SB 30th

Imagine that two half-reactions are each measured relative to a standard hydrogen electrode. The standard reduction potential for half-cell A is found to be 1.0 V, while the standard reduction potential for half-cell B is found to be 1.5 V. What will the standard cell potential be when half-cell A is connected to half-cell B to generate a spontaneous reaction?

+0.5 V

When the half-reactions below are balanced to account for electron transfer, the first reaction should be multiplied by _____, and the second reaction should be multiplied by _____. Equation 1: 2H2O → O2 + 4H+ + 4e- Equation 2: Ni2+ + 2e- → Ni

1, 2

When hydrogen atoms are balanced in the following (unbalanced) half-reaction, identify the amount of the substance that must be introduced, and where it will appear in the equation. Assume the reaction occurs in acidic medium. 2ClO3- → Cl2 + 6H2O

12 H+ must be added as a reactant.

Prior to balancing oxygen and hydrogen atoms, identify the missing coefficients in the half-reaction _____ NO2- → _____ NH4+.

1; 1

Select all the options that correctly reflect the result when the two reactions given are added together. Make sure you eliminate species that appear on both sides of the equation. Reaction 1: 2BiO+ + 4H+ + 6e- → 2Bi + 2H2O Reaction 2: 6H2O → 3H2O2 + 6H+ + 6e-

2 moles of H+ appear as a product. 4 moles of H2O appear as a reactant.

Mn

2 moles of H2O appear among the products. 2 moles of OH- appear among the reactants.

Select all that apply The reaction shown below occurs in a basic solution. Select all the options that correctly describe the balanced equation obtained after all resulting species are combined and/or canceled correctly. MnO2 + 4H+ + Zn → Mn2+ + 2H2O + Zn2+

2 moles of H2O appear among the reactants. 4 moles of OH- appear among the products.

Identify the half-reactions that occur at the cathode and the anode in the following overall electrochemical reaction: Fe3+ (aq) + Cu (s) → Cu+ (aq) + Fe2+ (aq) Instructions

2 moles of OH- appear among the reactants. 2 moles of H2O appear among the products.

When the half-reactions below are balanced to account for electron transfer, the first reaction should be multiplied by _____, and the second reaction should be multiplied by _____. Reaction 1: Cr2O72- + 14H+ + 6e- → 2Cr3+ + 7H2O Reaction 2: S + 3H2O → H2SO3 + 4H+ + 4e-

2, 3

Which of the following electrochemical reactions are spontaneous under standard conditions? Select all that apply.

2Co (s) + 3Cl2 (g) → 2CoCl3 (aq); Ecello = 1.6 V 2Cr (s) + 3Sn4+ (aq) → 2Cr3+ (aq) + 3Sn2+ (aq); Ecello = 0.89 V

What is the spontaneous reaction that occurs when the following half-cells are combined? Zn2+ (aq) + 2 e- → Zn (s); Eo = -0.76 Na+ (aq) + e- → Na (s); Eo = -2.71

2Na (s) + Zn2+ (aq) → 2Na+ (aq) + Zn (s)

When the two half-reactions below are added together (ensuring that the electrons cancel), which of the following is the net reaction? Reaction 1: Cu2+ + 2e- → Cu Reaction 2: Fe → Fe3+ + 3e-

3Cu2+ + 2Fe → 3Cu + 2Fe3+

Which of the following statements about a salt bridge in a galvanic cell are correct? Select all that apply.

A salt bridge typically consists of an inert electrolyte. A salt bridge allows cations and anions to flow from one half-cell to the other.

If we were to solve for the cell potential of the following reaction, which two reactions would we first need to find in a standard reduction table? 2 Ag+ (aq) + Zn (s) → 2 Ag (s) + Zn2+ (aq)

Ag+ (aq) + e- → Ag (s) Zn2+ (aq) + 2 e- → Zn (s)

Select all the options that correctly describe how to assign oxidation numbers for atoms in a given species. Assume in all cases that the element in question is bonded to an element other than itself.

