Solvation of Ionic compound in water

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Summary:

If the solution of "NaCl in water" a chemical reaction, then will the chemical properties of this solution differ than that of its constituents(NaCl and H2O)?
When you dissolve, for example, NaCl in water, then you get "NaCl in water" solution. Will the "NaCl in water " solution have different chemical properties from its constituents(NaCl and H2O)? i.e. is a "NaCl in water" solution a new compound with respect to NaCl or H2O ? And is the ion surrounded by water molecules (solvation shell) a new compound?
 

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  • #2
BvU
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At this level it's all physics (or phyical chemistry if you want) and the properties will differ. Example: conductivity, activity
You can look them up for NaCl, H2O and brine.
 
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  • #3
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When you dissolve, for example, NaCl in water, then you get "NaCl in water" solution. Will the "NaCl in water " solution have different chemical properties from its constituents(NaCl and H2O)? i.e. is a "NaCl in water" solution a new compound with respect to NaCl or H2O ? And is the ion surrounded by water molecules (solvation shell) a new compound?

[Mentor Note -- Two cross-posted threads have now been merged. Please do not cross-post.]
 
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  • #4
etotheipi
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Well when you dissolve the NaCl the resulting Na+ and Cl- ions are stabilised by water molecules, which form hydration spheres around the individual ions. When it's dissolved, you would just call it an aqueous solution of NaCl, i.e. NaCl(aq).
 
  • #5
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Well when you dissolve the NaCl the resulting Na+ and Cl- ions are stabilised by water molecules, which form hydration spheres around the individual ions. Whether or not the dissolution is exothermic or endothermic depends on the relative magnitudes of the lattice dissociation enthalpies and the hydration enthalpies. When it's dissolved, you would just call it an aqueous solution of NaCl, i.e. NaCl(aq).
Then does the ion surrounded by water molecules forms another compound?
 
  • #6
etotheipi
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NaCl(s) and NaCl(aq) are different structurally, if that's what you're asking. The former is a giant, regular, repeating lattice of ions (in this case, a face-centred cubic), whilst in the latter the ions have been separated from each other, and are hydrated by water molecules.
 
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  • #7
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NaCl(s) and NaCl(aq) are different structurally, if that's what you're asking. The former is a giant, regular, repeating lattice of ions (in this case, a face-centred cubic), whilst in the latter the ions have been separated from each other, and are hydrated by water molecules.
Then the NaCl(aq) will have different chemical properties(reactivity,etc) than NaCl(s) right?
 
  • #8
etotheipi
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Things like reaction rates, activity coefficients, what-not all definitely depend on the phase!

Another example; attaching some electrodes to a pile of salt isn't going to do much, but if you dissolve it in water, you have an electrolytic cell.
 
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Another example; attaching some electrodes to a pile of salt isn't going to do much, but if you dissolve it in water, you have an electrolytic cell.
That's correct. However, it also applies to solid and molten NaCl but nobody would say that melting is a chemical reaction. Whether dissolving NaCl in water is considered to be a chemical reaction or not depends on the circumstances. If you do it for recrystallisation it is reather a pure physical process. If you mix the NaCl solution with an aqueous AgNO3 solution than it could be seen as a first reaction step.

At the end of the day chemistry is just a part of physics. It is not a surprise that it is sometimes difficulty to distinguish between them.
 
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