Definition
The negative log(anti-log) of hydrogen ion cocentration is called pH.
Explanation
Hydrogen and hydroxyl ions affect the chemical reactions in the cell.Therefore,the concentrations of these ions in body fluids are inportant.
The higher the concentration of Hydrogen ion,the more acidic the solution.
The higher the concentration of Hydroxyl ions,the more basic (alkaline) the solution.
A neutral solution has equal number of hydrogen ion and hyroxyl ions.
The pH scale measures acidity and alkalinity .It runs from 0 to 14.
1.Acidic solution has pH less than 7
2.Basic solution has pH above 7
3.A pH of 7 is neutral.
Each whole number on pH scale epresent a ten fold change in acidity.Therefore a solution of pH 3 is 10 times more acidic than a solution with pH 4.A pH of 9 is 10 times more basic than a pH of 8.
pH of Water Solutions
In pure liquid water ( distilled water), a small fraction of the water
molecules split into ions of hydrogen (H ) and hydroxide (OH ); the
concentration of both ions is 10^-7moles/liter. An acidic substance,
when dissolved in water, contributes H ions to solution, thereby
increasing their concentration and causing an excess of H ions over
OH ions in solution. A basic substance does the reverse, contributing OH ions to the solution and making OH ions more common
than H ions. The degree to which a solution is acidic or basic is critical for most cellular processes and requires precise quantification and
control; the structure and function of dissolved proteins, for example,
depend critically on the concentration of H ions in the solution.
The pH scale quantifies the degree to which a solution is acidic
or basic. The scale ranges from 0 to 14 and represents the additive inverse of the logarithm (base 10) of the H concentration (in
moles/liter) of the solution. Pure liquid water therefore has a pH of 7
(H ions concentration 10^-7 moles/liter). A solution with pH 6.0 has
an H concentration ten times higher than that of pure water and is
acidic, whereas a solution with pH 8.0 has an H concentration ten
times lower than pure water and is basic. A concentrated strong acid,
such as hydrochloric acid (HCl, known commercially as “muriatic
acid” used to clean masonry) has an H concentration of ~1=10^0
mole/liter, giving a pH of 0 (a concentration of H 10,000,000 times
that of pure water). A concentrated base, such as sodium hydroxide
(NaOH, used commercially in liquid drain cleaners) has an H concentration of approximately 10^-14 mole/liter, giving a pH of 14.
Buffer Activity
A buffer is a dissolved substance (solute) that causes a solution to
resist changes in pH because the buffer can remove added H and
OH ions from solution by binding them into compounds. Dissolved
carbon dioxide in the form of bicarbonate (HCO 3
) is a buffer that
helps to protect human blood (pH 7.3 to 7.5) from changes in pH.
H ions are removed from solution when they react with bicarbonate
ions to form carbonic acid, which then dissociates into carbon dioxide
and water. The excess carbon dioxide is removed during exhalation. OH ions are removed from solution when this reaction is
reversed, forming bicarbonate and hydrogen ions. The excess bicarbonate ions are secreted in the urine, and the hydrogen ions
serve to increase blood pH back to normal levels. Severe health problems occur if the pH of blood drops to 7 or rises to 7.8.
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