Question

What is the chemical formula of Calcium Phosphate.
A. $Ca{{(P{{O}_{4}})}_{2}}$
B. $C{{a}_{3}}{{(P{{O}_{4}})}_{2}}$
C. $C{{a}_{3}}(P{{O}_{4}})$
D. $Ca(P{{O}_{4}})$

Answer 1

Hint: One should try to recall their criss-cross representation of an ionic compound. Also, you need to recall the ionic charge of calcium as well as phosphate group.

Complete Step by Step Solution:
Well, these types of questions are very crucial in examinations. The trick is to recall the radical charge and the criss-cross concept of an ionic compound.
Calcium phosphate is an ionic compound. There needs to be some understanding about the representation. Now, we should know or at least recall that Calcium exhibits -2 charge or the calcium ion is written as $C{{a}^{+2}}$.
Similarly, phosphate ion has a net -3 charge, which is represented as ($P{{O}_{4}}^{-3}$).
Now, in the criss-cross representation concept, for a particular ionic compound representation. Let us say the ions involved are ${{A}^{x}}$ and ${{B}^{y}}$, then the chemical representation of the feasible ionic compound which is formed is ${{A}_{y}}{{B}_{x}}$ .
Hence, for the above mentioned ionic radical options, the chemical formula would be $C{{a}_{3}}{{(P{{O}_{4}})}_{2}}$.
The other options namely A, C and D do not qualify as they are not possible in the current combination of the given ions, as they do not get written in a possible criss-cross representation form.
Therefore, the answer to the above problem is Option B.

Note: One should know the origin of the Calcium Phosphate. They belong to the family of materials or minerals containing Calcium ions as mentioned above and inorganic phosphate anions. There are other possible combinations when $C{{a}^{+2}}$is combined with phosphate as above, ${{H}_{2}}P{{O}_{4}}^{-}$ and $HP{{O}_{4}}{{^{-}}^{2}}$, the resultant compounds formed are Calcium Phosphate, monocalcium phosphate and dicalcium phosphate respectively.