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K >>1 Forward rxn dominates (rxn lies to the right). Mostly products at equilibrium, [products] >> [reactants]

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K <<1 Reverse rxn dominates (rxn lies to the left). Mostly reactants at equilibrium, [products] << [reactants]

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K 1 Forward and reverse rxn occur to roughly the same extent, [products] [reactants]

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2.0 moles of NH 3 gas are introduced into a previously evacuated 1.0 L container. At a certain temperature the NH 3 partially dissociates by the following equation. At equilibrium 1.0 mol of NH 3 remains. Calculate the equilibrium constant for this reaction.

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Reaction Quotient (Q) Q = K: The rxn is at equilibrium. No shift. Q < K: The rxn shifts right to produce products to increase Q. Q > K: The rxn shifts left to produce reactants to decrease Q.

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If a change (stress) is imposed on a system at equilibrium, the position of the equilibrium will shift in a direction that tends to reduce that change (stress). Le Chatelier’s Principle

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1.SO 2 (g) is removed. 2.O 2 (g) is added. 3.SO 3 (g) is added. 4.The volume of the reaction container is halved. 5.An inert gas like Ar is added. 6.A catalyst is added. 7.Temperature is increased.

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Le Chatelier’s Principle 1.CO 2 (g) is added. 2.CaCO 3 (s) is added. 3.The volume is increased. 4.The temperature is decreased.

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1.0 mol of N 2 O 4 (g) is placed in a 10.0 L vessel and then reacts to reach equilibrium. Calculate the equilibrium concentrations of N 2 O 4 and NO 2. K = 4.0 x 10 -7

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Brønsted-Lowry Model Acids – are proton donors Bases – are proton acceptors

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HC 2 H 3 O 2 is a stronger acid then HCN which Has the stronger conjugate base?

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Comments on the Conjugates of Acids and Bases. The weaker the acid the stronger its conjugate base. The weaker the base the stronger its conjugate acid. The conjugate base of a weak acid is a WEAK base. The conjugate base of a strong acid is worthless. The conjugate acid of a weak base is a WEAK acid.

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AcidKaKa Realative acid strength Conjugate base KbKb Relative base strength HCl~10 6 HF7.2 x HC 2 H 3 O x HOCl3.5 x NH x

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AcidKaKa Realative acid strength Conjugate base KbKb Relative base strength HCl~10 6 Cl - ~ HF7.2 x F-F- 1.4 x HC 2 H 3 O x C2H3O2-C2H3O x HOCl3.5 x OCl x NH x NH x 10 -5

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Stuff you should now know. 1.K a value is directly related to acid strength. 2.Weak acids vs. strong acids (K a ’s and % dissociation. 3.Conjugate acid-base pairs. 4.K a K b =K w 5.K b value is directly related to base strength. 6.How to write out K a and K b rxns and expressions. 7.The weaker the acid the stronger the conjugate base (and vice versa). 8.Conjugate bases of strong acids have no basic properties whatsoever! (K b << K w )

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Calculate the pH of a 0.10 M HBr solution.

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Calculate the pH of a 0.10 M HOCl solution. K aHOCl = 3.5 x 10 -8

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Calculate the pH of a 0.10 M NaF. K aHF = 7.2 x 10 -4

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Calculate the pH of a 0.10 M Ca(OH) 2 solution.

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Calculate the pH of a solution containing 0.10 M HOCl and 0.02 M NaOCl. K aHOCl = 3.5 x 10 -8

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Calculate the pOH of 0.05 M Ba(OH) 2.

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Calculate the pOH of 0.50 M KOCl. K aHOCl = 3.5 x 10 -8

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Calculate the pOH of 1.00 M HI.

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Calculate the pOH of 0.25 M NH 4 Cl. K a NH 4 + = 5.6 x

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Calculate the pOH of a solution containing 0.25 M NH 4 Cl and 0.10 M NH 3. K a NH 4 + = 5.6 x

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Calculate the pH of 1.6 x M HNO 3.

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A solution of 8.00 M HCOOH is 0.47% Ionized. What is the K a for the acid? pH?

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AcidK a HF7.2 x C 6 H 5 NH x HC 2 H 3 O x HCN6.2 x NH 4 +

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Acidic, Basic, or Neutral? 1.NaCN 2.NH 4 NO 3 3.KI 4.LiC 2 H 3 O 2 5.C 6 H 5 NH 3 Cl 6.KF 7.NaNO 3 8.HClO 4 9.Ca(OH) 2 10.NH 4 CN 11.NH 4 C 2 H 3 O 12.CaO 13.SO 3

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Acidic, Basic, or Neutral? 1.NaCN Na + - worthless, CN - - weak base, basic 2.NH 4 NO 3 NO worthless, NH weak acid, acidic 3.KI K + - worthless, I - - worthless, neutral 4.LiC 2 H 3 O 2 Li + - worthless, C 2 H 3 O weak base, basic 5.C 6 H 5 NH 3 Cl Cl - - worthless, C 6 H 5 NH weak acid, acidic 6.KF K + - worthless, F - - weak base, basic 7.NaNO 3 Na + - worthless, NO worthless, neutral 8.HClO 4 HClO 4 – strong acid, acidic 9.Ca(OH) 2 Ca(OH) 2 – strong base, basic 10.NH 4 CN K a NH 4 < K b CN - - basic 11.NH 4 C 2 H 3 O K a NH 4 = K b C 2 H 3 O - - neutral 12.CaO metal oxide - basic 13.SO 3 nonmetal oxide - acidic

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Buffers Buffer – A solution where a weak acid and its conjugate base are both present in solution. Buffers resist changes in pH

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Good Buffers Good buffers will have the following: –EQUAL concentrations of the weak acid and its conjugate base. –LARGE concentrations of the weak acid and its conjugate base. –pK a = pH of desired pH.

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Examples of Buffers HCN/CN - NH 4 + /NH 3 H 2 PO 4 - /HPO intracellular fluid buffer H 2 CO 3 /HCO blood buffer

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Calculate the pH of a solution that is 1.00 M HNO 2 and 1.00 M NaNO 2. K a HNO 2 = 4.0 x 10 -4

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Calculate the pH when 0.10 mol of HCl is Added to a 1.00 L solution containing 1.00 M HNO 2 and 1.00 M NaNO 2. K a HNO 2 = 4.0 x 10 -4

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Calculate the pH when 0.10 mol of NaOH are added to a 1.0 L solution containing 1.00 M HNO 2 and 1.00 M NaNO 2. K a HNO 2 = 4.0 x 10 -4

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Calculate the pH of a solution formed by Mixing mL of M NH 3 and mL of M HCl. K b NH 3 = 1.8 x 10 -5

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You want to prepare a HOCl buffer of pH You want to make a 500. mL solution and use all of the 0.75 mol of HOCl you have on hand. How many mol of KOCl must you add? K a HOCl = 3.5 x 10 -8

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Calculate the pH of a solution formed by mixing 500. mL of 1.50 M HCN with 250. mL of 1.00 M NaOH. K a HCN = 6.2 x

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Total Points in course: 800 Points to be decided next week: ~415

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Proposed Study Plan Thursday: HE III Material (finish Lon Capa) Friday: HE I Material Saturday: HE II Material Sunday: HE III Material Monday: HE III Material Tuesday: He III Material Wednesday: HE I, II Material Thursday: HE I, II, III Material

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A 100. mL solution of 0.10 M HF is titrated by 0.10 M NaOH. Calculate the pH when 0.0, 25.0, 50.0, 100.0, and mL of NaOH have been added. K a HF = 7.4 x 10 -4

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