MetE Board Review Inorganic Chemistry II

8/22/2019 MetE Board Review Inorganic Chemistry II

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SMEP METALLURGICAL ENGINEERING LECTURE SERIES


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REACTION RATES

Reaction Rate- describes how fast the concentration of areactant or product changes with time

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

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

Instantaneous Rate of Reaction- determined from theslope of a tangent lines to a concentration-time graph

Initial Rate of Reaction- reaction rate when the reactantsare 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 of all

the exponents.

Rate constant, k- relates the rate of reaction to reactantconcentrations, the larger the value, the faster thereaction goes.


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ZERO ORDER REACTIONS

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

A

products The concentration-time graph is a straight line with a

negative slope

The rate of reaction, which is equal to k and remainsconstant throughout the reaction, is the negative of the

slope of this line. The units of k are the same as the units of the rate of a

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. A common type is a singlereactant decomposes into products.

A products

2 H2O2 2 H2O + O2

Integrated rate equation:

Half life of a reaction is the time required for one-half of areactant to be consumed.

Akreactionofrate

22OHkreactionofrate

ktA

A t 0ln

0lnln AktA t

k

t2ln

2/1


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SECOND ORDER REACTIONS

The second order reaction has a rate equation in

which the sum of the exponents is equal to 2.A products

Integrated rate equation: 2

Akreactionofrate

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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EQUILIBRIUM CONSTANT, Kc- allows us to calculateequilibrium concentrations of reactants 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 acorresponding factor, we raise the equilibrium constant to thecorresponding power.

When we divide the coefficients in a balanced equation by a commonfactor, we take the corresponding root of the equilibrium constant.

ba

hg

cBA

HGK


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When the individual equations are combined their equilibriumconstants are multiplied to obtain the equilibrium constant for the netreaction.

Equilibrium constant expressions do not contain concentration termsfor solid or liquid phase of a single component (pure solids or liquids)

A reaction is most likely to reach a state of equilibrium in whichsignificant quantities of both reactants and products are present if thenumerical value of Kc is neither very large nor very small, roughly fromabout 10-10 to 10+10.

When an equilibrium system is subjected to a change in temperature,pressure, or concentration of reacting species, the system responds by

attaining a new equilibrium that partially offsets the impact of thechange


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Reaction quotient, Qc ratio of initialconcentrations in a reaction mixture that has

the same form as the equilibrium constantexpression

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 in the form of ions,whereas a weak electrolyte exists partly as ions and partly asmolecules.

A neutralization reaction involves the combination of hydrogen ionsand hydroxide ions to form water.

HClH+ + Cl-

NaOHNa+ +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 proton acceptor

NH3 + H2ONH4+ + OH-

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

amphoteric substances- can act either as an acidic or basic

oxide (Al2O3), associated with elements having

electronegativities in an intermediate range.


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LEWIS ACID AND BASE THEORY

Lewis acid-base theory is not limited to reactions

involving H+

and OH-

, it extends to reactions ingases and in solids.

Lewis acid is a species (atom, ion or molecule)

that is an electron pair acceptor and a Lewis base

is a species that 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+) and hydroxide (OH-) ions are formed.H2O + H2O H3O

+ + OH-Kc=[ H3O

+][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 proportion of ionizedmolecules on a percentage basis.

Percent ionization of a weak acid or a weak baseincreases as the solution becomes more dilute.

Polyprotic or polybasic acids- acids with more than oneionizable H atom per molecule.

%1003 xHAofmolarityinitial

HAfromderivedOHmolarityionizationpercent


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Hydrolysis- a reaction between an ion and water

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 Strong Acids/Bases The common ion effect is the suppression of the ionization of a weak

electrolyte caused by the addition of an ion that is also a product ofthe ionization equilibrium of weak electrolyte.

When a strong electrolyte supplies the common ion (H3O+ for acids,and OH- for bases) the equilibrium shifts.

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 one another in aqueous solution. Thepresence of the common ion suppresses the ionization of the weakacid/base.


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Buffer solutions

The pH values of buffer solutions change only very slightly on

the addition of small amounts of either an acid or a base.

Buffer solutions require two components, one of which is ableto neutralize acids and the other able to neutralize bases, but

the two components must not neutralize each other.

Common buffer solutions are a mixture of a weak acid and its

conjugate base or a weak base and its conjugate acid.


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Buffer capacity- the amount of acid or base that a buffer canneutralize before its pH change appreciably. The maximum buffercapacity exists when the concentration of a weak acid and itsconjugate base are kept large and approximately equal to each other.

Buffer range- pH range in which a buffer effectively neutralizesadded acids and bases and maintains a fairly constant pH.

A range of 2 pH units is the maximum range to which a buffer solutionshould be exposed.

acid

baseconjugatepKpH a log


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Complex ion- is a polyatomic cation or anion composed of a centralmetal ion to which other groups (molecules or ions) are bonded.Substances containing complex ions belong to a category ofcompounds called coordination compounds.

Kf- formation constant is the equilibrium constant that is used to dealwith a complex ion equilibrium, it describes the formation of acomplex ion from a central ion and its ligands.

Kfare usually large numbers which distinguish Kffrom otherequilibrium constants.


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Qualitative Analysis of Cations- aims at identifying the cations present in a mixture but not theirquantities

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

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 aresoluble

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 HNO33CuS (s) + 8 H

+(aq) + 2NO3(aq) 2 Cu2+(aq) + 3 S (s) +2 NO (g)+ 4 H2O

A few metal sulfides dissolve in basic solution with a highconcentration of HS-. The subgroup consisting of HgS , PbS,

CuS , Bi2S3 and CdS remains undissolved after treatment withan alkaline solution with an excess of HS- but As2S3. Sb2S3 andSnS2 dissolve.


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Volumetric analysis- a technique that employs the measurement ofvolumes to determine quantitatively the amount of a substance insolution. In any reaction between two or more species, the reactionequation will show the stoichiometric ratio of reacting species.

Gravimetric analysis- based upon the measurement of mass. The

precipitation method of gravimetric analysis involves isolation of anion in solution by a precipitation reaction, filtering, washing theprecipitate free of contaminants, conversion of the precipitate to aproduct of known composition, and finally weighing the precipitateand determining its mass by difference. From the mass and knowncomposition of the precipitate, the amount of the original ion can be

determined.

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MetE Board Review Inorganic Chemistry II

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