Question

Which of the following expressions is equal to the number of iron ($Fe$) atoms present in $10.0$ g $Fe$ ? (atomic mass of $Fe$ = $55.9$ amu)

• A. $10\times 55.9\times (6.022\times {10}^{23})$ atoms
• B. $\frac{(6.022\times {10}^{23})}{10}\times 55.9$ atoms
• C. $10\times \frac{(6.022\times {10}^{23})}{55.9}$ atoms
• D. $\frac{55.9}{10}\times (6.022\times {10}^{23})$
• E. $\frac{10}{(55.9\times 6.022\times {10}^{23})}$ atoms

Answer 1

Answer: (C)

$10\times \frac{(6.022\times {10}^{23})}{55.9}$ atoms

The expression $10\times (6.022\times {10}^{23})/55.9$ is equal to the number of iron (Fe) atoms present in 10.0 g Fe.
The atomic mass of Fe is 55.9 g/mol.
The mass of Fe is 10.0 g. Mass is divided with atomic mass to obtain number of moles.
The number of moles of Fe $=\frac{10.0}{55.9}$ moles.
The number of moles is multiplied with avogadro's number to obtain the number of Fe atoms.
The number of Fe atoms $=\frac{10.0}{55.9}\times 6.023\times {10}^{23}$.