15. How do you know when a formula is an empirical formula? 16. Calculate the %Fe in hemoglobin. 17. Explain why knowing the % composition of all of the elements would not be enough information to determine the molecular formula of a compound using hemoglobin as an example. 18. Show the calculation that demonstrates that the complete combustion of a 4.824104g sample of hemoglobin would produce 159.7g of Fe2O3. (include units on each value in your calculation)