Calculate the mass of nitrogen dissolved

[Agent M27]

Homework Statement

Calculate the mass of nitrogen dissolved at room temperature in a 92.0 L home aquarium. Assume a total pressure of 1.0 atm and a mole fraction for nitrogen of 0.78.

Homework Equations

$$PV=nRT$$

The Attempt at a Solution

$$P_{total}=1 atm$$

$$P_{N}=.78 atm$$

$$V=92L$$So here is what I did:
$$n=\frac{PV}{RT} = \frac{(.78)(92)}{(.08206)(298.15)}$$

$$n=2.93303$$

$$mass = (2.93303 mol)\frac{28.02g}{mol}$$

$$mass = 82.1834g$$

This is an online homework assignment and it keeps rejecting my answer. It only wants two sig figs. Any ideas where I am going wrong? Thanks in advance.

Joe

 

[zorro]

You can't solve this unless Henry's Law constant or Proportionality Constant (in Henry's Law) for Nitrogen is given

 

[zorro]

The mass you calculated is not the mass DISSOLVED.
Instead it is the mass of Nitrogen gas that would be present in a container (evacuated) of 92L at a pressure of 0.78 atm

 

[Agent M27]

Thanks guys, the Henry's law relationship worked out. This was an online HW so we were allowed to look certain constants up. For the exam he will provide the necessary constants.

Joe

 

[DeeNos]

Hello Joe, your approach and calculations seem correct. The only issue may be with the number of significant figures. When using the given data, the final answer should be rounded to 80 g (two significant figures). Try re-doing the calculations with this rounding and see if your answer is accepted. If not, there may be an error in the system or in the given data.