The pH scale measures the acidity of a substance.

p = potential H = Hydrogen ions (H+) in a water solution What is an ion? ______________________________________An atom that has lost or gained an

electron

As the percentage of H+ ions increase in a solution, the acidity increases.

Acid = a compound that forms H+ ions in solution with water.

Example: CO2 + H2O H2CO3 (carbonic acid)

Carbonic acid then dissociates into H2CO3 H+ + HCO3

- The release of H+ lowers the pH of the

solution.

As the percentage of OH- ions increase in a solution, it becomes more base.

Base = a compound that forms OH- ions in solution with water.

Example: NH3 + H2O NH4 + OH-

The release of OH- increases the pH of the solution.

The scale measures from 0 – 14.

Strong acids range from 1-3.

Strong bases range from 11-14.

The scale is logarithmic.

This means each pH value below 7 is ten times more acidic than the next higher value.

How much more acidic is pH 4 than pH 5? _______

How does the acidity of pH 6 compare to pH 4?_______________________

Freshwater fish thrive at pH 7. They die at pH 4. How much more acidic is pH 4 than pH 7? __________

10 times

1/100 or .01 times the acidity

1000 times

Stomach acid (hydrochloric acid) has a pH of <2.0

Pure water has a pH of 7.0

MOST cells in the Human Body require a pH of 6.5-7.5.

If the pH is higher or lower than this, chemical reactions cannot occur.

Extremely high or low pH values generally result in complete loss of activity for most enzymes.

However, each enzyme has a different “optimum” pH. This depends on where it is found in the body.

Enzyme pH OptimumLipase (pancreas)8.0Lipase (stomach)* 4.0 - 5.0Lipase (castor oil)4.7Pepsin* 1.5 - 1.6Trypsin 7.8 - 8.7Urease 7.0Invertase** 4.5Maltase 6.1 - 6.8Amylase (pancreas) 6.7 - 7.0Amylase (malt)** 4.6 - 5.2Catalase 7.0 * Stomach**Intestines 

Rainwater in the northeast has become acidic from the mixture of water with air pollutants.

When acid rain falls, the pH of ponds and lakes in the northeast decreases.

This has a direct effect on aquatic life.

Read and or discuss article from USGS (United States Geological Survey) on Acids, Bases and pH