chem exam 2

boron forms..

3 bonds — contrary to octet rule

boron is found in

boric acid — ant killer

borax — detergent

nitrogen & its oxidation states

(-3 to +5) — very reduced to very oxidized

ex.

-3 NH₃ (ammonia) gained electrons

0 N₂ (gas in air) neutral

+1 N₂O (laughing gas) slightly oxidized

+2 to +4 NO, NO₂ (smog) reactive gases

+5 NO₃⁻ (nitrate) very oxidized

haber process

process where ammonia is made from H2 and N2 at low temp with a catalyst

• plants cant use N2 so it must be converted to NH3

nitrogen is found in…

explosives, fertilizers, laughign gas, viagra, smog, and preservatives

the 3 allotropes of carbon

C60: forms spherical or tube-like structures

graphite: sp2 hybridized

diamond: sp3 hybridized

carbonate (CO₃²^- )

an inorganic form of carbon that is an essential part of carbon cycle involving the greenhouse gas, CO2, a diprotic acid, and limestone, CaCO3.

carbon cycle

CO2​(gas) → CO2​ (aq, after dissolved in water))→H2​CO3​ (carbonic acid) →HCO3^−​ (bicarbonate) →CO₃^2−​ (carbonate) →CaCO3​(solid, limestone)

phophorus is found in

soaps, toothpaste, fertilizer, and pesticides

phosphorus is extracted from…

rock

Ca₃(PO4)₂

phosphate is the backbone of…

nucleic acids like DNA

phosphate can cause ______ which causes from increasingly discouraged use in the envrionment

algae bloom

halides

group 17

• small radii (atomic radius) = small atom = hold onton their electrons TIGHT

• high ionization energy (energy needed to remove an electron)

• high electronegtaivity

• form -1 anions

when halides bind with oxygen or hydrogen forming oxides and hydrides, the result is…

oxides and hydrides are acidic!!

ex. hydrochloric acid (HCl), hydroflouric acid (HF),

Flouride’s role in teeth

Fluoride (F–) inserts instead of OH– in tooth enamel to protect from decay.

• normal enamel is made of the mineral hydroxyapatite which contain OH

• Fl in toothpaste replaces the OH- ion in the mineral → flourapatite mineral → stronger enamel thats more acid resistant

Chloride’s role

manufactured as Cl₂

• a strong oxidizing agent (takes electrons from other substances)

• used in disinfection and sanitation — takes electrons from harmful substances

• used to make PVC (polyvinyl chloride) tubing

noble gases are

inert w 2 or 8 electrons — chemically inactive, stable and don’t rlly be in reactions

special uses of noble gases

Helium: in cryogens (extremely cold coolant)

Ar: inert gases to prevent reactions and cryogen

Neon (Ne): used in bright colored lights and signs

What is the most manufactured chemical in the world?

Sulfuric acid (H₂SO₄)

What is sulfuric acid mainly used for?

To solubilize phosphate in rocks for fertilizer production (wet method)

wet method

Ca₁₀(PO₄)₆F₂ + H₂SO₄ → H₃PO₄

• used to make phosphoric acid for fertilizers

What does the Claus process produce?

Elemental sulfur (S) from H₂S (hydrogen sulfide — toxic gas)

• two-step oxidation produces elemental sulfur from H2S, which is a contaminant in natural gas, methane

What is H₂S and where is it found?

A contaminant in natural gas (methane)

What type of reaction is the Claus process?

Oxidation (two-step oxidation)

contact process

produces Sulfuric acid (H₂SO₄) from sulfur (S)

• A four-step oxidation process produces H2SO4 from

  elemental sulfur, S.

What is the order of the three processes involving sulfuric acid production and use?

H₂S → S → H₂SO₄ → H₃PO₄

Claus → Contact → Wet (toxic gas → elemental sulfur → acid → fertilizer for use!!)

sulfuric acid is

a strong acid, a strong oxidizing agent, and a strong dehydration agent (removing water).

how much sulfuric acid is used to solubilize phosphate in rcoks by ___ method

50%; wet

solublizeed phosphate (through the ____ method) is used in __________

wet; fertilizers

oxidation vs. reduction

oxidation: loss of electrons

reduction: gain of electrons

OIL RIG

oxidation number

number that shows how many electrons an atom has lost or gained in a compound

if # increases in reaction: oxidation (loss)

if # decreases in reaction: reduction (gain)

oxidation number of a free element is…

0

ex. Mg = 0, Cl₂ = 0, O₂ = 0

oxidation number of a single ion is…

their charge

ex.: Mn²⁺ = +2

group 1 metals are +1

alkali metals (group 1)

+1

hydrogen’s oxidation number

+1

UNLESS H₂ = 0, or NaH = -1 or H2O = +1

oxygen’s oxidation number

-2

EXCEPT in peroxides (H₂O₂), it is -1 and if O2 = 0,

periodic table trends of oxidation numbers

group 1: +1

group 2: +2

group 3: +3 or -5

group 4: +4 or -4

group 5: +5 or -3

group 6: -2

group 7: -1

group 17: -1

all oxidation #s must add up to __________ of the molecule or ioon

total charge

oxidizing agent

takes away electrons from others ; cause them to LOSE e

reducing agent

gives electrons to others; causes others to GAIN e

what does it mean when something is plated on another metal?

A solid layer of a metal forms on the surface of another material.

table of reduction potentials (top left)

strong oxidizing agents

• As you move UP the table, the species on the left are EASIER TO

  REDUCE (stronger oxidizing agents).

• easier to reduce (gain e-) and more likely to TAKE others e-

table of reduction potentials (bottom right)

• As you move DOWN the table, the species on the right are EASIER TO

  OXIDIZE (stronger reducing agents).

