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Weak electrolyte

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Since only fraction, a, of electrolyte is actually presents as ions, the measure ... Molar conductivity for electrolytes. Molar conductivity of individual ions. ... – PowerPoint PPT presentation

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Title: Weak electrolyte


1
Weak electrolyte
  • Weak electrolytes are not fully ionized in
    solution, such as weak acids and bases.
  • Degree of ionization (a) defined as the ratio of
    the amount of ions being formed in the solution
    and the amount of electrolyte added to the
    solution.
  • For the acid HA at a molar concentration c,
  • H3O ac, A- ac , HA c ac
  • Since only fraction, a, of electrolyte is
    actually presents as ions, the measure
    conductivity ?m, is given by
  • ?m a?0m

2
Ostwalds dilution law
3
24.7 The mobility of ions
  • Drift speed the terminal speed reached when the
    accelerating force is balanced by the viscous
    drag.
  • Accelerating force induced by a uniform electric
    field (E ?ø/l)
  • F z e E z e ?ø/l
  • Friction force Ffric (6p?a)s, a is the
    hydrodynamic radius
  • Mobility of an ion

4
Mobility and conductivity
  • For the solution
  • ?0m (zuv z-u-v-) F

5
Transport numbers
  • The fraction of total current carried by the ions
    of a specified type.
  • The limiting transport number, t0,

6
Conductivities and ion-ion interactions
7
24.8 The thermodynamic view of diffusion
  • The maximum amount of work can be done when
    moving a substance from local x to xdx is
  • When expressed with an opposite force
  • dw - F dx
  • Then one gets
  • Therefore The slope of the chemical potential
    can be interpreted as an effect force,
    thermodynamic force. This force represents the
    spontaneous tendency of the molecules to disperse.

8
Connections between the thermodynamic force and
the concentration gradient
  • Since µ µ? RTlna
  • One get
  • Using concentrations to replace the activity
  • Recall Ficks first law of diffusion

9
24.9 The diffusion equation
10
Derivation of the diffusion equation
  • The amount of particles enter the slab in the
    time interval dt equals
  • JAdt, where J is the
    matter flux
  • The increase in molar concentration inside the
    slab is
  • JAdt / (Al t) J/l
  • Consider the outflow through the right-hand side
  • -JAdt / (Al t) J/l
  • The net change is
  • Then

11
Designing electrochemical cells
  • Example 1 5Zn 2MnO4- 16H ? 5Zn2
    2Mn2 8H2O
  • Example 2 Pt H2(g) HCl (aq), AgCl(s) Ag(s)
  • Example 3 Zn(s) ZnCl2(aq) KCl(aq) CuCl2
    Cu(s)

12
Highlights of Chapter 9
  • Extent of the reaction.
  • Reaction Gibbs energy.
  • The relationship between the reaction Gibbs
    energy and chemical potential.
  • The relationship between the reaction Gibbs
    energy and chemical equilibrium.
  • Expressing equilibrium constant in terms of the
    standard reaction Gibbs energy.
  • Calculations of the reaction Gibbs energy.
  • Le Chateliers principle.
  • Vant Hoff equation.
  • Changes of pH during the titration of weak acids
    (at the beginning, in the process, at the
    stoichiometric point, beyond the ending point).

13
Highlights from Chapter 10
  • Standard enthalpy and Gibbs energy of formation
    for ions.
  • Thermodynamic cycle.
  • The standard enthalpy and Gibbs energy of
    formation of H is used as the reference for
    other ions.
  • Activity coefficient.
  • Debye-Huckel theory to calculate the mean
    activity coefficient.
  • Galvanic cell and electrolytic cell.
  • Electrodes and half reactions.
  • Cell potentials.
  • Calculations of the standard cell potential.
  • Applications of the standard potential.
  • Temperature coefficient of cell potential.

14
Highlights from Chapter 24
  • Kinetic theory.
  • Flux of matter.
  • Flux of energy.
  • Flux of momentum.
  • Effusion.
  • Collision flux, collision frequency, and their
    connection with the measurement of vapor
    pressure.
  • Molar conductivity for electrolytes.
  • Molar conductivity of individual ions.
  • Kohlrauschs law.
  • Ostwalds dilution law.
  • Thermodynamic view of diffusion.
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