There can be two reactions depending on the concentration and temperature of nitric acid solution. You know nitric acid is an oxidizing acid. So it can oxidize other compounds while nitric acid is reduced. With sodium thiosulfate too, nitric acid can react in two ways to give products. We will discuss them in this tutorial.
In thiosulfate ion, there are two sulfur atoms. But, these two sulfur atoms do not exist at same oxdation state. One sulfur atom is at 0 oxidation state while other one is at +4 oxidation state. It is important to know oxidation states of elements to understand about some reactions.
With dilute nitric acid sodium nitrate (NaNO3), sulfur dioxide (SO2), sulfur (S) and water (H2O) can be given as products.
Yellow/white colour precipitation (sulfur) can be observed when reaction is started. Also, unpleasant smell of SO2 is felt.
With dilute nitric acid, sodium sulfate (Na2SO4), nitrogen dioxide (NO2), sulfur (S) and water (H2O) can be given as products.
Yellow/white colour precipitation (sulfur) can be observed in this occasion too. Here brown colour nitrogen dioxide gas with unpleasant smell is felt.
In this reaction, nitric acid is reduced to nitrogen dioxide. Sulfur atom which is +4 oxidation state in thiosulfate ion is oxidized to sulfate. Therefore, this reaction is a redox reaction.
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