1 / 7

Ch. 5. ACTIVITY COEFFICENTS OF DISSOLVED SPECIES

Ch. 5. ACTIVITY COEFFICENTS OF DISSOLVED SPECIES. 5-1. Introduction What is activity of a dissolved species? Effective concentration Equivalent to the concentration acting in effect Why do we need activity (or have activity)? Interactions among the dissolved matter

eydie
Download Presentation

Ch. 5. ACTIVITY COEFFICENTS OF DISSOLVED SPECIES

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Ch. 5. ACTIVITY COEFFICENTS OF DISSOLVED SPECIES • 5-1. Introduction • What is activity of a dissolved species? • Effective concentration • Equivalent to the concentration acting in effect • Why do we need activity (or have activity)? • Interactions among the dissolved matter • Interference among the dissolved matter •  causes partial influences on the solution properties • Where can we observe the activity effect? • Boiling point increase, freezing point decrease • Conductivity • Others

  2. 5-2. Activity Coefficient & Ionic Strength • Activity coefficient: A function of the ionic strength of the solution • ai = gimi • Ionic strength: A measure of the ionic characteristics of the solution • Lewis & Randall (1921) • I = ½ S zi2mi • Examples • Mono-monovalent salts: KCl I=mKCl • Mono-divalent salts: K2SO4  I=3mK2SO4 • Di-divalent salts: CaSO4  I = 4mCaSO4

  3. Approximate estimation of I from TDS • Eqn (4.4) to (4.6) on p.124 • Approximate estimation of I from SpC • Eqn (4.7) to (4.9) on p.124 • Otherwise? • Should be calculated from the chemical composition

  4. 5-3. Mean Ion-Activity Coefficients • The coefficients measured for a solutions which is due to the net effect of both cations and anions • g± =[gn+gn-]1/n , n = (n+ + n-) • Fig. 4.1 on p.125 • McInnes convention (McInnes 1919) • g±KCl = gK = gCl • Obtain gK and gCl fromg±KCl • Then other gusing the above relation • Example 4.1 on p.127

  5. 5-4. Theoretical Calculation of the Activity Coefficients Debye-Hückel limiting law (DHLL) When I <0.001: eqn (4.30) on p.129 Extended Debye-Hückel equation (EDHE) When I<0.1: eqn (4.28) on p.128 A=1.824928*106ro1/2(eT)-3/2, 0.5092 (at 25C) B=50.3(eT)-1/2, 0.3283 (at 25C) Table 4.1 for effective ionic radii on p.130 Fig. 4.3 on p.132 Other equations for higher I Davies et al.; eqn (4.31) on p.132 Trusdell & Jones (1974) Bronsted-Guggenheim-Scatchard specific ion interaction theory (SIT) equaton: eqn (4.32) p.133 Fig. 4.4. p.135. Pitzer model; eqn (4.49) p.138

  6. 5-5. Limitation of Debye-Huckel Theory All interactions are not purely ionic Ions are not point charges Ion size varies with I Ions do interact w/ other ions and even with the same species

  7. 5-6. Activity Coefficients of Molecular Species In most cases, approximately g=1 Generally follow Setchenoweqn (Lewis & Randall, 1961) Log gi = KiI, where Ki = 0.02 ~ 0.23 Table 4.5 on p.144.

More Related