LaMotte SMART3 Colorimeter - Manual (Page 245)

pH
COLORIMETRIC METHOD • CODE 3700-01-SC
QUANTITY CONTENTS CODE
60 mL Chlorphenol Red Indicator V-2209-H
60 mL Phenol Red Indicator V-2304-H
60 mL Thymol Blue Indicator V-2213-H
3 Pipets, 0.5 mL, plastic w/caps 0369
The term pH (always written with a lower case p and an upper case H) is correctly
defi ned as the negative logarithm of the hydrogen ion concentration. More simply,
the term pH can be considered to be an index of the amount of hydrogen ion
present in a substance, or is a measure of the acidity of the substance. This index
is important as it can be used to quickly identify the acid, neutral or alkaline (basic)
nature of materials. Acidic substances have a pH less than 7.0, neutral substances
have a pH equal to 7.0 and alkaline substances have a pH greater than 7.0.
Most natural waters have pH values from pH 5.0 to pH 8.5. Acidic, freshly fallen
rain water may have a pH value of pH 5.5 to pH 6.0. When it reacts with soils and
minerals containing weakly alkaline materials, the hydroxyl ion concentration will
increase and the hydrogen ion concentration will decrease. Then the water may
become slightly alkaline with a pH of 8.0 to 8.5. Natural sea water has a pH value
of 8.1, and changes from this value indicate that water from an inland source is
entering the body of sea water.
Waters more acidic than pH 5.0 and more alkaline than pH 8.5 to 9.0 should be
viewed with suspicion. Mine drainage and acidic industrial wastes are the principal
factors in increasing the acidity of water, and alkaline industrial wastes are the
cause of high pH values.
Because pH measurements can be made so simply, and because they can tell so
much about the past and future reactions of water, they are routinely made in water
quality studies. Sudden changes in pH values serve as warning signals that water
quality may be adversely affected through the introduction of contaminants.
SMART3 Test Procedures 11.10 pH
Test P
rocedures