Question

How many nitrogen atoms does a 50mg caffeine sample contain?

Answer 1

mass of caffeine = 50 mg

caffiene = C₈H₁₀N₄O₂

moles of caffeine = 50 x 10^-3 / 194.2

                           = 2.57 x 10^-4 mol

1 mol -----------> 6.023 x 10^23

2.57 x 10^-4 mol ------------->??

number of caffeine molecules = 2.57 x 10^-4 x 6.023 x 10^23

                                                = 1.55 x 10^20

number of nitrogen atoms in caffiene = 4

number of nitrogen atoms = 6.20 x 10^20 atoms