+ All Categories
Transcript
  • 7/28/2019 Inorganic Chemistry II

    1/23

    INORGANIC CHEMISTRY II

    SMEP METALLURGICAL ENGINEERINGLECTURE SERIES

  • 7/28/2019 Inorganic Chemistry II

    2/23

    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.

  • 7/28/2019 Inorganic Chemistry II

    3/23

    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.

  • 7/28/2019 Inorganic Chemistry II

    4/23

    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

  • 7/28/2019 Inorganic Chemistry II

    5/23

    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

  • 7/28/2019 Inorganic Chemistry II

    6/23

    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

  • 7/28/2019 Inorganic Chemistry II

    7/23

    THE EFFECT OF TEMPERATURE ONREACTION RATES

    RTEaAek /

    211

    2 11ln

    TTR

    E

    k

    k a

  • 7/28/2019 Inorganic Chemistry II

    8/23

    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

  • 7/28/2019 Inorganic Chemistry II

    9/23

  • 7/28/2019 Inorganic Chemistry II

    10/23

    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)

  • 7/28/2019 Inorganic Chemistry II

    11/23

    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

  • 7/28/2019 Inorganic Chemistry II

    12/23

    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.

  • 7/28/2019 Inorganic Chemistry II

    13/23

    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.

  • 7/28/2019 Inorganic Chemistry II

    14/23

    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

  • 7/28/2019 Inorganic Chemistry II

    15/23

    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

  • 7/28/2019 Inorganic Chemistry II

    16/23

    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

  • 7/28/2019 Inorganic Chemistry II

    17/23

    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.

  • 7/28/2019 Inorganic Chemistry II

    18/23

  • 7/28/2019 Inorganic Chemistry II

    19/23

    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

  • 7/28/2019 Inorganic Chemistry II

    20/23

    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.

  • 7/28/2019 Inorganic Chemistry II

    21/23

    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+

  • 7/28/2019 Inorganic Chemistry II

    22/23

    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.

  • 7/28/2019 Inorganic Chemistry II

    23/23

    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.


Top Related