Sodium thiosulfate is a chemical compound with the formula Na2S2O3. It is commonly used as a fixer in photographic processing and as a reducing agent in certain chemical reactions.
| IUPAC Name | Sodium thiosulfate |
| Molecular Formula | Na2S2O3 |
| CAS Number | 7772-98-7 |
| Synonyms | Sodium hyposulfite, Sodium thiosulphate, Thiosulfuric acid disodium salt, Sodium thiosulfate pentahydrate |
| InChI | InChI=1S/2Na.H2O3S2/c;;1-5(2,3)4/h;;(H2,1,2,3,4)/q2*+1;/p-2 |
Sodium Thiosulfate Properties
Sodium Thiosulfate Formula
The chemical formula of sodium thiosulfate is Na2S2O3. It consists of two Na+ ions and two S2O3 2- ions. The formula shows the types and number of atoms present in a molecule of the compound.
Sodium Thiosulfate Molar Mass
The molar mass of Na2S2O3 is 158.11 g/mol. It is calculated by adding the atomic masses of all the atoms present in one mole of the compound. This value is useful in determining the amount of Na2S2O3 needed for a specific reaction or in calculating the concentration of a solution.
Sodium Thiosulfate Boiling Point
Na2S2O3 does not have a boiling point as it decomposes before reaching its boiling point. At normal pressure, it decomposes around 48-55°C, releasing sulfur dioxide gas. This property makes it unsuitable for high-temperature applications.
Sodium Thiosulfate Melting Point
The melting point of Na2S2O3 is 48.3°C. This is the temperature at which the solid compound changes its state to a liquid. It has a relatively low melting point compared to other inorganic salts, making it easy to dissolve in water.
Sodium Thiosulfate Density g/mL
The density of Na2S2O3 is 1.667 g/mL. This value refers to the mass of the substance per unit volume. It is higher than the density of water, which means that Na2S2O3 sinks in water.
Sodium Thiosulfate Molecular Weight
The molecular weight of Na2S2O3 is 158.11 g/mol. It is the sum of the atomic weights of all the atoms present in one molecule of the compound. The molecular weight is useful in determining the amount of Na2S2O3 needed for a specific reaction or in calculating the concentration of a solution.
Sodium Thiosulfate Structure
The structure of Na2S2O3 consists of two S2O3 2- ions, bonded to a sodium ion, Na+. The molecule has a trigonal pyramidal shape with a bond angle of approximately 103 degrees. The thiosulfate ion has a sulfur-sulfur bond and two sulfur-oxygen bonds.
Sodium Thiosulfate Solubility
Na2S2O3 is highly soluble in water. The solubility of Na2S2O3 in water increases with temperature, with approximately 70 g of the compound dissolving in 100 mL of water at 25°C. It is also soluble in glycerol and slightly soluble in alcohol. Its solubility makes it useful in various applications, such as in photographic processing and medical treatments.
| Appearance | White crystalline powder |
| Specific Gravity | 1.667 g/mL |
| Color | Colorless to white |
| Odor | Odorless |
| Molar Mass | 158.11 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 |
| Solubility | Soluble in glycerol and slightly soluble in alcohol |
| Vapour Pressure | Not applicable |
| Vapour Density | Not applicable |
| pKa | Not applicable |
| pH | Neutral (pH 7) |
Sodium Thiosulfate Safety and Hazards
Na2S2O3 is generally considered safe when handled properly. However, it can be hazardous if ingested, inhaled, or if it comes into contact with the eyes or skin. The compound can cause skin and eye irritation, and prolonged exposure can lead to dermatitis. Ingesting Na2S2O3 can cause gastrointestinal discomforts, such as nausea and vomiting. It is important to wear appropriate personal protective equipment, such as gloves and safety glasses when working with Na2S2O3. In case of exposure, the affected area should be flushed with water and medical attention sought if necessary.
| Hazard Symbols | None |
| Safety Description | Avoid contact with eyes, skin, and clothing. Do not ingest. Wear appropriate personal protective equipment. |
| UN IDs | UN3077 |
| HS Code | 2832.3010.00 |
| Hazard Class | 9 |
| Packing Group | III |
| Toxicity | Low toxicity; LD50 (oral, rat) is 6,200 mg/kg |
Sodium Thiosulfate Synthesis Methods
Various methods can synthesize Na2S2O3.
