Question

What is the formula for copper $\left( II \right)$ phosphate?

Answer 1

Hint : We have to know that crisscross method is one of the methods to write the chemical formula of the ionic compound. In the criss cross method, we have to cross over the numerical value of each of the ions to become the subscript of another ion. We have to drop the signs of the charges.

Complete Step By Step Answer:
We know that the crisscross method is used to determine the chemical formula. We can write the chemical formula of the ionic compound by the following steps using criss cross method,
We have to write symbols and charges of the anion and cation. The cation is written first, and then anion is written.
We have to transpose the number of positive charges to become the subscript of the anion and the number of negative charges to become the subscript of the cation.
We have to reduce to the smallest ratio.
The final chemical formula has to be written and the subscript that has one is left off.
The here we have given is copper $\left( II \right)$ phosphate. The first thing to note here is that the name of the compound provides you with the charge of the cation. Copper, $Cu$ a transition metal, can have multiple oxidation states, which is why compounds that contain copper are written using Roman numerals.
These Roman numerals describe the oxidation state of the transition metal in a given compound. In this case, the Roman numeral $\left( II \right)~$ means that copper has a $+2$ oxidation state, i.e. it has an overall $2+~$ positive charge.
We will need three copper $\left( II \right)~$ cations to get an overall positive charge of $6+$ and two phosphate anions to get an overall negative charge of $6-$ , and so the chemical formula for this compound will be:
$3\times [C{{u}^{2+}}]+2\times [PO_{4}^{3-}]\Rightarrow C{{u}_{3}}{{(P{{O}_{4}})}_{2}}$

Note :
Note that we can write the chemical formula of compounds by alternate method. The steps to write the chemical formula of compound by alternate method are discussed below: We have to write the symbol and charge of cation and anion. Using a multiplier we have to make the total charges of the anion and cation equal to each other. The multipliers are used as subscripts for each ion.