Questions about pH scale...

I realize to anyone who knows the answer I probably sound pretty dumb, or ill-informed... but really I'm just the latter.

Let me explain one other thing, which may clarify why I'm confused.

I got the impression from the professor that it was a ratio, and that each level was ten times the potency as the last. For example 1 to 10, then 1 to 100 and so on. The problem with that idea is that the scale does not seem to naturally terminate. It could get up to 1 to 1,000,000,000,000,000,000,000 and further, but would never terminate seeing as the one will always exist.

Well... I hope that clarifies. I think I'll have to wait until someone responds before I can see the many flaws in the explanation of what I want to know.

Okay, wait... okay, wait... okay... okay, wait... I have this one last theory that satisfies everything. Is 10^14 the most hydrogen atoms that can possibly fit in a liter? That would almost make sense, if hydroxide wasn't so much bigger... which would mean it couldn't be the inverse on the scale.

I'll shut up now.

I don't know if this answers your questions or not but it's what I know of the pH scale.

The scale runs (as I'm sure you know) from "1" to "14".

The center value of "7" is based on the number of hydrogen ions in distilled water.

Every other value is a logrithmic increase or decrease with a factor of 10. So "8" has 1/10th the number of hydrogen ions than distilled water has when compared at the same volume and "6" has 10x as many.

Does that make sense?

Every chemical reaction has an equilibrium point. For the reaction:

[H2O] <-> [H+] + [OH-]

the equilibrium constant is 1x10^-14. This means that the vast majority of the stuff in water is H2O, not the constituent ions. In pure water, the [H+] and [OH-] are equal, so each has a concentration of 1x10^-7, but if you add a source of [H+] or [OH-] you can distort that balance. pH is the negative of the base ten log of the [H+] concentration.

The product of the concentrations of [H+] and [OH-] is always 10^(-14). Hence, the sum of pH and pOH (seldom, if ever, used) is always 14.

Though a very concentrated strong acid might trump this, quenching virtually all OH- ions and adding excess hydronium, I suppose...

Why is the product of the concentrations always 10^-14?

When you refer to the concentration being 1x10^-7, or 1/10,000,000, does that mean 1 in ten million? If so, by number of atoms, volume, or mass? If it doesn't mean one in ten million, then what does it mean? That seems like it would make sense, if 8 on the scale meant 10 in 10,000,000, and all the way to 14 or zero, where either [H+] or [OH-] would be 10,000,000 in 10,000,000. But if that were the case, I don't see why you would make a reference to 10^14, which would be 10 million times greater...

I guess mostly I just need to know what the number has reference to. I have read up in the encyclopedia, but I aparantly lack the math skill and knowledge of chemistry termonology.

Since when one goes up the other goes down, is it in fact a ratio?

Thanks for everyone's responses so far.

The products of the concentrations are 10^-14 because that is the equilibrium constant for water going to [H+] and [OH-]. Typically, concentrations are in moles per liter. One gram mole of a material weighs as much in grams as its atomic weight, so one mole of [H+] weights one gram, one on [OH-] weighs 17 grams. Here is how you use the equilibrium constant. For the reaction

[H2O] <-> [H+] + [OH-]

the value of [H+]*[OH-] / [H2O] will equal 10^-14 (at room temperature).

If you deal with moles, then for each mole of [H2O] you have (18 gm), you will have 10^-7 moles of [H+] (weight 1 gm x 10^-7) and the same of [OH-] (weight 17 gm x 10^-7)

In direct answer to your question, number of moles is proportional to number of atoms, so atoms works, volume doesn't, mass has to take into account the atomic weight of the material. For every 10 million water molecules, you will have one [H+] ion and one [OH-] ion.

For the second question, remember that this is a chemical equilibrium. If you add in extra [H+], they will react with some of the [OH-] ions to form water. This will happen until the equilibrium is restored.

Thank you very much. I appreciate the effort and the information.