Question

The formula of chloric acid is $HCl{ O }_{ 3 }$. The formula for calcium chlorate is:
A- $CaCl{ O }_{ 3 }$
B- $Ca\left( Cl{ O }_{ 3 } \right) _{ 2 }$
C- $Ca_{ 2 }Cl{ O }_{ 3 }$
D- $Ca\left( Cl{ O }_{ 3 } \right) _{ 3 }$

Answer 1

Hint: Try to figure out valency chlorate ion. We should consider elements other than chlorine to exhibit their general valency. Equating positive and negative charges of the final compound to zero we can find the formula of a given compound.

Complete step by step answer: We are asked to find a formula for calcium chlorate. We can find it by balancing charges. Except chlorine remaining elements exhibit their general valencies. Let valency of chlorine in chloric acid be x. The total charge will be 0 on chloric acid. Hydrogen exhibits +1, oxygen exhibits -2.
\[+1\quad +\quad x\quad +\quad 3\quad \times \left( -2 \right) \quad =\quad 0\]
\[+1\quad +\quad x\quad +\quad \left( -6 \right) \quad =\quad 0\]
\[x\quad -\quad 5\quad =\quad 0\]
Sending -5 to the other side it becomes +5.
\[x\quad =\quad +5\]
The valency of chlorine is +5 in chloric acid. Valency of chlorate ion will be -1 as chloric acid has one hydrogen. Calcium in general exhibits +2 valency. Let the formula of calcium chlorate be $Ca_{ p }\left( Cl{ O }_{ 3 } \right) _{ q }$. The total valency of the compound must be 0.
\[p\quad \times \left( +2 \right) \quad +\quad q\quad \times \left( -1 \right) \quad =\quad 0\]
\[2p\quad -\quad q\quad =\quad 0\]
\[2p\quad =\quad q\]
The ratio of p and q is 1:2 and equating p to 1 we get the simplest formula. The final formula is $Ca\left( Cl{ O }_{ 3 } \right) _{ 2 }$.

Therefore option B is correct.

Note: We should not take the valency of chlorine as -1. Chlorine can exhibit different valencies. Oxygen and calcium will exhibit their general valency. Hydrogen generally exhibits +1 valency in presence of more electronegative elements.