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Westminster H.S.  AP Chemistry
Name ___________________________________
Period ___ Date ___/___/___
Acid-Base Equilibria
BUFFER CALCULATIONS
The weak acid, acetic acid, has the formula, HC2H3O2. Ka acetic acid = 1.8x10-5
(a) A buffer solution is prepared by adding 0.10 Liter of 2.0 molar acetic acid solution to 0.10 Liter of a 1.0
molar sodium hydroxide solution. Compute the hydrogen ion concentration of the buffer solution.
PROBLEM BREAKDOWN:
(i) Calculate moles of HC2H3O2.
(ii) Calculate moles of OH-.
(iii)What is the total volume (in Liters)?
(iv) Fill in this NEUTRALIZATION chart using Molarities
HC2H3O2
+
OH-

H2O(l)
+
C2H3O2-

H3O+
+
C2H3O2-
(v) Fill in this EQUILIBRIUM chart:
HC2H3O2
+
H2O(l)
(vi) Write the equilibrium expression for HC2H3O2.
Substitute the equilibrium values into the expression and compute the hydrogen ion concentration.
Ka acetic acid = 1.8x10-5
(b) Suppose that 0.010 Liter of 0.50 M hydrochloric acid is added to 0.20 Liter of the buffer prepared in (a).
Compute the hydrogen ion concentration of the resulting solution.
PROBLEM BREAKDOWN:
(i) Calculate moles of HC2H3O2 and C2H3O2-.
(ii) Calculate moles of H+.
(iii)What is the total volume (in Liters)?
(iv) Fill in this chart using Molarities
C2H3O2-
+

H+
HC2H3O2
(v) Fill in this chart:
HC2H3O2
+
H2O(l)

H3O+
+
C2H3O2-
(vi) Write the equilibrium expression for HC2H3O2.
Substitute the equilibrium values into the expression and compute the hydrogen ion concentration.