Question

The formula of sodium carbonate is $N{a_2}C{O_3}$ and that of calcium hydrogen carbonate is:
a.) $CaHC{O_3}$
b.) $Ca{\left( {HC{O_3}} \right)_2}$
c.) $C{a_2}HC{O_3}$
d.) $Ca{\left( {HC{O_3}} \right)_3}$

Answer 1

Hint: Valency for Calcium is +2 while hydrogen carbonate has charge (-1). By interchanging, we can find out the formula.

Complete answer:
To write the formula of Calcium hydrogen carbonate; first, we will find calcium in the periodic table and write its chemical symbol which is ‘Ca’.
Now for hydrogen carbonate which is also called bicarbonate; its formula is not in the periodic table. But from the table of common oxides, we know that it is written as - ${\left( {HC{O_3}} \right)^ - }$.
Now, we also know that Calcium ion has a valency of two. And from the above formula of hydrogen carbonate; we can see it (-1).
Thus, by interchanging subscripts, we can write it as –
$Ca{\left( {HC{O_3}} \right)_2}$

So, option b.) is the correct answer.

Additional Information:
The compound exists in the aqueous form where the solution has calcium ions, bicarbonate ions and carbonate ions all three dissolved together in carbon dioxide. When we try to prepare solid calcium hydrogen carbonate; the solution dryness results in the formation of calcium carbonate.

Note:
We can check whether we have made the correct formula by following the method.
This molecule as a whole does not hold any charge.
Calcium has a valency of +2 while hydrogen carbonate has a charge (-1).
Thus, one atom of Calcium = +2
And two molecules of bicarbonate = (-1) * 2= (-2)
So, overall 2-2=0.
And there is no overall charge on the molecule. So, we have made the correct formula.