Exam Study Guide: Alkalinity

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When faced with a licensing exam, don't struggle with test anxiety! Use the question below and others from our Exam Study Guide series to study and prepare for exam questions. Take a look at this sample water treatment licensing question along with an explanation of the correct answer.

Sample question:

Total alkalinity is the sum of the bicarbonate, carbonate and hydroxide forms of alkalinity. At what pH level will all three forms of alkalinity be found in the water at the same time?

A) pH range of 8.3 to 9.4
B) pH range of 9.4 to 11
C) pH range of 4.6 to 8.3
D) At no pH range will all three forms of alkalinity be present at the same time.


When water has a pH less than 8.3, all alkalinity is in the bicarbonate form. The form of alkalinity will change as the pH rises. At a pH range of 8.3 to 9.4, the alkalinity is bicarbonate and carbonate. With a pH range of 9.4 to 11, the alkalinity is carbonate and hydroxide. So water will never have all three forms of alkalinity at the same time.

So, the correct answer is D.

Reference: Water Treatment Plant Operation. 5th Edition, Volume ll, California State University, Sacramento. Page 80, 81

About the author
Drew Hoelscher is program director of drinking water operations at the Environmental Resources Training Center (ERTC) in Edwardsville, Illinois.


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