Question

By means of ion/electron part equations, write fully balanced equations for the following reaction: the production of hydrogen by the action of hydrochloric acid on magnesium.

I'm so confused as to why Cl, because it says hydrochloric acid, is not used as part of any of the two half equations.
Mg → Mg2+ + 2e- and 2H+ + 2e– → H2 are the only two I need according to the answers to solve. Any explanation for this would be greatly appreciated.

Answer 1

You have written fully balanced equations for the oxidation half and the reduction half. The reason Cl doesn't show up is because it is neither oxidized nor reduced. The balanced molecular equation would be
Mg + 2HCl ==> MgCl2 + H2. The Cl^- is called a spectator ion because it never enters into the reaction. It's there just to balance the charges. You can't add H^+. H^+ must be added by using HCl, HBr, HF, etc In each case the Cl^-, Br^- and F^- are spectator ions.

Answer 2

Ohh that makes more sense. Thanks