Acid base review key
Acids, Bases, Buffers and Ksp– Problem Set
1. The acid HX has an ionization constant of 1 x 10-4. A solution is made that is 0.1 M in HX and 1 M in
the salt NaX. What is the approximate H+ ion concentration?
a) 1 x 10-3 M
b) 2 x 10-3 M
c) 1 x 10-5 M
d) 1 x 10-8 M
2. How many moles of pure NaOH must be used to prepare 10.0 L of a solution that has a pH of 13.00?
a) 1.0 mole
b) 0.10 moles
c) 0.011 moles d) 0.0010 moles
3. Consider the reaction CH3NH2 (aq) + H2O (l)  CH3NH3+ (aq) + OH-(aq) where Kb = 4.4 x 10-4.
To a solution formed from the addition of 2.0 moles of CH3NH2 to 1.0 L of water is added 1.0
mole of KOH. (assume no volume change). What is the concentration of CH3NH3+ at equilivbrium?
a) 3.2 x 10-2 M
b) 2.2 x 10-4 M c) 2.0 x 10-3 M
d) 8.8 x 10-4 M
4. A 2.0 M solution of a weak acid, HZ, has a pH of 3.0. What is the Ka of this acid?
a) 0.60
b) 1.0 x 10-3
c) 2.0 x 10-4
d) 5.0 x 10-7
5. Which statement is a correct conclusion based on the fact that a 0.10 M solution of KC2H3O2 is less
basic than a 0.10 M solution of KCN?
a) HCN is a weaker acid than acetic acid
b) HCN is less soluble in water than acetic acid
c) Cyanides are less soluble than acetates
d) Acetic acid is a weaker acid than HCN
6. Which of the following would not make a good buffering system?
a) SO42- and H2SO4
c) NH3 and NH4+
b) HCO3- and H2CO3
d) CH3COO- and CH3COOH
7. A buffer solution is made by adding 0.500 moles of sodium acetate and 0.500 moles of acetic acid to
1.00 L of water. What is the pH of this solution at equilibrium? (Ka = 1.80 x 10-5)
a) 5.05
b) 4.74
c) 4.44
d) 2.38
8. How many grams of NaCH3COO (MW = 82.0 g/mol) should be added to 500.0 mL of a
0.200 M acetic acid solution (Ka = 1.80 x 10-5) in order to make a buffer with a pH of 5.00?
a) 69.0 grams
b) 0.180 grams c) 14.8 grams
d) 29.5 grams
9. What volumes of 0.500 M HNO2 (Ka = 4.00 x 10-4) and 0.500 M NaNO2 must be mixed to make a 1.00 L
buffer solution with a pH of 3.55?
a) 500. mL of each solution
b) 703 mL of 0.500 M HNO2 and 297 mL of 0.500 M NaNO2
c) 413 mL of 0.500 M HNO2 and 587 mL of 0.500 M NaNO2
d) 297 mL of 0.500 M HNO2 and 703 mL of 0.500 M NaNO2
e) 587 mL of 0.500 M HNO2 and 413 mL of 0.500 M NaNO2
10-. HCN is a weak acid (Ka = 6.2 x 10¯10). NH3 is a weak base (Kb = 1.8 x 10¯5). A 1.0 M
solution of NH4CN would be
(A) strongly acidic (C) neutral
(B) weakly acidic
(D) weakly basic
11. How many moles of HCOONa must be added to 1.0 L of 0.10 M HCOOH to prepare a
buffer solution with a pH of 3.4? (HCOOH Ka = 2 x 10¯4)
(A) 0.01
(C) 0.1
(B) 0.05
(D) 0.2
12. The acid-base indicator methyl red has a Ka of 1 x 10¯4. Its acidic form is red while its
alkaline form is yellow. If methyl red is added to a colorless solution with a pH = 7, the
color will be
(A) pink
(C) orange
(B) red
(D) yellow
13. Which mixture forms a buffer when dissolved in 1.0 L of water?
(A) 0.2 mol NaOH + 0.2 mol HBr
(B) 0.2 mol NaCl + 0.3 mol HCl
(C) 0.4 mol HNO2 + 0.2 mol NaOH
(D) 0.5 mol NH3 + 0.5 mol HCl
14. A buffer solution is prepared in which the concentration of NH3 is 0.30 M and the
concentration of NH4 is 0.20 M. What is the pH of this solution?
The equilibrium
5
constant, Kb for NH3 equals 1.8 x 10¯ .
(A) 8.73
(C) 9.43
(B) 9.08
(D) 11.72
15. For which titration would the use of phenolphthalein introduce a significant error?
Kindicator for phenolphthalein = 1 x 10¯9
16. The titration curves labeled 1 and 2 were obtained by titrating equal volumes of two
different acid samples with portions of the same sodium hydroxide solution.
What conclusions can be drawn about the relative concentrations and strengths of acids 1
and 2 from these curves?
(A) The concentrations are the same but acid 1 is weaker than acid 2.
(B) The concentrations are the same but acid 1 is stronger than acid 2.
(C) Acid 1 is the same strength as acid 2, but it is less concentrated.
(D) Acid 1 is the same strength as acid 2, but it is more concentrated.
17. A 0.100 M solution of acetic acid (Ka = 1.8 x 10¯5) is titrated with a 0.1000 M solution of
NaOH. What is the pH when 50% of the acid has been neutralized?
(A) 2.38
(C) 5.70
(B) 4.74
(D) 7.00
18. The pKa values for several acid-base indicators are given in the table. Which indicator
should be used in the titration of a weak base with a strong acid?
Indicator, pKa
2,4-dintrophenol 3.5
bromthymol blue 7.0
cresol red
alizarin yellow R
(A) 2,4-dintrophenol
(B) bromthymol blue
(C) cresol red
(D) alizarin yellow R
19.
8.0
11.0
Ml
Answer the questions based on the above graph
_____ A. Point at which the [conjugate base]=[weak acid]
_____ B. The half equivalence point
_____ C. If point at which moles of H+ = moles OH_____ D. point at which pH is determined by salt concentration
_____ E point at which pH is determined by concentration of excess OH- added
19. If 25 mL of 0.20 M NaOH is added to 50. mL of 0.10 M acetic acid (Ka = 1.80 x 10-5), what is the pH?
14. Calculate the pH of dissolving 10.5 g of NaF in 500 mL of water. (Ka of HF = 7.00 x 10-4)
15. Stomach acid is approximately 0.0200 M HCl. What volume of this acid is neutralized by an antacid
tablet that has a mass of 330. mg and contains 41.0 % by mass Mg(OH)2?
16. Calculate the [H+] of a solution prepared by diluting 100.0 mL of a 0.200 M Ba(OH)2 solution with
enough
water to make 500.0 mL of solution.
17. Determine the percent dissociation of a 2.25 M weak base solution with a pH of 11.8.
18. A sample of 20.0 mL of 0.100 M HCN (Ka = 6.2 x 10-10) is titrated with 0.150 M NaOH.
a) What volume of NaOH is used in this titration to reach the equivalence point?
b) What is the molar concentration of CN- at the equivalence point?
c) What is the pH of the solution at the equivalence point?
d) What is pH of this solution when only 6.667 mL of the 0.150 M NaOH.is added to 20.0 mL of
the 0.100 M HCN