The chemical formula Na2S2O3 represents Sodium Thiosulfate, a crystalline compound composed of sodium (Na), sulfur (S), and oxygen (O). Let’s understand its properties and applications in detail
Sodium thiosulfate (Na2S2O3) is a salt composed of sodium (Na+), sulfur (S), and oxygen (O). It is a white, crystalline substance that dissolves readily in water. The compound consists of two sodium ions and one thiosulfate ion (S2O32-). The thiosulfate ion is an interesting structure with a sulfur atom at the center, bonded to three oxygen atoms and another sulfur atom. The overall charge on the thiosulfate ion is -2.Sodium thiosulphate molecular weight is 158.11 grams per mole. The more commonly available pentahydrate form, Na2S2O3·5H2O, has a molar mass of 248.18 g/mol.
Here is a representation of the Crystals of Sodium Thiosulphate
Sodium thiosulfate is prepared by neutralizing sulfur dioxide with sodium hydroxide and is often encountered as the pentahydrate Na2S2O3·5H2O, a colorless, monoclinic crystalline substance that is readily soluble in water.
The name "thiosulfate" is derived from the presence of sulfur and oxygen in the molecule. In chemical reactions, sodium thiosulfate can undergo various transformations, including redox reactions where it can either gain or lose electrons. Understanding its chemical structure and reactivity is crucial for its diverse applications in photography, medicine, water treatment, and analytical chemistry.
Sodium thiosulfate (Na2S2O3) has several notable physical properties:
Sodium thiosulfate (Na2S2O3) exhibits various chemical properties due to its composition and the nature of the thiosulfate ion. Here are some key chemical properties:
Na2S2O3 + 2 HCl → 2 NaCl + S + SO2 + H2O
2Na2S2O3 + 4Cl2 → 4NaCl + 2Na2SO4
Sodium thiosulphate ( Na2S2O3 ) finds applications in various industries and scientific fields due to its unique properties. Some notable applications include:
1. Photography: Sodium thiosulphate solution is a key component in photographic fixing solutions. It is used to remove unexposed silver halide from developed photographic emulsions, stabilizing the final image.
2. Medical Use: Sodium thiosulfate is employed as an antidote for cyanide poisoning. It forms a complex with cyanide ions, reducing their toxicity. This application is critical in emergency medicine.
3. Water Treatment: Sodium thiosulphate solution is used to dechlorinate water. It reacts with chlorine, neutralizing its presence in tap water, swimming pools, and wastewater before discharge.
4. Analytical Chemistry: Sodium thiosulfate is widely used in analytical chemistry for titrations, particularly in the determination of iodine concentration. It is also used to standardize solutions of other substances.
5. Gold Extraction: In certain gold extraction processes, sodium thiosulfate is used as an alternative to traditional cyanide-based methods. This is especially relevant in environmentally conscious mining practices.
6. Chemical Reduction Reactions: Sodium thiosulfate is involved in redox reactions, serving as both an oxidizing and reducing agent. This versatility makes it useful in various chemical processes and experiments.
7. Hair Care Products: In the cosmetic industry, sodium thiosulfate is used in hair care products to neutralize or remove residual hair dyes, preventing discoloration.
8. Wastewater Treatment: It is utilized to neutralize excess chlorine in wastewater before discharge, contributing to environmental protection.
(i)
(ii) 2Na2S + Na2CO3 + 4SO2 → 3Na2S2O3 + CO2
(iii) 6NaOH + 4S → Na2S2O3 + 2Na2S + 3H2O
3Ca(OH)2 + 12 S → CaS2O3 + 2CaS5 + 3H2O
(iv) Na2SO3 + Na2S + I2 → Na2S2O3 + 2NaI (spring reaction)
(v) 2Na2S + 2O2 + H2O → Na2S2O3 + 2NaOH
[Na2S is readily oxidised in air giving rise to Na2S2O3]
Na2S2O3 + I2 → Na2S4O6 + 2NaI
Na2S2O3 + Cl2 – water → NaHSO4 + S + 2HCl
Na2S2O3 + Br2 – water → NaHSO4 + S + 2HBr
Na2S2O3 + 4Cl2 + 5H2O → Na2SO4 + H2SO4 + 8HCl
↓
2NaHSO4
(Session 2025 - 26)