Question

What precipitate will form when aqueous solutions of sodium carbonate calcium `Na_2CO_3` and calcium chloride `CaCl_2` are mixed?

Answer 1

Calcium carbonate.

Explanation:

Sodium carbonate, `"Na"_2"CO"_3`, and calcium chloride, `"CaCl"_2`, are soluble ionic compounds that dissociate in aqueous solution to form cations and anions.

You can thus say that the sodium carbonate solution will contain sodium cations, `"Na"^(+)`, and carbonate anions, `"CO"_3^(2-)`

`"Na"_ 2"CO"_ (3(aq)) -> 2"Na"_ ((aq))^(+) + "CO"_(3(aq))^(2-)`

Likewise, the calcium chloride solution will contain calcium cations, `"Ca"^(2+)`, and chloride anions, `"Cl"^(-)`

`"CaCl"_ (2(aq)) -> "Ca"_ ((aq))^(2+) + 2"Cl"_((aq))^(-)`

Now, when you mix these two solutions, the calcium cations will pair up with the carbonate anions and for calcium carbonate, `"CaCO"_3`, an insoluble ionic compound that precipitates out of solution.

This double replacement reaction will also produce aqueous sodium chloride.

The complete ionic equation looks like this

`2"Na"_ ((aq))^(+) + "CO"_ (3(aq))^(2-) + "Ca"_ ((aq))^(2+) + 2"Cl"_ ((aq))^(-) -> "CaCO"_ (3(s)) darr + 2"Na"_ ((aq))^(+) + 2"Cl"_ ((aq))^(-)`

Eliminate the spectator ions

`color(red)(cancel(color(black)(2"Na"_ ((aq))^(+)))) + "CO"_ (3(aq))^(2-) + "Ca"_ ((aq))^(2+) + color(red)(cancel(color(black)(2"Cl"_ ((aq))^(-)))) -> "CaCO"_ (3(s)) darr + color(red)(cancel(color(black)(2"Na"_ ((aq))^(+)))) + color(red)(cancel(color(black)(2"Cl"_ ((aq))^(-))))`

to get the net ionic equation

`"CO"_ (3(aq))^(2-) + "Ca"_ ((aq))^(2+) -> "CaCO"_ (3(s)) darr`