Question

Limestone (calcium carbonate) is insoluble in water but dissolves in aqueous hydrochloric acid. 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.

Short answer

\(\text{CaCO}_3 (s) + 2\text{H}^+ (aq) \rightarrow \text{Ca}^{2+} (aq) + \text{H}_2\text{O} (l) + \text{CO}_2 (g)\)

Step-by-step solution

- Write the Chemical Formula for the Reaction

Identify the reactants and products. The reactants are limestone (calcium carbonate) and hydrochloric acid. The products are calcium chloride, water, and carbon dioxide. The chemical equation is:\(\text{CaCO}_3 (s) + 2\text{HCl} (aq) \rightarrow \text{CaCl}_2 (aq) + \text{H}_2\text{O} (l) + \text{CO}_2 (g)\).

- Write the Total Ionic Equation

Dissociate all strong electrolytes into their constituent ions. The total ionic equation is:\(\text{CaCO}_3 (s) + 2\text{H}^+ (aq) + 2\text{Cl}^- (aq) \rightarrow \text{Ca}^{2+} (aq) + 2\text{Cl}^- (aq) + \text{H}_2\text{O} (l) + \text{CO}_2 (g)\).

- Write the Net Ionic Equation

Eliminate the spectator ions from the total ionic equation. The spectator ions are chloride ions, \(\text{Cl}^-\). The net ionic equation is:\(\text{CaCO}_3 (s) + 2\text{H}^+ (aq) \rightarrow \text{Ca}^{2+} (aq) + \text{H}_2\text{O} (l) + \text{CO}_2 (g)\).

Key concepts

chemical equations

Chemical equations represent reactions occurring between substances. They show the initial substances, known as reactants, and the resulting substances, called products. In the reaction of limestone (calcium carbonate, CaCO₃) with hydrochloric acid (HCl), the equation is:

\[ \text{CaCO}_3 (s) + 2\text{HCl} (aq) \rightarrow \text{CaCl}_2 (aq) + \text{H}_2\text{O} (l) + \text{CO}_2 (g) \]
This equation indicates that solid calcium carbonate reacts with aqueous hydrochloric acid to form aqueous calcium chloride, liquid water, and gaseous carbon dioxide.
Understanding chemical equations is crucial for studying how reactants transform into products in chemical reactions, and it helps visualize the conservation of mass and atoms during the reaction.

total ionic equation

The total ionic equation provides deeper insight into the reaction by showing all soluble ionic substances dissociated into their respective ions. This makes it more explicit about the involved ionic species in the reaction.

For the reaction between limestone and hydrochloric acid, the total ionic equation is:

\[ \text{CaCO}_3 (s) + 2\text{H}^+ (aq) + 2\text{Cl}^- (aq) \rightarrow \text{Ca}^{2+} (aq) + 2\text{Cl}^- (aq) + \text{H}_2\text{O} (l) + \text{CO}_2 (g) \]
Notice that all strong electrolytes, like HCl and CaCl₂, are split into their ions. The solid CaCO₃ remains as a solid because it is not soluble in water. The total ionic equation helps to see the actual species present in solution during the reaction.

net ionic equation

Net ionic equations simplify total ionic equations by removing spectator ions, which are ions that do not participate in the actual chemical change. This focuses on the substances and ions directly involved in the reaction.

For this reaction, the net ionic equation is:

\[ \text{CaCO}_3 (s) + 2\text{H}^+ (aq) \rightarrow \text{Ca}^{2+} (aq) + \text{H}_2\text{O} (l) + \text{CO}_2 (g) \]
Here, the chloride ions (\text{Cl}^-) are excluded because they appear on both sides of the total ionic equation and do not change during the reaction.
The net ionic equation is especially useful for highlighting the essence of the reaction, making it clearer which species are directly involved in the chemical transformation.

proton-transfer process

The reaction of limestone with hydrochloric acid can also be seen as a proton-transfer process. This involves the transfer of protons (H⁺ ions) from one substance to another. In this case, the H⁺ ions from HCl are transferred to the carbonate ions (CO₃²⁻) in CaCO₃.

When H⁺ ions react with CO₃²⁻ ions, they form carbonic acid (H₂CO₃), which rapidly decomposes into water (H₂O) and carbon dioxide (CO₂).
\[ \text{CO}_3^{2-} + 2\text{H}^+ \rightarrow \text{H}_2\text{CO}_3 \rightarrow \text{H}_2\text{O} + \text{CO}_2 \text{g} \]
This transfer and subsequent decomposition underline the critical role of proton transfer in the chemical reaction.
Understanding proton transfer is essential in acid-base chemistry and helps explain how acids interact with different substances to produce various products.