Question

What is the number of electrons in an oxygen atom in 0.3 g Mohr’s salt?
$FeS{O_4}{\left( {N{H_4}} \right)_2}S{O_4}.6{H_2}O$
A.4.2${N_A}$
B.42 ${N_A}$
C.25.2 ${N_A}$
D.33.6 ${N_A}$

Answer 1

Hint: Ammonium iron (II) sulfate, or Mohr's salt, is the inorganic compound containing two different cations, it is classified as a double salt of ferrous sulfate and ammonium sulfate. It is a common laboratory reagent because it is readily crystallized, and crystals resist oxidation by air. Like the other ferrous sulfate salts, ferrous ammonium sulfate dissolves in water to give the aquo complex, which has octahedral molecular geometry. Its mineral form is mohrite.

Complete Step By Step Solution:
 The number of electrons in oxygen atoms in 0.3 g molecule of mohr's salt is
We know that
1 g molecule = ${N_A} = 6.023 \times {10^{23}}$
Therefore 0.3 g molecules will be 0.3 x ${N_A}$ = 0.3${N_A}$ molecules of Mohr’s salt.
1 molecule of mohr’s salt has 14 oxygen atom
So, 0.3${N_A}$ molecules have 0.3${N_A}$ x 14 = 4.2${N_A}$ oxygen atom.
1 oxygen atom has 8 electrons.
Therefore, 4.2${N_A}$ oxygen atoms will have 4.2${N_A}$ x 8 = 33.6${N_A}$

Hence, the correct option is (d).

Note: The mole is an amount unit similar to familiar units like pair, dozen, gross, etc. It provides a specific measure of the number of atoms or molecules in a bulk sample of matter. A mole is defined as the amount of substance containing the same number of discrete entities (atoms, molecules, ions, etc.)
The mole is the unit of measurement for the amount of substance in the International System of Units. A mole of a substance or a mole of particles is defined as exactly ${N_A} = 6.023 \times {10^{23}}$ particles, which may be atoms, molecules, ions, or electrons. The current definition was adopted in November 2018 as one of the seven SI base units, revising the previous definition that specified it as the number of atoms in 12 grams of carbon-12, an isotope of carbon.