Chem Exam 3

Boron

• usually forms only three covalent bonds, which is contrary to the octet rule

• found in boric acid which is used to kill ants

• found in borax which is used as a detergent

Nitrogen

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

• found in explosives, fertilizers, and as an oxide in laughing gas, Viagra, smog, and preservatives

• ammonia is made with the Haber process from H2 and N2 at low temperature with a catalyst

Carbon

• has three allotropes

• 1st allotrope= C60, which forms interesting tubular and spherical structures

• 2nd allotrope= graphite, which is sp2 hybridized

• 3rd allotrope= diamond, which is sp3 hybridized

• C03- is an inorganic form of _____that is an essential part of a cycle involving the greenhouse gas, CO2, a diprotic acid, and limestone, CaCO3

Phosphorous

• found in many common materials including soaps, toothpaste, fertilizer, and pesticides

• extracted from Ca(PO4)2 rock

• the backbone in nucleic acids like DNA

• cause algae bloom and increasingly their use is discouraged for environmental reasons

Halides

• have small radii

• high ionization energy

• high electronegativity

•  form -1 anions

• Their oxides and hydrides are acidic

Fluoride (F)

• inserts instead of OH in tooth enamel to protect from decay

Chlorine

• manufactured as Cl2, a strong oxidizing agent

• used in disinfection and sanitation

• used to make PVC tubing

Noble gases

• inert with 2 or 8 electrons in filled shells

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

Wet method

• Reactant(s): Ca10(PO4)6F2, H2S04

• Products): HзPO4

Claus method

• Reactant(s): H2S

• Product(s): S

A two-step oxidation produces elemental sulfur from H2S, which is a contaminant in natural gas, methane. Combines w/ Contact process to produce H2SO4 through a series of oxidation and acid/base reactions

Contact method

• Reactant(s): S

• Products): H2S04

A four-step oxidation process produces H2SO4 from elemental sulfur, S. Combines with Claus process to produce H2SO4 through a series of oxidation and acid/base reactions

Sulfuric Acid Facts

• It is the most manufactured chemical in the world.

• About half of all _____ is used to solubilize phosphate in rocks by the wet method. In turn the solubilized phosphate is used in fertilizers.

• a strong acid and a strong oxidizing agent and a strong dehydration agent (removing water)

Oxidation Number Rules

1. Free elements have an oxidation # of 0 (Examples: Mg has 0, Cl2 has 0)

2. Individual ions are their charge, and alkali metals (Group I) have +1 (Examples: Mn2+ has +2, AI3+ has +3, NaCI, Na has +1, Li2O, Li has +1)

3. Hydrogen has +1, unless Rules 1 or 2 apply (Examples: H2 has 0 (Rule 1), H2O, H has +1 (Rule 3))

4. Oxygen has -2, unless any Rules 1-3 apply (Examples: O2 has 0 (Rule 1), NaO2, O has -0.5 (Rule 2), H202, 0 has - 1 (Rule 3), MgO, O has -2 (Rule 4))

5. Otherwise, oxidation numbers are typically assigned by group on PT (Examples: CH4 H has +1 so C has -4, NO3 O has -2 so N has +5)

Group I: +1

Group V: -3 or +5

Group II: +2

Group VI: -2

Group III: +3 or -5

Group VIl: -1Group IV: +4 or -4

6. Sum of individual charges must equal overall charge on molecule

OIL RIG

• Oxidation is Loss of electrons

• Reduction is Gain of electrons

Oxidizing agent

the species that causes oxidation of other species. This is the species that is being reduced

Reducing agent

he species that causes reduction of other species. This is the species that is being oxidized

Ranking Strength of Oxidizing and Reducing Agents

• As you move UP the table, the species on the left are EASIER TO REDUCE (stronger oxidizing agents) (Part of the half-cell with the largest POSITIVE reduction potential)

• As you move DOWN the table, the species on the right are EASIER TO OXIDIZE (stronger reducing agents) (Part of the half-cell with the largest NEGATIVE reduction potential)

Steps for Balancing in Neutral Water

1. Assign oxidation numbers.

2. Create brackets to identify oxidation and reduction.

3. Balance the atoms that are not hydrogen or oxygen.

- This multiplies the charge around the bracket.

4. Find least common multiple and balance.

- This is n

Steps for Balancing in ACID

First follow steps for balancing in neutral water:

1. Assign oxidation numbers.

2. Create brackets for oxidation and reduction.

3. Balance atoms that are not hydrogen or oxygen.

4. Find least common multiple and balance. This is n.

Then, balance under acidic conditions:

5. In acid, find deficient O and put the same #of H20 on deficient side and double H* on opposite side.

Steps for Balancing in BASE

First follow steps for balancing in neutral water:

1. Assign oxidation numbers.

2. Create brackets for oxidation and reduction.

3. Balance atoms that are not hydrogen or oxygen.

4. Find least common multiple and balance. This is n.

Then, balance under basic conditions:

5. find deficient 0 and put same # of H2O on opposite side and double OH on the deficient side.

