iv.15. calculations involving kb (hebden p. 152 – 154)
TRANSCRIPT
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IV.15. CALCULATIONS INVOLVING Kb
IV.15. CALCULATIONS INVOLVING Kb
(Hebden p. 152 – 154)(Hebden p. 152 – 154)
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•Need to calculate Kb from Ka table.
•Basic solutions, so use [OH-], not [H3O+]
•Need to calculate Kb from Ka table.
•Basic solutions, so use [OH-], not [H3O+]
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p.153: #84p.153: #84SO3
-2 + H2O HSO3- + OH-
I #M - 0 0
C - x - +x +x
E (#M - x) - x x
SO3-2 + H2O HSO3
- + 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 = [HSO3-][OH-]/ [SO3
-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)[SO3
-2] = 0.024M
Kb = Kw/Ka = 1.0 x 10-14 / 1.0 x 10-7
= 1.0 x 10 -7
Kb = [HSO3-][OH-]/ [SO3
-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)[SO3
-2] = 0.024M
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IV. 16. TITRATIONS
IV. 16. TITRATIONS
(Hebden p. 154-158)
(Hebden p. 154-158)
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TitrationTitration•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
•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 PointEquivalence 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
•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:Example:
•If 25.9 mL of H3PO4 with an unknown molarity react with 34.6 mL of 0.400 M KOH according to the rx, what is the molarity of the H3PO4?
•If 25.9 mL of H3PO4 with an unknown molarity react with 34.6 mL of 0.400 M KOH according to the rx, what is the molarity of the H3PO4?
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H3PO4 + KOH K3PO4 + H2OH3PO4 + KOH K3PO4 + H2O
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% Yield
= mass of product obtained x 100%mass of product expected
= mass of product obtained x 100%mass of product expected
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% Purity % Purity
= mass of pure reactant x 100%mass of impure reactant
= mass of pure reactant x 100%mass of impure reactant