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Can someone help me with Mole Conversion?

I'm struggling to understand on how to do this, I'm currently trying to use dimensional analysis to solve the problems, please help.
1. What is the mass of 12.5 moles of silicon?
2. How many moles in 3.4 x 10^45 moles of CO₂?
3. What is the mass of 1.7 x 10^67 atoms of Pb?

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J.R. S. | Ph.D. in Biochemistry--University Professor--Chemistry TutorPh.D. in Biochemistry--University Profes...
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You should be able to use dimensional analysis for these problems. Here is how to set them up.
1.  12.5 moles silicon x 28.086 g/mole silicon = 351 grams (3 significant figures).  moles cancel, leaving grams.
2.  Makes no sense. It asks how many moles are in a given number of moles. 
3.  1.7x1067 atoms Pb x 1 mole Pb/6.02x1023 atoms x 207 g/mole Pb = 5.8x1044 grams, if you really meant 1.7x1067. In this calculation, atoms cancel, and moles cancel, leaving grams.