January 2019 NY Regents Chemistry Exam
46 Given the balanced ionic equation representing a reaction:
Zn(s) + Co^2+(aq) → Zn^2+(aq) + Co(s) Which statement describes the electrons
involved in this reaction?
(1) Each Zn atom loses 2 electrons, and each Co2+ ion gains 2 electrons.
(2) Each Zn atom loses 2 electrons, and each Co2+ ion loses 2 electrons.
(3) Each Zn atom gains 2 electrons, and each Co2+ ion loses 2 electrons.
(4) Each Zn atom gains 2 electrons, and each Co2+ ion gains 2 electrons.
Solution: Zn has the oxidation number of 0 (all free, neutral elements have an oxidation number of zero) to the left of the arrow. It has the oxidation number of 2+ to the right of the arrow. Let's remember that electrons are negative. Going from 0 to +2 means 2 electrons are lost, eliminating choices 3 and 4. Copper goes from +2 charge to 0, which means it is gaining 2 electrons.
Answer: 1
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