Video Transcript
Consider the reaction Zn solid plus two HCl aqueous reacts to produce ZnCl2 aqueous plus H2 gas. Which of the following is true about this reaction? (A) Zinc gains two electrons; therefore, it is reduced. (B) Each of the hydrogen ions gains an electron; therefore, hydrogen is oxidized. (C) Zinc loses two electrons; therefore, it is oxidized. Or (D) each of the hydrogen ions loses an electron; therefore, hydrogen is reduced.
In this question, we want to know which of the available answers is a correct description of the reaction with regards to oxidation numbers. We should always keep in mind that oxidation refers to the loss of electrons in a reactant, while reduction denotes that the reactant gains electrons. Through oxidation, the oxidation number of an element becomes more positive. And in reduction, the number becomes more negative.
The elemental form of atoms are all denoted by an oxidation number of zero because they are all neutral compounds. In our reaction, we are working with zinc and hydrochloric acid. Zinc is a d block metal and frequently has a plus two oxidation number when found in compounds with other atoms. And when zinc is in its elemental form, as it is in the reactants, it will have an oxidation number of zero. So for zinc, as the oxidation number has gone from zero to plus two, there has been an increase in oxidation number. This means that it has undergone oxidation. Thus, zinc has lost electrons. Specifically, it has lost two electrons. Thus, the true statement is (C). Zinc loses two electrons; therefore it is oxidized.
