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Chemistry LibreTexts

Homework 1: Electrochemistry

Redox Basics

Q1

Xenon forms several nonionic compounds with F and O. Give the oxidation number of the central Xe atom in each of the following compounds: XeO4, XeF2, XeO3, XeF4, and XeF6.

Q2

Xenon can also form a number of ionic compounds, including CsXeF7, and Cs2XeF8. What are the ions in each compound? What is the formal charge and oxidation number of Xe in each ion containing Xe?

Q3

What is the oxidation number of nitrogen in each of the following ions or molecules: NH3, N2H4, NO, NO2, NO2-, NO3-?

Q4

What is the oxidation number of platinum in the complex ion PtCl42-?

Q5

Assign oxidation numbers to the atoms in the following chemical species:

  1. gold, Au
  2. iodine, I2
  3. barium chloride, BaCl2
  4. ethane, C2H6
  5. stannous oxide, SnO
  6. stannic oxide, SnO2
  7. nitrous oxide, N2O
  8. phosphorus pentoxide, P2O5
  9. magnesium hydroxide, Mg(OH)2
  10. sulfurous acid, H2SO3
  11. telluric acid, H6TeO6
  12. hypochlorous acid, HClO
  13. perchloric acid, HCIO4
  14. dichromate, Cr2O72-
  15. cyanide, CN-

Q6

What is the oxidation number of the underlined element in each ion or molecule: VO2+, P2O74-, PH3, KNO2, H2O2, LiH, Mg3N2, NF3, ICl5, Ag(NH3)2+?

Redox Equations

Q7

When the equation

MnO2 + I- + H+ → Mn2+ + I2 + H2O

is balanced, what is the net charge on each side of the equation? What element is oxidized? What element is reduced?

Q8

Multiple Choice: In the following reaction, which element that is oxidized and which is the oxidizing agent.

2 Al + 3 Br2 → 2 AlBr3

(a) aluminum…..aluminum
(b) bromine…..bromine
(c) aluminum…..bromine
(d) bromine…..aluminum

Q9

For each of the following reactions, list the substance reduced, the substance oxidized, the reducing agent, and the oxidizing agent.

  1. 6H+ + MnO4- + 5SO32- → 5SO42- + 2Mn2+ + 3H2O
  2. 8H+ + Cr2O72- + 6HI → 2Cr3+ + 312 + 7H2O
  3. 3Cl2 + 6OH- → CIO3- + 5Cl- + 3H2O

Q10

Phosphine, PH3, is a colorless, highly toxic gas that smells like rotten Fish and is produced in small amounts when animal and vegetable matter decay in moist situations such as damp graveyards, Traces of P2H4 are produced simultaneously and cause the PH3 to ignite in air to give pale, flickering lights commonly called “corpse candles" or "will-o’-the-wisps." In the laboratory, phosphine can be prepared by adding water to calcium phosphide. Write a balanced equation for the reaction. Assign oxidation numbers to each of the elements present.

Q11

Balance the reaction

MnO4- + H+ + H2S → Mn2+ + H2O + S

What is the oxidation number of Mn in MnO4-? What element is oxidized? What element is the oxidizing agent? Is this latter element oxidized or reduced?

Electrochemistry

Q12

A standard Cl2 | Cl- half-cell has been What is ΔG (in joules) for the spontaneous coupled to a Cl2(1.00 atm) l Cl- (0.010M) half-cell. What is the cell voltage? Determine ΔG (at room temperature) for this reaction.

Q13

The following cell

Ag | Ag+(0.10M) || Ag+(1.0M) | Ag

is a concentration cell and is capable of electrical work.

  1. What is the cell potential? 
  2. Which side of the cell is the cathode and which is the anode?
  3. What is the \(\Delta G\) (in joules) for the spontaneous cell reaction?

Q14

Two copper electrodes are placed in two copper sulfate solutions of equal concentration and connected to form a concentration cell. What is the cell voltage? One of the solutions is diluted until the concentration of copper ions is one-fifth its original value. What is the cell volt age after dilution?

Spontaneity

Q15

Assuming unit activities for all substances, determine which of the following reactions will be spontaneous:

  1. Zn + Mg2+ → Zn2+ + Mg
  2. Fe + Cl2 → Fe2+ + 2Cl-
  3. 4Ag + O2 + 4H+ → 4Ag+ +2H2O
  4. 2AgCl → 2Ag + Cl2

Half-Cell Potentials

Q16

What are the potentials for the following cells or half-cells?

  1. Eo for the cell:  Zn(s) | Zn2+|| Cu2+ l Cu(s)
  2. E for the half-cell: Zn(s) l Zn2+(0.001M)
  3. E for the half-cell: Cu2+ (1O-36M) | Cu(s)

Q17

What are the standard potentials, Eo, for the following half-cells?

  1. S2- | CuS (s) | Cu(s)
  2. NH3(aq), Zn(NH3)42+ | Zn(s)