2
$\begingroup$

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

$\endgroup$
  • $\begingroup$ What temperatures are we talking about? $\endgroup$ – andselisk Dec 11 '19 at 8:09
  • $\begingroup$ Ordinary heating $\endgroup$ – Just A Young Artist Dec 11 '19 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 '19 at 8:26
  • $\begingroup$ About the boiling point of H2O $\endgroup$ – Just A Young Artist Dec 11 '19 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 '19 at 8:58
4
$\begingroup$

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.

References

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

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

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