Why is the salt solubility curve flat?

In summary, the solubility of most salts in water increases with temperature, but some have an inverse relationship. NaCl, however, remains relatively constant regardless of temperature due to its enthalpy change of dissociation and the cancellation of its endothermic and exothermic processes. Additionally, the free energy of NaCl is more influenced by entropy rather than temperature.
  • #1
MadViolinist
18
0
I know most salts' have increased solubility in 100g of water with an increase in temperature, a few have an inverse relationship, but why does NaCl flatline regardless of temperature? Like is there a mechanism that explains this phenomenon? Thanks in advance.
 
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  • #2
Is it completely flat? Not just mostly flat?

My guess is that the enthalpy change of dissociation is sufficient that temperature has a negligible effect.

I know that Sodium and Chlorine are strong acids/bases respectively, and we were taught that strong acids/bases dissociate completely.
 
  • #3
It is not perfectly flat.

Note that if some salts have solubility that increases with temperature and some have solubility that decreases with temperature, there is nothing strange with some salts being in between - and having temperature coefficient of solubility close to zero. NaCl happens to be one of these salts.
 
  • #4
The solubility curve is related to the molar enthalpy of ion formation in solution,
NaCl(s) --> Na+ + Cl- (aq)
ΔH (298K) = 3.9 kJ/mole
Which is a two part process : Lattice enthalpy, breakdown of crystal lattice and ionic enthalpy of hydration.
The first is endothermic the second exothermic. So with Le Chatelier principle a temperature
increase favors the first process and is against the second process.
In the case of NaCl these two parts of the process cancel each other out with increasing temperature.
Entropy is more important than temperature in free energy.
Δ G = ΔH - TΔS , - 8.94 kJ/mole = 3.9 kJ/mole - 12.84 kJ/mole
 
  • #5


The flatness of the salt solubility curve for NaCl is due to its unique chemical properties. NaCl, or sodium chloride, is an ionic compound composed of positively charged sodium ions and negatively charged chloride ions. When NaCl is dissolved in water, the water molecules surround and separate the ions, allowing them to move freely and create a solution.

The solubility of a substance is affected by several factors, including temperature, pressure, and the nature of the solute and solvent. In the case of NaCl, the temperature has a minimal effect on its solubility. This is because the attraction between the sodium and chloride ions is strong enough that it is not significantly affected by temperature changes. As a result, the solubility of NaCl remains relatively constant regardless of temperature.

Furthermore, the structure of the NaCl molecule also plays a role in its solubility. The ionic bonding between the sodium and chloride ions creates a lattice-like structure, which makes it difficult for water molecules to penetrate and dissolve the compound. This is why NaCl has a relatively low solubility in water compared to other compounds.

In conclusion, the flatness of the salt solubility curve for NaCl is due to its strong ionic bonding and unique molecular structure, which are not significantly affected by changes in temperature. This phenomenon is well understood and can be explained by the principles of chemistry.
 

What is a salt solubility curve?

A salt solubility curve is a graphical representation of the relationship between the solubility of a salt and its temperature. It shows the maximum amount of salt that can be dissolved in a given amount of water at different temperatures.

Why does the salt solubility curve flatten out at higher temperatures?

The salt solubility curve flattens out at higher temperatures because as the temperature increases, the kinetic energy of the water molecules also increases, causing them to move faster and break apart the bonds between the salt ions more easily. This leads to a higher solubility of the salt in water at higher temperatures.

What factors affect the flatness of the salt solubility curve?

The flatness of the salt solubility curve is affected by several factors, including the type of salt, the strength of the bonds between the salt ions, and the presence of other substances in the solution that may interfere with the solubility of the salt.

Why is the solubility of different salts different at the same temperature?

The solubility of different salts is different at the same temperature because each salt has a unique structure and chemical composition, which affects its ability to dissolve in water. Additionally, the strength of the bonds between the salt ions also plays a role in determining the solubility.

Can the salt solubility curve ever be completely flat?

No, the salt solubility curve can never be completely flat. This is because there will always be a limit to the amount of salt that can be dissolved in a given amount of water, even at high temperatures. Additionally, the presence of impurities or other substances in the solution can also affect the solubility of the salt, preventing it from being completely flat.

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