What is the Van't Hoff factor for NaCl in seawater?

In summary: It appears that the Van't Hoff factor is 2.In summary, the conversation discusses the process of estimating the concentration of NaCl in seawater in molality units. The participants use equations and conversions to calculate the molar fraction and molality, but there is confusion about the correct answer due to the impact of strong electrolytes and complete ionization of NaCl. The conversation ends with a suggestion to check the Van't Hoff factor, which may affect the final result.
  • #1
amcavoy
665
0
At 25oC the vapor pressure of pure water is 23.76 mmHg and that of seawater is 22.98 mmHg. Assuming that seawater contains only NaCl, estimate its concentration in molality units.

[tex]X_1=\frac{n_1}{n_1+n_2}\implies n_2=\frac{n_1-X_1n_1}{X_1}[/tex]

where n1 is the moles of solvent and n2 is the moles of solute.

[tex]22.98=X_1\left(23.76\right)\implies X_1=.9672[/tex]

and 1000 g of water is equal to 55.49 mol (n1), so plugging this all in gives:

[tex]n_2=1.88\text{mol}[/tex]

which would be the same as the molarity.

However, my textbook says that the molarity is .920 m. Where did I go wrong? Thanks a lot.
 
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  • #2
NaCl is dissolved.
 
  • #3
Right, Na++Cl-->NaCl.

Thanks for the help.
 
  • #4


Can someone please explain this to me, because I'm not quite sure how to solve this problem. I only reached the part where I got the mole fraction of water and NaCl, but that's just it. I don't know what to do next. Help would be greatly appreciated. :(
 
  • #5


You mean you have no idea how to convert molar fraction to molality?

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  • #6


Okay, I found out how to convert it molality, but I keep getting 1.88 m not .920 m. How does the strong electrolyte/complete ionization of NaCl make a difference?
 
Last edited:
  • #7


Check what Van't Hoff factor is.

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FAQ: What is the Van't Hoff factor for NaCl in seawater?

What is the definition of vapor pressure of pure water?

The vapor pressure of pure water is the pressure exerted by the water vapor molecules above the surface of pure water at a given temperature.

How does temperature affect the vapor pressure of pure water?

The vapor pressure of pure water increases with increasing temperature. This is because at higher temperatures, the water molecules have more kinetic energy and are able to escape into the gas phase more easily.

What is the relationship between vapor pressure and boiling point of pure water?

Vapor pressure and boiling point are inversely related. As the vapor pressure of pure water increases, the boiling point decreases. This is because at higher vapor pressures, the water molecules are able to escape into the gas phase more easily, resulting in a lower boiling point.

How is the vapor pressure of pure water affected by atmospheric pressure?

The vapor pressure of pure water is affected by atmospheric pressure, as it is the pressure exerted by the surrounding air molecules on the water. At higher atmospheric pressures, the vapor pressure of pure water will also be higher, as the air molecules will be pushing down on the water surface with more force.

Why is the vapor pressure of pure water important in everyday life?

The vapor pressure of pure water is important in everyday life because it plays a crucial role in the water cycle, as well as many industrial and commercial processes. It also affects the weather and can impact the moisture content in the air, which can have implications for human health and agriculture.

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