1 / 19

Exam 1 Stats

Exam 1 Stats. Average 51.8 ± 22.1 High 92.5 (2 of you) Low 14. Chapter 8 Activity. The “true” nature of ionic species in solution. Ions are charged molecules As a result, they tend to attract polar solvent molecules (like water, for instance) and other ions Hydrated radius

alexander-roth
Télécharger la présentation

Exam 1 Stats

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. Exam 1 Stats • Average 51.8 ± 22.1 • High 92.5 (2 of you) • Low 14

  2. Chapter 8Activity

  3. The “true” nature of ionic species in solution • Ions are charged molecules • As a result, they tend to attract polar solvent molecules (like water, for instance) and other ions • Hydrated radius • Ionic atmosphere • The thickness of the ionic atmosphere is a function of the ionic strength of the solution “the concentration of charge”

  4. Hydrated radius _ + _ + water Chloride Sodium ion

  5. + + + + - - + + + + + + + + + + Ionic Atmosphere and Shielding Low ionic strength High ionic strength - - + + - - - - + + - - + - - - + - + - + - - - - - + - - + - - - - - - - + + - _ + + - Calcium ion Chloride ion Sulfate ion Sodium ion

  6. Activity • All ionic species in any equilibrium expression are more accurately expressed as activities. A Ca2+ = [Ca2+]gCa2+ or A + H2O ↔ A- + H3O+ Ka = A A-A H3O+ / [A] = [A-]gA-[H3O+]gH3O+ / [A] where g is the activity coefficient and is a function of the ionic radius of the ion and the ionic strength of the solution.

  7. Activity - continued • The higher the ionic strength of the solution, the larger the smaller the activity coefficient. • Rationalization: At higher ionic strengths the ion cloud around any ion is thicker, which weakens the attractive forces between the ion and its counterpart, inhibiting recombination.

  8. Ionic strength • A measure of the concentration of ions in solution m = ½ ∑ cizi2 0.010 M Ca(NO3)2 m = ½ ([NO3-](-1)2 + [Ca2+](2+)2) = ½ {(0.02)(-1)2 + (0.01)(2)2 } = 0.03 M gCa2+@m=0.03 = ? Use extended Debye-Huckle eq or Table 8.1 and extrapolation

  9. Take home message • At high ionic strengths, solubility increases slightly (by a factor of 2-10). • pH is influenced by ionic strength • Weak acid and base dissociation is influenced a little by ionic strength • Significant figures?

  10. Example 8-12 • Solubility of Hg2Br2 • in pure water • in 0.00100 M KNO3 • in 0.0100 M KNO3 • in 0.100 M KNO3

  11. In pure water Hg2Br2 Hg22+ + 2Br- Ksp = [Hg22+]gHg22+ [Br-]2gBr-2 2[Hg22+] = [Br-] and let [Hg22+] = x Ionic strength is very low. gHg22+ and gBr- are close to 1.00 so, Ksp = 4 [x]3 = 5.6E-23 x = 2.4E-8 M

  12. Activity coefficient as a function of ionic strength Table 8 -1

  13. in 0.00100 M KNO3 m = ½ ((.001)(+1)2 + (0.001)(-1)2 = 0.001 M gHg22+@ m = 0.001 = 0.867 gBr-2 @ m = 0.001 = 0.964 Ksp = 4 gHg22+gBr-2 [x]3 = 5.6E-23 x = 2.6E-8M

  14. in 0.0100 M KNO3 m = ½ ((.01)(+1)2 + (0.01)(-1)2 = 0.01 M gHg22+@ m = 0.001 = 0.660 gBr-2 @ m = 0.001 = 0.898 Ksp = 4 gHg22+gBr-2 [x]3 = 5.6E-23 x = 3.0E-8M

  15. in 0.100 M KNO3 m = ½ ((0.1)(+1)2 + (0.1)(-1)2 = 0.1 M gHg22+@ m = 0.001 = 0.335 gBr-2 @ m = 0.001 = 0.75 Ksp = 4 gHg22+gBr-2 [x]3 = 5.6E-23 x = 4.2E-8M

  16. pH and ionic strength • True definition of pH • pH = -logAH+ = -log {[H+]gH+} • pH of a 0.00100 M HCl solution • Ionic strength, m, = 0.001; gH+ = 0.967 • pH = -log(.001*.967) = 3.01 • pH of a 0.100 M HCl solution • Ionic strength, m, = 0.1; gH+ = 0.83 • pH = -log(0.1*0.83) = 1.08 • pH of a 0.00100 M HCl/0.100 M NaCl solution • Ionic strength, m, = 0.1; gH+ = 0.83 • pH = -log(0.001*0.83) = 3.08

  17. What is the concentration H+ an OH- in a 0.100 M NaCl solution? Kw = [OH-]gOH-[H+]gH+ = 1.01E-14 At m = 0.100, gOH- = 0.76 and gH+ = 0.83 H2O is the only source of H+ and OH- so let x = [H+] = [OH-] Kw = (0.76)(0.83) x2 x = 1.27E-7 M

  18. EDTA Prob 12-31 • A 50 mL sample containing Ni2+ is treated with 25.00 mL of 0.0500 M EDTA to complex all of the Ni2+. The excess EDTA is back-titrated, requiring 5.00 mL of 0.0500 M Zn2+. What is the concentration of Ni2+ IN THE ORIGINAL SAMPLE?

More Related