When aqueous sodium sulfite is added to hydrochloric acid
CHEMISTRY · Multi-part · AP · Chemistry · Chemical Reactions · Chemical Reactions
Problem
When aqueous sodium sulfite is added to hydrochloric acid, vigorous bubbling is observed and the resulting solution is essentially neutral. A simplified molecular equation for the reaction is
Na2SO3(aq)+2HCl(aq)→2NaCl(aq)+H2O(l)+SO2(g)
(a) Assign oxidation numbers to sulfur in the reactant ion and in the gaseous product. State whether sulfur is oxidized, reduced, or undergoes no change in oxidation state.
(b) Identify the dominant reaction class for the process. Justify your answer by explicitly discussing the species that are exchanged and the energetic or physical driving force involved.
(c) The SO2(g) produced is often employed to remove residual Cl2(g) from drinking-water treatment streams. Propose a balanced chemical equation for this secondary reaction and explain how it supports the classification you chose in part (b).
(d) Suppose the original sulfite–acid reaction is carried out in the presence of Ca2+(aq). Predict any additional observable outcome, write the net-ionic equation for the new process, and classify the additional reaction class that now occurs.