hydrogen ions.
There's other definitions for what it means
to be an acid or base and we'll go into depth
in chemistry class on that,
but this is why it's connected with the term pH.
Now what are examples of things that are acidic?
Well, you see it on this chart right over here.
Here, we're going in the vertical direction.
Things in our everyday life that are quite acidic,
a lot of fruits are quite acidic,
for example, lemons and grapefruits
and orange juice are quite acidic.
They're at the low end of the scale.
And some of the telltale signs for acidity
is if you were to drink it or eat it,
that it would have this kind of sharp sour taste to it,
while if you go to the other end of the spectrum,
things that are basic, these would be things like bleaches
and ammonia solution and we can even go
super basic to liquid drain cleaner,
and these are going to have more of a slimy texture to it.
In fact, even soap is quite basic.
And of the basic things that you could eat,
you might have a bitter taste associated with it.
But to be clear, I really don't recommend
eating or drinking anything that is either highly basic
or highly acidic, and the reason is
is that things that are at the extreme of the pH scale,
so things that are either extremely basic
or things that are extremely acidic
like battery acid or hydrochloric acid,
because they're so reactive, they will damage you.
If you pour it in your skin, it will damage you.
If you ingest it, it will damage your cells
and it can even kill you.
So don't try to taste things to see
whether they're acid or basic, and if you do,
try to make sure that they're closer
to this middle range of our pH scale.
So I've talked a lot about things that are acidic
or basic, but also what's interesting
is things that we consider to be neutral.
So our blood, for example, is quite neutral,
and this is something that doctors might measure
because if your pH in your blood gets a little bit too high
or a little bit too low,
that can cause some serious problems.
Sea water is pretty close to being neutral.
Milk is not that far off of being neutral.
Now with that said, in order to read
the pH scale appropriately or appreciate the differences
in acidity and basicity, it's important to realize
that it is not a linear scale.
So for example, something that has a pH of eight
is not twice as basic as something that has a pH of four.
It turns out, when you go form one level of our pH scale
to the other, you are going up in basicity,
say going from a pH four to a pH of five,
by a factor of 10.
And so, comparing something with a pH of four
to a pH of eight, that thing with the pH of four
would be 10, 100, 1,000,
10,000 times more acidic,
or you could say the thing with a pH of eight
is 10, 100, 1,000,
10,000 times more basic.
So I'll leave you there.
Keep a lookout when people talk about pH balance
or blood pH, and we're also, as we study
more and more biology, we're gonna talk about
how pH might influence some biological reactions
and especially once you get into chemistry,
pH will inform us what type of reaction is likely to happen.