Chapter 12

Question 1

What does the oxidation number of oxidation state describe

Answer 1

It describes how many electrons an atom is donating or accepting in the overall bonding of the molecule. Many elements can assume different oxidation states depending on the bonds they make.
*pg264

Question 2

Oxidation-reduction reaction (redox)

Answer 2

A reaction in which oxidation numbers of any of the reactants change. In this reaction atoms gain or lose electrons as new bonds are formed. The total number of electrons does not change, they’re just redistributed among the atoms.
*pg264

Question 3

Oxidation vs reduction

Answer 3

Oxidation: when an atom loses electrons and its oxidation number increases. (LEO)
Reduction: When an atom gains electrons and the oxidation number decreases (GER)
*pg264

Question 4

Reducing agent vs oxidizing agent

Answer 4

Reducing: An atom that is oxidized in a reaction (the one that loses electrons)
Oxidizing: An atom that is reduced (The one that gains electrons)
*pg264

Question 5

Galvanic or voltaic cell

Answer 5

A device to generate an electric current using a spontaneous redox reactions.
*pg265 (image on the page)

Question 6

Anode and cathode

Answer 6

one electrode, which is composed of a metal (labeled the anode) gets oxidized, and the electrons its atoms lose travel along the wire to a second metal electrode (labeled the cathode). The cathode is where reduction takes place. The anode acts as the electron source while the cathode acts as an electron sink. Electrons always flow from the anode to cathode.
*pg266

Question 7

Soectator ions

Answer 7

Ions that are there for any other use such as balancing but dont participate in the reaction. These are not included in the hald reactions.
*pg266

Question 8

Cell diagram

Answer 8

A shorthand notation to identify species present in a galvanic cell. the general form:
Anode / Anodic solution (concentration) // cathodic solution (concentration) / cathode
If the conc are not specified assume they are 1 M
*pg266

Question 9

Salt Bridge

Answer 9

An ion rich junction bw the anodic and cathodic chambers of an electrochemical cell that prevents charge separation that would otherwise stop the cell from functioning. Anions always migrate toward the anode, and cations always migrate towards the cathode of any cell.
*glossary

Question 10

How do we find out if the redox reaction of a cell is spontaneous and can produce electric current?

Answer 10

We need to figure out the cell voltage. Each half reaction has a potential (E), which is the cell voltage it would have if the other electrode were the standard reference electrode (to note standard conditions we put the º)
Tables of half reaction potentials are given in reduction, for oxidation you just have to reverse the sign.
The overall cell voltage of the reaction is the sum of the half reaction potential
If the cell voltage is positive the redox reaction will be spontaneous (ΔGº Will be negative)
*pg267/268

Question 11

Standard reference electrode

Answer 11

The site of the redox reaction 2H+ + 2e- –> H2, which is assigned a potential of 0.00 volts
*pg267

Question 12

Half reaction for example

Answer 12

oxidation: Zn –> Zn2+ + 2e-
reduction: Cu2+ + 2e- –> Cu

Question 13

The free energy change for a redox reaction formula (standard condition)

Answer 13

ΔGº = -nFEº

• • n is the # of moles of e transferred
• • F stands for faraday (the magnitude of the charge of one mole of electrons, approx 96,500 C)
• • if ΔGº is positive = non-spontaneous
• • if ΔGº is negative = spontaneous
• Pg268

Question 14

The strength of reducing/oxidizing agents

Answer 14

The more negative the reduction potential. the weaker the reactant is an oxidizing agent, and the stronger the product is as a reducing agent.
The strength depends a lot on depends on what the atom is being compared to.
If one of them is negative and one is positive the negative one will be the oxidizing agent
*pg269

Question 14

The strength of reducing/oxidizing agents

Answer 14

The more negative the reduction potential. the weaker the reactant is an oxidizing agent, and the stronger the product is as a reducing agent.
The strength depends a lot on depends on what the atom is being compared to.
*pg269

Question 15

The free energy change formula for non standard conditions

Answer 15

called the nernst equation
ΔG = ΔGº + RT lnQ 
or
E = Eº - (RT/nF) ln Q
*pg271/272

Question 16

Concentration cells

Answer 16

A concentration cell is a galvanic cell that has identical electrodes but which has half cells with different ion con centrations. Because the beakers Have the same identities the Eº would be zero. But these cells are not standard because both electrolytic solutions in the half cells are not 1M. This is why there will be a potential difference between them and an electric current will be produced. The electrode with the lower conc will be the anode and the higher one will be the electrode. When the conc are equal the flow of electrons will stop.
*pg272

Question 17

Redox titrations

Answer 17

Similar to the titration of an acid with a strong base. Uses an indicator for colour change but the colour changes due to a change in oxidation state rather than gain/loss of a proton. One common indicator used is the Ce4+ ion (bright yellow in colour). This titration graph is E vs reference electrode on the y axis the volume of indicator on the x axis. At the half equivalence point the valye of E is equal to the value of Eº for the redox couple being titrated.
*pg273

Question 18

Electrolytic cell and electrolysis

Answer 18

unlike a galvanic cell this Uses an external voltage source (such as battery) to create an electric current that forces non spontaneous redox reaction to occur. This is known as electrolysis. A typical example is NaCl. cathode is still the site of reduction and anode oxidation but bc this is a non spontaneous reaction, the anode is positive and the cathode is negative. (opposite of galvanic). The total Eº of reaction is negative.
*pg274 (table of differences on this page)

Question 19

Electroplating

Answer 19

the process of plating a thin layer of metal on top of another material done by the electrolytic cells.
*pg275

Question 20

Rechargeable batteries

Answer 20

galvanic cells can use 2 different oxidation-states of Pb and sulfuric acid as an electrolyte. Often referred to as lead-acid batteries. These can go from charged to discharged. Recharging a discharged battery involves reversing the electron flow of discharge with applied voltage, as an electrolytic cell. The recharging restores the initial potential of the cell
*pg276

Question 21

Faraday’s law of electrolysis

Answer 21

The amount of chemical change is proportional to the amount of electricity that flows through the cell.
*pg277

Question 22

Formula to determine the amount of electricity (in C) that flowed through the cell in a certain time

Answer 22

Q = It

• • I: current
• • t: time
• -Q : charge
• pg277