# How much space does FeCl3*6H20 occupy?

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Here is an interesting question.

Suppose you have to prepare a half liter of 10^5 ppm solution of Iron in 15% HCl using Ferric chloride hexahydrate.

So (10^5 mg/L Fe) x (0.5L/1) x (1g/1000mg) x (~270g FeCl3*6H2O/~55g Fe) = ~ 245g of FeCl3*6H20.

Now my question is. How much concentrated HCl (lets say 35%) should I be adding to get a 15% solution ... taking into consideration the hexahydrate is going to be taking up space??

I have an idea myself but I'd like to see how others come up with a solution as well.

Thanks guys/gals.

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it has a Density of 2.9 at SRTP, you should be able to extrapolate from there

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The density will give you a good start but you cannot really calculate this sort of thing from first principles. After all the density of the solid gives you the mass of a given volume of the solid. When that's disolved in water there's no reason to supose it will be the same volume.

The real answer is to calculate the amount of FeCl3. 6H2O you need, add the calculated volume of HCl and then place the mixture in a 500 ml volumetric flask. Then you make the mixture up to 500 ml with water.

BTW, what do you want it for? there's no way it's going to be accurate because the hydration will be variable.

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