A friend of mine recently asked to borrow
some moisturizer.
I handed her my favourite, and said it contained
hyaluronic acid.
She recoiled in horror and said she was afraid
to put acid on her face.
I really didn’t know what to say to her.
Clearly she had a big gap in her knowledge
of chemistry.
And it made me wonder how many people were
afraid of the word acid, thinking it meant
you were going to get burned.
Just about all the water-based solutions in
your house
are going to be either acidic or basic.
Water is perfectly neutral, with a pH of 7.
What does that actually mean?
pH refers to the concentration of H+ ions
in a solution.
Water autoionizes - breaks up a tiny bit on
its own - and it has a H+ concentration of
1 x 10-7 moles per liter.
That’s a very low concentration of H+ ions.
So what’s an acid?
It’s anything that, in a solution of water,
causes more H+ to be produced.
Acids have a pH less than 7, which implies
the concentration of H+ is greater
than 1 x 10-7 moles per liter.
Bases, on the other hand, cause less H+ to
be present in solution in water.
Bases have a pH greater than 7, which implies
the concentration of H+ is lower than
1 x 10-7 moles per liter.
If you want to know the exact relationship
between pH and H+ concentration, we have an
equation for that:
pH = -log [H+].
This is log base 10.
So something with pH 5 has 10x the concentration
of H+ ions as something with pH 6, and 100x
the concentration of H+ ions as something
with pH 7.
Now.
Back to my squeamish friend.
Was she right to be worried about an acid?
No.
The words acid and base merely tell you the
direction the solution has moved away from
neutral.
If we hear the word acid, we know the solution
has more H+ ions than water, but we don’t
know HOW MUCH more.
That’s what’s really important.
For that, we need to know what is the pH.
So let’s put my friend’s mind to rest.
We’ll test the pH of my moisturizer, along
with some other common liquids we come in
contact with every day.
We’re using a pH meter from Rozway - they
were kind enough to send one of their electronic
meters to Socratica for us to test out!
Water.
So this is tap water from Los Angeles, CA.
It's perfectly healthy tap water - it just tastes like a swimming pool.
So I'm going to immerse my electrode...
Okay...and then turn the pH meter on.
I'm expecting it to be neutral - around pH 7.
And we get...
pH 7.45
Coffee
This is some homemade coffee...
Here's a little sample here.
And we put the meter in...
And then turn it on...
I'm expecting coffee to be slightly acidic.
Tastes that way.
And I see it is settling right around pH 5, and pH 5 IS acidic.
So my coffee measured pH 5.07.
This is...window cleaner.  This blue stuff!  We always talk about glass cleaner being made of ammonia, but
this actually has several different ingredients in it.
The main ingredient is water - it's a water-based solution,
and it has isopropanol (rubbing alcohol) in it, as well as ammonia,
and some dye.
So I'm expecting this to be basic, because    I know ammonia has basic behavior.
Oh! and it's quite basic.
So here it's settling over 9...
pH 9.94! So that's quite basic.
And you can feel that!  When you touch ammonia,
it feels quite slippery.
And that's characteristic of bases.
Soda
I think soda's going to come out to be acidic, because
of the phosphoric acid in it, but...we'll see!
It's bubbling a little.
I'm turning the meter on.
It started right around pH 4, and it's dropping...
Okay, now it's in the threes...
It stopped at pH 2.87.
Here's the moisturizer
that my poor friend was so afraid of,
with the Hyaluronic acid.
All right.  Dipping my electrode into the moisturizer...
Turning it on...
We're starting at around pH 6.6...6.5...
pH 5.24.
OK!  Not too dangerous, at pH 5.24.
Vinegar
We use vinegar all the time.  We use it for salad dressing...
We use it for cleaning...
So, you know, we don't think of it as harmful, but
it is made with acetic acid.
Vinegar is an acetic acid solution.
So, I'm expecting this to be acidic.
So let's see HOW acidic.  Let's test the pH.
pH 2.27 for vinegar.
Sriracha - very spicy.
Because I think most hot sauces have vinegar in them, I'm going to guess this is acidic.
Ah, I can smell it. It smells delicious!
OK. So I'm going to ...
drop in the electrode...
and turn it on...
Yes! It is acidic!
Watch it go all the way to the pH of vinegar.
OK, there - I'm going to call that. pH 3.93
Shampoo
I'm thinking basic...
because basic things tend to feel slippery.
And shampoo and all sorts of detergents tend to feel slippery in your hands.
So let's see what the pH is of shampoo.
It would be nice for your shampoo to be really close to your body pH.
Like your skin, which is slightly acidic...
closer to 5 - point - something.
But I think with shampoos, they are still basic.
OK. So I'm going to submerge the electrode, and turn it on...
I'm wrong!!!
Guess what.  My shampoo...good for them!
It is really close to neutral, and in fact it is slightly acidic.
That should make it healthier for your scalp than, say, laundry detergent.
OK, very good!
All right. pH 6.10 for my shampoo.
Milk
I don't have any expectations about the pH of milk...so...let's test it!
This is whole milk, by the way.
Milk has fat globules in it - micelles...
and it has several kinds of sugars...
So if I think about how sugars interact with water,
I'm expecting it to be neutral, around pH 7
But, yeah, I don't know, so...let's see!
What is the pH of milk?
turn it on...
No!  It is acidic!  haha.  Just kidding.
So...it's VERY close to neutral.
The pH of milk is 6.58, so very slightly acidic.
And now, let's do Lemon Juice
This is a lemon from our tree here, at Socratica Studios.
They're Meyer lemons, which are maybe a little milder than some other varieties of lemons, but
they're very delicious.
We can grow lemons here in Southern California year-round.
Don't come here! {laughing}  It's already too crowded.
So now we're ready to test the pH of this lemon juice.
Freshly squeezed lemon juice.
So I'm dipping my electrode into the lemon juice...
turning it on...
All right. It's settling down right at pH 2.42 for our lemons.
Here’s an 
exercise for you at home - now that you know
the pH of these everyday household items,
can you calculate their H+ concentrations?
Post your answers in the comments.
And let us know if there are other things
you want to test!
If we get enough requests, we'll make a follow-up video!
If you’d like to see more of these great
chemistry videos, make sure to
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