Question

What is the molar mass of $C{a_3}{(P{O_4})_2}$?
(A) 310 g/mol
(B) 154 g/mol
(C) 67 g/mol
(D) 83 g/mol
(E) 115 g/mol

Answer 1

In order to find the Molar mass of $C{a_3}{(P{O_4})_2}$ we must calculate the molar mass by multiplying number of moles present in an atom and mass of the atom in a molecule and later adding these values. Molar mass is also known as Molecular weight.

Complete step by step answer:
Molar mass is defined as the mass of one mole of the substance. It can also be called as the molecular weight. Its SI unit is g/mol. It’s quite different from molecular mass.
Various steps to be followed in order to find the molar mass. They are:
- Identify the formula of the given compound.
- Calculate the number of moles of atoms present in the given compound.
- Multiply the mass of the atom with the number of moles of the atom.
- This must be done for every element present in the compound. Later, these values are added.
- The obtained value is expressed in the unit g/mol.
In the compound $C{a_3}{(P{O_4})_2}$, there are three elements namely Calcium, Phosphorus and Oxygen. $C{a_3}{(P{O_4})_2}$ contains 3 moles of Ca, 2 moles of Phosphorus and 8 moles of oxygen.
$Mass{\text{ of }}C{a_3}{(P{O_4})_2} = (3 \times {\text{atomic mass of Ca) + (2}} \times {\text{atomic mass of P) + (8}} \times {\text{atomic mass of O)}}$
$= (3 \times 40.08) + (2 \times 30.47) + (8 \times 16.00)$
$= 120.24 + 61.94 + 128$
$= 310.18g/mol$
So the correct answer is “A”:

Additional Information:
- $C{a_3}{(P{O_4})_2}$ is called Calcium phosphate.
- It appears as white crystalline or amorphous powder which is tasteless and odourless.
- It is soluble in nitric and hydrochloric acid but only slightly soluble in water.
- It is used in antacid, dietary supplements, production of fertilisers, manufacture of luminescent materials etc.

Note: Molar mass is quite different from molecular mass. Their difference is given below

MOLAR MASS	MOLECULAR MASS
Ii is the mass of one mole of a substance.	It is the mass of the molecule.
It is expressed in g/mol.	It is expressed as amu.
It is also known as the molecular weight.	It determines the mass of the single molecule.