Question

A mothball, composed of naphthalene (C10H8), has a mass of 1.72 g .How many naphthalene molecules does it contain?

Answer 1

To go to mass to number of particles, these are the steps:
Mass divided by molar mass gives moles
moles x avogadros number [will be using 6.02x10^23] gives number of particles.

So:
1.72/128.17 = 0.0134 moles.
0.0134 x 6.02x10^23= 8.07xx10^21 molecules of naphthalene. [rounded to 3 significant figures]

Answer 2

Answer:  $0.0809\times 10^{23}$

Explanation:

According to avogadro's law, 1 mole of every substance weighs equal to the molecular mass and contains avogadro's number $6.023\times 10^{23}$ of particles.

To calculate the number of moles, we use the equation:

${\text{Number of moles}}=\frac{\text{Given mass}}{\text{Molar mass}}$

${\text{Number moles}}=\frac{1.72g}{128g/mol}=0.0134moles$

1 mole of napthalene $C_{10}H_8$ contains =$6.022\times 10^{23}$ molecules

Thus 0.0134 moles of napthalene $C_{10}H_8$ contain=$\frac{6.022\times 10^{23}}{1}\times 0.0134=0.0809\times 10^{23}$ molecules

Thus there are $0.0809\times 10^{23}$ napthalene molecules.