Fnding the rms speed of hydrogen

[qspartan570]

Homework Statement

The rms speed of nitrogen molecules in air at some temperature is 493 m/s. What is the rms speed of hydrogen molecules in air at the same temperature?

Homework Equations

V_rms

The Attempt at a Solution

 

[Delphi51]

Better read this first: http://en.wikipedia.org/wiki/Root-mean-square_speed

 

[qspartan570]

Finding the rms speed of hydrogen

Homework Statement

The rms speed of nitrogen molecules in air at some temperature is 493 m/s. What is the rms speed of hydrogen molecules in air at some temperature?

Homework Equations

root-mean-square speedv_rms= $\sqrt{v²}$=$\sqrt{\frac{3kT}{m}}$

The Attempt at a Solution

m_nitrogen=$\frac{28.0 g}{6.02 X 10²³}$=4.65 X 10^-26

m_hydrogen=$\frac{2.0 g}{6.02 X 10²³}$= 3.32 X 10^-27

493= $\sqrt{\frac{(3)(1.38 X 10^-23)(T)}{4.65 X 10^-26}}$
T= 233 K

V_rms of hydrogen= $\sqrt{\frac{(3)(1.38 X 10^-23(T)}{3.32 X 10^-27}}$=340.43 m/s

The answer is actually 1840 m/s.

What did I do wrong?

 

[Delphi51]

Wow, all that work and it didn't come out right!
Better to just think for a bit. The atomic mass for the H2 is lighter by a factor of 14.
So the 3kT/m will be 14 times larger for the hydrogen. And its square root will be sqrt(14) times larger.