Preparation and properties of sodium thio sulphate
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Preparation: Sodium thiosulfate can be prepared by heating sulfur with either aqueous sodium sulfite solution or aqueous sodium hydroxide solution.
6 NaOH + 4 S → Na2S2O3 + 2 Na2S + 3 H2O
Physical properties : Sodium thiosulfate is a white crystalline solid which is odorless and highly water soluble. It has a density of 1.667 g/mL and a melting point of 48.3°C.
Chemical properties: Sodium thiosulfate is a neutral salt which readily dissociates in water to give sodium and thiosulfate ions. Na2S2O3 is a stable solid under normal conditions, but decomposes upon heating to give sodium sulfate and sodium polysulfide:
4 Na2S2O3 → 3 Na2SO4 + Na2S5
It also decomposes when treated with dilute acids to give sulfur and sulfur dioxide (called 'clock reaction'):
Na2S2O3 + 2 HCl → 2 NaCl + S + SO2 + H2O
It reacts stoichiometrically (in equimolar amounts) with aqueous solutions of iodine, and so, it is widely used in laboratories for iodine based titrations.
6 NaOH + 4 S → Na2S2O3 + 2 Na2S + 3 H2O
Physical properties : Sodium thiosulfate is a white crystalline solid which is odorless and highly water soluble. It has a density of 1.667 g/mL and a melting point of 48.3°C.
Chemical properties: Sodium thiosulfate is a neutral salt which readily dissociates in water to give sodium and thiosulfate ions. Na2S2O3 is a stable solid under normal conditions, but decomposes upon heating to give sodium sulfate and sodium polysulfide:
4 Na2S2O3 → 3 Na2SO4 + Na2S5
It also decomposes when treated with dilute acids to give sulfur and sulfur dioxide (called 'clock reaction'):
Na2S2O3 + 2 HCl → 2 NaCl + S + SO2 + H2O
It reacts stoichiometrically (in equimolar amounts) with aqueous solutions of iodine, and so, it is widely used in laboratories for iodine based titrations.
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