Question

Tarnish is produced by a redox reaction that occurs when a metal reacts with a nonmetallic compound. The green tarnish on a copper penny might be produced by a reaction between copper and hydrogen sulfide. What occurs during this reaction?

A. Copper atoms lose electrons to sulfur atoms.
B. Copper atoms gain electrons from sulfur atoms.
C. Hydrogen sulfide acts as an acid, and copper acts as a base.
D. A double-replacement reaction takes place.

Answer 1

Answer:

Reaction of zinc metal in copper sulfate solution.

The process that occurs in this redox reaction is shown below as two separate half-reactions, which can then be combined into the full redox reaction.

& text{Oxidation}: quad quad text{Zn}(s) rightarrow text{Zn}^{2+} (aq) + 2e^- \& underline{text{Reduction}: quad quad text{Cu}^{2+}(aq) + 2e^- rightarrow text{Cu}(s) qquad qquad qquad }\&text{Full Reaction}: quad text{Zn}(s) + text{Cu}^{2+}(aq) rightarrow text{Zn}^{2+}(aq) + text{Cu}(s)

Why does this reaction occur spontaneously? The activity series is a listing of elements in descending order of reactivity. An element that is higher in the activity series is capable of displacing an element that is lower on the series in a single-replacement reaction. This series also lists elements in order of ease of oxidation. The elements at the top are the easiest to oxidize, while those at the bottom are the most difficult to oxidize. The Table below shows the activity series together with each element’s oxidation half-reaction.

Activity Series of Metals (in Order of Reactivity)

Element Oxidation Half Reaction  

Lithium Li(s) → Li+(aq) + e– Most active or most easily oxidized

Potassium K(s) → K+(aq) + e–  

Barium Ba(s) → Ba2+(aq) + 2e–  

Calcium Ca(s) → Ca2+(aq) + 2e–  

Sodium Na(s) → Na+(aq) + e–  

Magnesium Mg(s) → Mg2+(aq) + 2e–  

Aluminum Al(s) → Al3+(aq) + 3e–  

Zinc Zn(s) → Zn2+(aq) + 2e–  

Iron Fe(s) → Fe2+(aq) + 2e–  

Nickel Ni(s) → Ni2+(aq) + 2e–  

Tin Sn(s) → Sn2+(aq) + 2e–  

Lead Pb(s) → Pb2+(aq) + 2e–  

Hydrogen H2(g) → 2H+(aq) + 2e–  

Copper Cu(s) → Cu2+(aq) + 2e–  

Mercury Hg(l) → Hg2+(aq) + 2e–  

Silver Ag(s) → Ag+(aq) + e–  

Platinum Pt(s) → Pt2+(aq) + 2e–  

Gold Au(s) → Au3+(aq) + 3e–

Explanation:

Answer 2

Answer: The correct answer is (A); Copper atoms lose electrons to sulfur atoms.

Explanation:

• Redox reactions are those reactions in which oxidation and reduction reactions both take place.
• Oxidation is the loss of electrons and accompanied by increase in the oxidation state of atom
• Reduction is the gain of electrons and accompanied by decrease in the oxidation state of the atom.

• Reaction between copper metal and hydrogen sulfide:

             $Cu (s) + H_{2} S (g)$ → $Cu S (s) + H_{2} (g)$

• Here copper metal is oxidized from $0$ oxidation to $+2$ in $CuS$ and hydrogen is reduced from $+2$ $(H_{2} S)$ oxidation state to $0$ in $H_{2}$. Therefore correct option is (A).

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