Enter your version number in the correct column on your scan sheet (see p.2 for details)
1. The pH of a 0.01 M aqueous solution of a strong base is:
2. Which of the following combinations of aqueous solutions would give a buffer? (All
solutions are 1.0 M).
A) 10 mL HClO + 40mL KClO 2
B) 15 mL HClO + 45mL KClO 4
C) 20 mL HClO + 40mL KOH
D) 20 mL HClO + 20mL KClO 4
E) 10 mL HClO + 20mL KOH
3. Which of the following compounds will produce a basic solution when placed into
(i) Na2O (ii) N4 Cl (iii) LiBr (iv) CH3COOK (v) CH 3H 2
A) iii, v
B) i, ii
C) ii, iii, iv
D) ii, iv
E) i, iv, v
4. MES is a common buffer in chemical biology. At pH 6.5, the ratio of MES, a weak base,
to irs conjugate acid, MESH , is [MES]/[MESH ] = 2.19. What is the pK of MESH ? +
C) 6.76 D) 5.65
5. Which of the following statements about buffers is false?
A) The percent ionization of the weak acid or weak base in a buffer is negligible
(close to zero)
B) Weak acid-strong base titration curves show a buffer region right up until the
C) Buffers resist changes in pH by converting strong base into weak base, or strong
acid into weak acid.
D) The buffer capacity for a weak acid (HA)/weak base (A ) system is at a maximum
when [HA] and [A] are equal.
E) A buffer’s capacity can be exceeded by adding excess amounts of strong acid.
6. What is [H O 3 (in M) in 1.0 M CH COOH(3q)?
K aCH C3OH) = 1.8 x 10 -5
A) 1.66 x 10
B) 1.34 x 10
C) 3.22 x 10 -3
D) 4.24 x 10
E) 7.18 x 10
7. A buffer is made using only Tris (weak base) and TrisHCl (weak acid). What mass (in g)
of solid TrisHCl would be used to make 0.20 L of a buffer solution with a total buffer
concentration ([Tris] + [TrisH ]) of 0.050 M, and pH 7.80?
TrisH + H O 2 Tris + H O 3 +
pK aTrisH ) = 8.30
mol wt(TrisHCl) = 157.6 g/mol mol wt(Tris) = 121.1 g/mol
8. What is the pH of the solution that results when the following substances are added to
water to create 1.00 L of solution?
0.100 mol HNO 3
0.100 mol HNO 2
0.300 nol NaNO 2
Ka(HNO ) 2 7.2 x 10
9. Bromophenol blue is an acid-base indicator with a pK of 4.0. The acidic form is yellow
and the basic form is blue-violet. A few drops of this indicator are added to the titration of
benzoic acid (beaker, pK a 4.20) with NaOH(aq) (buret). Find the false statement(s)
about this titration experiment.
(i) The indicator starts to change from yellow to blue-violet at about pH 3 and
completes the change from to blue-violet at about pH 5. (ii) The indicator will be yellow over the entire buffer region of the titration curve.
(iii) The bromophenol blue indicator is not an appropriate choice for locating the
equivalence point of this titration.
A) No statements are false
E) i, iii
10. Which would be the best pH indicator to find the endpoint in a titration of 0.050 M
cacodylic acid with 1.100 M LiOH? (Cacodylic acid is a monoprotic acid.)
K acacodylic acid) = 5.7 x 10
Indicator Colour change range (pH)
A) Methyl orange 3.1 – 4.4
B) Thymolphthalein 9.3 – 10.5
C) Cresol red 7.2 – 8.8
D) Bromophenol blue 3.0 – 4.6
E) Bromophenol blue 6.0 – 7.6
11. Some parts of human cells, like the endosomes, are acidic, with pH ≈ 5.5. Which of
the following weak acids would be the most effective acid component of a buffer to
maintain pH 5.5 (assuming equal concentrations of all buffers)?
Weak acid Ka
A) glycine 4.6 x 10 -3
B) lactic acid 1.4 x 10 -4
C) H PO - 6.3 x 10 -8
2 4 -7
D) H 2O 3 4.5 x 10
E) NH 4 5.5 x 10
12. If the pH indicator cresol red (yellow at low pH, purple at high pH) is placed in a buffer
solution with pH 7.40, what percenta