Given the balanced equation representing a reaction:Ni(s) + 2HCl(aq) → NiCl2(aq) + H2(g) In this re

June 2018 NY Regents Chemistry Exam

46 Given the balanced equation representing a reaction:
Ni(s) + 2HCl(aq) → NiCl2(aq) + H2(g) In this reaction, each Ni atom
(1) loses 1 electron

(2) loses 2 electrons

(3) gains 1 electron

(4) gains 2 electrons

Solution: Let's look at the oxidation numbers of nickel to the left of the arrow and the right. Free, neutral elements have an oxidation number of 0. Therefore Ni(s) has an oxidation number of 0. Next, we can calculate the oxidation number of Ni in NiCl2. The oxidation number of Cl is -1 according to the Periodic Table. The overall charge of the molecule is 0 since it is neutral.

x+(-1*2)=0

x= +2

Therefore, nickel goes from 0 on the reactant side to +2 on the product side. Remember that electrons are negative. It must be loses 2 electrons.

Answer: 2

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