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Finding the Equivalence Point (calculation method)

Finding the Equivalence Point (calculation method). Strong Acid vs. Strong Base 100 % ionized! pH = 7 No equilibrium! Weak Acid vs. Strong Base Acid is neutralized; Need K b for conjugate base equilibrium Strong Acid vs. Weak Base

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Finding the Equivalence Point (calculation method)

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  1. Finding the Equivalence Point(calculation method) Strong Acid vs. Strong Base 100 % ionized! pH = 7 No equilibrium! Weak Acid vs. Strong Base Acid is neutralized; Need Kb for conjugate base equilibrium Strong Acid vs. Weak Base Base is neutralized; Need Ka for conjugate acid equilibrium Weak Acid vs. Weak Base Depends on the strength of both; could be conjugate acid, conjugate base, or pH 7

  2. Exactly 100 mL of 0.10 M HNO2 are titrated with 100 mL of a 0.10 M NaOH solution. What is the pH at the equivalence point ? HNO2(aq) + OH-(aq) NO2-(aq) + H2O (l) Initial (M) 0.01 Change (M) [NO2-] = = 0.05 M NO2-(aq) + H2O (l) OH-(aq) + HNO2(aq) 0.200 Equilibrium (M) x2 [OH-][HNO2] = Kb = 0.05-x [NO2-] start (moles) 0.01 0.01 end (moles) 0.0 0.0 0.01 Final volume = 200 mL 0.05 0.00 0.00 -x +x +x 0.05 - x x x pOH = 5.98 = 2.2 x 10-11 pH = 14 – pOH = 8.02 0.05 – x 0.05 x 1.05 x 10-6 = [OH-]

  3. 2- Co2+(aq) + 4Cl-(aq) CoCl4(aq) 2+ Co(H2O)6 2- CoCl4 Complex Ion Equilibria and Solubility A complex ion is an ion containing a central metal cation bonded to one or more molecules or ions. 16.10

  4. 16.10

  5. Complex Ion Formation These are usually formed from a transition metal surrounded by ligands (polar molecules or negative ions). As a "rule of thumb" you place twice the number of ligands around an ion as the charge on the ion... example: the dark blue Cu(NH3)42+ (ammonia is used as a test for Cu2+ ions), and Ag(NH3)2+. Memorize the common ligands.

  6. Common Ligands

  7. Names Names: ligand first, then cation Examples: tetraamminecopper(II) ion: Cu(NH3)42+ diamminesilver(I) ion: Ag(NH3)2+. tetrahydroxyzinc(II) ion: Zn(OH)4 2- The charge is the sum of the parts (2+) + 4(-1)= -2.

  8. When Complexes Form Aluminum also forms complex ions as do some post transitions metals. Ex: Al(H2O)63+ Transitional metals, such as Iron, Zinc and Chromium, can form complex ions. The odd complex ion, FeSCN2+, shows up once in a while Acid-base reactions may change NH3 into NH4+ (or vice versa) which will alter its ability to act as a ligand. Visually, a precipitate may go back into solution as a complex ion is formed. For example, Cu2+ + a little NH4OH will form the light blue precipitate, Cu(OH)2. With excess ammonia, the complex, Cu(NH3)42+, forms. Keywords such as "excess" and "concentrated" of any solution may indicate complex ions. AgNO3 + HCl forms the white precipitate, AgCl. With excess, concentrated HCl, the complex ion, AgCl2-, forms and the solution clears.

  9. Coordination Number Total number of bonds from the ligands to the metal atom. Coordination numbers generally range between 2 and 12, with 4 (tetracoordinate) and 6 (hexacoordinate) being the most common.

  10. Some Coordination Complexes

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