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Chapter 18: Problem 17

Specify which of the following equations represent oxidationreduction reactions, and indicate the oxidizing agent, the reducing agent, the species being oxidized, and the species being reduced. a. \(\mathrm{CH}_{4}(g)+\mathrm{H}_{2} \mathrm{O}(g) \rightarrow \mathrm{CO}(g)+3 \mathrm{H}_{2}(g)\) b. \(2 \mathrm{AgNO}_{3}(a q)+\mathrm{Cu}(s) \rightarrow \mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2}(a q)+2 \mathrm{Ag}(s)\) c. \(\mathrm{Zn}(s)+2 \mathrm{HCl}(a q) \rightarrow \mathrm{ZnCl}_{2}(a q)+\mathrm{H}_{2}(g)\) d. \(2 \mathrm{H}^{+}(a q)+2 \mathrm{CrO}_{4}^{2-}(a q) \rightarrow \mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}(a q)+\mathrm{H}_{2} \mathrm{O}(l)\)

Short Answer

Expert verified
In summary: a. Redox reaction - Oxidizing agent: \(\mathrm{H}_{2}\mathrm{O}\) - Reducing agent: \(\mathrm{CH}_{4}\) - Species oxidized: C in \(\mathrm{CH}_{4}\) - Species reduced: O in \(\mathrm{H}_{2} \mathrm{O}\) b. Redox reaction - Oxidizing agent: \(\mathrm{AgNO}_{3}\) - Reducing agent: \(\mathrm{Cu}\) - Species oxidized: Cu - Species reduced: Ag c. Redox reaction - Oxidizing agent: \(\mathrm{HCl}\) - Reducing agent: \(\mathrm{Zn}\) - Species oxidized: Zn - Species reduced: H d. Not a redox reaction

Step by step solution

01

Determine the oxidation states of each element

For reactants: C(-4), H(+1), O(-2) For products: C(+2), H(+1), O(-2)
02

Check for changes in oxidation states

Yes, there are changes in oxidation states: C from -4 to +2 (oxidation) O from -2 to -2 (no change) H from +1 to +1 (no change)
03

Identify the redox agents and species

Oxidizing agent: \(\mathrm{H}_{2}\mathrm{O}\) (contains species reduced, O) Reducing agent: \(\mathrm{CH}_{4}\) (contains species oxidized, C) Species oxidized: C in \(\mathrm{CH}_{4}\) Species reduced: O in \(\mathrm{H}_{2} \mathrm{O}\) b. \(2 \mathrm{AgNO}_{3}(a q)+\mathrm{Cu}(s) \rightarrow \mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2}(a q)+2 \mathrm{Ag}(s)\)
04

Determine the oxidation states of each element

For reactants: Ag(+1), N(+5), O(-2), Cu(0) For products: Cu(+2), N(+5), O(-2), Ag(0)
05

Check for changes in oxidation states

Yes, there are changes in oxidation states: Ag from +1 to 0 (reduction) Cu from 0 to +2 (oxidation) N from +5 to +5 (no change) O from -2 to -2 (no change)
06

Identify the redox agents and species

Oxidizing agent: \(\mathrm{AgNO}_{3}\) (contains species reduced, Ag) Reducing agent: \(\mathrm{Cu}\) (contains species oxidized, Cu) Species oxidized: Cu Species reduced: Ag c. \(\mathrm{Zn}(s)+2 \mathrm{HCl}(a q) \rightarrow \mathrm{ZnCl}_{2}(a q)+\mathrm{H}_{2}(g)\)
07

Determine the oxidation states of each element

For reactants: Zn(0), H(+1), Cl(-1) For products: Zn(+2), Cl(-1), H(0)
08

Check for changes in oxidation states

Yes, there are changes in oxidation states: Zn from 0 to +2 (oxidation) H from +1 to 0 (reduction) Cl from -1 to -1 (no change)
09

Identify the redox agents and species

Oxidizing agent: \(\mathrm{HCl}\) (contains species reduced, H) Reducing agent: \(\mathrm{Zn}\) (contains species oxidized, Zn) Species oxidized: Zn Species reduced: H d. \(2 \mathrm{H}^{+}(a q)+2 \mathrm{CrO}_{4}^{2-}(a q) \rightarrow \mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}(a q)+\mathrm{H}_{2} \mathrm{O}(l)\)
10

Determine the oxidation states of each element

For reactants: H(+1), Cr(+6), O(-2) For products: Cr(+6), O(-2), H(+1), O(-2)
11

Check for changes in oxidation states

No, there are no changes in oxidation states: H from +1 to +1 (no change) Cr from +6 to +6 (no change) O from -2 to -2 (no change) Since there are no changes in oxidation states in reaction (d), it is not a redox reaction.

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Most popular questions from this chapter

A galvanic cell is based on the following half-reactions: $$\begin{array}{ll}\mathrm{Fe}^{2+}+2 \mathrm{e}^{-} \longrightarrow \mathrm{Fe}(s) & \mathscr{E}^{\circ}=-0.440 \mathrm{~V} \\ 2 \mathrm{H}^{+}+2 \mathrm{e}^{-} \longrightarrow \mathrm{H}_{2}(g) & \mathscr{E}^{\circ}=0.000 \mathrm{~V} \end{array}$$ where the iron compartment contains an iron electrode and \(\left[\mathrm{Fe}^{2+}\right]=1.00 \times 10^{-3} M\) and the hydrogen compartment contains a platinum electrode, \(P_{\mathrm{H}_{2}}=1.00 \mathrm{~atm}\), and a weak acid, \(\mathrm{HA}\), at an initial concentration of \(1.00 M .\) If the observed cell potential is \(0.333 \mathrm{~V}\) at \(25^{\circ} \mathrm{C}\), calculate the \(K_{\mathrm{a}}\) value for the weak acid HA.

How can one construct a galvanic cell from two substances, each having a negative standard reduction potential?

A standard galvanic cell is constructed so that the overall cell reaction is $$2 \mathrm{Al}^{3+}(a q)+3 \mathrm{M}(s) \longrightarrow 3 \mathrm{M}^{2+}(a q)+2 \mathrm{Al}(s)$$ where \(\mathrm{M}\) is an unknown metal. If \(\Delta G^{\circ}=-411 \mathrm{~kJ}\) for the overall cell reaction, identify the metal used to construct the standard cell.

Calculate \(K_{\mathrm{sp}}\) for iron(II) sulfide given the following data: $$\begin{aligned}\mathrm{FeS}(s)+2 \mathrm{e}^{-} \longrightarrow \mathrm{Fe}(s)+\mathrm{S}^{2-}(a q) & & \mathscr{b}^{\circ} &=-1.01 \mathrm{~V} \\\\\mathrm{Fe}^{2+}(a q)+2 \mathrm{e}^{-} \longrightarrow \mathrm{Fe}(s) & & \mathscr{b}^{\circ} &=-0.44 \mathrm{~V} \end{aligned}$$

Consider the electrolysis of a molten salt of some metal. What information must you know to calculate the mass of metal plated out in the electrolytic cell?
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