Similar to what 'Rosael' noted (thanks Rosael!) instead of just multiplying the 2 mols that Phosphorus has, in it's Cu3(PO4)2 compound... we need to recognize that the total amount of moles in 8.10 moles of the compound is actually (2 mols P x 8.10 mols of Cu3(PO4)3).... from here we know that Cu3(PO4)2 contains 16.2 mols of P.... but because we are asked to figure out how many ATOMS 16.2 MOLS of P actually are... this is where we utilize Avagadro's wonderful #.... (i saw wonderful because it magically helps us switch back and forth from these sorts of things.)
We do this by saying:
16.2 mols of P x ( 6.022x10^23 atoms of P ) / 1 mol of P
writing this out will help you to see how the mols then cancel, and we end up only with atoms of P.... *Rember that Avagadro's # is there to help! It may not always go on top... sometimes you will need to divide by it to find how many mols is in something...* Hope this helped!
