What is the definition of pH?

Answer 1

Its the Power of Hydrogen

the formula is -log [H+]

H+ is the concentration of hydrogen ions in the solution.

Answer 2

"Potential"? "Power"? I always thought it was "Parts". Regardless, it's the negative of the log of the concentration of hydrogen.

If the concentration of something is, e.g., 10^-5 molar, then its pSomething is 5. If the molarity is 10 (10^1), the pSomething is -1.

The use of it is that numbers like 5, 12, etc. are easier to work with than 10^-5, 10^-12, etc. For example, we know the Kw (auto-disassociation constant) of water is 10^-14, that is:

[H+] [OH-] = 10^-14

(where [something] is the molarity of something). But since multiplying numbers means adding exponents, we can write this more easily with p:

pH + pOH = 14

In fact, this is why you almost never see pOH. If you have something like 1 molar NaOH, so that [OH] is 1, then pOH is indeed 0 (since log 1 = 0). But we prefer pH, which is simply 14-0=14.

The equation is:

pX = -log [X]

What's the use of pH? Well, in neutral, pure water, pH = pOH (since it's neutral, after all, and the concentration of H+ and OH- ions must be the same). So we combine that with the above equation and get pH = 7 for pure water. If the hydrogen concentration is greater (we added something like HCl, an acid), then the pH will decrease (because of the negative sign in the formula), so anything with pH < 7 is acidic. Similarly, if the hydroxide concentration is greater, the pOH will decrease and the pH will increase, so anything with pH > 7 is basic.

Again, it's easier to manipulate numbers like "the pH of blood is 7.4 instead of "the [H+] of blood is 4*10^-8" to find that blood is slightly basic. (10^7.4 = 4*10^-8, log 4*10^-8 = 7.4)

Answer 3

pH is a measure of the acidity of a solution in terms of activity of hydrogen ions (H+). For dilute solutions, however, it is convenient to substitute the activity of the hydrogen ions with the molarity (mol/L) of the hydrogen ions (however, this is not necessarily accurate at higher concentrations [1] [2]).

In aqueous systems, the hydrogen ion activity is dictated by the dissociation constant of water (Kw = 1.011 × 10−14 M2 at 25 °C) and interactions with other ions in solution. Due to this dissociation constant, a neutral solution (hydrogen ion activity equals hydroxide ion activity) has a pH of approximately 7. Aqueous solutions with pH values lower than 7 are considered acidic, while pH values higher than 7 are considered basic.

The concept was introduced by S.P.L. Sørensen in 1909, and is purported to mean "pondus hydrogenii" in Latin.[3] However, most other sources attribute the name to the French term pouvoir hydrogène. [4] [5] [6] In English, pH can stand for "hydrogen power,"[4] [5] [6] "power of hydrogen," [7] [8] or "potential of hydrogen."[3] [9] [10] All of these terms are technically correct.

Definition
Though pH is generally expressed without units, it is not an arbitrary scale; the number arises from a definition based on the activity of hydrogen ions in the solution. The pH scale is a reverse logarithmic representation of relative hydrogen proton (H+) concentration. Most scales are linear in nature and progress in a smooth incremental manner. On the pH scale, a shift up in value by one number represents a ten-fold decrease in value. For example, a shift in pH from 2 to 3 represents a decrease in total concentration of ten times less H+ concentration, and a shift from 2 to 4 represents a one-hundred fold decrease (10 X 10) in H+ concentration.

You could get more information from the link below...

Answer 4

As some others have said, the pH formula is -log[H+].
pH level determines if the solution is an acid or base with the determinance of H+ ion concentration. 1-6.9 are acidic, 7 is neutral, and 7.1-14 are base (or alkaline).

Answer 5

the pH is the negative of the logarithm of the H+ ion concentration in a solution...

For example

if the concentracion of H+ is 0,001 (mol/L) then the log will be -3...

so.. the pH will be 3

Answer 6

Potential of Hydrogen

Answer 7

pH is defined as the negative logarithm of hydrogen ion concentration........ pH = -log[H+]

Answer 8

http://en.wikipedia.org/wiki/PH

Here ya go...