Question

How many moles of magnesium phosphate $$M{g}_3{\left(P{O}_4\right)}_2$$ will contain 0.25 moles of oxygen atoms?
(A) $$3.125\times {10}^{-2}$$
(B) $$1.25\times {10}^{-2}$$
(C) $$2.5\times {10}^{-2}$$
(D) $$2\times {10}^{-2}$$

Answer 1

Hint: Try to recall that one mole is defined as the amount of a substance that contains as many atoms, molecules, ions, electrons or other elementary particles as there are atoms in exactly 12g of Carbon-12. Now, by using this you can easily find the correct option from the given option.

Complete step by step solution:
* It is known to you that 1 mole of magnesium phosphate $$M{g}_3{\left(P{O}_4\right)}_2$$ contains 3 mole of magnesium (Mg) atoms, 2 mole of phosphorus atoms and 8 moles of oxygen atoms and 8 mole of oxygen (O) atoms.
* Calculation:
1 mole of magnesium phosphate ($$M{g}_3{\left(P{O}_4\right)}_2$$) contains 8 moles of oxygen atoms
Or, we can say that 8 moles of oxygen atoms are present in 1 mole of magnesium phosphate ($$M{g}_3{\left(P{O}_4\right)}_2$$).
So, 1 mole of oxygen atoms is present $${\displaystyle \frac{1}{8}}=0.125$$ mole of magnesium phosphate ($$M{g}_3{\left(P{O}_4\right)}_2$$).
Therefore, 0.25 mole of oxygen atom is present in $$0.125\times 0.25=0.03125=3.125\times {10}^{-2}$$ moles of magnesium phosphate ($$M{g}_3{\left(P{O}_4\right)}_2$$).
Therefore, from above calculations we can easily conclude that option A is the correct option to the given question.

Note:
* It should be remembered to you that Avogadro’s number and mole concept help in the chemical calculation of the number of atoms or molecules in a given mass of the element or the compound.
* Also, you should remember that it also helps in the calculation of the number of molecules present in a given volume of the gas under given conditions.