Question

select the correct answer.
the atomic mass of iron is 55.85, and oxygen is 16.0. what is the mass of 6.02 × 10^{23} molecules of fe_{2}o_{3}?
a. 71.85 g
b. 143.7 g
c. 159.7 g
d. 199.55 g
e. 215.55 g

Explanation:

Step1: Calculate molar - mass of Fe₂O₃

The molar - mass of Fe₂O₃ is calculated as follows:
There are 2 iron (Fe) atoms and 3 oxygen (O) atoms in Fe₂O₃. The atomic mass of Fe is 55.85 and of O is 16.0.
$M(Fe_2O_3)=2\times55.85 + 3\times16.0$
$M(Fe_2O_3)=111.7+48$
$M(Fe_2O_3)=159.7\ g/mol$

Step2: Use Avogadro's number

$6.02\times 10^{23}$ molecules of a substance is 1 mole of that substance.
The mass of 1 mole of a substance is equal to its molar - mass.
So, the mass of $6.02\times 10^{23}$ molecules of Fe₂O₃ is 159.7 g.

Answer:

C. 159.7 g