# Homework Help: Calculate the mass of nitrogen dissolved

1. Sep 17, 2010

### Agent M27

1. The problem statement, all variables and given/known data

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.

2. Relevant equations

$$PV=nRT$$

3. 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

2. Sep 18, 2010

### zorro

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

3. Sep 18, 2010

### 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

4. Sep 19, 2010

### 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