Question

What is the mass of 2.90 ×1022 molecules of NaOH (Molar mass = 40.0 g/mol)?

Answer 1

40.0 g ( 1 mole ) --------------- 6.02x10²³ molecules
      ? ? --------------------------- 2.90x10²² molecules

mass = 2.90x10²² * 40.0 /  6.02x10²³

mass = 1.16x10²⁴ / 6.02x10²³

mass = 1.9269 g

hope this helps!