Question

A mothball, composed of naphthalene (C10H8), has a mass of 1.98 g . How many naphthalene molecules does it contain?

Answer 1

Carbon's mass number =12
Hydrogen's mass number=1
( 10×12)+(8×1)
=128
128g =1mol
------- -------
1.98g ?

1.98
------=0.015
128

1mol =6.0×10^23
------ --------------
0.015mol ?

0.015mol×6.0×10^23= 9×10^21

Thus the number of particles in 1.89 grams of napthalene is 9×10^21.

I sincerely hope this is correct.