Extra Credit Assignment (10 points):
1) Submit your answers to the following 8 questions for 5 extra credit points by Friday,
December 5, 2008
2) One of these questions will appear on the final exam. In addition to the final exam
points, 5 extra credit points will be granted if the correct answer and the correct
explanation are given .
1) The indicator methyl red has a pKHIn = 4.95. It changes from red to yellow over
the pH range from 4.4 to 6.2, respectively. If the indicator is placed in a buffer
solution of pH = 4.55 what percent of the indicator will be present in the acid form,
HIn, and what percent will be in the conjugate base form, In-?
2) Phenol red indicator changes from yellow to red in the pH range from 6.6 to 8.0,
respectively. Without making detailed calculations, state which color the indicator
will assume in each of the following solutions:
a) 0.10 M KOH
b) 0.10 M CH3COOH
c) 0.10 M NH4NO3
d) 0.10 M HBr
e) 0.10 M NaCN
f) 0.10 M CH3COOH/0.10 M NaCH3COO
3) Two solutions are mixed: 100.0 mL of HCl(aq) with pH = 2.50 and 100.0 mL of
NaOH(aq) with pH = 11.00. What is the pH of the resulting solution?
4) Before resorting to looking up the equilibrium constant for any substance below,
determine without doing detailed calculations whether a solution can be
simultaneously:
a) 0.10 M NH3 and 0.10 M NH4Cl with pH = 6.07
b) 0.10 M NaCH3COO and 0.058 M HI
c) 0.10 M KNO2 and 0.25 M KNO3
d) 0.050 M Ba(OH)2 and 0.65 M NH4Cl
e) 0.018 M HC7H5O2 and 0.018 M NaC7H5O2 with pH = 4.20
f) 0.68M KCl, 0.42 M KNO3, 1.2 M NaCl, and 0.55 M NaCH3COO, with pH = 6.4
5) The single equilibrium equation applies to different phenomena.
CH3COOH + H2O  H3O+ + CH3COOOf the four phenomena, ionization of a pure acid, common-ion effect, buffer
solution, and hydrolysis, indicate which occurs if:
a) [H3O+] and [CH3COOH] are high but [CH3COO-] is very low
b) [CH3COO-] is high but [H3O+] and [CH3COOH] are very low
c) [CH3COOH] is high but [H3O+] and [CH3COO-] are very low
d) [CH3COO-] and [CH3COOH] are high but [H3O+] is very low
6) Using LeChâtelier’s principle discuss what happens when a small amount of
strong acid or strong base is added to a solution containing:
a) HCO2H/KHCO2
b) C6H5NH2/C6H5NH3Cl
c) KH2PO4/Na2HPO4
Make sure to choose the dominant equilibrium and for completeness look at both the
addition of strong base and strong acid.
7) To increase the ionization of formic acid HCO2H(aq) which of the following
should be added: NaCl, NaHCO2, H2SO4, NaHCO3?
8) The most acidic of the following 0.10 M salt solutions is Na2S, NaHSO4, NaHCO3,
Na2HPO4