Chem 113 Exam 3

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arrhenius acid
answer

produces H+ in aqueous solutions
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arrhenius base
answer

produces OH- in aqueous solutions
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bronsted-lowry acid
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H+ donor
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bronsted-lowry base
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H+ acceptor
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KA
answer

[image]
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strong acid
answer

yields a WEAK conjugate base ionization equilibrium lies far to the RIGHT. HCl HBr HI HClO4 HNO3 H2SO4

large Ka value.

smaller pKa value

will have H+ bound to F, N, or O atoms that can be donated

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Weak acid
answer

ionization equilibrium lies far to the LEFT
weaker the acid, the stronger its conjugate base
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strong bases
answer

LiOH NaOH KOH RbOH CsOH Ca(OH)2 Sr(OH)2

Ba(OH)2

larger Kb

smaller pKb

will have N or O atoms that have lone pair electrons that can attract H+

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amphoteric
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can behave as either an acid or base
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acidic and basic solutions
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if [H+] > [OH-] = solution is acidic if [H+] < [OH-] = solution is basic if [H+] = [OH-] = solution is neutral

Kw=[OH][H+]

Kw=1.0×10-14

question

The pH scale
answer

pH=-log[H+] or -log[H3O+]

pH decreases as [H+] increases 

pH<7 = acidic solution

pH>7 = basic solution

pH=7 = neutral solution 

question

If a solution of HCl has a pH of 4.50, what is the [H3O+] of the solution? Is this solution acidic, basic or neutral?
answer

pH=-log[H+]=4.5

log[H+]=-4.5

10log[H+]=10-4.5

[H+]=3.16×10-5 M

 

the solution is acidic 

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percent ionization
aka: percent dissociation
answer

[H3O+]from HA

             ______________ x 100 %

[HA]initial

 

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Kw
answer

Ka x Kb = Kw

 

pKa + pKb = pKw

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polyprotic acids
answer

an acid that contains more than one ionizable H atom per molecule
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acid-base properties of salts (cations)
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  • cations may act as acids in water except:

Li+, Na+, K+, Rb+, Cs+, Ca2+, Sr2+, Ba+2

  • these are pH neutral
  • these are the conjugate acids of strong bases and are such super weak acids that they will not act as an acid in water¬†
  • (strong bases without OH)

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acid-base properties of salts (anions)
answer

 

  • anions may act as base in water except:

 

Cl, Br, I, NO3, HSO4, ClO4, BrO4, IO4

 

  • these are pH neutral
  • these are the conjugate bases of strong acids and are such super weak bases that they will not act as a base in water
  • (strong acids without H+)

 

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oxyacids
answer

  • contains the group H-O-X
  • for a given series the acid strength increases with an increase in the number of oxygen atoms attached to the central atom
  • the greater the ability of X to draw electrons toward itself, the greater the acidity of the molecule

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lewis acid
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electron PAIR acceptor
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lewis base
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electron PAIR donor
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common ion effect
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the suppression of the ionization of the ionization of a weak electrolyte caused by the addition of an ion that is also a product of the ionization equilibrium of the weak electrolyte

  • shift in equilibrium position that occurs because of the addition of an ion already involved in the equilibrium reaction.

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buffered solutions
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resists a change in pH
they are weak acids containing a common ion
after addition of strong acid or base, deal with stoichiometry first, then the equilibrium
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Henderson-Hasselbalch Equation for Buffers
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pH = pKa + log (nbase/nacid)
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characteristics of buffered solutions
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buffers contain relatively large amounts of weak acid and corresponding conjugate base
added H+ reacts to completion with the conjugate base
added OH- reacts to completion with the weak acid
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buffering capacity
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the amount of acid or base that a buffer can neutralize before its pH changes is appreciable

  • when the ratio nbase/nacid¬†is close to 1, the buffer has its maximum buffer capacity¬†

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buffer region
answer

a weak acid/conjugate base pair acts best as a buffer around the pH region equal to the pKa. usually within¬†¬Ī 1 pH unit of the pKa
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equivalence point
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point in the titration when enough titrant has been added to react with the substance in solution being titrated
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solubility
answer

how much of a substance that will dissolve in a given amount of solvent at a given temperature
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solubility product
answer

the equilibrium constant expression for a salt dissolving in water

CaF2(s) РCa2+(aq) +2F(aq)

Ksp= [Ca2+][F]2

the larger the Ksp, the more solid that will dissolve

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precipitation and qualitative analysis
answer

  • Q > Ksp¬†; precipitation occurs and will continue until the concentrations are reduced to the point that they satisfy Ksp.¬†
  • Q < Ksp¬†; no precipitation occurs

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complex ion
answer

a charged species consisting of a metal ion surrounded by ligands
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ligands
answer

a lewis base (a molecular ion having a lone electron pair that can be donated to an empty orbital on the metal ion to form a covalent bond)
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spontaneous process
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a change that occurs in a system left to itself; once started no external action is necessary to make this process continue Ex: the “souring” of cream
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nonspontaneous process
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will not occur unless some external action is continuously applied
Ex: riding on a playground swing
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thermodynamics
answer

lets us predict whether a process will occur but gives no information about the amount of time required for the process
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entropy
answer

thermodynamic property related to the degree of disorder in a system

 

tends to increase if:

 

  • liquids are formed from solids 
  • gases are formed from either solids or liquids
  • the number of molecules of gas increases as a result of a chemical reaction
  • the temperature of a substance increases 
  • the more complex the molecule

