Does the pyrolysis of $\ce{CaCl2 · 2 H2O}$ give $\ce{CaCl2 + 2 H2O}$ or $\ce{Ca(OH)2 + 2 HCl}?$

  • $\begingroup$ What temperatures are we talking about? $\endgroup$
    – andselisk
    Dec 11, 2019 at 8:09
  • $\begingroup$ Ordinary heating $\endgroup$ Dec 11, 2019 at 8:22
  • 2
    $\begingroup$ I did synthesis of uranium tungstates for quite some time and was imprinted to me that "ordinary heating" is supposed to be 900–1100 °C. An organic chemist would probably understand "ordinary heating" as some elevated temperature around the boiling point of water. So, again, what temperatures are we talking about? $\endgroup$
    – andselisk
    Dec 11, 2019 at 8:26
  • $\begingroup$ About the boiling point of H2O $\endgroup$ Dec 11, 2019 at 8:28
  • 1
    $\begingroup$ @andselisk Actually, I think I would consider ordinary heating reflux for whatever the solvent is. Which can go down to room temperature for ether or DCM ;) $\endgroup$
    – Jan
    Dec 11, 2019 at 8:58

1 Answer 1


All calcium chloride hydrates give away water of crystallization upon heating without forming a hydroxide, and the anhydrous $\ce{CaCl2}$ melts without decomposition [1, p. 162]:

anhydrous salts melts at 772 °C, while the mono-, di-, tetra- and hexahydrates decompose at 260 °C, 175 °C, 45.5 °C and 30 °C, respectively; the anhydrous salt vaporizes at 1935 °C.

$$\ce{CaCl2 · x H2O ->[\pu{260 °C}] CaCl2 + x H2O}$$

Calcium chloride dihydrate would remain intact until its melting/decomposition point at 175 °C. When heated quickly in the absence of desiccant, the powdered salt is dissolved in its own water of crystallization forming glass-alike solid upon cooling.


  1. Patnaik, P. Handbook of Inorganic Chemicals; McGraw-Hill handbooks; McGraw-Hill: New York, 2003. ISBN 978-0-07-049439-8.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.