An experiment is performed to measure the mass percent of CaCO3(s) in eggshells. Five different samp — Stoichiometry Chemistry Question

STEPS:

1. Identify the reaction type and expected products:
The chemical reaction between solid calcium carbonate ($\text{CaCO}_3(s)$) and hydrochloric acid ($\text{HCl}(aq)$) is an acid-carbonate reaction. This class of reaction produces a salt, water, and a gas. Specifically, the reactants yield aqueous calcium chloride ($\text{CaCl}_2$), liquid water ($\text{H}_2\text{O}$), and carbon dioxide gas ($\text{CO}_2$).

2. Understand how the species exist in aqueous solution:
Because the question asks for the species that react and the species that are produced, the process is best represented using a net ionic equation. To write this, we must examine the physical state of each substance in water:
* $\text{CaCO}_3(s)$ is an insoluble ionic solid, so it remains intact as a solid reactant.
* $\text{HCl}(aq)$ is a strong acid that dissociates completely in water to exist as free $\text{H}^+(aq)$ and $\text{Cl}^-(aq)$ ions.
* $\text{CaCl}_2(aq)$ is a highly soluble ionic salt that exists as dissociated $\text{Ca}^{2+}(aq)$ and $\text{Cl}^-(aq)$ ions.
* $\text{H}_2\text{O}(l)$ and $\text{CO}_2(g)$ are covalent molecular substances that do not dissociate into ions.

3. Write the complete ionic equation:
By representing all strong electrolytes as dissociated ions, we get the complete ionic equation:
$$\text{CaCO}_3(s) + 2\ \text{H}^+(aq) + 2\ \text{Cl}^-(aq) \rightarrow \text{Ca}^{2+}(aq) + 2\ \text{Cl}^-(aq) + \text{H}_2\text{O}(l) + \text{CO}_2(g)$$

4. Identify and remove spectator ions:
Spectator ions are ions that appear chemically unchanged on both the reactant and product sides of the equation. In this reaction, chloride ions ($\text{Cl}^-(aq)$) are spectators. Because spectator ions do not participate in the chemical change, they are omitted to produce the net ionic equation.

5. Formulate the final net ionic equation:
Canceling out the chloride ions on both sides leaves the net ionic equation:
$$2\ \text{H}^+(aq) + \text{CaCO}_3(s) \rightarrow \text{Ca}^{2+}(aq) + \text{H}_2\text{O}(l) + \text{CO}_2(g)$$
This matches Option B.

*

WHY_OTHERS_WRONG:

• Option A is incorrect: This equation suggests the reaction produces carbonate ions ($\text{CO}_3^{2-}$) and hydrogen gas ($\text{H}_2$). Acids react with carbonates to produce carbon dioxide gas and water, not hydrogen gas.
• Option C is incorrect: This option proposes the formation of carbon monoxide ($\text{CO}$) gas and basic hydroxide ($\text{OH}^-$) ions, which is chemically incorrect for an acid-carbonate neutralization reaction.
• Option D is incorrect: Although this equation is stoichiometrically balanced and lists the correct products, it represents the reaction in molecular/complete ionic form by failing to cancel the spectator chloride ions ($\text{Cl}^-$) and keeping $\text{HCl}$ in molecular form. A proper representation of reacting species in solution must omit spectator ions.