Thiosulfate: Uses & Formula

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  • 0:00 What Is Thiosulfate?
  • 2:35 Thiosulfate Formula &…
  • 3:24 Uses of Thiosulfate
  • 5:35 Lesson Summary
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Lesson Transcript
Instructor: Danielle Reid

Danielle has taught middle school science and has a doctorate degree in Environmental Health

Thiosulfate is a compound with a variety of uses ranging from medicinal to the processing of photography film. Explore this lesson to learn more about these uses, what thiosulfate is, and its structure and formula.

What Is Thiosulfate?

Thiosulfate might sound like a chemical created in a lab, but it can actually be found in nature. If you wanted to go looking for it, you might find it in geysers and hot springs. Even the hot springs at Yellowstone National Park were tested and found to contain a small amount of thiosulfate. So, what exactly is thiosulfate?

Thiosulfate is a type of ion, specifically an oxyanion of sulfur. The molecular weight of this ion is 112.12 g/mol. What is an ion, and more importantly, what is an oxyanion? An ion is a molecule or atom that carries a negative or positive charge. An oxyanion is a type of ion that has an oxygen atom present in its formula. Here's the reaction used to create the thiosulfate oxyanion from sulfur.

thiosulfate caption=

In the presence of boiling water, when a sulfur atom (molecule 'a') reacts with a sulfite ion (molecule 'b'), a thiosulfate product is formed. The thiosulfate molecule is labeled 'c.' Can you spot the oxyanion in this reaction? That's right: it's the product formed, or thiosulfate. Again, you can tell thiosulfate is an oxyanion given the presence of an oxygen atom in its formula in addition to its negative charge.

As mentioned earlier, thiosulfate is naturally found in places such as hot springs and geysers. However, the quantity of thiosulfate found in these natural sources is small. With regards to its properties, thiosulfate is known to be a great reducing agent. A reducing agent is a compound that is willing to donate its electrons to another compound in a specific reaction called the oxidation-reduction reaction. When we discuss the uses of thiosulfate, we'll understand the benefit it has as a reducing agent.

Another property of thiosulfate is its ability to form a complex ion with metals. This process occurs when several thiosulfate ions function as ligands binding to a metal. The benefit of forming complex ions with metal serves to increase the water solubility of a metal or metal compound.

You may encounter a variety of compounds that contain the thiosulfate ion. In fact, there are several different compounds, such as sodium sulfate, calcium thiosulfate, and barium thiosulfate, that contain this ion. As we'll see shortly, each thiosulfate compound can be used for a specific purpose.

Thiosulfate Formula & Structure

The molecular formula of thiosulfate is S2O32-. Thiosulfate has a central sulfur atom surrounded by three oxygen atoms and one sulfur atom. Specifically, a double bond is present between the bonding of two oxygen atoms to the sulfur atom. Keep in mind that thiosulfate is an ion. This explains the presence of a -2 charge in its structure.

Molecular Structure of Thiosulfate

The molecular geometry of thiosulfate is classified as a tetrahedral shape. Now why would thiosulfate have this particular shape? Great question! It has a central atom (sulfur) with four atoms bonded at exact angles of 109.5. This bond angle is a key requirement when classifying a compound's structure as tetrahedral.

Uses of Thiosulfate

We can discuss the uses of thiosulfate in two broad categories: thiosulfate ion and thiosulfate compounds. As a thiosulfate ion, this molecule is useful when acting as either a reducing agent or complex ion.

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