A match has about 21 milligrams of red phosphorus coating the tip. How many atoms of phosphorus is this?

Answer 1

Phosphorus' atomic weight is 31 amu. Therefore, to find the number of atoms, we can convert from mass to moles and then to atoms using Avogadro's number:

21 mg P x (1 g P/1000 mg P) x (1 mol P/31 g P) x (6.022 x 10²³ atoms P/1 mol P) =

4.08 x 10²⁰ atoms P