The key difference between free ammonia and total ammonia is that the term free ammonia refers to the gaseous NH3 molecules, whereas the term total ammonia refers to the sum of NH3 molecules and ammonium ions.
Ammonia is a toxic, gaseous substance having the chemical formula NH3. In biological systems, ammonia can occur in two types as ionized form and as the unionized form. The ionized form is the ammonium ion which has the chemical formula NH4+.
CONTENTS
1. Overview and Key Difference
2. What is Free Ammonia
3. What is Total Ammonia
4. Side by Side Comparison – Free Ammonia vs Total Ammonia in Tabular Form
5. Summary
What is Free Ammonia?
Free ammonia is the unionized form of ammonia having the chemical formula NH3. When an ammonia molecule is ionized, it forms the ammonium ion. This ammonium ion is less toxic. However, the unionized ammonia or free ammonia in water is highly toxic to fish and other organisms that live in the water.
Figure 01: Structure of Ammonia Molecule
Chloramination is a common water treatment method that is important in producing drinking water. This water treatment is done using chloramine disinfectant. During this treatment method, chlorine and ammonia enter the water, forming monochloramine. Here, the amount of ammonia that is not combined with chlorine is called free ammonia.
What is Total Ammonia?
Total ammonia is the sum of free ammonia and ammonium ions in water. Usually, ammonia is present in surface water, groundwater and mainly in wastewater. When we are disinfecting these three types of water via adding chlorine, interactions between chlorine and ammonia takes place; these can form chloramine. Sometimes, ammonia is intentionally added to water to get monochloramine (a chemical species that is less reactive with organic compounds in water). Here, we can use the term total ammonia to express the total amount of free ammonia and ionized ammonia present in the water.
We can easily determine the total ammonia in a water sample via performing an analysis of free ammonia and a separate analysis of monochloramines, and the higher chloramines. Then the total ammonia value can be obtained by summing up the free ammonia and chloramines in the water. This value is very important in controlling chloramination of water.
What is the Difference Between Free Ammonia and Total Ammonia?
Ammonia is a toxic, gaseous substance having the chemical formula NH3. In water, there can be two forms of ammonia as free ammonia and total ammonia. The key difference between free ammonia and total ammonia is that the term free ammonia refers to the gaseous NH3 molecules, whereas the term total ammonia refers to the sum of NH3 molecules and ammonium ions.
When considering the values of these two parameters, for the same water sample, the value of total ammonia is always higher than the value of free ammonia. This is because we add the amount of ionized ammonia to the value of free ammonia to determine the total ammonia.
Below infographic summarizes the difference between free ammonia and total ammonia.
Summary – Free Ammonia vs Total Ammonia
The terms free ammonia and total ammonia are commonly used regarding the description of the properties of waterways. The key difference between free ammonia and total ammonia is that the term free ammonia refers to the gaseous NH3 molecules whereas the term total ammonia refers to the sum of NH3 molecules and ammonium ions.
Reference:
1. What Is Free Ammonia and When Is It Used? Hach – Water Quality Testing and Analytical Instruments, Available here.
Image Courtesy:
1. “Ammonia-2D” By Radio89 – Own work (CC BY-SA 3.0) via Commons Wikimedia