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Exam 20: Principles of Chemical Reactivity: Electron Transfer Reactions

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Question 1

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Calculate the equilibrium constant for the reaction below at 25 °C. Co(s) + 2 Cr³⁺(aq) → Co²⁺(aq) + 2 Cr²⁺(aq) The standard reduction potentials are as follows: Co²⁺(aq) + 2 e^- → Co(s) E° = -0.28 V Cr³⁺(aq) + e^- → Cr²⁺(aq) E° = -0.41 V

A) 4.0 × 10^-5
B) 2.5 × 10⁴
C) 1.0 × 10⁵
D) 1.2 × 10⁵
E) 1.3 × 10⁵

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Question 2

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Calculate the charge, in coulombs, is required to deposit 1.5 g of solid magnesium from a solution of Mg²⁺(aq) ion.

A) 4.1 × 10² C
B) 6.0 × 10³ C
C) 1.2 × 10⁴ C
D) 2.9 × 10⁵ C
E) 3.1 × 10⁶ C

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Question 3

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Write a balanced chemical equation for the following reaction in a basic solution. ClO^-(aq) + Cr(OH) ₃(s) ? Cl^-(aq) + CrO₄^2-(aq)

Use the following standard reduction potentials to determine which species is the strongest oxidizing agent. Fe²⁺(aq) + 2 e^- ? Fe(s) ; E° = -0.41 V Pt²⁺(aq) + 2 e^- ? Pt(s) ; E° = 1.18 V Cr₂O₇^2-(aq) + 14 H⁺(aq) + 6 e^- ? 2 Cr³⁺(aq) + 7 H₂O( $\ell$ ) ; E° = 1.33 V

Which of the following statements is true for electron transfer reactions?

Use the following standard reduction potentials to determine which species is the best oxidizing agent. $\begin{array} { l l } \mathrm { O } _ { 2 } ( \mathrm {~g} ) + 4 \mathrm { H } ^ { + } ( \mathrm { aq } ) + 4 \mathrm { e } ^ { - } \rightarrow 2 \mathrm { H } _ { 2 } \mathrm { O } ( \ell ) & E ^ { \circ } = + 1.229 \mathrm {~V} \\\mathrm {{ Hg } _ { 2 }} ^ { 2 + } ( \mathrm { aq } ) + 2 \mathrm { e } ^ { - } \rightarrow 2 \mathrm { Hg } ( \ell ) & E ^ { \circ } = + 0.789 \mathrm {~V} \\\mathrm { I } _ { 2 } ( \mathrm {~s} ) + 2 \mathrm { e } ^ { - } \rightarrow 2 \mathrm { I } ^ { - } ( \mathrm { aq } ) & E ^ { \circ } = + 0.535 \mathrm {~V}\end{array}$

Calculate E_cell for the following electrochemical cell at 25 °C. Pt(s) | Fe³⁺(aq, 0.100 M) , Fe²⁺(aq, 0.040 M) || Cl^-(aq, 0.50 M) | AgCl(s) | Ag(s) The standard reduction potentials are as follows: AgCl(s) + e^- → Ag(s) + Cl^-(aq) E° = +0.222 V Fe³⁺(aq) + e^- → Fe²⁺(aq) E° = +0.771 V

Write the balanced oxidation half-reaction for the following overall reaction: 2 H⁺(aq) + Ca(s) → Ca²⁺(aq) + H₂(g)

Calculate the copper(II) ion concentration at 25 °C in the cell Zn(s) | Zn²⁺(aq, 1.0 M) || Cu²⁺(aq) | Cu(s) if the measured cell potential is 1.06 V. The standard cell potential is 1.10 V.

Claculate the mass of chromium that can be deposited by electrolysis of an aqueous solution of chromium(III) sulfate, Cr₂(SO₄) ₃, for 180 min using a constant current of 11.0 A. Assume 100% current efficiency. (F = 96485 C/mol)

Calculate the value of the reaction quotient, Q, for the voltaic cell constructed from the following two half-reactions when the Zn²⁺ion concentration is 0.0110 M and the Ag⁺ ion concentration is 1.27 M? $\mathrm { Zn } ^ { 2 + } ( \mathrm { aq } ) + 2 \mathrm { e } ^ { - }$ ? $\mathrm { Zn } ( \mathrm { s } ) ; E ^ { \circ } = - 0.76 \mathrm {~V}$ $\mathrm { Ag } ^ { + } ( \mathrm { aq } ) + \mathrm { e } ^ { - }$ ? $\mathrm { Ag } ( \mathrm { s } ) ; E ^ { \circ } = 0.80 \mathrm {~V}$

Consider the following half-reactions. Ag⁺(aq) + e^- → Ag(s) E° = +0.80 V Cu²⁺(aq) + 2 e^- → Cu(s) E° = +0.34 V Pb²⁺(aq) + 2 e^- → Pb(s) E° = -0.13 V Fe²⁺(aq) + 2 e^- → Fe(s) E° = -0.44 V Al³⁺(aq) + 3 e^- → Al(s) E° = -1.66 V Which of the following species will oxidize lead, Pb(s) ?

If the $E _ { \text {cell } } ^ { \circ }$ = -0.362 V for a given electrochemical cell at 25 °C, calculate the pH of the solution at the cathode. Pt | H₂(g, 1.0 atm) | H⁺(aq, 1.00 M) || H⁺(aq) | H₂(g, 1.0 atm) | Pt

When the given oxidation-reduction reaction in an acidic solution is balanced, what is the lowest whole-number coefficient for H⁺, and on which side of the balanced equation should it appear? MnO₄^-(aq) + Br^-(aq) → Mn²⁺(aq) + Br₂(l)

Aluminum(III) ion (Al³⁺) is reduced to solid aluminum at an electrode. If a current of 2.75 amperes is passed for 36 hours, calculate the mass of aluminum deposited at the electrode. (Assume 100% current efficiency.)

Write a balanced net ionic equation for the reaction below in an acidic solution. Cr₂O₇^2-(aq) + Ni(s) ? Cr³⁺(aq) + Ni²⁺(aq)

Write a balanced chemical equation for the oxidation of solid cadmium by concentrated nitric acid, producing nitrogen dioxide gas and Cd²⁺(aq) ion.

Write the balanced reduction half-reaction for the following overall reaction: 2 Fe(s) + 3 Cl2(aq) → 2 Fe3+(aq) + 6 Cl-(aq)

Which of the following statements is true for the following reaction, assuming the given reaction proceeds in the forward direction? 3 Sn⁴⁺(aq) + 2 Cr(s) → 3 Sn²⁺(aq) + 2 Cr³⁺(aq)

When a secondary battery provides electrical energy, it is acting as a voltaic cell. When the battery is recharging, it is operating as a(n) _____ cell.