 

question

entropy change ΔS
answer

the difference in entropy between two states

 

  • nature tends toward disorder. ie: a driving force for a spontaneous process is an increase in the entropy of the universe

to determine the sign of ΔS°, look at the coefficients of the gases

     

    question

    positional entropy
    answer

    a gas expands into a vacuum because the expanded state has the highest positional probability of states available to the system

     

    therefore;

    Ssolid < Sliquid << Sgas

     

    greater volume, the greater the entropy 

    question

    the second law of thermodynamics 
    answer

    in any spontaneous process there is always an increase in the entropy of the universe

    ΔSuniv>0

    where ΔSuniv = ΔSsys + ΔSsurr

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    the effect of temperature on spontaneity
    answer

     

    • the sign of ΔSsurr depends on the direction of the heat flow
    • the magnitude of ΔSsurr depends on the temperature
    • ΔSsurr =qrev/T = ΔH/T

     

    qrev: heat gained in a reversible process (joules)

     

    T: temperature (Kelvin)

     

    • since the change to the system is the reverse of the change to the surroundings 

    ΔSsurr=ΔHsurr/T = – ΔHsys/T

    question

    free energy
    answer

     

    • ΔG = ΔH – TΔS (from the standpoint of the system)
    • a process (at constant T, P) is spontaneous in the direction in which free energy decreases 
    • a “-” ΔG means “+” ΔSuniv
    • test for spontaneity
      • ΔG < 0 (negative) = spontaneous
      • ΔG >0 (positive) = nonspontaneous
      • ΔG = 0 = equilibrium
    • chemical equilibrium occurs at the lowest value of energy available to the reaction system
      • ΔG° = RTln(K) = ΔH° – TΔS°

     

    question

    the dependence of free energy on pressure 
    answer

    ΔG = ΔG° + RT ln(Q)

    •  
      • R: gas law constant; 8.3145 J/k*mol
      • T: temperature (kelvin)
      • Q: reaction quotient (in partial pressures)
      • ΔG°: the free energy change at the standard state

    question

    free energy and work
    answer

    • maximum possible useful work obtainable from a process at constant temperature and pressure is equal to the change in free energy 
      • Wmax = ΔG
    • first law: you can’t win, you can only break even.
    • second law: you can’t break even. 

    question

    electrochemistry
    answer

    the study of the interchange of chemical and electrical energy
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    oxidation-reduction (redox) reaction
    answer

    involves a transfer of electrons from the reducing agent (loss of electrons) to the oxidizing agent (gain of electrons)
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    oxidation
    answer

    loss of electrons
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    reduction
    answer

    gain of electrons
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    reducing agent
    answer

    electron donor
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    oxidizing agent
    answer

    electron acceptor 
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    half reactions
    answer

    the overall reaction is split into two half reactions, one involving oxidation and one reduction.
    question

    balancing by half-reaction method in ACID
    answer

    • write separate reduction, oxidation reactions.
    • for each half reaction:
      • balance elements (except H,O).
      • balance O using H2O.
      • balance H using H+.
      • balance charge using electrons.
    • If necessary, multiply by integer to equalize electron count.
    • Add half reactions.
    • check that elements and charges are balanced.

    question

    half-reaction method balancing in BASE
    answer

    • balance as in acid
    • add OH that equals H+ions (both sides!)
    • form water by combining H+, OH
    • check elements and charges for balance

    question

    galvonic cells
    answer

    a device in which chemical energy is changed into electrical energy.

    this is done with a oxidation-reduction (redox) reaction.

    when a half reaction is reversed, the sign of E° is reversed.

    when a half-reaction is multiplied by an integer,E° remains the same. 

    a galvanic cell runs spontaneously in the direction that gives a positive value for E°cell

    question

    anode
    answer

    the electrode where oxidation occurs
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    cathode
    answer

    the electrode where reduction occurs
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    cell potential or electromotive force (emf)
    answer

    the “pull” or driving force on the electrons (E°)
    question

    volt
    answer

    the unit of electrical potential defined as one joule of work per coulomb of charge transferred
    question

    volt meter
    answer

    an instrument that measures cell potential by drawing electrical current through a known resistance
    question

    line notation
    answer

     

    • anode components are listed to the LEFT
    • cathode components are listed to the RIGHT
    • anode and cathode are separated by double vertical lines.
    • a phase difference is indicated by a single vertical line.
    Mg (s) | Mg2+ (aq) || Al3+ (aq) | Al (s)

     

    question

    maximum cell potential
    answer

    directly related to the free energy difference between the reactants and the products in the cell

    ΔG°= -nFE°

    n=numbers of moles of electrons

    F=Faraday = 96,485 coulombs per mole of electrons 

    question

    the Nernst equation
    answer

    used to calculate the potential of a cell in which some or all of the components are not in their standard states.

    E = E° – (RT/nF)*(ln(Q))

    at 25° C, the nernst equation becomes…..

    E= E° – (0.0591/n)*(log(Q))

    question

    ion-selective electrodes
    answer

    an electrode sensitive to the concentration of a particular ion in solution
    question

    glass electrode
    answer

    an electrode for measuring pH from the potential difference that develops when it is dipped into an aqueous solution containing H+ ions.
    question

    electrolysis
    answer

    process that involves forcing a current through a cell to cause a nonspontaneous chemical reaction to occur.

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