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IV.15. CALCULATIONS INVOLVING Kb (Hebden p. 152 – 154)

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Need to calculate Kb from Ka table. Basic solutions, so use [OH - ], not [H 3 O + ] Need to calculate Kb from Ka table. Basic solutions, so use [OH - ], not [H 3 O + ]

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p.153: #84 SO 3 -2 + H 2 O HSO 3 - + OH - I#M - 0 0 C - x - +x +x E(#M - x) - x x SO 3 -2 + H 2 O HSO 3 - + OH - I#M - 0 0 C - x - +x +x E(#M - x) - x x

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pH = 9.69 pOH = 4.31 [OH - ] = 4.8978 x 10 -5 M So x = 4.90 x 10 -5 M pH = 9.69 pOH = 4.31 [OH - ] = 4.8978 x 10 -5 M So x = 4.90 x 10 -5 M

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Kb = Kw/Ka = 1.0 x 10 -14 / 1.0 x 10 -7 = 1.0 x 10 -7 Kb = [HSO 3 - ][OH - ]/ [SO 3 -2 ] = (1.0 x 10 -7 ) 2 / (#M - 4.90 x 10 - 5 ) *Assume x (4.90 x 10 -5 ) is so small so… 1.0 x 10 -7 = (1.0 x 10 -7 ) 2 / (#M) [SO 3 -2 ] = 0.024M Kb = Kw/Ka = 1.0 x 10 -14 / 1.0 x 10 -7 = 1.0 x 10 -7 Kb = [HSO 3 - ][OH - ]/ [SO 3 -2 ] = (1.0 x 10 -7 ) 2 / (#M - 4.90 x 10 - 5 ) *Assume x (4.90 x 10 -5 ) is so small so… 1.0 x 10 -7 = (1.0 x 10 -7 ) 2 / (#M) [SO 3 -2 ] = 0.024M

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IV. 16. TITRATIONS (Hebden p. 154-158)

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Titration Process in which a measured amount of a solution is reacted with a known volume of another solution (one of the solutions has an unknown concentration) until a desired EQUIVALENCE POINT is reached

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Equivalence Point The point in a titration where the ratio of the moles of each species involved exactly equals the ratio of the coefficients of the species in the balanced rx equation

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Example: If 25.9 mL of H 3 PO 4 with an unknown molarity react with 34.6 mL of 0.400 M KOH according to the rx, what is the molarity of the H 3 PO 4 ?

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H 3 PO 4 + KOH K 3 PO 4 + H 2 O 25.9 ml 34.6 ml # M 0.400 M 25.9 ml 34.6 ml # M 0.400 M

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% Yield = mass of product obtained x 100% mass of product expected

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% Purity = mass of pure reactant x 100% mass of impure reactant

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Titrations. The process of adding measured volumes of an acid or base of known concentrations to an acid or base of unknown concentration until neutralization.

Titrations. The process of adding measured volumes of an acid or base of known concentrations to an acid or base of unknown concentration until neutralization.

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