Question

How much does 1 atom of Iron $$\left(\text{Fe}\right)$$ weigh in grams. (Molecular Weight of $$\text{Fe = 56 g/mole}$$ )
A. $$9.3\times {10}^{-23}$$
B . $$6.3\times {10}^{-23}$$
C. $$5.3\times {10}^{-23}$$
D . $$4.3\times {10}^{-23}$$

Answer 1

Hint:Use the concepts of molecular weight and Avogadro’s number. To obtain the mass of one iron atom, divide the mass of one mole of iron atom with the number of iron atoms present in one mole.

Complete answer:
The molar mass of iron is $$\text{ 56 g/mole}$$ . The molar mass of a substance is the mass of one mole of the substance. Thus, the mass of one mole of iron is $$\text{ 56 g}$$ .
Avogadro’s number gives the number of atoms/molecules/ions present in one mole of a substance. The Avogadro’s number is $$6.023\times {10}^{23}\text{ atoms/mole}$$
One mole of iron contains $$6.023\times {10}^{23}$$ iron atoms.
Also, the mass of one mole of iron is $$\text{ 56 g}$$ .
Thus, $$\text{ 56 g}$$ of iron contains $$6.023\times {10}^{23}$$ iron atoms.
Calculate the mass of one atom of iron
Therefore mass of one atom of iron $$={\displaystyle \frac{56\text{ g/mole}}{6.023\times {10}^{23}\text{ atoms/mole}}}=9.3\times {10}^{-23}\text{ g/atom}$$
Thus, one atom of Iron $$\left(\text{Fe}\right)$$ weighs $$9.3\times {10}^{-23}$$ grams.

Hence, the correct option is the option (A).

Additional information:
The mass of an atom is the sum of the masses of protons, neutrons and electrons present in an atom. The atomic number of iron is 26 and its mass number is 56. Thus, one atom of iron contains 26 protons, 30 neutrons and 26 electrons. Thus, the mass of one iron atom is equal to the sum of the masses of 26 protons, 30 neutrons and 26 electrons.

Note:
One mole of any substance contains Avogadro’s number of particles. The particles can be either atoms or molecules or ions. Thus, the number of hydrogen molecules present in one mole is equal to the number of helium atoms present in one mole. Thus, the Avogadro’s number is independent of the identity of the substance.