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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.

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