pH, Wide Range (figs. 2-11 and 2-12, and para 2-18).
(1) pH is defined as the logarithm of the reciprocal of the
hydrogen ion activity expressed in moles per liter.
More simply, the
pH value of water sample expresses its tendency to accept or donate
hydrogen ions on a scale of 0 (very acidic) to 14 (very basic).
water at 25°C (77°F) is neutral and has a defined pH value of 7.
The pH value represents the instantaneous hydrogen ion activity rather
than the buffering capacity or the total reserve as in acidity and
(a) Most natural waters range from pH 4 to pH9 and are often
slightly basic due to the presence of carbonates and bicarbonates. A
major deviation from the normal pH for a given water indicates the
intrusion of strongly acidic or strongly basic industrial wastes. pH
adjustment is a common pratice in water treatment processes and is
used to control corrosion within the distribution system.
waters in the United States have pH values ranging from around 6.0 to
8.5, while surface waters vary between 6.5 to 8.5 pH units.
The pH of
some waters is held at lower levels by redox reactions, such as the
oxidation of sulfur and ferrous iron.
(b) The importance of pH in virtually every phase of water
supply and waste treatment is well established.
The 5.8 and 8.2
values are minimum and maximum aesthetic limits, respectively, speci-
fied by the U.S. Army for short-term consumption.
(c) The pH of water can be determined calorimetrically by
choosing indicators whose colors are highly pH dependent.
recommended the Wide Range pH test below be performed on the sample
initially to determine the approximate pH value, followed by a second
test using a more specific range and indicator.
(2) pH, Wide Range Test Procedure.
Wide Range pH Indicator.
May cause permanent
Keep well closed and in a cool place.
flush with water.
remove from exposure.
induce vomiting (salt in warm water).
Water may be ineffective.