One common method involves reacting sodium sulfite with sulfur in the presence of an alkaline solution. Another method involves reacting sodium sulfite with sulfur dioxide gas under pressure.
A method to prepare Na2S2O3 involves dissolving sulfur in a hot solution of sodium sulfite and sodium hydroxide. The solution cools down and someone filters it to obtain a solid product.
In this method, one reacts sulfur dioxide with sodium hydroxide to produce sodium sulfite and then reacts it with elemental sulfur to produce Na2S2O3.
To produce Na2S2O3, one can react with sulfuric acid with sodium sulfite, followed by heating the resulting solution and adding sulfur. The sodium sulfite will then react with the sulfur to form Na2S2O3.
Another method involves reacting sodium hydroxide with sulfur, followed by the addition of sodium sulfite to form Na2S2O3.
Sodium Thiosulfate Uses
Na2S2O3 has a wide range of uses in various industries and applications, including:
- Photography: Used as a fixing agent to remove unexposed silver halide from photographic prints and films.
- Water treatment: Used to dechlorinate water by neutralizing chlorine and preventing its harmful effects on aquatic life.
- Medical applications: Used in the treatment of cyanide poisoning, as it reacts with cyanide to form thiocyanate, which is less toxic and can be excreted from the body.
- Industrial applications: Used as a reducing agent in chemical processes and as a preservative in textiles, leather, and paper.
- Analytical chemistry: Used as a titrant in the analysis of various metals, such as copper and arsenic.
- Food and beverage industry: Used as a food preservative to prevent discoloration and as a flavor enhancer.
- Horticulture: Used to neutralize the effects of chlorine in water used for irrigating plants.
Questions:
Q: What is sodium thiosulfate used for?
A: Na2S2O3 has a wide range of applications, including photography, water treatment, medical treatments, industrial processes, analytical chemistry, food and beverage preservation, and horticulture.
Q: How to make sodium thiosulfate?
A: Na2S2O3 can be synthesized by reacting sodium sulfite with sulfur or sulfur dioxide in the presence of an alkaline solution. Other methods involve reacting sodium hydroxide with sulfur or sulfur dioxide to produce sodium sulfite, which is then reacted with sulfur to produce Na2S2O3.
Q: What is gold sodium thiosulfate?
A: Gold Na2S2O3 is a complex compound formed by the reaction of gold chloride and Na2S2O3. It is used in gold plating and in analytical chemistry to detect and quantify gold.
Q: Where to buy sodium thiosulfate?
A: Na2S2O3 can be purchased from chemical suppliers, laboratory supply companies, and online retailers.
Q: Where to find sodium thiosulfate?
A: Na2S2O3 can be found in various products, including photographic chemicals, water treatment products, and medical treatments.
Q: What is the oxidation number of sulfur in Na2S2O3?
A: The oxidation number of sulfur in Na2S2O3 is +2 in the thiosulfate ion (S2O3^2-) and +6 in the sulfate ion (SO4^2-).
Q: How to find the weight of Cu from the titration of Na2S2O3?
A: The weight of Cu can be calculated from the volume and molarity of the Na2S2O3 solution used in the titration, using the balanced chemical equation for the reaction between Cu and Na2S2O3.
Q: How will you know when a stoichiometric amount of Na2S2O3 has been added?
A: A stoichiometric amount of Na2S2O3 has been added when the endpoint of the reaction is reached, as indicated by a change in color or other physical or chemical property.
Q: If 5 drops of 0.15 M KI are added to 40 drops of Na2S2O3, what is the final concentration of KI?
A: The final concentration of KI cannot be determined without additional information, such as the volume or concentration of the Na2S2O3 solution.
Q: How to find the molarity of Na2S2O3?
A: The molarity of Na2S2O3 can be calculated from the mass of the sample and the volume and concentration of the solution used to dissolve it, using the formula Molarity = moles of solute/volume of solution in liters.