Question

How many grams of CaO are required to react with 852 g of ${{P}_{4}}{{O}_{10}}$ ?
(A) 825 g
(B) 1008 g
(C) 85 g
(D) 7095 g

Answer 1

For solving this, we need to consider the mole concept. The mole concept defines mole as the amount of substance that contains exactly $6.02214076\times {{10}^{23}}$ elementary entities of the given substance.
$\text{Number of moles=}\dfrac{\text{given mass}}{\text{molar mass}}$

Complete step by step answer:
-We will begin solving this question by writing a balanced equation for the question, i.e.
$6CaO+{{P}_{4}}{{O}_{10}}\to 2C{{a}_{3}}{{(P{{O}_{4}})}_{2}}$
-Now calculating the molar mass of ${{P}_{4}}{{O}_{10}}$for the calculation of moles $=4\times 31+10\times 16=284g$
Moles of ${{P}_{4}}{{O}_{10}}$ $=\dfrac{\text{given mass}}{\text{molar mass}}=\dfrac{852}{284}=3moles$

-From the balanced equation, it is clear that 1 mol of ${{P}_{4}}{{O}_{10}}$ reacts with 6 moles of CaO.
Therefore, 3 moles of ${{P}_{4}}{{O}_{10}}$will react with $=3\times 6=18\text{ mol of CaO}$

-Now calculating the weight of the CaO,
The molecular weight of CaO = 40 + 16 = 56 g
Mass of 18 moles of CaO = $18\times 56=1008g$
So, the correct answer is “Option B”.

Note: There are some confusing terms in the mole concept like atomic mass, molecular mass, molar mass, gram atomic mass, and gram molecular mass. The mass of one atom of the element expressed in the atomic mass unit is known as the Atomic mass of an element. The atomic mass of an element is roughly equal to the sum of all the nucleons. The sum of all the atomic masses of all the constituent elements is known as the molecular mass of the element. The total mass of one mole of the substance is known as the molar mass of a substance. The mass of one mole of the elements is known as the gram atomic mass of an element. The mass of a single mole of a compound is known as the gram molecular mass of a compound.