Predict the products of the following reaction. If no reaction will occur, use the NO REACTION button. Be sure your chemical equation is balanced!
The Correct Answer and Explanation is:
Balanced Chemical Equation:
CaSO3(s)+2HCl(aq)→CaCl2(aq)+SO2(g)+H2O(l)\text{CaSO}_3(s) + 2\text{HCl}(aq) \rightarrow \text{CaCl}_2(aq) + \text{SO}_2(g) + \text{H}_2\text{O}(l)CaSO3(s)+2HCl(aq)→CaCl2(aq)+SO2(g)+H2O(l)
Explanation
The given reaction involves calcium sulfite (CaSO3\text{CaSO}_3CaSO3) reacting with hydrochloric acid (HCl\text{HCl}HCl). Calcium sulfite is a salt of a weak acid (sulfurous acid, H2SO3\text{H}_2\text{SO}_3H2SO3) and a strong base (calcium hydroxide). When this salt comes into contact with a strong acid like hydrochloric acid, a reaction does occur. This is an example of an acid-sulfite reaction, which typically produces a salt, water, and sulfur dioxide gas.
The hydrogen ions from the hydrochloric acid react with the sulfite ion (SO32−\text{SO}_3^{2-}SO32−) in calcium sulfite to form sulfurous acid (H2SO3\text{H}_2\text{SO}_3H2SO3). However, sulfurous acid is unstable and readily decomposes into sulfur dioxide (SO2\text{SO}_2SO2) and water (H2O\text{H}_2\text{O}H2O):H2SO3→SO2(g)+H2O(l)\text{H}_2\text{SO}_3 \rightarrow \text{SO}_2(g) + \text{H}_2\text{O}(l)H2SO3→SO2(g)+H2O(l)
Simultaneously, the calcium ion (Ca2+\text{Ca}^{2+}Ca2+) combines with the chloride ions from hydrochloric acid to form calcium chloride (CaCl2\text{CaCl}_2CaCl2), which is soluble in water and remains in the aqueous phase.
To balance the overall equation, two moles of hydrochloric acid are needed for each mole of calcium sulfite. One mole of HCl\text{HCl}HCl neutralizes one hydroxide equivalent (due to the 2+2+2+ charge on calcium), and the other proton contributes to forming H2SO3\text{H}_2\text{SO}_3H2SO3.
The visible signs of this reaction include the evolution of sulfur dioxide gas (which has a sharp, choking odor) and the dissolution of the solid calcium sulfite. This reaction demonstrates both acid-base behavior and gas evolution, making it a type of double displacement followed by decomposition.
Because gas is released and products are formed, this is not a case of “no reaction.” The reaction is chemically feasible and proceeds as written.
