Thiosulfate

Some salts come from sulfur.

These salts are found in nature. They help make colors for clothes. They are also used to make paper.

People use them in old photos. This helps the photos stay clear. They can even help get gold from rocks. They can also help doctors in emergencies. These salts do many big jobs.

Thiosulfate is a type of salt made from sulfur.

Some thiosulfate salts are found in nature. People use them in many ways. They help dye clothes with color. They also help make paper.

Thiosulfate can do many jobs in science. It can pull gold and silver from rocks. This is a safer way than using cyanide. In old film photography, it was used as a fixer. A fixer is a chemical that keeps a photo clear. People often called sodium thiosulfate "hypo."

This salt can also help in medical emergencies. It can help the body fight cyanide. An enzyme called rhodanase helps this work. This enzyme turns bad cyanide into safer parts.

In nature, tiny bacteria use thiosulfate for food. They use it to make their own energy. This helps them grow. Thiosulfate can also be part of rare minerals. One example is a mineral called sidpietersite.

A chart showing how sulfur changes.

Thiosulfate is a special kind of sulfur compound. It is an oxyanion, which is a group of atoms with a negative charge. You might find it in salts like sodium thiosulfate or ammonium thiosulfate. These salts can be found in nature. They are very useful in many different industries. For example, they help dye textiles with bright colors. They are also used in the paper-making industry to stop bleaching.

How does this tiny molecule work? At its center, there is a sulfur atom. This central atom is shaped like a tetrahedron. A tetrahedron is a solid shape with four triangular sides. The sulfur atom has a valence of 6. This means it can form six bonds. There is also an external sulfur atom with a valence of 2. Oxygen atoms in the group have a valence of 2 as well.

Scientists have studied thiosulfate for a long time. For many years, they thought the sulfur atoms had specific charge levels. They believed the central atom was +6 and the end atom was -2. However, new tools called XANES spectroscopy changed what we know. These measurements showed the charges are actually +5 and -1. This discovery helps explain how bacteria get energy from it. This process is called disproportionation.

Thiosulfate has many important uses in our world. In old film photography, people used sodium thiosulfate to fix photos. They often called it "hypo." Today, photographers use ammonium thiosulfate because it works three to four times faster. It can also help pull gold and silver out of rocks. This is a safer way than using a chemical called cyanide. It can even help in medical emergencies to fight cyanide poisoning.

Even tiny living things rely on thiosulfate. Some bacteria use it as an electron donor to grow. They take electrons from thiosulfate to make their own food. They also use carbon from carbon dioxide to build their bodies. This happens through a way of working called the reverse Krebs cycle. You can even find thiosulfate in very rare minerals. One such mineral is called sidpietersite.

Thiosulfate is a specific type of sulfur oxyanion with the chemical formula S2O3^2-. This molecule is a group of atoms that carries a negative charge. In chemistry, the term thiosulfate can also describe the salts of thiosulfuric acid. Common examples include sodium thiosulfate (Na2S2O3) and ammonium thiosulfate ((NH4)2S2O3). These compounds occur naturally in the environment. They are highly useful in many industries because of their unique chemical properties.

The structure of the thiosulfate ion is quite specific. At the center of the ion sits a sulfur atom. This central sulfur atom is arranged in a tetrahedral shape. A tetrahedron is a three-dimensional shape with four triangular faces. This central sulfur atom has a valence of 6. There is also an external or terminal sulfur atom. This outer sulfur atom has a valence of 2. The oxygen atoms in the molecule have a valence of 2. In sodium thiosulfate, the bond distance is about 2.4 Å. This distance is appropriate for a single bond. It is also slightly shorter than the bond distances found in sulfate.

For many years, scientists had a specific theory about the oxidation states of the sulfur atoms. They believed the central sulfur atom had an oxidation state of +6. They also thought the terminal sulfur atom had an oxidation state of -2. This was similar to the way atoms are arranged in sulfate or sulfide. However, this view made it hard to explain certain biological processes. It seemed impossible for thiosulfate to undergo a disproportionation reaction. Disproportionation is a process where one substance turns into two different products. This reaction provides energy to bacteria in sediments under anaerobic conditions. If the oxidation states did not change, there would be no energy release.

Modern science has corrected this older understanding. Scientists used a technique called X-ray absorption near edge structure, or XANES, spectroscopy. These measurements revealed that the charge densities are actually different. The central sulfur atom has an oxidation state of +5. The terminal sulfur atom has an oxidation state of -1. This new discovery matches what we see in nature. It explains how microbial fermentation can free up energy through disproportionation. This process allows bacteria to thrive in environments without oxygen.

Thiosulfate is also known for its many chemical reactions. When thiosulfate ions react with acids, they produce sulfur dioxide. They also create various sulfur rings. This specific reaction can be used to create sulfur colloids. These colloids demonstrate a phenomenon called Rayleigh scattering. This is the same mechanism that colors our sky blue during the day and orange at dusk.

Thiosulfate also reacts with iodine to produce tetrathionate ions. This reaction is a key part of a process called iodometry. Additionally, thiosulfate can be oxidized into sulfate when it reacts with bromine or chlorine.

In the world of industry and photography, thiosulfate is very important. In film photography, thiosulfate salts act as a fixer reagent. They form coordination complexes with silver to remove unexposed silver from film. Sodium thiosulfate was historically known as "hypo." Today, modern "rapid" fixers use ammonium thiosulfate instead. This is because ammonium thiosulfate works three to four times faster than the old method. Thiosulfate is also used to leach gold and silver from ores. This serves as a less toxic alternative to using cyanide.

Thiosulfate plays a vital role in medicine and biology as well. The enzyme rhodanase, or thiosulfate sulfurtransferase, helps the body detoxify cyanide. It does this by turning cyanide and thiosulfate into thiocyanate and sulfite. In emergency medicine, sodium thiosulfate is used in cyanide antidote kits. It is most effective when given immediately by emergency personnel. This helps reverse hypoxia, which is a lack of oxygen in the cells. Furthermore, some bacteria like Chlorobium limicola forma thiosulfatophilum use thiosulfate as an electron donor. They use these electrons and carbon from carbon dioxide to synthesize compounds through the reverse Krebs cycle.