Potassium thiosulfate (K2S2O3) is a chemical compound used in photography, as a reducing agent, and to neutralize chlorine in swimming pools. It has a white crystalline appearance and is soluble in water.
| IUPAC Name | Potassium thiosulfate |
| Molecular Formula | K2S2O3 |
| CAS Number | 10294-66-3 |
| Synonyms | Potassium hyposulfite, potassium thiosulphate, potassium thiosulfate pentahydrate, potassium thiosulphate pentahydrate, potassium sulfurothioate, potassium sulfurothioic acid |
| InChI | InChI=1S/2K.H2O3S2/c;;1-4(2)3/h;;(H2,1,2,3)/q2*+1;/p-2 |
Potassium Thiosulfate Properties
Potassium Thiosulfate Formula
The chemical formula for potassium thiosulfate (K2S2O3) indicates the number and type of atoms present in the compound. The formula consists of two potassium atoms, two sulfur atoms, and three oxygen atoms. The potassium atoms have a positive charge, while the sulfur and oxygen atoms have a negative charge.
Potassium Thiosulfate Molar Mass
The molar mass of K2S2O3 is 190.33 g/mol. Molar mass is the mass of one mole of a substance and is calculated by summing the atomic masses of all the atoms in the chemical formula. In the case of K2S2O3, the formula consists of two potassium atoms, two sulfur atoms, and three oxygen atoms.
Potassium Thiosulfate Boiling Point
K2S2O3 does not have a boiling point because it decomposes before reaching its boiling point. Decomposition occurs when the temperature is raised to about 100 °C, and sulfur dioxide gas is released. Therefore, the compound is not typically used in high-temperature applications.
Potassium Thiosulfate Melting Point
The melting point of K2S2O3 is 48.3 °C. This temperature is relatively low compared to other chemical compounds. When heated to this temperature, the solid K2S2O3 will become a liquid.
Potassium Thiosulfate Density g/mL
The density of K2S2O3 is 1.667 g/mL. Density is a measure of how much mass is contained within a certain volume. This value means that one milliliter of K2S2O3 has a mass of 1.667 grams.
Potassium Thiosulfate Molecular Weight
The molecular weight of K2S2O3 is 190.33 g/mol. The molecular weight is the sum of the atomic weights of all the atoms in the compound. It is often used to convert between moles and grams of a substance.
Potassium Thiosulfate Structure
The structure of K2S2O3 consists of two potassium atoms, two sulfur atoms, and three oxygen atoms. The sulfur atoms are connected to each other through a double bond, while the other sulfur atom is bonded to one of the oxygen atoms. The potassium atoms are bonded to the remaining oxygen atoms.
Potassium Thiosulfate Solubility
K2S2O3 is highly soluble in water, with a solubility of 432 g/L at 20 °C. This makes it an effective compound for use in water treatment and as a photographic fixing agent. However, it is not soluble in organic solvents such as ethanol or acetone.
| Appearance | White crystalline solid |
| Specific Gravity | 1.667 |
| Color | Colorless to white |
| Odor | Odorless |
| Molar Mass | 190.33 g/mol |
| Density | 1.667 g/mL |
| Melting Point | 48.3 °C |
| Boiling Point | Decomposes before boiling |
| Flash Point | Not applicable |
| Water Solubility | Highly soluble (432 g/L at 20 °C) |
| Solubility | Insoluble in organic solvents |
| Vapour Pressure | Not applicable |
| Vapour Density | Not applicable |
| pKa | Not applicable |
| pH | 6.0 – 9.0 (5% aqueous solution) |
Potassium Thiosulfate Safety and Hazards
K2S2O3 is generally considered to be safe to handle and use when proper precautions are taken. However, it is important to be aware of some potential hazards associated with this compound. Exposure to the dust or vapors of K2S2O3 may cause irritation to the eyes, skin, and respiratory system. Ingestion of the compound can also cause nausea, vomiting, and diarrhea. In addition, contact with the compound may cause dermatitis or skin sensitization in some individuals. As with any chemical, it is important to follow proper safety protocols when handling K2S2O3 to avoid exposure and reduce the risk of accidents.
