what is ph a measurment of in water?

Answer 1

In solution at 25 °C, a pH of 7 indicates neutrality (i.e. the pH of pure water) because water naturally dissociates into H+ and OH− ions with equal concentrations of 1×10−7 mol/L. A lower pH value (for example pH 3) indicates increasing strength of acidity, and a higher pH value (for example pH 11) indicates increasing strength of basicity. Note, however, that pure water, when exposed to the atmosphere, will take in carbon dioxide, some of which reacts with water to form carbonic acid and H+, thereby lowering the pH to about 5.7.

Neutral pH at 25 °C is not exactly 7. pH is an experimental value, so it has an associated error. Since the dissociation constant of water is (1.011 ± 0.005) × 10-14, pH of water at 25 °C would be 6.998 ± 0.001. The value is consistent, however, with neutral pH being 7.00 to two significant figures, which is near enough for most people to assume that it is exactly 7. The pH of water gets smaller with higher temperatures. For example, at 50 °C, pH of water is 6.55 ± 0.01. This means that a diluted solution is neutral at 50 °C when its pH is around 6.55 and that a pH of 7.00 is basic.

Most substances have a pH in the range 0 to 14, although extremely acidic or extremely basic substances may have pH less than 0 or greater than 14. An example is acid mine runoff, with a molar concentration of 3981 M and a pH = -3.6.

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

Answer 2

pH is the log (logarithm) of the H+ ion concentration in a liquid. Regular old water molecules occasionally split up to form Hydrogen Ions (H+) and Hydroxide ions (OH-).

The concentration of these two ions in water is extremely small. Most of the water stays together as H2O. In neutral water, only 0.0000001 moles of H+ ions are present per litre of water. The same is true of OH- ions. (sorry no superscripts in this text editor!)

That concentration is expressed as 1.0 x 10 -7 moles per litre or 1.0 x 10 -7 M.

If some other chemical substance is added to the water, it can cause a greater concentration of H+ ions. For example, adding a very small amount of Sulphuric Acid (H2SO4), might result in a concentration of Hydrogen ions of 0.01 moles per litre. This would be expressed as 1.0 x 10 -2 and the pH would then be 2.

It all depends on the concentration of H+ ions in the solution. The higher the concentration, the lower the pH. Stomach acid has a pH as low as 1.8.

If the something is added that increases the concentration of OH- ions, the concentration of H+ ions goes down. For example, adding Sodium Hydroxide (Lye, NaOH), could make the H+ ion concentration drop to 0.000000000001 moles per litre. Then the pH would be 11. (1.0 x 10 -11)

Strongly acidic solutions have a pH lower than 2.0. Strong bases have a pH higher than 12.0.

A related measure is the log of the (OH-) ion concentration called the pOH. For water based solutions, the pH and the pOH add up to 14. (check out the disassociation constant for water if you need more information on that little tidbit!)

Answer 3

pH is the measure of the concentration of hydronium ions [H^+1] present in a solution. The actual pH is a log of this concentration. The other answers are correct in that pure water's pH is 7 which is neutral. A pH higher than 7 is associated with basic solutions, and a pH lower than 7 is associated with acidic solutions.

Notice how most acid formulas start with "H"

This is because when they are added to water, they dissociate and release their H to become hydronium ions.

I hope this helped.

Answer 4

Under 7 ph = Acidic
Over 7 ph = Basic

Answer 5

7

Answer 6

In distilled water, ph is 7. It could be a tiny bit more/ less depending on the type of water.

Ph has an equal amount of hydroxide and hydronium ions.. OH- and H+ respectively.

Answer 7

It is 7

Answer 8

On a slightly different tack pH is also used as a measure of conductivity which increases with higher concentration of ions

Answer 9

If it is just plain water, the PH value should be 7 (Neutral).
If it is more Alkaline (Basic), the PH value should be more than 7
If it is more Acidic, the PH value should be less than 7

Answer 10

Pure water should have a pH of 7.0. It is neutral. Tap water is not gaenerally 7 because of impurities,metals from pipes, dissolved salts and gases, an etc.