[Schwarz107]

Let's say we have a one litre solution with pH 2.

According to the chart below, that would mean there are 0.01 mol of hydrogen cations per liter.

Hyrdogen is the lighest element with only one proton, so 1 mol of hydrogen weighs approx 1 gram.

So some 0.01 grams of hydrogen cations would be in that solution. Right?

One litre weighs about a kilo.

So at pH 2 we would have 0.01 gram of 1000 gram, which means about 0.001 % of the mass is hydrogen cations?

And let's say we had a solution with pH 0. That would mean 1 gram per 1000 gram, so about 0.1 % of the mass would be hydrogen cations?

[Borek]

Looks about right.

[Corribus]

Keep in mind free hydrogen ions don't really exist in aqueous solution.

[Schwarz107]

Yes, Corribus.

I am adding this for future reference.

So, what we're talking about when we talk about pH, is the concentration of hydronion ions (H₃O+), measured in mole per liter.



Do you know what the "c" stands for in the picture? It says c(H₃O+)

[Borek]

concentration

[Schwarz107]

So, what we're talking about when we talk about pH, is the concentration of hydronion ions (H₃O+), measured in mole per liter.

I am correcting what I wrote for future reference.

What we are talking about when we talk about pH is the thought concentration of hydrogen ions measured in mole per liter.

Because hydrogen is lightweight, 10 mole of hydrogen ions would be more reactive than 10 mole of the more clunky H₃O+ (bigger molecule, but only lacking one electron).

In a real solution, the vast majority of ions wouldn't be H+ but rather H₃O+.

[Borek]

What we are talking about when we talk about pH is the thought concentration of hydrogen ions measured in mole per liter.

More accurately it is negative logarithm of the concentration. Even more correctly: negative value of the logarithm of the activity of the H⁺.

In a real solution, the vast majority of ions wouldn't be H+ but rather H₃O+.

To make things even more complicated, it is not just a single ion H₃O⁺, it is actually a series of ions with the general formula (H₂O)_nH⁺ (with n being a small integer).