# Diffusion, isn't this the formula I'm supposed to be using?

1. Nov 25, 2007

### rocomath

A sample of an unknown gas takes 434 s to diffuse through a porous plug at a given temperature. At the same temperature, N2(g) takes 175 s to diffuse through the same plug. What is the molar mass of the unknown gas?

$$\frac {Rate_{A}}{Rate_{B}} = \sqrt {\frac {\mathcal{M}_{B}}{\mathcal{M}_{A}}}$$

2. Nov 25, 2007

### eli64

faster vs slower gas

which one is the faster gas? would the faster gas be the lighter or heavier gas?

faster gas = sqrt (Mslower/Mfaster)
slower gas

3. Nov 25, 2007

### ace123

Yes the formula is correct but how are you using it? That is show what your getting

4. Nov 25, 2007

### rocomath

thanks, the answer doesn't even appear as one of the choices.

5. Nov 25, 2007

### eli64

what did you get as an answer?

Last edited: Nov 25, 2007
6. Nov 25, 2007

### rocomath

i appreciate your help but i was really only concerned about the equation, thanks.