# When acid and calcium carbonate are added together in a tube, and the CO2 is collected in a tube of limewater, what are all the signs that a chemical has taken place?

## Question above.

##### 1 Answer
May 15, 2018

$\text{...the formation of a new substance...}$

#### Explanation:

Chemical change is characterized by the formation of new substances, and the making and breaking of STRONG chemical bonds. And in practice this manifests in a colour change, a dead giveaway for chemical change, OR the evolution of a gas, OR the deposit of an insoluble precipitate.

And here we treat calcium carbonate with acid....

$C a C {O}_{3} \left(s\right) + 2 H X \left(a q\right) \rightarrow C a {X}_{2} \left(a q\right) + 2 {H}_{2} O \left(l\right) + C {O}_{2} \left(g\right) \uparrow$

Certainly, the rather insoluble calcium carbonate would go up to give a clear, and colourless solution upon treatment with acid, but what else would you see?

And here we shunt the evolved gas to a solution of $C a {\left(O H\right)}_{2}$...the reverse reaction should occur as calcium carbonate deposits ... it this a chemical change?

$C {O}_{2} \left(g\right) + C a {\left(O H\right)}_{2} \left(a q\right) \rightarrow C a C {O}_{3} \left(s\right) \downarrow + {H}_{2} O \left(l\right)$