Electrochemistry

Oxidation Numbers

100

What is the oxidation state of F₂(g),O₂(g), and N₂(g)

Elements have an oxidation number of 0

200

What is the oxidation number of Chromium in Cr₂O₇^-2?

What is +3

300

What is the oxidation number of Iodine in IO₃^{-1 ?}

+5

400

What is the oxidation number for Manganese for    MnO₄^-1

+7

500

When does hydrogen (H) have an oxidation number other than +1?

When hydrogen is in its elemental state, it’s oxidation number is 0

Redox

100

What is an oxidizing agent? 

A substance that is reduced in a redox reaction

200

What is a reducing agent?

A substance that is oxidized in a redox reaction

300

What is the value of E_cell for the cell with the following half reactions?

Au³⁺_(aq)+e^- —> Au_(s)          E^o=1.5    

Pb_(s) -> 2e^- + Pb²⁺_(aq)            E^o=0.126

E_cell=1.626

400

Δ G for a redox reaction in a cell is positive. What is the sign of the voltage of the cell? Is the reaction thermodynamically favorable?

Volatage: negative

The reaction is thermodynamically unfavorable 

500

In an electrochemical cell, two half reactions occur at each electrode:

Electrode A: 2H₂O_(l) —> O_2(g) + 4H⁺_(aq) + 4e^-_(aq)  E^o=-1.23

Electrode B: Cd²⁺_(aq) + 2e^- —> Cd_(s) E^o=-0.403

Identity the direction of the electron flow. Identify the anode and the cathode.

Electrons flow from electrode A to electrode B.

Electrode A: Anode

Electrode B: Cathode

Galvanic Cells

100

Why is the salt bridge needed?

To maintain charge balance between the half-cells of the battery. Anions flow through the salt bridge to the anode, and cations flow through the salt bridge to the cathode.

200

Zn²⁺+2e^-—>Zn          E^o=-0.762

Cu²⁺+2e^-—>Cu.         E^o=+0.337

A galvanic cell uses Zn and Cu. Which substance is in the anode, and which is in the cathode? Explain why.

Zn is in the anode, Cu is in the cathode. Since Cu reduces more easily than Zn, electrons flow from Zn to Cu in a galvanic cell.

300

As the cell continues to run, will the cathode or anode gain mass? Why?

The cathode will gain mass because aqueous cations are being reduced to form metallic particles which attach to the electrode.

400

In the following reaction. What is the anode and what is going to be the cathode? 

Zn⁺²(aq) + 2F^-(aq) -> Zn(s) + F₂(g)

Cathode- Zinc

Anode- Flourine

500

What is a Galvanic Cell?

A cell which derives electrical energy from a spontaneous redox reaction within the cell.

Practice problems

100

Given the following reaction and that the standard reduction potential of Zn⁺² to Zn is -0.76V , determine the E^o for the reduction of Cu⁺² to Cu 

 Zn(s) + Cu⁺²(aq) ---> Zn⁺²(aq) + Cu(s)  

Ecell=1.10V

0.34V

200

What are the fully balanced half reactions for the following redox reaction. (this includes the electrons being balanced)

MnO₄^-(aq)+SO₃^-2(aq)⟶MnO₂(s)+SO₄^-2(aq)

6e^-+8H⁺+2MnO₄^-(aq)⟶2MnO₂(s)+4H₂O(l)

 3H₂O(l)+3SO₃^-2(aq)⟶3SO₄^-2(aq)+6H⁺+6e^-

300

Determine the Cell potential of the galvanic cell using the following half-reactions: 

Cathode: Cl_2(g) + 2e^- —> 2Cl^-_(aq)   E^o = +1.36V 

Anode: I_2(s) + 2e^- —> 2I^-_(aq)         E^o = +0.54V

0.82

400

Write the balanced half reactions for the following reaction: 

NO₃^- + I₂ ---> IO₃^- + NO₂

3H₂O + I₂ ---> IO₃^-1 + 5e^- + 6H⁺

10H⁺ + 5NO₃^-1 + 5e^- ---> 5NO₂ + 5H₂O

500

Given the following reaction, what is Δ G?

4Ag_(s) + O_2(g) + 4H⁺_(aq) —> 4Ag⁺_(aq)+ 2H₂0_(l)

Half reactions:

 O_2(g) + 4H⁺_(aq)+ 4e^- —> 2H₂O_(l)      E^o = +1.23V 

Ag⁺_(aq) + e^- —> Ag_(s)                      E^o = +0.80V

F=96,485

76,030J 

Misc

100

What do you call the method in which most power storage on Earth is done? 

pumped hydro

200

What country has the best scuba diving according to Kubin?

Indonesia

300

What is the capital of Romania

Bucharest

400

Which vitamins can you overload on more easily

fat soluble vitamins (A,D,E)

500

What happens to the voltage of a battery when the reducing agent concentration increases 

The voltage will increase