Question

redox reactions refer to a pair of reactions in which a particular oxidation is coupled to a corresponding reduction. although neither can occur independently of the other, it can be helpful to write each oxidation or reduction as a half - reaction to help us understand and calculate the flow of energy. in this exercise, sort each listed half - reaction as either an oxidation or a reduction. (drag and drop into the appropriate area below) half reactions (8 items): acetaldehyde + 2e⁻+ 2h⁺→ethanol; ca⁰→ca²⁺+ 2e⁻; ½o₂ + 2h⁺+ 2e⁻→h₂o; h₂→2h⁺+ 2e⁻; fe³⁺+ e⁻→fe²⁺; nadh + h⁺→nad⁺+ 2h⁺+ 2e⁻; hs⁻→s⁰+ 2h⁺+ e⁻; fad + 2h⁺+ 2e⁻→fadh₂

Explanation:

Step1: Recall oxidation - reduction rules

Oxidation is the loss of electrons and reduction is the gain of electrons.

Step2: Analyze each half - reaction

acetaldehyde + 2e⁻+ 2H⁺→ethanol

The acetaldehyde gains electrons and hydrogen ions to form ethanol, so it is a reduction reaction.

Ca⁰→Ca²⁺ + 2e⁻

Calcium loses electrons to form a calcium ion, so it is an oxidation reaction.

½O₂ + 2H⁺+ 2e⁻→H₂O

Oxygen gains electrons and hydrogen ions to form water, so it is a reduction reaction.

H₂→2H⁺ + 2e⁻

Hydrogen loses electrons to form hydrogen ions, so it is an oxidation reaction.

NADH + H⁺→NAD⁺+ 2H⁺+ 2e⁻

NADH loses electrons, so it is an oxidation reaction.

Fe³⁺+ e⁻→Fe²⁺

Iron(III) ion gains an electron to form iron(II) ion, so it is a reduction reaction.

HS⁻→S⁰+ 2H⁺+ e⁻

The sulfide ion loses electrons, so it is an oxidation reaction.

FAD + 2H⁺+ 2e⁻→FADH₂

FAD gains electrons and hydrogen ions, so it is a reduction reaction.

Answer:

Oxidation reactions: Ca⁰→Ca²⁺ + 2e⁻, H₂→2H⁺ + 2e⁻, NADH + H⁺→NAD⁺+ 2H⁺+ 2e⁻, HS⁻→S⁰+ 2H⁺+ e⁻
Reduction reactions: acetaldehyde + 2e⁻+ 2H⁺→ethanol, ½O₂ + 2H⁺+ 2e⁻→H₂O, Fe³⁺+ e⁻→Fe²⁺, FAD + 2H⁺+ 2e⁻→FADH₂