Activity 1 The distribution diagram for
CH3COOH/CH3COO- is shown.
a) What is W at pH 3.7? At pH 5.7? pKa for
acetic acid is at 4.7. One unit below this, at pH 3.7, log W is -1 and R is 0.1. 1 unit above this, at pH 5.7, log
W is 1 and W is 10
b) If a solution contains 0.1 M total acetate and has pH = 6, what are
the concentrations of CH3COO-, CH3COOH, and OH-. log
W = pH - pKa = 6-4.7 = 1.3, so R = 19.95. The
fraction of acetate in the deprotonated form is 19.95/20.95. Multiplying
this by 0.10 gives [CH3COO-] = 0.095 M, [CH3COOH] = 0.005 M. Because pH =
6, pOH = 8 and [OH-] = 10-8 M.
c) A 0.1 M solution of CH3COOH is prepared. Use an arrow to
show the location of the solution on the distribution diagram. This is a
solution of a weak acid, so [H3O+] = (Co*Ka)1/2 =
(0.10*1.8*10-5) = 1.3*10-3 M; pH = 2.87. Put an
arrow in the distribution diagram pointing to 2.87 along the pH axis.
Activity 2 "Slide" the acetate distribution diagram
along the pH axis to generate distribution diagrams for
NH4+/NH3 and
HSO4-/SO42-. Click here to see the diagrams.
Activity 3 Draw a predominance diagram incorporating all of the
conjugate pairs, CH3COOH/CH3COO-, HF/F-, and
HSO4-/SO42-. Click here to see the diagram.
a) If equal volumes of 0.1 M solutions of Na2SO4
and HF are mixed, what species will predominate in the solution at
equilibrium? HF and SO42- are stable in overlapping pH ranges; therefore,
they will react together to only a minor extent, and will be the
predominant species at equilibrium.
Activity 4 Locate all 3 conjugate pairs on a predominance line.
Indicate which of the following pairs of species can coexist together in
solution without undergoing proton transfer.
F-, HSO4-: NO
NH3, SO42-: YES
CH3COOH, SO42-: YES
CH3COO-, HF: NO
To answer these, look at whether the stability regions for the two species overlap. If so, they can coexist.
