I have tried for several hours to answer this question with no luck. I believe I may be missing a couple of steps or I am not utilizing the given information properly. Nonetheless, some guidance will be greatly appreciated.

The concentration of $\ce{N2}$ in the ocean at 25C is 445 $\ce{\mu}$M. The Henry's Law constant for $\ce{N2}$ is 0.61 x $\ce 10^{-3}$ mol $\ce L^{-1}$ atm $\ce L^{-1}$.

Part A:

Calculate the mass of $\ce{N2}$ in a liter of ocean water.

4.45 x $\ce 10^{-4}$ mol/kg = molality

$\ce{N2}$ in moles = 28.014 g/mol

Using Molality Equation

Molality = $\frac{amount of solute (mols)}{mass of solvent(kg)}$

I want kilograms, thus:

4.45 x $\ce 10^{-4}$ $\frac{mol}{kg}$ = $\frac{28.014 g}{mol}$

Where do I go from here?

Part B:

Calculate the partial pressure of $\ce{N2}$ in the atmosphere

Use C = K x $P_(gas)$

4.45 x $\ce 10^{-4}$ = (0.61 x $\ce 10^{-3}$ mol $\ce L^{-1}$ atm $\ce L^{-1}$)x

x = 0.73 atm

  • 2
    $\begingroup$ No one can help me with this question? $\endgroup$
    – Cetshwayo
    Feb 14, 2015 at 16:58
  • 2
    $\begingroup$ I formatted your question using MathJax meta.chemistry.stackexchange.com/questions/86/… This makes your question computer readable and typing out your whole is generally the way to go, so it can potentially help others (and in increases the chance of a response.) If you hit edit on your question, you can see some of the functions I used to format it. I kept your image in case I made an error. Best of luck finding the answer to your question, I'm studying something fairly similar right now. $\endgroup$ Feb 14, 2015 at 22:18

1 Answer 1


Part A: Why do you want to use the molality?! You have the concentration i.e the number of moles in one liter. So the mass of nitrogen in one liter is simply:

Number of moles in one liter $\times$ molar mass.

Part B: It's correct.

  • $\begingroup$ Thnaks. I do not understand the definition well enough. $\endgroup$
    – Cetshwayo
    Feb 14, 2015 at 22:10

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