Can someone help me with Mole Conversion?

Question

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?

Answer 1

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.