Difference Between Chelating Agent and Sequestering Agent

Main Difference – Chelating Agent vs Sequestering Agent

Both chelating agents and sequestering agents have the same role in a system, i.e., to mask a metal ion by forming a stable complex with metal ions. This helps to prevent these metal ions from undergoing chemical reactions or interfering with other chemical reactions. Therefore, these are very important compounds. Although both these compounds do the same thing, there are differences between the two types. The main difference between chelating agent and sequestering agent is that a chelating agent can bind with a single metal ion at a time whereas a sequestering agent can bind with few metal ions at a time.

Key Areas Covered

1. What is a Chelating Agent
      – Definition, Properties Related to Chelation
2. What is a Sequestering Agent
      – Definition, Properties Related to Chelation
3. What is the Difference Between Chelating Agent and Sequestering Agent
      – Comparison of Key Differences

Key Terms: Chelating Agent, Chelation, EDTA, Heavy Metals, Lone Electron Pair, Sequestering Agents, Sequestration

What is a Chelating Agent

A chelating agent is a chemical compound that can bind with a metal ion and prevent that metal from undergoing other chemical reactions. Here, the chelating agent can form a stable complex with a metal ion that is water soluble. This complex is known as a coordination complex.

These chelating agents are composed of atoms with lone pairs. These lone pairs can be donated to a metal ion (metal ions are always positively charged). The donation of one lone electron pair to the metal atom forms a coordinate covalent bond. The number of coordinate covalent bonds present in a coordination complex is called the coordination number.

Chelating agents are very useful in isolating heavy metals to remove them from drinking water, to deactivate metal ions that can cause precipitation and sealing, to limit available metal ion content, etc. Therefore, the applications of chelating agents are in the field of medical sciences, water treatment, corrosion control, etc.

Chelating agents can be found as either natural compounds or synthetic compounds. Amino acids, herbs like Cilantro, onions, and garlic are composed of chelating agents. Therefore, these natural sources are good at chelation.

Figure 1: A Metal-EDTA Complex

EDTA is a common example of a chelating agent. It is a multidentate ligand. This means it can bind with the metal ion via several atoms by forming coordinate covalent bonds. There are some other chelating agents that are Bidentate. They form only two coordinate covalent bonds.

What is a Sequestering Agent

A sequestering agent is a chemical compound that is capable of forming a complex with metal ions and helps to remove these ions from a solution. These sequestering agents can bind with several metal ions at a time. When a sequestering agent has formed a complex with metal ions, these metal ions cannot undergo any other chemical reactions.

Sequestering agents form ring-like structures around metal ions. These ring structures can be removed from the solution along with the metal ions they are bound to. There are several active sites in sequestering agents; thus, these compounds are more reactive.

Figure 2: The adverse effects of hard water can be avoided by using sequestering agents to treat hard water.

One common application of sequestering agents is the removal of water hardness. These compounds can bind with both calcium and magnesium ions in water. These compounds can bind with other heavy metals present in water as well. Therefore, these agents are useful in treating water chemically. Some commercially available sequestering compounds include sugar acrylates, polyacrylates, etc.

Difference Between Chelating Agent and Sequestering Agent

Definition

Chelating Agent: A chelating agent is a chemical compound that can bind with a metal ion and prevent that metal from undergoing other chemical reactions.

Sequestering Agent: A sequestering agent is a chemical compound that is capable of forming a complex with metal ions and helps to remove these ions from a solution.

Active Sites

Chelating Agent: Chelating agents have one active site per molecule.

Sequestering Agent: Sequestering agents have several active sites per molecule.

Reactivity

Chelating Agent: Chelating agents are less reactive compared to sequestering agents.

Sequestering Agent: Sequestering agents are more reactive due to the presence of several active sites.

Applications

Chelating Agent: Chelating agents are commonly used to prevent metal ions from undergoing chemical reactions or interfering with certain chemical reactions.

Sequestering Agent: Sequestering agents are commonly used to remove calcium ions, magnesium ions, and heavy metals from water.

Conclusion

Chelating agents are chemical compounds that can bind with metal ions in order to prevent these ions from undergoing or interfering chemical reactions. Sequestering agents are chemical compounds that can be used for the removal of hardness of water. The main difference between chelating agent and sequestering agent is that a chelating agent can bind with a single metal ion at a time whereas a sequestering agent can bind with few metal ions at a time.

References:

1. “What is a Chelating Agent? – Definition from Corrosionpedia.” Corrosionpedia, Available here.
2. “22.9: Chelating Agents.” Chemistry LibreTexts, Libretexts, 8 Sept. 2017, Available here.
3. Md. Mazadul Hasan Shishir, Production Officer at Intramex textile ltd Follow. “Sequestering agents.” LinkedIn SlideShare, 22 May 2014, Available here.

Image Courtesy:

1. “Metal-EDTA” By Smokefootderivative work: Chamberlain2007 (talk) – Medta.png (Public Domain) via Commons Wikimedia
2. “hard water” by Graeme Maclean (CC BY 2.0) via Flickr