Determine the mass in grams of the following

A) 2.00 x 10^-15 mol of HF

B) 3.00 x 10^20 HF molecules

A) (2.00 x 10^-15 mol HF/1)(20.0 g HF/1 mol HF)=4.0x10^-14 g HF

B) There are 6.022 x 10^23 molecules (Avogadros' Number) in 1 mol of a substance.

(3.00x10^20 molecules HF/1)(1 mol HF/6.022 x 10^23 molecules HF)(20.0 g HF/1 mol HF)=9.96 x 10^-3 g HF