Unraveling the Mystery of NaCl's Low Solubility Curve

In summary, the conversation discusses the difference in the slope of the solubility curve for NaCl compared to other ionic compounds like KCl and NaNO3. The conversation also mentions the relationship between the slope of the solubility curve and the enthalpy of dissolution, and the use of the Van't Hoff equation to understand this relationship. It is also mentioned that the negative sign for ΔH was dropped in the conversation. Finally, a quote from H. E. Armstrong is mentioned in reference to the discussion on ionic theory.
  • #1
enthropy
8
0
Why is Δsolubility / Δtemperature so much lower for NaCl than for other ionic compounds like KCl and NaNO3? (It's solubility curve is almost flat).
 
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  • #2
Do you know how the slope of the solubility curve is related to the enthalpy of dissolution? This is generally covered in any standard Physical Chemistry text in the chapter on Solutions. Or it may appear in the discussion about Le Chatelier's principle.
 
  • #3
It doesn't, but I found the Van't Hoff equation and from there it is fairly straightforward.
 
  • #4
enthropy said:
It doesn't but I found the Van't Hoff equation and from there it is fairly straightforward.
Could you explain further?
 
  • #5
Sure. Integrating and solving for K, we get [tex]K \alpha e^{\Delta H /RT}[/tex]. Smaller ΔH means smaller rate of change, and NaCl's is much smaller than KCl
 
  • #6
Close enough (your signs may be off or you use a non-standard sign convention).

I hope you realize that the ΔH here is the enthalpy of dissolution, which is what I was referring to above. And that's why your response "It doesn't" had me a little confused.
 
  • #7
I dropped the negative sign when typing it here, it becomes [tex]K\proptoe^{\frac{-\Delta H}{RT}}[/tex]
"it doesn't" referred to it's appearance in the text, not my awareness of the relation.
 
  • #8
Dissolving NaCl?
"Such unjustified aspersion of the molecular character of our most necessary condiment must not be allowed any longer to pass unchallenged."
-- H. E.. Armstrong, Nature, v120, p478 (1927)

He was the last hold-out against ionic theory. :smile:
 

1. What is NaCl's solubility curve?

NaCl's solubility curve is a graph that shows the relationship between the temperature and the solubility of NaCl in water. It demonstrates how much NaCl can dissolve in a given amount of water at different temperatures.

2. Why is NaCl's solubility curve considered to be low?

NaCl's solubility curve is considered to be low because it shows that the solubility of NaCl in water decreases as the temperature increases. This means that at higher temperatures, less NaCl can dissolve in water compared to lower temperatures.

3. What factors affect NaCl's solubility curve?

The factors that affect NaCl's solubility curve include temperature, pressure, and the presence of other substances in the solution. Temperature and pressure directly influence the solubility of NaCl, while other substances can affect its solubility by changing the chemical environment of the solution.

4. How can we explain NaCl's low solubility curve?

The low solubility curve of NaCl can be explained by its strong ionic bonds. As the temperature increases, the kinetic energy of the water molecules also increases, making it more difficult for the Na+ and Cl- ions to interact and form bonds with the water molecules. This results in a decrease in the solubility of NaCl in water.

5. What applications does understanding NaCl's solubility curve have?

Understanding NaCl's solubility curve has various applications in different areas, such as in the production of salt solutions, food and beverage industry, and pharmaceuticals. It also helps us understand the behavior of other ionic compounds in water and provides insights into the properties of different solutions.

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