• less likely to be reduced and more likely to GIVE e-

table of oxidation potentials

• top left: easier to oxidize; strong reducing agents

• bottom right: easier to reduce; strong oxidizing agents

standard cell potential (E°cell)

the maximum voltage of an electrochemical cell under standard conditions (1 M concentration, 1 atm pressure, 25°C)

• how storngly a reaction WANTS to happen

if needing to balance an equation before balancing charges, what needs to be done

multiply charge by the number you use to balance

balancing redox reactions in acid

find the deficient O and put the same number of H2O on the deficient side and double the H+ on the oppositie side

balancing redox reactions in base

find the deficient O and put the same number of H2O on the opposide side and double the OH- on the same side

e- are attracted to which side

+ (cathode)

free energy in a battery (voltanic, galvanic)

ΔG = -

spontaneous

K in a battery (voltanic, galvanic)

equilibrium constant

> 1

products favored

** when at equilibrium, its dead battery

E^° in a battery (voltanic, galvanic)

+

reduction occurs in

cathode

• An Ox, Red Cat

oxidation occurs in

anode

• An Ox, Red Cat

e- flow

anode to cathode

cathode in a battery (voltanic, galvanic)

+

electrons are attracted to this side

anode in a battery (voltanic, galvanic)

-

losing electrons; electrons not attrcate dhere

battery (voltanic, galvanic) cell

produces electricity

spontaneous

electrolytic cell

uses electricity; does NOT produce

non-spontaneous

ΔG in an electrolytic cell

ΔG = +

non-spontnaeous

K in an electrolytic cell

K < 1

dead battery

reactants favored

E^° in an electrolytic cell

-

• e- dont want to flow

anode in an electrolytic cell

+

cathode in an electrolytic cell

-

electrode (anode or cathode) is ALWAYS…

solid

shorthand cell notation

Zn | Zn2+ || Cu2+ | Cu

• left side is anode

• || is salt bridge

• right side is cathode

What are Pt and Au electrodes and why are they used?

They are inert electrodes — they do NOT participate in the reaction.

• when the redox reaction involves only ions in solution (no solid metal naturally available to be the electrode).

• Pt/Au just conducts the electrons in and out.

electrochemical cell diagram

the electrons always flow from anode to cathode

• electrodes are always solid

anions go through

oxidation

cations go through

reduction

group I

• Li, Na, K

highly reactive

reacts to cold water

group II

• Mg, Ca

moderately reactive

react in hot water

Transition Metals

• Fe, V

• slightly reactive

• react in acid

coinage metals

• Cu, Ag, Pt, Ag

• don’t react, inert and stable

the least reactive metals are located where on the standard reduction potential chart?

in the top right corner (Au is the weakest reducing agent)

the most reactive metals are located where on the standard reduction potential chart?

lower right corner (Li is the strongest reducing agent)

General displacement reaction:

M1 + M2X → M2 + M1X

in which Metal 1, which is more active, replaces Metal 2, which is less active.

standard conditions in the standard reduction potential table

278K, 1 M, 1 atm, pH = 0

how to find oxidation potentials?

find it in the reduction potential table and flip the sign

standard hydrogen electrode (SHE)

every species is measure in voltage in relation to hydrogen

• 0.0V

• found in the middle of the table

• if +E^° : species easier to reduce than H

• if -E^° : species is hardre to reduce than H+

coinage metals

• Cu, Ag, Au

• + E^°

• DO NOT REACT

• resists oxidation

• upper portion of table

famous electrolysis products

anything w a -E^°

means it was non spontaneous and went through electrolysis

rust

the oxidation of Fe

when Fe reacts with oxygen and water

how to prevent rusting

To prevent this, you use a metal that is a stronger reducing agent than iron

• any metal below iron on the table (more negative E°) will sacrifice itself to protect iron from rusting.

ways rust is prevented

• waxing and coating (prevent water and oxygen from reacting w Fe)

• sacrifical electrodes w Mg and Al (easy to oxidize— take the place of Fe in oxidation)

• stainless steel with Cr and V added to Fe

• galvanization (adding a protective coating) with Zn

what 2 elements in stainless steel can be added to Fe to prevent rusting?

Cr, V

atom economy

the efficiency of a reaction by calculating the percentage of reactant atoms that end up in the desired final product

• high atom economies = desirable

atom economy equation

MW of DESIRED product atoms utilized/MW of all reactants * 100%

• be careful to not include byproducts

primary batteries

batteries are disposed of after one cycle

example of primary batteries

• alkaline battery (duracell)

• Zn-C

• Zn-air, Zn-Hg (in hearing aids

secondary batteries

batteries that can be reused and recharged; built with consideration to minimize liquid and gas production; contents of reaction are better contained in the battery

examples of secondary batteries

• lithium ion in electronics

• lead-acid batteries in cars (gas-powered) — recharged by alternator

• NiMH batteries: common household rechargebale battery

• NiCd: household battery

modern batteries are made with ________ and _____ rather than ____ and _____ to avoid losses of material

solids and paste

liquids and gases

secondary batteries are

environmentally superior and convienient

inefficient batteries produce…

heat NOT work

• controlling heat is important for practically and for safety

the problem with lithium ion batteries

they are known to catch fire

• not allowed to be shipped as commercial cargo on planes

parts of a lithium ion battery

• cathode +

• lithium metal ocide

• electrolyte

• porous separator

• lithium carbon (graphite)

  • lithium ion

• anode =

lightweight batteries

higher charge density, less dense (ex. lithium)

F

faraday constant (10⁵ C/mole)

key thing when converting E to G

multiply terms together and divide by 1000