LaMotte SMART Spectro Spectrophotometer - Manual (Page 194)

pH
COLORIMETRIC METHOD • CODE 3700-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 defined 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.
SMART SPECTRO TEST PROCEDURES 05.04 pH 1/2