Posted by **sara** on Wednesday, December 13, 2006 at 8:07pm.

A mole of helium gas contains 6.02x10^23 helium atoms. How many helium atoms are there in a micromole of helium? How many moles of helium does 1.25x10^20 atoms of helium represent?

~I have no idea how to start or what the value of a micromole is? Constructive help would be great... thanx

If there are 6.02x10^23 atoms in a mole of He atoms, then how many mols must there be in 1.25x10^20 atoms. You know 1.25x10^20 atoms MUST be less than 1 mole. Or look at it another way.

How many mols in 6.02x10^23 atoms? 1.0

How many mols in 3.01x10^23 atoms? 0.5

How many mols in 1.5x10^23 atoms?

How many mols in 0.75x10^23 atoms?

Get the idea? How many mols are there in 1.25x10^20 atoms.

A micrometer is 1x10

^{-6}meters.

A microliter is 1x10

^{-6} liters.

A micromole must be 1x10

^{-6} mols. So you want to know the number of atoms in 1x10

^{-6} mol He atoms. Show your work if you get stuck and I can give you other hints. But I predict you won't need them.

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