Chemistry
posted by Anonymous .
What mass of iodine contains the same number of atoms as 50.0g of chlorine?

mols Cl2 = 50/70.9 = ? mols.
mols I2 must be 50/70.9 , then
g I2 = mols I2 x molar mass I2. 
Mols Cl2= 50/70.9=? mols.
Mols I2 must be 50/70.9, then gI2= mols I2x molar mass I2
I am still not understanding could you please explain further? 
1 mol Cl2 contains 70.9g.
mols Cl2 = 50/70.9 =0.705 mol. How many molecules will that be? Since 1 mol conains 6.02E3 molecules then molecules in 0.705 mol = 0.705 x 6.02E23 = 4.245E23 molecules or 2*4.245E23 = 8.49E23 atoms Chlorine.
8.49E23 atoms Iodine and 8.49E23/2 = 4.245E23 molecules I2. How many mols is that? That's 4.245E23/6.02E23 = 0.705 mols I2. g = mols x molar mass = 0.705 x 253.8 = 179 g I2.
That's the LOOOOng way of doing it. I'm sure your prof (or the one who made up the problem) wants you to recognize that 1 mol of Cl2 = 1 mol I2 = 1 mol H2 and they all contain the same number of molecules and that is 6.02E23 (They have difference masses but 1 mol is 1 mol is 1 mol when we are talking about diatomic molecules such as H2, Cl2, I2.
Therefore, you don't need to go through that long process above to determine how many molecules (then how many atoms) are in the Cl2. You just recognize that you have 50/70.9 = 0.705 mols Cl2 so 50/70.9 mols I2 will contain the same number of I2 molecules (and atoms). And the mass of 50/70.9 molecules I2 is mols x molar mass = (50/70.9)*253.8 = about 179 grams.