Find the molar mass of 30si if the average molar mass of si is 28.09 g/mol? ? silicon has three naturally occurring isotopes (28si, 29si, and 30si). the molar mass and natural abundance of 28si are 27.98 g/mol and 92.20%, respectively, while the molar mass and natural abundance of 29si are 28.98 g/mol and 4.67%, respectively. i'm really stuck on how to solve this, it's a practice final exam question for