inorganic chemistry ii

7/28/2019 Inorganic Chemistry II

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INORGANIC CHEMISTRY II

SMEP METALLURGICAL ENGINEERINGLECTURE SERIES


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EQUILIBRIUM PRINCIPLES AND ITSAPPLICATIONS TO IONIC EQUILIBRIA INAQUEOUS SOLUTIONS

REACTION RATES

Reaction Rate- describes how fast theconcentration of a reactant or product changes

with time Rate of change [A] = delta [A]/ delta time

Rate of reaction [A] = - rate of change [A]

Instantaneous Rate of Reaction- determinedfrom the slope of a tangent lines to aconcentration-time graph

Initial Rate of Reaction- reaction rate whenthe reactants are first brought together.


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RATE LAW The rate of reaction depends on the concentrations of

reactants.

aA + bB + gG + hH

The exponents, m,n.. are not generally related to thestoichiometric coefficients. They are the order ofreactions. The overall order of reaction is the sum ofall the exponents.

Rate constant, k- relates the rate of reaction toreactant concentrations, the larger the value, thefaster the reaction goes.


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ZERO ORDER REACTIONS

The zero-order reaction as a rate equation in whichthe sum of the exponents m+n+.. is equal to 0.

A products

The concentration-time graph is a straight line with anegative slope

The rate of reaction, which is equal to k and remainsconstant throughout the reaction, is the negative ofthe slope of this line.

The units of k are the same as the units of the rate ofa concentration (mol/L-s)

Integrated rate equation:y= mx + b [A]t = -kt + [A]0


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FIRST ORDER REACTIONS The first order reaction has a rate equation in

which the sum of the exponents is equal to 1. Acommon type is a single reactant decomposes

into products.A products

e.g. 2 H2O2 2 H2O + O2

Integrated rate equation:

Half life of a reaction is the time required forone-half of a reactant to be consumed.

Akreactionofrate

22OHkreactionofrate

ktA

A t 0

ln 0lnln AktA t

k

t2ln

2/1


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SECOND ORDER REACTIONS

The second order reaction has a rateequation in which the sum of the

exponents is equal to 2.

A products

Integrated rate equation:

2Akreactionofrate

0

11

Akt

A t


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THE EFFECT OF TEMPERATURE ONREACTION RATES

RTEaAek /

211

2 11ln

TTR

E

k

k a


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ACIDS AND BASES

EQUILIBRIUM CONSTANT, Kc- allows usto calculate equilibrium concentrations ofreactants and products

aA + bB = gG +hH

When we reverse an equation, we invert the value of Kc

When we multiply the coefficients in a balanced equation

by a corresponding factor, we raise the equilibriumconstant to the corresponding power.

When we divide the coefficients in a balanced equation bya common factor, we take the corresponding root of theequilibrium constant.

ba

hg

cBA

HGK


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Reaction quotient, Qc ratio ofinitial concentrations in a reactionmixture that has the same form asthe equilibrium constant expression

If Qc=Kc a reaction is at equilibrium

If QcKc a net reaction proceeds from

right to left (reverse direction)


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ARRHENIUS THEORY

In aqueous solution a strong electrolyte exists only inthe form of ions, whereas a weak electrolyte existspartly as ions and partly as molecules.

A neutralization reaction involves the combination ofhydrogen ions and hydroxide ions to form water.

HCl H+ + Cl-

NaOH Na+ +OH-

Neutralization reaction:

H+ + Cl- + Na+ +OH- Na+ + Cl- + H2OAcid base salt

Net ionic equation: H+ + OH- H2O


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BRONSTED-LOWRY THEORY

Acid is proton donor, and a base is a protonacceptor

NH3 + H2O NH4+ + OH-base acid acid base

amphiprotic substances- can act either as anacid or a base (H+)

amphoteric substances- can act either as anacidic or basic oxide (Al2O3), associated withelements having electronegativities in anintermediate range.


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LEWIS ACID AND BASE THEORY

Lewis acid-base theory is not limited toreactions involving H+ and OH-, it

extends to reactions in gases and insolids.

Lewis acid is a species (atom, ion ormolecule) that is an electron pairacceptor and a Lewis base is a speciesthat is an electron pair donor.


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SELF IONIZATION OF WATER AND THE pH SCALE Self Ionization of water- for each H2O molecule that acts as

an acid another acts as base, and hydronium (H3O+) andhydroxide (OH-) ions are formed.

