Chapter 12 - Oxidation and Reduction

What does oxidation mean?

Loss of electron(s) by an atom

What does reduction mean?

Gain of electron(s) by an atom

What common mnemonic can be used to remember oxidation and reduction?

LEO goes GER

What does an oxidizing agent promote?

Promotes oxidation of another molecule. In the process, they themselves are reduced

What does a reducing agent promote?

Promotes reduction of another molecule. In the process, they themselves are oxidized

What are common oxidizing agents?

O2, O3, H2SO4, Halogens

What are common reducing agents?

H2, Fe, Zn, Alkali Metals

What is the oxidation state?

the positive or negative number that is given to an atom to establish its degree of oxidation/reduction

Al → Al 3+, is this oxidation or reduction?

Oxidation

Fe 2+ → Fe+, is this oxidation or reduction?

Reduction

What is the oxidation number for atoms in their elemental state (e.g. O2, Br2)?

Zero

What is the oxidation number for atoms in monoatomic ions?

Their oxidation number will be equal to their charge

What is the oxidation number for fluorine?

-1

What is the typical oxidation number for Group 1 metals?

+1

What is the typical oxidation number for Group 2 metals?

+2

What is the typical oxidation number for oxygen?

-2

What is the oxidation number for oxygen when it is as a peroxide?

-1

What is the oxidation number of carbon in CO2?

+4

What is the oxidation number of nitrogen in NH3?

-3

What are the 5 rules for determining the oxidation state?

1. Atoms in their elemental state are 0

2. Oxidation numbers for atoms in monatomic (1 atoms) ions are = to their charge

3. F is always -1. Oxygen is often -2. Hydrogen is usually +1

4. Oxidation number of alkali metals in a compound +1. Alkaline earth metals is +2.

5. the sum of oxidation numbers = overall charge of molecule

What are the exceptions to the oxidation rule?

• If oxygen is in peroxide (H2O2), oxidation # is -1

• If oxygen is bonded to fluorine, oxidation # is +1

• If hydrogen is part of metal hydride (MgH2), oxidation # is -1

What is an half-reaction?

the individual oxidation and reduction components of redox reaction

What is the first step involved in balancing redox reactions?

Break the redox reaction into half reactions, one for the reduction portion and another for the oxidation portion

What are the 7 steps to balance a redox reactions under acidic conditions?

1. Write out oxidation and reduction half-reactions

2. Balance all atoms in equation, except for O & H

3. Balance O atoms by adding the same number of H2O molecules to opposite side of reaction

4. Balance H atoms by adding H+ ions to the side lacking H

5. Determine if the charges on both sides are the same. If not balance the charge by adding electrons to the more positive side

6. The number of e in both half reactions MUST be the same. If not, multiply the whole equation by appropriate integers.

7. Combine the half-reactions and simplify.

What are the 7 steps to balance redox reactions under basic conditions?

1. Write out oxidation and reduction half-reactions

2. Balance all atoms in equation, except for O & H

3. Balance O atoms by adding the same number of H2O molecules to opposite side of reaction

4. Balance H atoms by adding H+ ions to the side lacking H

5. For each H+ added, add the same number of OH- to both sides. On the side where H+ ions were added, combine H+ and OH- to create H2O.

6. Determine if the charges on both sides are the same. If not balance the charge by adding electrons to the more positive side

7. The number of e in both half reactions MUST be the same. If not, multiply the whole equation by appropriate integers.

8. Combine the half-reactions and simplify.

What is the nmemonic for electrochemical cells?

An Ox, Red Cat

What arre electrochemical cells?

batteries that facilitate the conversion between chemical and electrical energy. the conversion is through redox reactions through the movement of electrons

What is chemical energy?

Energy produced from chemical reactions where energy is stored in the bonds of atoms/molecules.

What is electrical energy?

energy produced from the flow of electrons.

What two types of electrochemical cells are there?

Galvanic (voltaic) cells and electrolytic cells

Which type of electrochemical cell is spontaneous?

Galvanic (voltaic) cells

Which type of electrochemical cell is non-spontaneous?

Electrolytic

What type of energy input is used to power electrolytic cells?

Electrical energy

When a battery is providing energy to a device, is it acting as a galvanic or electrolytic cell?

Galvanic

When a battery is being recharged, is it acting as a galvanic or electrolytic cell?

Electrolytic

The electrode where oxidation occurs is called what?

Anode

The electrode where reduction occurs is called what?

Cathode

What direction do electrons flow in regards to the two electrodes, the anode and cathode?

Electrons always flow from anode to cathode

In a galvanic cell, what does the salt bridge allow for?

Allows for balancing of charges as the redox reaction proceeds. It will anions to flow to the anode and cations to flow to the cathode

In a galvanic cell, which electrode is considered positive?

Cathode

In a galvanic cell, which electrode is considered negative?

Anode

Why is the anode considered the negative electrode in a galvanic cell?

It attracts negatively charged ions from the salt bridge, due to the anode donating its electrons to the cathode

In a galvanic cell, which electrode will shrink in size?

The anode

Will the potential of galvanic cells be positive or negative?

Positive

In an electrolytic cell, which electrode is considered positive?

Anode

In an electrolytic cell, which electrode is considered negative?

Cathode

Is a salt bridge needed in an electrolytic cell?

No

What is used in place of a salt bridge in an electrolytic cell?

A porous barrier that allows for ion flow

Will the potential of electrolytic cells be positive or negative?

Negative

Do electrolytic cells require an external power source?

Yes, as it is a nonspontaneous redox reaction

What are the 2 types of electrolytic set-ups?

Molten Electrolysis and Electroplating

When does molten electrolysis occurs?

occurs at high temperatures, where an ionic commpound is melted to form a conductive liquid electrolyte

What is the process of electroplating?

the process of depositing a metal onto a conductive object by using electrical current in an electrolytic cell

In this electrochemical cell, Zn | Zn2+ || Cu2+ | Cu, which is considered the anode?

The Zn portion. Anode is always written on the left side and cathode on the right side

What does the double vertical lines in Zn | Zn2+ || Cu2+ | Cu represent?

The salt bridge

What does the single vertical line in Zn | Zn2+ || Cu2+ | C represent?

A phase change

What is standard cell potential?

the sum of the oxidation potential and reduction potential, measured in voltage (V)

What is the formula for calculating overall standard cell potential?

E cell = E reduction + E oxidation

Does standard cell potential depend on coefficients?

No. You do not multiple cell potential if you multiplied the half reaction

What are the 4 steps for determining standard cell potential?

1. Write the oxidation and reduction half reactions for the cell (if not given)

2. Look up the reduction potential (E reduction) or the reduction half-reaction in a table of reduction potentials (if not given)

3. Balance the half-reactions and reverse the sign for oxidation potential

4. Add the potentials of the half-cells to get the overall standard cell potential

Ag+ + e- → Ag has a standard reduction of 0.80 V. If you were to reverse this reaction, what would happen to the reduction value?

It would become - 0.80 V

What is Coulomb (C)?

SI unit of electrical charge

What is the formula for volts?

Volt = Joule / Coulomb

What is the formula for calculating amperes?

Ampere = Coulumb / second

What is the value of Faraday's constant?

96500 Coulombs/mol of e-

What is the formula for calculating the moles of materials deposited by electroplating?

I x ts / n x F = moles of products

What is the formula for calculating free energy using cell potential?

∆G = -nFE

A spontaneous reaction will have a (positive/negative) cell potential and a (positive/negative) free energy

Positive cell potential and negative free energy

A non-spontaneous reaction will have a (positive/negative) cell potential and a (positive/negative) free energy

Negative cell potential and positive free energy