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?

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1 Answer
May 15, 2018

#"...the formation of a new substance..."#


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....

#CaCO_3(s) + 2HX(aq) rarr CaX_2(aq) + 2H_2O(l) + CO_2(g)uarr#

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 #Ca(OH)_2#...the reverse reaction should occur as calcium carbonate deposits ... it this a chemical change?

#CO_2(g) + Ca(OH)_2(aq) rarr CaCO_3(s)darr +H_2O(l)#