| Hazard Symbols | Xi |
| Safety Description | S22 – Do not breathe dust. S24/25 – Avoid contact with skin and eyes. S37/39 – Wear suitable gloves and eye/face protection. |
| UN IDs | UN 3077 |
| HS Code | 2832.10.00 |
| Hazard Class | 9 – Miscellaneous hazardous materials |
| Packing Group | III |
| Toxicity | LD50 (oral, rat): 2,500 mg/kg |
Potassium Thiosulfate Synthesis Methods
One can synthesize K2S2O3 through various methods, including reacting sulfur with potassium sulfite in the presence of an alkali metal hydroxide.
Another method involves the reaction of potassium hydroxide with sulfur and sulfur dioxide gas. This reaction produces K2S2O3 and potassium sulfate as byproducts.
An alternative synthesis method involves the reaction of potassium sulfite with sodium thiosulfate in an aqueous solution. One can filter and wash the resulting precipitate to obtain pure K2S2O3.
To prepare K2S2O3 in a laboratory setting, one can react potassium hydroxide with sulfur and then add sulfur dioxide gas to the mixture. The resulting product is a white crystalline solid that can be further purified by recrystallization.
Potassium Thiosulfate Uses
K2S2O3 has several important uses across a variety of industries. Here are some of its most common applications:
- Photography: potassium thiosulfate is used as a fixing agent in photographic processing to remove unused silver halides and prevent image fading.
- Agriculture: potassium thiosulfate is used as a fertilizer to supply plants with sulfur and potassium, which are important nutrients for growth and development.
- Water treatment: potassium thiosulfate is used to remove chlorine from the water in swimming pools and spas, as well as to neutralize the effects of chlorine in industrial wastewater treatment.
- Analytical chemistry: potassium thiosulfate is used in analytical chemistry as a reducing agent to determine the concentration of iodine and other oxidizing agents.
- Medical treatments: potassium thiosulfate has been used in some medical treatments, such as the treatment of cyanide poisoning.
- Industrial applications: potassium thiosulfate is used in various industrial applications, such as electroplating, leather tanning, and oil extraction.
Questions:
Q: How to determine if something is a reducing agent of Potassium Thiosulfate?
A: K2S2O3 is a reducing agent because it has the ability to donate electrons to other molecules or ions, which reduces their oxidation state.
Q: What makes Potassium Thiosulfate a reducing agent?
A: K2S2O3 has a sulfur atom with a lower oxidation state than in sulfate, which allows it to donate electrons to other molecules or ions and act as a reducing agent.
Q: Does potassium thiosulfate burn greens?
A: No, K2S2O3 does not burn greens. It is a white crystalline solid and is not known to exhibit any green coloration.
Q: What is the molar solubility of AgCl in 1.0 M K2S2O3?
A: The molar solubility of AgCl in 1.0 M K2S2O3 is dependent on various factors such as temperature and ionic strength. A precise value cannot be determined without additional information.
Q: What is the charge or oxidation number of K in 2(K2S2O3)?
A: The charge or oxidation number of K in 2(K2S2O3) is +1.
Q: What is the oxidation state of S in K2S2O3?
A: The oxidation state of S in K2S2O3 is +2.
Q: How many molecules are in 4 moles of K2S2O3?
A: There are approximately 4 x 6.022 x 10^23 molecules of K2S2O3 in 4 moles of K2S2O3, which is equivalent to 2.409 x 10^24 molecules.
Q: How much is 4 moles of K2S2O3?
A: The mass of 4 moles of K2S2O3 can be calculated by multiplying the molar mass of K2S2O3 (190.31 g/mol) by 4, which equals 761.24 grams. Therefore, 4 moles of K2S2O3 is equivalent to 761.24 grams.