I understand that ionic compounds tend to have higher melting points, but I was surprised to see zinc nitrate having an unusually low melting point. I tried understanding it in terms of lattice energy and the electrostatic interactions between the ions but I don't have a conclusive answer.
1 Answer
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Your melting point is not a melting point. Rather it represents the loss of water from a hydrate salt, which commonly occurs at much lower temperature than what would be required to actually liquefy the ions.
Nor does zinc nitrate truly melt at higher temperature; instead it decomposes to an oxide like most other nitrate salts. Thermogravinetric analysis, for instance from Ref. 1, indicates that the process of dehydration and decomposition is complete at 300-400°C.
- Gregorio, Flores & Carrillo-López, J & López, J. & Martinez, Rafael & Espinosa, Nestor & Rabanal, Maria. (2014). "Structural and Morphological Properties of Nanostructured ZnO Particles Grown by Ultrasonic Spray Pyrolysis Method with Horizontal Furnace." Advances in Materials Science and Engineering 6. 10.1155/2014/780206.
answered Mar 16, 2023 at 10:11
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$\begingroup$ Thanks for the reply, this leads to another question, so when we observe a "colourless liquid" upon heating initially, what is this substance that we are observing, is it simply aqueous zinc nitrate? $\endgroup$– dcyw6006Commented Mar 16, 2023 at 13:21
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1$\begingroup$ Possibly. Hydrated salts sometimes dissolve into their own water of hydration as well. I see no reference fir this, so I did not mention it in tye answer, but for instance ferric chloride hexahydrate is well known to do this. $\endgroup$ Commented Mar 16, 2023 at 13:45