Battery (Voltaic, Galvanic)

• - △G

• K >1

• E +

• Reduction- Cathode

• Oxidation- Anode

• e- flow- Anode to cathode

• Cathode +

• Anode -

Electrolytic

• + △G

• K <1

• E -

• Reduction- Cathode

• Oxidation- Anode

• e- flow- Anode to cathode

• Cathode -

• Anode +

Electrode

a cathode or anode that is always SOLID (not l, g, aq, or an ion)

Electron Flow

from anode to cathode ALWAYS

Cathodes in Electrolysis of Molten Salts

the CATIONS

Anodes in Electrolysis of Molten Salts

the ANIONS

How to Find the Oxidation Potentials in Electrolysis of Molten Salts

for species being oxidized (the anions) find the reduction potential of the rxn from the table and flip the sign

Battery Ecell

+

Electrolytic Cell Ecell

-

How to Find Q in Nernst Equation

right/left; products/reactants

Q<1

more reactants than products (E is greater than E°)

Q=1

equal products and reactants (E is equal to E°)

Q>1

more products than reactants (E is less than E°)

Q=K

the system is at equilibrium/ the battery is dead (E equals 0)

Nernst Equation Application to Concentration Cells

when anodes and cathodes are composed of the same metals, the anodic and cathodic solutions have the same metal ions and to create equilibrium electrons flow from the side with a smaller ion concentration to the larger one (concentrated side= reduction, diluted side= oxidation—> Q= diluted/concentrated)

K in Dead Battery Calculation

K is equal to Q (so find Q)

What is log(10^x)

it equals x

Aluminum

• lightest metal

• commonly used in commercial applications

• obtained from Bayer (aluminum oxide from bauxite) and Hall (aluminum from aluminum oxide) Processes

• oxide that forms ruby, sapphire, and topaz

Alkali Metals

• large radii

• low ionization energy

• low electronegativity

• form +1 cations

• oxides and hydrides are basic

• react vigorously in water

Beryllium

forms covalent bonds due to small size and ability to attract electrons

Calcium

building materials from concrete to teeth

Mg2+

in chlorophyl; makes molecule more rigid to permit electron transport through photosynthesis

E° (+) means △G is…

-

E° (-) means △G is…

+

△G Calculations kj Conversions

divide answer by 1000

Converting Between K and △G

△G=-RTlnK

Converting Between K E° cell

E°cell= (RT/nF)lnK

Converting Between E° and △G

△G=nFE°cell

K>1

product is favored, △G is (-) spontaneous

K=Q

reaction at equilibrium and △G=0

K<1

reactant is favored and △G is (+) nonspontaneous

Group 1

Ex: Na, K, etc…

• reactive in cold water (strongest reactivity)

Group 2

Ex: Mg, Ca, etc…

• react in hot water (strong reactivity)

Transition Metals

Ex: V, Fe

• react in acids (weak reactivity)

Coinage Metals

Ex: Cu, Ag, Pt, Au

• DONT react (weakest reactivity)

Finding E cell from Delta G

Ecell= delta G/-nF

Finding K from Delta G

K= e^(-delta G/RT)

Secondary Batteries

built to minimize liquid or gas production so contents of reaction are better contained in battery casing for recharging- more environmentally superior and convenient

Secondary Batteries Examples

1. Lithium-Ion batteries in electronics and electrical vehicles

2. Lead-acid batteries found in vehicles (gas-powered)- recharged by alternator when engine is running

3. NiCd used in households

4. NiMH batteries have replaced NiCd as common household rechargeable battery

Lithium-Ion Batteries

known to catch fire and are not allowed to be shipped as commercial cargo on planes

Modern Batteries

made with solids and pastes rather than liquids and gases to avoid loss of material

Primary Batteries

single use/disposed of after one cycle; less superior than secondary batteries (rechargeable)

Primary Batteries Examples

1. Common alkaline battery (Duracell)

2. Inexpensive Zn-C

3. Smaller specialty batteries like Zn-air used in hearing aids (some rechargeable)

Inefficient Batteries

produce heat, not work; controlling heat dissipation is important practically and for safety

Lightweight Batteries

less dense, higher charge density materials like lithium

Rust

• made by oxidation of iron in the presence of water and air for extended periods of time (Fe+H2O+O2—>Fe(OH)2+Fe(OH)3

• can be prevented by adding in metals that are easier to oxidize than iron:

1. Galvanization w/ Zn

2. Sacrificial electrodes w/ Mg, Al

3. Stainless steel w/ Cr and V added to Fe

4. Waxes and coating

Atom Economy

want to maximize incorporation of all materials used into the final product

• high atom economies are desirable (fewer atoms go to waste)

• low atom economies are undesirable (more atoms go to waste)