CH 302 Electrochemistry

These flashcards cover key terms and concepts related to electrochemistry from the lecture notes.

This element can assume many oxidation states (-3 to +5)

Nitrogen

This element is found in explosives, fertilizers, as an oxide in laughing gas, viagra, smog, and peservatives

Nitrogen

this element is found in man common materials including soaps, toothpaste, fertilizer, and pesticides. It is extracted from Ca3(PO4)2 rock.

phosphorus

_________ is the backbone in nucleic acids like DNA. _________ cause algae bloom and increasingly their use is discouraged for environmental reasons.

phosphates

H₂SO₄

Sulfuric Acid

________ is the chemical manufactured in the largest quantities; it is made by a two-step process, Claus and contact.

H₂SO₄

This element has many uses as a strong acid, oxidizing agent, and dehydrating agent, including extraction of phosphate from rock, production of paper, and as a reactant in production of many other important chemicals

H₂SO₄

_______ have small radii, high ionization energy, high electronegativity, and form -1 anions. Their oxides and hydrides are acidic.

Halides

_________ inserts instead of OH– in tooth enamel to protect from decay

Fluoride (F^-)

________ is manufactured as ___₂, a strong oxidizing agent. It is used in

disinfection and sanitation. It is also used to make PVC tubing.

Chlorine, CL₂

_____ gases are inert with 2 or 8 electrons in filled shells. Specialty uses

include as cryogens (He), inert gases (Ar), and lights (Ne)

Noble

_________ and _______ processes combine to produce ________ through a series of oxidation and acid/base reactions.

Claus, Contact, H2SO4

Claus process

A two-step oxidation produces elemental sulfur from H2S,

which is a contaminant in natural gas, methane.

Contact Process

A four-step oxidation process produces H2SO4 from

elemental sulfur, S

Rule #1 in assigning Oxidation Numbers

Free elements have an oxidation # of 0.

examples:

• Mg has 0

• Cl₂ has 0

Rule #2 in assigning Oxidation Numbers

Individual ions are their charge, and alkali metals (Group I) have +1.

examples:

• Mn2+ has +2, Al3+ has +3

• In NaCl, Na has +1

• In Li2O, Li has +1

Rule #3 in assigning Oxidation Numbers

Rule #4 in assigning Oxidation Numbers

Rule #5 in assigning Oxidation Numbers

Oxidation numbers are typically assigned by group on the periodic table:

Group I: +1, Group II: +2, Group III: +3 or -5, Group IV: +4 or -4,

Group V: -3 or +5, Group VI: -2, Group VII: -1

Examples

• CH4, H has +1, so C has -4

• NO3–, O has -,2 so N has +5

Rule #6 in assigning Oxidation Numbers

Sum of individual charges must equal overall charge on molecule.

The ________ agent is the species that causes oxidation of other

species. This is the species that is being ________.

oxidizing, reduced

The ________ agent is the species that causes reduction of other

species. This is the species that is being ________.

reducing, oxidized

As you move ______ the table of reduction potentials, the species on the left are easier to ________ (stronger oxidizing agents). These are the parts of the half-cell with the largest ________ reduction potential.

Up, Reduce, Positive

As you move ______ the table of reduction potentials, the species on the right are easier to ________ (stronger reducing agents). These are the parts of the half-cell with the largest ________ reduction potential.

Down, Oxidize, Negative

For a Battery(Voltaic, Galvanic) cell type, ΔG is (positive/negative), K is (<1,>1), E is (positive/negative), the cathode is (positive/negative), and the anode is (positive/negative).

negative, k >1, E is positive, cathode is positive, anode is negative

For a Electrolytic cell type ΔG is (positive/negative), K is (<1,>1), E is (positive/negative), the cathode is (positive/negative), and the anode is (positive/negative).

positive, k <1, E is negative, cathode is negative, anode is positive

electrons from (anode/cathode) to (anode/cathode)

anode to cathode

what are the standard conditions?

1M and 1 atm, 298K

how are reduction and oxidation potential found?

by measuring the potential difference between a half-cell of a substance and a standard hydrogen electrode

Where the strong oxidizing and reducing agents are found?

top of the table for oxidizing agent, bottom of tabled for reducing agent.

Where famous coinage metals are found?

copper, silver, gold, and platinum

Where the elements that prevent rust are found?

Elements that prevent rust (corrosion of iron) typically have a more positive standard reduction potential than iron

When E > E°, there are more reactants than products then Q will be _____ than 1

less

When E = E°, there are equal products and reactants, Q will be _____ to 1.

equal

When E < E°, there are more products than reactants, Q will be _____ than 1.

Greater

When E = 0, the system is at equilibrium (dead battery) Q will be ______ to K

equal

a battery is dead when it has _____ cell potential, which happens when:

0, the cell reaches equilibrium.

groups ___ and ___ react in cold water

1 and 2

groups ___ and ___ react in steam/acid

3 and 4

groups ___ and ___ don’t react

5 and 6

what element is the strongest reducing agent

lithium

what is the weakest reducing agent?

Au

what are secondary batteries are built with consideration given to?

minimizing liquid or gas production

Modern batteries fun facts

Modern batteries are made with solids and pastes rather than

liquids and gases to avoid losses of material.

secondary batteries fun facts

Rechargeable = secondary

batteries are environmentally superior and convenient

why are inefficient batteries bad?

• Inefficient batteries produce heat, not work. Controlling heat

dissipation is important practically and for safety

light wheight batteries use:

use less dense, higher charge density materials like lithium.

famous examples of primary batteries

• Common alkaline battery (think Duracell)

• The inexpensive Zn-C

• Smaller specialty batteries like Zn-air battery used in hearing aids (although some Zn-air are now rechargeable)

Secondary Batteries

Built with consideration given to minimizing liquid or gas production so that the contents of the reaction are better contained in the battery casing for recharging.

famous secondary batteries

• lithium-ion batteries in electronics

• Lead-acid batteries found in cars that are recharged by an alternator when the engine is running

• NiMH batteries that have replaced NiCd batteries as the common household rechargeable battery

How is rust made?

by oxidation of iron in the presence of water and air for a long period of time:

Fe + H2O + O2 → Fe(OH)2 + Fe(OH)3

how can rust be prevented?

by adding in metals which are easier to oxidize than iron through specific processes:

• Galvanization with Zn

• Sacrificial electrodes with Mg, Al

• Stainless steel with Cr and V added to Fe

• Waxes and coating

Atom economy formula:

equation: ((molecular weight of product atoms utilized)/(molecular weight of all reactant’s) )(100%)