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.

the correct option is c.

isotopes refers to different forms of the same element with the same atomic number but different mass number as a result of difference in their neutron numbers. isotopes have different relative atomic mass but share the same chemical properties.