Question

Question #ebe44

Answer 1

Here's why.

Explanation:

The idea here is that the calcium cation, `"Ca"^(2+)`, carries a `2+` charge and the hypochlorite anion, `"ClO"^(-)`, carries a `1-` charge, so in order for the two ions to form an ionic compound, they must combine in a `1:2` ratio.

Since ionic compounds are neutral, the overall negative charge coming from the anions must balance out the overall positiev charge coming from the cations.

In this case, you will need `2` hypochloriet anions to get a total negative charge of

`2 xx (-1) = 2-`

in order to balance out the `2+` charge of the calcium cation.

To show that we need `2` hypochlorite anions for every `1` calcium cation, we use parentheses around the hypochlorite anion and a subscript of `2`.

`"Ca"("ClO")_ 2 => "1 formula unit of Ca"("ClO") = {(1 xx "Ca"^(2+)), (2 xx "ClO"^(-)) :}`

The parentheses are used to show that the subscript is applied to both elements that make up the anion, i.e. to `"Cl"` and `"O"`.

By comparison, something like

`"CaClO"_ 2`

would imply that the subscript is only applied to the oxygen atoms, which would be incorrect given the fact that the hypochlorite anion contains `"Cl"` and `"O"`.