# Question e0777

Apr 10, 2016

Here's how you could do that.

#### Explanation:

You can make calcium carbonate, ${\text{CaCO}}_{3}$, by passing carbon dioxide, ${\text{CO}}_{2}$, through a solution of calcium hydroxide, "Ca"("OH")_2.

Calcium oxide, $\text{CaO}$, which is sometimes referred to as quicklime, will react with water to form calcium hydroxide, or slacked lime

"CaO"_ ((s)) + "H"_ 2"O"_ ((l)) -> "Ca"("OH")_ (2(s))#

The resulting solution of calcium hydroxide is called limewater. Pure limewater is colorless. When limewater contains excess calcium hydroxide, its color changes to mily, which is why you'll see it referred to as milk of lime.

In order to form calcium carbonate, or limestone, you need to pass carbon dioxide through this calcium hydroxide solution. The limewater, which is clear when pure, will turn milky as a result of the formation of the insoluble calcium carbonate

${\text{Ca"("OH")_ (2(s)) + "CO"_ (2(g)) -> "CaCO"_ (3(s)) darr + "H"_ 2"O}}_{\left(l\right)}$

The calcium carbonate will precipitate out of solution, and can then be separated by filtration.

As an interesting fact, heating the calcium carbonate will cause it to undergo decomposition to reform calcium oxide and carbon dioxide

${\text{CaCO"_ (3(s)) stackrel(color(red)(Delta)color(white)(aa))(->) "CaO"_ ((s)) + "CO}}_{2 \left(g\right)}$ $\uparrow$