The volume of a concentrated ionic solution

[McCrunchy]

Hello everyone,

 

I was recently preparing a concentrated (1 molal) solution of CaCl24H2O, which involved putting 184 g of the salt into a liter of water. The amount of salt being all but negligible, the final volume of my solution was more than a liter, something like 1,2 liters.

 

I was wondering: is this volume bigger or smaller than that occupied by my initial dry salt + the liter of water ? A few thoughts

 

1) The hydration shell that builds up around very ion would tend to increase the volume occupied by the ionic solution: it makes the water less densily packed.

 

2) However, the voids between the dry crystal lattice get filled by water, which would tend to decrease the overall volume.

The volume fraction gained in this process can be easily calculated knowing the lattice structure of the salt.

 

3) This brings to the conclusion: measuring the quantity

 

volume of my final solution - volume of water - volume of crystal + volume of voids in the crystal

 

I could get info on the density of water in the hydration shell of an ion vs it's normal (bulk) density. Which could be pretty interesting.

 

Does anyone know of any literature on the subject ? I wasn't able to find anything. This experiment seems so obvious, someone must have done it. Or my line of reasoning is flawed.

 

Thanks in advance for your input,

 

McCrunchy

[max.yevs]

well given that the crystal lattice dissolves,

increase in solution volume = increase volume by hydration shells - volume of voids

 

you know the increase in solution volume, but unless you know the increase by those hydration shells, you can't find the volume of voids

 

but i agree it would be interesting, you could use it to calculate salt densities or maybe even estimate hardness... best of luck