Answer:
1.84x10^-4 moles of cyanocobalamin
Step-by-step explanation:
The challenge here is to find the molar mass of cyanocobalamin. The molecule has the chemical formula of:
C63H88CoN14O14P
Molar mass is calculated by adding the atomic masses of each atom in the compound. (e.g., 63 carbons at 12 each, etc.). The molar mass is found to be 1355.4 g/mole.
1355.4 grams of cyanocobalamin will contain 1 mole, or 6.02x10^23 molecules of cyanocobalamin. But we only have 250 mg, or 0.250 grams of the compound. Use the molar mass as a conversion factor by dividing the mass by the molar mass:
(0.250 g)/(1355.4 g/mole) = 1.84x10^-4 moles
The grams cancel and the moles moves to the top, leaving only moles cyanocobalamin. While 1.84x10^-4 moles of cyanocobalamin doesn't sound like much, it represents:
(1.84x10^-4 moles)*(6.02x10^23 molecules/mole) = 1.11x10^20 molecules of cyanocobalamin