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BaOH2.8H2O 2NH4SCN BaSCN2 2NH3 10H2O

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BaOH2.8H2O 2NH4SCN BaSCN2 2NH3 10H2O

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    1. Ba(OH)2.8H2O + 2NH4SCN ? Ba(SCN)2 + 2NH3 + 10H2O What is the sign of DG in this reaction? What is the sign of DH in this reaction? What is the driving force in this reaction? How does the reaction proceed even though both reactants are solids?

    3. Example problem For reaction: H2O (l) === H+ + OH- K = 1.0 x 10-14 @ 25oC. The [ ] of the system out of equilibrium = [H+] = 3.0 x 10-5M and [OH-] = 2.0 x 10-7M will reaction go toward the reactants or products to reach equilibrium?

    4. How will reaction be affected if you remove product? How will reaction be affected if you add product? How will reaction be affected if you remove reactant? How will reaction be affected if you add reactant?

    5. Ba(OH)2.8H2O + 2NH4SCN ? Ba(SCN)2 + 2NH3 + 10H2O If the temperature is raised, which direction will equilibrium shift toward? If the temperature is lowered? If the temperature of an exothermic reaction is raised? If the temperature of an exothermic reaction is lowered?

    6. Remember! Just because a reaction is thermodynamically favored K is big does not mean it is fast. Kinetics and thermodynamics are distinct!

    7. Resources to find methods Standard Methods for the Examination of Water and Wastewater Journal of Chemical Education ASTM Methods Analytical Chemistry for Technicians Environmental Chemistry: Experiments and Demonstrations Analytical Chemistry: Practice Methods for environmental trace analysis NIOSH manual of analytical methods /  <Print Book>

    8. Steps in Experimental Design Formulate the question Develop the hypothesis Hypothesis must be testable Make predictions What will the data look like if the hypothesis is supported? Not supported? Plan methods for testing hypothesis What experimental methods will be used for testing the hypothesis?

    9. Steps in Experimental Design 5. Collect data 6. Evaluate data Does it support the hypothesis? Do additional experiments need to be done?

    10. Hypotheses Study of the effectiveness of laundry detergents Taking aspirin reduces the length of headache time versus taking Tylenol Lightbulbs: longevity vs. cost Application of fertilizer increases the concentration of nitrate in nearby surface water Null hypothesis: Increasing the size of the buffer zone between a farm field and surface water does not result in reduced nutrient levels.

    11. Why can we ignore the concentration ratio of solvent (usually water) in equilibrium expressions? (Hint: consider the case of the dissociation of 0.1M acetic acid if you would like a concrete example.) Why is it also permissible to omit the concentration of solids in equilibrium expressions? (If you want a concrete example use Mn, the density of Mn is 7.21g/mL.)

    12. Solubility Product

    13. Solubility Product Example Calculate the solubility product of Ag3PO4 if 500.mL of saturated solution contains 0.00325g of dissolved salt. Neglect any hydrolysis effects.

    14. Another Ksp example Calculate the solubility of Ag2CrO4 @ 25oC in moles/liter. Ksp = 2.4 x 10-12.

    15. Common ion effect Addition of a common ion displaces reaction toward reactants, less will dissolve. A salt will be less soluble if one of its constituent ions is already present in solution. Solubility, like any other equilibria expression is affected by addition of common ions

    16. Common ion effect example Calculate the solubility of AgCl @ 25oC in 0.010M AgNO3 solution.

    17. Common Ion Effect Demo The solubility of KCl at room temperature is 3.7M Each test tube contains 20mL of saturated KCl initially To test tube #1 20mL of 6M HCl is added To test tube #2 20mL of 12M HCl is added

    18. A waste bottle contains 0.01M Cu+1 and Sn+2 ions. For waste disposal, it is considerably cheaper if these two metals were precipitated separately rather than co-precipitated. Is such a separation possible? What would you precipitate the solutions with? (Use the Ksp values given at the back of your book.)

    19. Solubility Rules When applying solubility rules focus mainly on the anion portion of your molecule Always soluble: Group I metals and ammonium salts are soluble Nitrates, acetates, and perchlorates are soluble Cl-, Br-, and I- are soluble except with Ag+, Pb2+, Cu+, and Hg2+ Sulfates are soluble except with Ca2+, Sr2+, Ba2+, and Pb2+ Always insoluble: CO32- are insoluble except with Group I and NH4+ PO43- are insoluble except with Group I and NH4+ S2- except Group I, II, and NH4+ OH- except with Group I, NH4+, Ca2+, Sr2+, and Ba2+

    20. Acids and Bases Review Bronsted – Lowry Acid: Proton donor Bronsted – Lowry Base: Proton acceptor Lewis acid: e- pair acceptor Lewis base: e- pair donor Salt: ionic solid can be thought of as the product of an acid base reaction

    21. Demonstration: pH of distilled water Why is the pH of distilled water acidic? Write it down in your notebook. How can this be minimized? How can the CO2 be removed?

    22. Strong acids & bases completely dissociate Strong Acids: Everything else is weak Strong Bases: Alkali earth metal OH R4NOH R are all organic groups Alkaline earth metal OH (but not always soluble) Everything else is weak

    23. Explain why, if benzoic acid is a weak acid with a Ka of 6.28 x 10-5, sodium benzoate is basic. Use equilibria. If you have a 0.100M solution of sodium benzoate, what will be the pH of the solution?

    24. Buffers Buffer resists changes in pH How does a buffer work? It contains significant amounts of both an acid and its conjugate base at equilibrium such that with the common ion effect/ L’Chatlier’s Principle it is able to minimize the effects of additions of acid or base

    25. Buffer Example What is the pH of 0.180 mole of NaNO2 mixed with 0.230 moles of HNO2 in 1.0 liter of solution?

    26. Buffer capacity How well a buffer resists changes to pH when a strong acid or strong base is added. Buffers are most effective closer to their pKa Do not want to generally make a buffer more than 1 pH unit from its pKa

    27. Buffer example 2 How would you make a buffer at a pH of 7.80? (There is more than one correct answer.)

    28. Buffer example 3 What would the pH be of a buffer solution containing 100.0mL of 0.15M NH3 and 4.25mL of 1.0M HCl?

    29. Buffer example 4 How will the pH change when 10.0mL of 0.1M HCl is added to a buffer containing 0.15moles of Sodium acetate and 0.12 moles of acetic acid in 1.0 liter of solution?

    30. Ladder Diagrams

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