What is the mass (in grams) of 9.15 × 1024 molecules of methanol (ch3oh)?

Solution:

first we have to calculate  the mass of 1 mole of CH3OH?  

C = 12  

H3 = 3x1 = 3  

O = 16  

H =1  

total mass 12+3+16+1=32g.

Total 32g So we know 6.02x10^23 molecules weigh in32g  

therefore,

1 molecule weighs 32/6.02x10^23 g  

now,

9.95x10^24 molecules weighs 9.95x10^24 x (32/6.02x10^23) = 9.95x32x10/6.02=99.5x32/6.02

          =528.90g

thus the mass in grams is 528.90g.