Q4.49P - Chemistry: Molecular Nature Of Matter And Change

Question

Limestone (calcium carbonate) is insoluble in water but dissolves when a hydrochloric acid solution is added. Write balanced total ionic and net ionic equations, showing hydrochloric acid as it actually exists in water and the reaction as a proton-transfer process.

Step-by-Step Solution

Answer

A carbonate ion is a base and hydrochloric acid    is an acid. When both react, they form  ${\mathbf{\text{H}}}_{\mathbf{\text{2}}}{\mathbf{\text{CO}}}_{\mathbf{\text{3}}}$ which further decomposes into ${\mathbf{\text{CO}}}_{\mathbf{\text{2}}}$  gas and water as the final products.

Step 1: Determine different types of equations to represent aqueous ionic reactions

The molecular equation reveals the least about the species in solution and is actually somewhat misleading because it shows all the reactants and products as if they were intact undissociated compounds.

The total ionic equation is a much more accurate representation of the reaction because it shows all the soluble ionic substances dissociated into ions.

The net ionic equation is the most useful because it omits the spectator ions and shows the actual chemical change taking place.

Step 2: Write the net ionic equation of the reaction between calcium carbonate and hydrochloric acid

Balanced molecular reaction:

 ${\mathrm{CaCO}}_3\left(\mathrm{s}\right)+2\mathrm{HCl}\left(\mathrm{aq}\right)\to {\mathrm{CaCl}}_2\left(\mathrm{aq}\right)+{\mathrm{H}}_2{\mathrm{CO}}_3\left(\mathrm{aq}\right)$

Total ionic equation:

 ${\mathrm{CaCO}}_3\left(\mathrm{s}\right)+2{\mathrm{H}}^{+}\left(\mathrm{aq}\right)+2{\mathrm{Cl}}^{-}\left(\mathrm{aq}\right)\to {\mathrm{Ca}}^{2+}\left(\mathrm{aq}\right)+2{\mathrm{Cl}}^{-}\left(\mathrm{aq}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)+{\mathrm{CO}}_2\left(\mathrm{g}\right)$

Net ionic equation:

 ${\mathrm{CaCO}}_3\left(\mathrm{s}\right)+2{\mathrm{H}}^{+}\left(\mathrm{aq}\right)\to {\mathrm{Ca}}^{2+}\left(\mathrm{aq}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)+{\mathrm{CO}}_2\left(\mathrm{g}\right)$