Question Video: Describing How Oxidation Changes a Chemical Species in the Reaction between Elemental Zinc and the Lead(II) Ion Chemistry • Third Year of Secondary School

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Consider the following ionic equation: Zn (s) + Pb²⁺ (aq) → Zn²⁺ (aq) + Pb (s) Which of the following statements is correct ? [A] Zinc has been oxidized because it has gained oxygen [B] Lead has been oxidized because it has gained oxygen [C] Zinc has been reduced because it has lost two electrons [D] Zinc has been oxidized because it has lost two electrons [E] Lead has been oxidized because it has lost two electrons.

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Video Transcript

Consider the following ionic equation: Zn solid plus Pb2+ aqueous react to form Zn2+ aqueous plus Pb solid. Which of the following statements is correct ? (A) Zinc has been oxidized because it has gained oxygen. (B) Lead has been oxidized because it has gained oxygen. (C) Zinc has been reduced because it has lost two electrons. (D) Zinc has been oxidized because it has lost two electrons. (E) Lead has been oxidized because it has lost two electrons.

First of all, the provided ionic equation represents a redox reaction, which is a chemical reaction that involves the transfer of electrons between species. Both oxidation and reduction happen during a redox reaction. When a species is oxidized, it loses electrons. When a species is reduced, it gains electrons. To determine if lead and zinc have been oxidized or reduced, we will need to use oxidation numbers. If oxidation has occurred, we will see an increase in the oxidation number. If reduction has occurred, we will see a decrease in the oxidation number.

One of the reactants is elemental zinc. Any atom in its elemental state will have an oxidation number of zero. Therefore, the oxidation number of elemental lead on the product side of the equation is also zero. Now, the oxidation number of an ion is equal to its charge. This means that the oxidation numbers of the Pb2+ and Zn2+ ions will be positive two.

Now that we’ve assigned all the oxidation numbers, let’s see how they changed during the reaction. Moving from the reactants to the products, we notice that the oxidation number of zinc increased from zero to positive two. This means that zinc lost two electrons and was oxidized. We also notice that the oxidation number of lead decreased from positive two to zero. This means that the Pb2+ ion gained two electrons and was reduced.

Now, let’s take a look at answer choices (A) and (D). We know that zinc was oxidized in the reaction because its oxidation number increased. However, during the reaction, zinc did not gain oxygen; it lost two electrons. In conclusion, the statement that is correct about the ionic equation is answer choice (D). Zinc has been oxidized because it has lost two electrons.