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 \[\dfrac{1}{8} = 0.125\] 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.