Posted by **Rossi** on Saturday, October 21, 2006 at 9:43am.

It takes 208.4 kJ of energy to remove 1 mole of electrons from an atom on the surface of rubidium metal. What is the maximum wavelength (in nm) of light capable of removing a single electron from an atom on the surface of rubidium metal?

Ok, I know I have to find how many kJ will be needed to remove one electron. Do I find this number by dividing 208.4kJ by 6.022 x 10^23? I have been doing it that way and I get the wrong answer. How do I find how many kJ will be needed to remove ONE electron?

Once I find the energy, I divide hc by the energy, to get lambda, right?

The is the right approach. You don't want kJ, however, you want it in Joules.

Then, use Energy=Plancksconst*speedlight/lambda

solve for lambda. You have it correct, but watch for the correct units.

Well, this is what I have done:

208.4 kJ/ 1 mol x 1 mol/ 6.0221x10^23 = 3.461x10^-22 kJ = 3.461x10^-19 J

therefore,

6.626x10^-34 x 2.9979x106^8 / 3.461x10^-19 = 5.740x10^-7m = 574.0 nm (final answer)

This is an online homework problem, and each time I submit that answer it tells me I am wrong... that is why I believe I am not doing this problem correctly. Is there an error I am making?

I don't get

* exactly you answer on Joules per electron, and it does affect the last digit of the wavelength answer. Otherwise, I don't see anything wrong.
*

I've tried with rounding to the correct sig figs throughout the problem and then not rounding to the correct sig figs until the end, and no matter what form I put, it tells me I am wrong. This is stressing... thank you though
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