How do I determine the amount of atoms in a given substance.
For example: Determine the number of atoms in 2.50 mol Zn

What is the definition of a Mole ?

Then it's a simple case of multiplying from there.

Avogadro's Number - Google Search (http://www.google.com/search?hl=en&safe=off&client=firefox-a&rls=org.mozilla:en-US:official&hs=J9I&ei=7rBOS5zPGM_mlAer3JW5Cg&sa=X&oi=spellfullpage&resnum=0&ct=result&cd=2&ved=0CAcQvwUoAQ&&q=Avogadro%27s+Number&spell=1)