Re: pinhole salt solubilities

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From: NFetter@aol.com
Date: Mon Jan 29 2001 - 21:14:23 PST 

From: NFetter@aol.com
Message-ID: <e8.fd3da91.27a7a7af@aol.com>
Date: Tue, 30 Jan 2001 00:14:23 EST
Subject: Re: pinhole salt solubilities

Hi Geoff,
Not really. When a salt dissolves in water, two energies must be considered.
One is the energy required to pull the ions apart (lattice energy) and the
other is the energy of hydration. The first requires energy (heat) and is
endothermic. The latter releases energy (heat) and is exothermic. If the two
energies are nearly equal, the solubilty of the salt is not effected by
temperature changes. Sodium chloride (NaCl) is one of these. If the lattice
energy is larger than the hydration energy, the solubility increases rapidly
with increasing tempearture. Potassium nitrate (KNO3) is an example. In a few
salts, the hydration energy is larger than the lattice energy and their
solublity decreases with increasing temperature. I think sodium sulfate
(Na2SO4) is one of them.
Neil Fetter

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