Fri October 07, 2011 By: Swati Singh

why the ph scal is end the 14

Expert Reply
Mon October 10, 2011

Basically a pH scale measures the concentration of H+ and OH-. The pH of a solution is defined as a negative logarithm of the hydrogen ion concentration and the pH scale measures this and places a value on it ranging from 0 to 14.

The pH scale was developed because the concentration of the solution can vary by so many factors they found over time, and a pH scale was the easiest way to express the variation of the solution.

The pH scale ranges from 0 to 14. The 0 end of the scale is where the concentration is increasingly acidic.

the difference in hydrogen ion concentrations in typical solutions could vary by a factor of 1014, and that in a neutral solution the hydrogen ion concentration is 1.0 x 10-7

Water molecules exist in equilibrium with hydrogen ions and hydroxide ions.

H2O <--> H+ + OH-

The water equilibrium constant is written as:

Kw = [H+] [OH-]

Experimentally, it has been found that the concentration of:
H+ = OH- = 10-7

Therefore: Kw = [10-7][ 10-7] = [10-14]


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