Question

na₂co₃(aq) + 2 hcl(aq) → 2 nacl(aq) + h₂o(l)+co₂(g)
a student combined two colorless aqueous solutions. one of the solutions contained na₂co₃ as the
solute, and the other contained hcl. the chemical reaction that took place is represented by the equation
above. what experimental result would be evidence that a chemical reaction took place when the solutions
were combined?
a bubbles formed when the two solutions were combined.
b the total volume of the mixture is close to the sum of the initial volumes.
c the resulting solution is colorless.
d the resulting solution conducts electricity.

Explanation:

• Option A: Formation of bubbles (due to \(CO_2\) gas production as per the reaction \(Na_2CO_3(aq)+2HCl(aq)\to2NaCl(aq)+H_2O(l)+CO_2(g)\)) is a clear sign of a chemical reaction.
• Option B: Volume being close to the sum of initial volumes is a physical property (related to solution mixing, not a chemical reaction indicator).
• Option C: Both reactant solutions (\(Na_2CO_3\) and \(HCl\)) are colorless, and the product solution (\(NaCl\) solution) is also colorless. Color - less nature is not a proof of a chemical reaction.
• Option D: Both \(Na_2CO_3\) (a strong electrolyte) and \(HCl\) (a strong electrolyte) solutions conduct electricity, and the product \(NaCl\) (a strong electrolyte) solution also conducts electricity. Conductivity does not prove a chemical reaction.

Answer:

A. Bubbles formed when the two solutions were combined.