The key difference between total alkalinity and pH is that total alkalinity is the total concentration of all alkaline substances dissolved in water whereas pH is the minus log of the concentration of hydrogen ions in water.
Most of the times, we confuse with the two terms total alkalinity and pH because both these terms are equally useful in aquatic chemical determinations. Indeed, these two terms relate to each other, but they are not the same. Thus, there exist a definite difference between total alkalinity and pH
CONTENTS
1. Overview and Key Difference
2. What is Total Alkalinity
3. What is pH
4. Side by Side Comparison – Total Alkalinity vs pH in Tabular Form
5. Summary
What is Total Alkalinity?
Total alkalinity is the water’s ability to resist changes in pH. In other words, it is the measurement of total concentration of all the alkaline species dissolved in water. The principle alkaline species include hydroxide ions, carbonate and bicarbonate ions. These ions can buffer the pH of water by neutralizing acids, that’s why we can say that the total alkalinity is the ability of water to resist the changes in pH.
Figure 01: Most Natural Water Sources have Alkaline Water
Moreover, the aquatic chemist uses the unit milligrams per litre of calcium carbonate (mg/L CaCO3) to measure this parameter. Or else, we can simply use the unit ppm (parts per million). The ideal range of this parameter for good quality water is 80-120 ppm.
What is pH?
pH is the “power of hydrogen”. We can calculate the pH of water by taking the minus log value of hydrogen ion concentration in water. Therefore, using this parameter, we can determine how acidic or how basic a water sample is. Thus, we can determine the quality of water.
The pH value has no unit since it is a log value. There is a pH scale that we use to determine the alkalinity or acidity of water. Here, the pH scale has values from 1 to 14. The pH 7 is the neutral value and the values below 7 are acidic values and values above 7 are basic values.
Figure 02: pH Scale
Herein, managing the pH value of a water source is critical in maintaining the quality of water. It determines whether the water is suitable for consumption or not. For example, most of the natural water sources have alkaline nature. Therefore, high pH water can cause scale formation, cloudy water, etc. While, the low pH water can cause damage to pool liners and etching of plaster, skin and eye damage, etc.
What is the Difference Between Total Alkalinity and pH?
We can define total alkalinity as the water’s ability to resist changes in pH whereas pH is the “power of hydrogen”. The theory behind these two terms is that the total alkalinity is the total concentration of all alkaline substances dissolved in water while the pH is the minus log of the concentration of hydrogen ions in water. Hence, this is the key difference between total alkalinity and pH. Above all, we measure the total alkalinity using ppm or milligrams per litre of calcium carbonate (mg/L CaCO3) whereas there is no unit for pH measurement since it is a log value.
The below infograhic describes the difference between total alkalinity and pH in more detail.
Summary – Total Alkalinity vs pH
We talk about the two terms total alkalinity and pH of water in aquatic chemistry. The key difference between total alkalinity and pH is that the total alkalinity is the total concentration of all alkaline substances dissolved in water whereas the pH is the minus log of the concentration of hydrogen ions in water.
Reference:
1. Orenda Technologies. “What Is PH?” Total Alkalinity vs. PH, and Their Role in Water Chemistry. Available here
2. “PH.” Wikipedia, Wikimedia Foundation, 1 Aug. 2018. Available here
Image Courtesy:
1.”930167″ (CC0) via pxhere
2.”216 pH Scale-01″By OpenStax College – Anatomy & Physiology, Connexions Web site. Jun 19, 2013., (CC BY 3.0) via Commons Wikimedia