Alkaline earth metals (Group 2A) should always be assigned a +2 oxidation number. Fluorine should be always be assigned a -1 oxidation number when bonded to other elements. Alkali metals (Group 1A) should always be assigned a +1 oxidation number.

Which of the following conditions must be satisfied in order to assemble a standard hydrogen electrode? Select all that apply.

An inert electrode (such as platinum) should be present. HCl should be present at a concentration of 1 M. Hydrogen gas should be bubbled through the solution at a pressure of 1 atm.

The anodeBlank 1Blank 1 anode , Incorrect Unavailable is the electrode at which the reduction reaction occurs, and the cathodeBlank 2Blank 2 cathode , Incorrect Unavailable is the electrode at which the oxidation reaction occurs.

Blank 1: cathode Blank 2: anode

Cl2 (g) + 2e- → 2Cl- (aq); Eo = +1.36 V Given this information, which of the following options correctly relate the cell potential to the balanced half-reaction given in each case? Select all that apply.

Cl- (aq) → 1212Cl2 (g) + e-; Eo = -1.36 V 2Cl2 (g) + 4e- → 4Cl- (aq); Eo = +1.36 V

Which of the following is the proper cell notation for the electrochemical reaction shown below? 2 H+ (1 M, aq) + Cu (s) → Cu2+ (1 M, aq) + H2 (1 atm, g)

Cu (s) | Cu2+ (1 M) || H+ (1 M) | H2 (1 atm) | graphite

In which of the following reactions is Fe oxidized?

FeCl2 (aq) + 1212Cl2 (g) → FeCl3 (aq) 4Fe (s) + 3O2 (g) → 2Fe2O3 (s)

To which of the following half-reactions must 2 electrons appear as products in order to balance the equation?

H2 + 2OH- → 2H2O H2O + PbO → PbO2 + 2H+

For the chemical reaction shown below, which of the following (unbalanced) reactions should be used as the starting point for the reduction half-reaction? 2Na + 2H2O → 2NaOH + H2

H2O → H2

When a redox reaction that takes place in an acidic solution involves an oxygen imbalance, oxygen should be balanced by adding _____ as needed, while hydrogen should be balanced by adding _____.

H2O, H+

Which of the following must be balanced in order to balance a redox reaction? Select all that apply.

Number of atoms of each type Overall charge

When zinc metal is immersed in a 1.0 M solution of copper (II) chloride at 25oC, no electrochemical work may be extracted, even though a spontaneous reaction occurs. What is wrong with this cell design?

The oxidation and reduction reactions must be physically separated.

Select all the options that correctly describe the redox reaction shown. H2 (g) + Cl2 (g) → 2HCl (g)

The oxidation number of H changes from 0 to +1. The oxidation number of Cl changes from 0 to -1.

Which of the following options describing the assignment of oxidation numbers is/are NOT correct? Select all that apply.

The sum of the oxidation numbers of all of the elements in a single chemical species must be equal to zero. An oxidation number is a measure of the ability for an atom to draw electrons to itself.

Based on the following reaction, identify ALL the species that should be included in the oxidation half-reaction equation. Zn (s) + Cu2+ (aq) → Zn2+ (aq) + Cu (s)

Zn (s) Zn2+ (aq)

Which of the following best explains why the following chemical reaction is not balanced? Cu2+ (aq) + Fe (s) → Cu (s) + Fe3+ (aq)

charge not balanced

Select all the options that correctly describe how to assign oxidation numbers for atoms in a given species. Assume in all cases that the element in question is bonded to an element other than itself.

lkaline earth metals (Group 2A) should always be assigned a +2 oxidation number. Fluorine should be always be assigned a -1 oxidation number when bonded to other elements. Alkali metals (Group 1A) should always be assigned a +1 oxidation number. Need help? Review these concept resources.