The source of bitterness in dark chocolate is the compound theobromine, an alkaloid present in cocoa beans. In a sample of dark chocolate there are 6.62*1020 molecules of theobromine present. How many milligrams of theobromine are present in the sample? The molecular formula for theobromine is C7H8N4O2.

198 mg

Explanation:

The number of molecules of theobromine can be related to a measurable quantity using Avogadro's constant, which is the the number of molecules in a mole.

6.62 x x10²⁰ molecules : 6.022 x x 10²³ mol⁻¹ = 1.09930 ... x 10⁻³ mol

Moles can be related to grams using the molecular weight. The molecular weight of theobromine can be found by multiplying the number of each constituent atom by its respective atomic weight, then adding to obtain the molecular weight

7 (12.01) + 8 (1.01) + 4 (14.01) + 2 (16) = 180.19 g/mol

The moles of theobromine are converted to milligrams as follows:

1.09930 x 10⁻³ mol x 180.19 g/mol x 1000 mg/g = 198 mg