H2O + H2O H3O+ + OH-

Kc=[ H

3O+][OH-]

At 25oC: [ H3O+]=[OH-]= 1.0 x 10-7 MKw= [ H3O+][OH-]=1.0 x 10-14

pH- potential of hydrogen ion

pH= - log [H3O+] pOH= - log [OH-] pKw = pH + pOH= 14


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Percent ionization- gives the proportionof ionized molecules on a percentage basis.

Percent ionization of a weak acid or a weakbase increases as the solution becomesmore dilute.

Polyprotic or polybasic acids- acids withmore than one ionizable H atom permolecule.

%1003 xHAofmolarityinitial

HAfromderivedOHmolarityionizationpercent


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Hydrolysis- a reaction between an ion andwater

Salts of strong bases and strong acids do not

hydrolyze, pH=7 Salts of strong bases and weak acids hydrolyze,

pH>7 (anion acts as base)

Salts of weak bases and strong acids hydrolyze,pH


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Solutions of Weak Acids/Bases and StrongAcids/Bases The common ion effect is the suppression of the

ionization of a weak electrolyte caused by theaddition of an ion that is also a product of the

ionization equilibrium of weak electrolyte. When a strong electrolyte supplies the common ion

(H3O+ for acids, and OH- for bases) the equilibriumshifts.

Solutions of Weak Acids/Bases and Their Salts The salt of a weak acid/base is a strong electrolyte-

its ions become completely dissociated from oneanother in aqueous solution. The presence of thecommon ion suppresses the ionization of the weakacid/base.


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Buffer capacity- the amount of acid or base that abuffer can neutralize before its pH changeappreciably. The maximum buffer capacity existswhen the concentration of a weak acid and itsconjugate base are kept large and approximatelyequal to each other.

Buffer range- pH range in which a buffer effectivelyneutralizes added acids and bases and maintains afairly constant pH.

A range of 2 pH units is the maximum range to which abuffer solution should be exposed.

acid

baseconjugatepKpH

a

log


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Complex ion- is a polyatomic cation or anioncomposed of a central metal ion to which othergroups (molecules or ions) are bonded. Substancescontaining complex ions belong to a category ofcompounds called coordination compounds.

Kf- formation constant is the equilibrium constantthat is used to deal with a complex ion equilibrium, itdescribes the formation of a complex ion from acentral ion and its ligands.

Kfare usually large numbers which distinguish Kf fromother equilibrium constants.


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POSITIVE IONS BEHAVIOR ANDDETERMINATION

Qualitative Analysis of Cations- aims at identifying the cations present ina mixture but not their quantities

Cations are divided into five groups depending on differing solubilities of theircompounds.

Group I: Ag+, Hg22+, Pb2+

Precipitated in 1 M HCl

Group II: Bi3+, Cd2+, Cu2+, Hg2+, (Pb2+), Sb3+ and Sb5+, Sn2+ and Sn4+Precipitated in 0.1 M H2S solution at pH 0.5

Group III: Al3+, (Cd2+), Co2+, Cr3+, Fe2+ and Fe3+, Mn2+, Ni2+, Zn2+Precipitated in 0.1 M H2S solution at pH 9

Group IV: Ba2+, Ca2+, K+, Mg2+, Na+, NH4+Ba2+, Ca2+, and Mg+ are precipitated in 0.2 M (NH4)2CO3 solution at pH 10;the other ions are soluble

Group V: The resulting solution consists of the soluble ions in water, Na+,K+, NH4+


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Dissolving Metal sulfides Increase the solubility of any sulfide by allowing

it to react with acid.

Use an oxidizing acid such as HNO3

3CuS (s) + 8 H+(aq) + 2NO3(aq) 2 Cu

2+(aq) + 3 S (s) +2 NO (g)+ 4 H2O

A few metal sulfides dissolve in basic solutionwith a high concentration of HS-. The subgroup

consisting of HgS , PbS, CuS , Bi2S3 and CdSremains undissolved after treatment with analkaline solution with an excess of HS- butAs2S3. Sb2S3 and SnS2 dissolve.


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VOLUMETRIC ANDGRAVIMETRIC ANALYSIS

Volumetric analysis- a technique that employs themeasurement of volumes to determine quantitativelythe amount of a substance in solution. In any reactionbetween two or more species, the reaction equationwill show the stoichiometric ratio of reacting species.

Gravimetric analysis- based upon the measurementof mass. The precipitation method of gravimetricanalysis involves isolation of an ion in solution by aprecipitation reaction, filtering, washing theprecipitate free of contaminants, conversion of theprecipitate to a product of known composition, and

finally weighing the precipitate and determining itsmass by difference. From the mass and knowncomposition of the precipitate, the amount of theoriginal ion can be determined.

inorganic chemistry ii

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