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Sodium thiosulfate anhydrous vs. pentahydrate


shakti v.

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I just bought sodium thiosulfate from a chemical store. The label did not

indicate whether it was anhydrous or pentahydrate. I asked the store and they

said it was not indicated either. The chemical is from China. The detail is

only: sodium thiosulfate, 99% photo grade.

 

What I have here are big colourless crystals/granules. Does anyone here have

an idea whether this is anhy or penta? What are the differences in appearance

between sodium thiosulfate anhydrous and sodium thiosulfate pentahydrate?

 

I am still researching, but it will be a great help if someone here could give

me their advice. I hope someone can answer this question.

 

Thanks.

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Crystals would indicate pentahydrate. Also, when the pentahydrate is dissolved in water, a lowering of temperature is observed. You could use this as confirmation.

 

The pentahydrate contains "water of crystallization" and hence is less concentrated than the anyhydrous. If a recipe calls for anyhydrous, and you have crystalline (pentahydrate) you need more. Multiply the amount in the recipe by 1.56 (in other words, divide by 0.64). I'm not sure if that was expressed clearly in a post above.

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John, thank you. I got that. Yes, I have penta. I also used the conversion to make ammonium thiosulphate= 600 g ammonium chloride + 1406g sodium thiosulfate (using division by 0.64; 900g in anhy), in 1.5 L of water.

 

To those interested, I made a post about my process in making TF-3 alkaline fixer. Please post comments and suggestions on that thread.

 

Gracias.

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