1 / 40

Chapter 8

Chapter 8. Activity Goodbye Freshman Chemistry Hello Real World. Activity. Equilibrium up to this point has been based on a very simple model. Basically that ions (a species with a high density of charge) do not interact other than the interaction of interest. Activity.

landon
Download Presentation

Chapter 8

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. Chapter 8 Activity Goodbye Freshman Chemistry Hello Real World

  2. Activity • Equilibrium up to this point has been based on a very simple model. • Basically that ions (a species with a high density of charge) do not interact other than the interaction of interest.

  3. Activity • Real Solutions are rather complex in their nature. • Ion interact with all ions in solution and other polar species. • Ions will interact with water since water is a polar substance. • Ions will have these water molecules in their ‘waters of hydration’.

  4. Just how much water?

  5. Activity • In essence this ionic atmosphere shields the ions from each other which will diminish the interaction between the ions. • i.e. For a Ksp interaction the compound will be more soluble.

  6. Solubity • KT(s) = K+ (aq) + T- (aq)

  7. Potassium Tartarate

  8. Glucose

  9. Activity • How do we quantify this ionic atmosphere. We use a term called ionic strength. • It can be calculated

  10. Activity • Let’s do an example. • What is the ionic strength of a solution that is 0.010 M Na2SO4 and 0.050 M NaCl • We will prepare a Table and ask our first question. • What ions are present?

  11. Activity

  12. 0.010 M Na2SO4 and 0.050 M NaCl • What are the concentrations?

  13. Activity

  14. 0.010 M Na2SO4 and 0.050 M NaCl • What are the charges and charges squared?

  15. Activity

  16. 0.010 M Na2SO4 and 0.050 M NaCl • Let’s Finish the Math

  17. Activity

  18. Activity • It gets even more complex. Not all soluble salts will dissociate into the individual species. We get another form that will exist in solution. This is called and Ion Pair • MgSO4 (s)+ H2O = Mg2+(aq)+ SO42-(aq) + MgSO4(aq) • The MgSO4(aq) is the ion pair.

  19. Activity • You can see from Appendix J in the book the equilibrium constants for this pair formation. • Mg2+(aq) + SO42-(aq) = MgSO4(aq) • Log K = 2.23 • Which means that about ~93% will be in the ion pair form if the formal concentration of MgSO4 is 1M.

  20. Activity • Ion Pairing has important implications in areas such as drug transport and delivery. Any drug species must be in the proper form to give its activity.

  21. Activity • So how do we find the “Activity of an ion in solution”. Where A is the activity of species C g is “activity coefficient” [C] is the concentration in moles per liter

  22. Activity • Let’s revisit our equilibrium expression. • aA + bB = cC + dD • Which we write

  23. Activity • Lets revisit an equilibrium we have seen several times. The solubility of silver sulfide.

  24. Activity • How do we find the value for the “activity coefficient” ? • For ionic strengths from 0.1M and down we can look up the value on a Table or we can calculate from the Extended Debye-Huckel equation.

  25. Activity Where z is the ion charge, m is the ionic strength and a is the hydrated radius

  26. Hydrated Radius (a)

  27. Activity • You could also look up the value of the activity coefficient from Table 8-1 in the text.

  28. Activity • What if you want an intermediate value between two listed ionic strengths. • You will need to do a linear interpolation. (Do you remember this from using log tables in high school?)

  29. Activity • Effect of Ionic Strength, Ion Charge and Ion Size on Activity Coefficient (0 to 0.1M) • m increases g decreases • z increases the faster the departure from g from unity • smaller a then the greater activity effects

  30. Activity • Neutral Molecules • Not charged so no ionic interaction so we assume g is 1 • Gases • Not charged and again we can assume that g is 1. A = P(bar)

  31. Activity (In concentrated Solutions)

  32. Activity • What is the pH of very, very pure water? • Kw = AHAOH = 1.0 x 10-14 • AH = 1.0 x 10-7 Thus pH = 7.00 • What is the pH of 0.10 M NaCl? Would it still be 7.00?

  33. Activity • Kw = gH[H] gOH [OH] • Look up the g for H+ and OH- on Table 8-1. gH = 0.83 and gOH = 0.76 • [H+] = [OH-] • So Solving for [H+] = 1.26 x 10-7 • pH = - log AH = -log (0.83)(1.26 x 10-7) = 6.98

More Related