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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: mufan on January 14, 2007, 08:59:30 PM

Title: water and salt radii
Post by: mufan on January 14, 2007, 08:59:30 PM

Hey everybody,
I have been trying to do a search on google to find the size of a water molecule and the sizes of various salts.   I'm not even sure these measurements exist.  I would like to see a list of salts and their size in an aqueous solution.  I am trying to find a salt with a largest size.

I have a  membrane and I am fairly sure that water can pass through but I want to find a salt with a large radius to prevent it from passing through the membrane as well.

Title: Re: water and salt radii
Post by: Mitch on January 15, 2007, 01:04:05 AM

Just lookup the ionic radii http://www.chemicalforums.com/index.php?page=periodictable

Title: Re: water and salt radii
Post by: mufan on January 15, 2007, 01:58:14 PM

Maybe I'm missing something but that chart (which is nice) only gives information for individual atoms and not molecules.

Title: Re: water and salt radii
Post by: enahs on January 15, 2007, 02:10:53 PM

You said a salt.
A salt is a ionic compound that breaks apart into its constitutive cations and anions in water (this is just one of many definitions of a salt).

He means if you are looking for something like NaCl or KCl, because the size of the "salt" in water will be the size of the individual ionic radii.

It gets more complicated if you wish to include the hydrated radii.

For example the Na⁺ radii is ~ 1.16 Å;
Which has hydration number of ~17, this means there are ~17 water molecules operate in aqueous solution under the restraining influence of the cations positive charge to such an extent to be considered as bound to the cation. Giving it an approximate hydrated radii of ~ 2.76 Å.