Question

What is the formula for calcium bisulfate?

Answer 1

Hint: Calcium bisulfate is an ionic compound which is also known as calcium hydrogen sulphate as the prefix ‘bi-’ actually represents a hydrogen ion. It is generally prepared by the treatment of calcium hydroxide with sulphur dioxide.

Complete step by step answer:
As the name suggests, the given compound calcium bisulphate comprises a metal calcium and a group of nonmetals bisulphate. We know that any compound containing a metal and a non-metal is considered to be an ionic compound. In ionic compounds, we have to take into account the charges of each of the elements present in the compound. Now let us identify the formula for the given compound i.e. calcium bisulphate. Calcium bisulphate possess a polyatomic ion (i.e. group of nonmetals (bisulphate in this case) after the metal) so we'll use a table of names for the common polyatomic ions, along with the Periodic Table. Rules to write formula of a ternary ionic compound are listed below:
1. Using the periodic table, write down the symbol for the metal along with its charge.
In the present case, the symbol of metal calcium is $$Ca$$ having a charge +2.
2. Using the Common ion table, identify the symbol as well as charge of the polyatomic ion.
In the present case, polyatomic ion bisulphate is written as $$HS{O}_4$$ having a charge -1.
3. Check if the charges are balanced
In the present case it becomes $C{a}^{2+}HS{O}_4^{1-}$. The charges are balanced as summation of charges is non-zero i.e. $(+2)+(-1)=+1\ne 0$
4. If unbalanced charges are there, add subscripts following the criss-cross method such that net charge for the compound is zero.
In the present case, we will add subscripts to both metal and non-metal such that the net charge becomes zero. So it becomes $(C{a}^{2+}{)}_1(HS{O}_4^{1-}{)}_2$ and now the net charge is balanced i.e. $(1\times (+2))+(2\times (-1))=0$
Hence, the chemical formula for calcium bisulphate is $Ca(HS{O}_4{)}_2$.

Note: While writing the chemical formula of an ionic compound, never write the subscript '1'. And it should be noted that we can also have two polyatomic ions like $$N{H}_{4}N{O}_3$$ in the same compound. In this case, we have to find and write both of the names as identified from the Common Ion Table.