Question

The amount of oxygen in 3.6 moles of water is:
(A)- 115.2 g
(B)- 57.6 g
(C)- 28.8 g
(D)- 18.4 g

Answer 1

Hint: The amount of oxygen in the given moles of water will be evaluated by calculating the mass of oxygen in one mole of oxygen, which is further related to one mole of water. As one mole of water molecule has one mole of oxygen and two moles of hydrogen present in it.

Complete step by step solution:
In a water molecule, ${{H}_{2}}O$ it has two atoms of hydrogen and one atom of oxygen. So, we can say that, in one mole of water, one mole of oxygen is present.
Then, as the atomic mass of oxygen is = 16 amu. So, in one mole of oxygen, mass will be $=16\times 1.66\times {{10}^{-24}}\times 6.022\times {{10}^{23}}=15.99\approx 16g/mol$.
So, if in one mole of water, 16 g of oxygen atom is present. Then, in 3.6 moles of water, the mass of oxygen present will be $3.6\times 16=57.6\,g$.

Therefore, the amount of oxygen present in 3.6 g water is option (B)- 57.6 g.

Additional information:
Knowing the moles of the substance present, we have the relation as, \[\text{no}\text{. of moles =}\dfrac{\text{weight}\,}{\text{molecular}\,\text{mass}}\] . So, it can provide us with the mass of the substance consumed and also the number of atoms or molecules present in it.

Note: It can be seen that, from the moles of the molecule, the mass of each of its constituent atoms can be calculated individually and vice-versa.
And the molar mass (in gram) of an atom is equal to its atomic weight (amu), where $1\,amu=\,1.66\times {{10}^{-24}}g$ and the Avogadro’s number, ${{\text{N}}_{\text{A}}}\text{=6}\text{.022 }\!\!\times\!\!\text{ 1}{{\text{0}}^{\text{23}}}$gives the number of atoms present in a mole.