Question

Question #1ffde

Answer 1

Ok, lots to talk about here

First, let's look at the reactants for this equation.

`Ca(NO_3)_2 + KF ->` ???

You need the subscript 2 after the nitrate (`NO_3`) because the charge of the calcium ion is +2 and a single nitrate ion is -1, so you need two nitrate ions to balance the positive charge of the calcium ion to produce a neutral compound.

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`Ca(NO_3)_2 + KF ->` no chemical reaction

You might predict the following...
`Ca(NO_3)_2 + KF -> CaF_2 + KNO_3`

Review reaction prediction here:

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In this case, both predicted products (`CaF_2 and KNO_3`) are soluble in water, so no reaction will take place.

No net ionic equation because no reaction takes place with these reactants.

Review net ionic equations here:

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Hope this helps!

Answer 2

Well, in your case, the nitrate ion receives a subscript of 2 because that is the charge of calcium cation.

Because calcium is in group 2 of the periodic table, it tends to lose two electrons from its outermost shell and form cations that have a (+2) charge.

I won't go into details about how polyatomic ions get their charges, but as I'm sure you know, the nitrate ion has a (-1) charge.

This means that you need two nitrate anions to balance the positive charge of the calcium cation and form the neutral calcium nitrate, or `Ca(NO_3)_2`.

Not all polyatomic anions have a (-1) charge; for example, the sulfate ion has a (-2) charge, which means that when it combines with the calcium cation, you'll only need one sulfate to balance the positive charge and form calcium sulfate, or `CaSO_4`.

As a conclusion, you need to become familiar with the charges on the more common cations and anions, and with the charges on the more common polyatomic ions.

Once you develop a feel for what ion can have what charge, ionic compounds will be a walk in the park.