CH186
Acid-Base Exam Questions
From Spring 2001 Semester
Useful constants: Kw = 1.0 x 10-14; pKw = 14.00
1.Short Answer
a.Is an aqueous solution of the salt (C5H5NH)Br acidic, basic, or neutral?
b.Is an aqueous solution of the salt CsNO3 acidic, basic, or neutral?
c.Consider the following weak acids and Ka values: HA (Ka = 10-6), HB (Ka = 10-2), HC (Ka = 10-4), HD (Ka = 10-8). Which of these acids is the strongest acid?
d.Which of the acids in c above has the strongest conjugate base?
e.For the following reaction, which species serves as the Lewis base:
SO3 + OH- HSO4-
f.For the following reaction, label each chemical species as a Bronsted-Lowry acid (A) or base (B), and clearly indicate the conjugate acid-base pairs.
H2PO4- + OH- H2O + HPO42-
g.Consider the following weak base ionization: B + H2O HB+ + OH-. Will addition of a salt containing the HB+ ion increase, decrease, or have no effect on the pH of a solution of weak base B?
h.Give the formula for the conjugate base of HSO3-.
2.Indicate whether each of the following solutions is acidic, basic, or neutral at 25C.
a.pH = 2.5d.[OH-] = 0.0035 M
b.[H3O+] > [OH-]e.pOH = 7.0
c.[H3O+] = 1.0 x 10-7 Mf.pH = 10.0
3.A biologist regularly uses a buffer solution that contains Na2HPO4 and NaH2PO4 in his lab. Write a balanced chemical equation showing the reaction that takes place when (a) sodium hydroxide, NaOH, is added to the buffer, and (b) hydrobromic acid, HBr, is added to the buffer. (You may omit spectator ions.)
4Calculate the pH for each of the following solutions at 25C.
a.[H3O+] = 1.3 x 10-10 M
b.0.0024 M nitric acid, HNO3(aq)
c.0.0018 M strontium hydroxide, Sr(OH)2(aq)
d.0.095 g of potassium hydroxide, KOH (FW = 56 g/mol), in 0.300 L of solution
5.A pharmaceutical chemist synthesized a new drug molecule, HB, that is weakly acidic in water. In fully characterizing the properties of this drug, the Ka value was determined. If a 0.045 M solution of HB was observed to have a pH of 4.42, calculate the Ka for this molecule.
6.Hypobromous acid, HBrO, is a weak acid with a Ka of 2.5 x 10-9. Calculate the pH of a 0.35 M solution of sodium hypobromite, NaBrO.
7.Calculate the pH of the solution formed by adding 0.900 g sodium hypochlorite, NaClO (FW = 75 g/mol) to 0.500 L of 0.043 M hypochlorous acid, HClO (Ka = 3.0 x 10-8).
8.Calculate the pH of the solution that is formed by mixing 0.100 L of 0.50 M perchloric acid, HClO4, and 0.200 L of 0.23 M potassium hydroxide, KOH.
9.Is it ever possible for a solution of a weak acid to have a lower pH than a solution of a strong acid? Explain!
Answers for Spring 2001 Acid-Base Exam Questions
1.a. acidic
b. neutral
c. HB
d. HD
e. OH-
f. acid/base
H2PO4-/HPO42-
H2O/OH-
g. decrease
h. SO32-
2.a. acidic
b. acidic
c. neutral
d. basic
e. neutral
f. basic
3.a. NaH2PO4 + NaOH Na2HPO4 + H2O
b. Na2HPO4 + HBr NaH2PO4 + NaBr
4.a. pH = 9.89
b. pH = 2.62
c. pH = 11.56
d. pH = 11.75
5.Ka = 3.2 x 10-8
6.pH = 11.07
7.pH = 7.27
8.pH = 1.88
9.Yes, if the weak acid solution is much more concentrated than the strong acid solution.
CH186
Acid-Base Exam Questions
From Fall 1999 Semester
Useful constants: Kw = 1.0 x 10-14; pKw = 14.00
1.Indicate whether each of the following solutions is acidic, basic, or neutral at 25C.
a.pOH = 7.0b. pH = 8.9
c. [OH-] = 2.4 x 10-9 M d. [H3O+] = 1.0 x 10-4 M
2.Indicate whether each of the following salts is acidic, basic, or neutral.
a.NaClO4c.FeBr3
b.KNO2
3.Using the Bronsted-Lowry concept, write the chemical equation for the reaction between methylamine, CH3NH2, and hydrofluoric acid, HF. Indicate the conjugate acid-base pairs in the reaction, and be sure to specifically identify the acid and conjugate base for each pair.
4.For each of the following reactions, identify the Lewis acid and Lewis base.
a.2S2O32- + Ag+ Ag(S2O3)23-
b.NaHCO3 + NaOH H2O + Na2CO3
c.BCl3 + Cl- BCl4-
5.Arrange the following solutions in order of decreasing pH, i.e., from most basic to least basic. Assume that all solute concentrations are equivalent.
SolutionSolute(s)
1(CH3)2NH (Kb 10-3)
2(CH3)2NH (Kb 10-3) and [(CH3)2NH2]Cl
3HOBr (Ka10-9)
4Ba(OH)2
5NaI
6HClO4
______> ______> ______> ______> ______> ______
highest pH lowest pH
6.Calculate the pH and pOH for each of the following aqueous solutions.
a.0.0082 M Ba(OH)2(aq)
b.a solution with [OH-] = 0.45 M
c.0.075 M HNO3
d.a 0.066 M solution of the weak base morphine, C17H19O3N (Kb = 7.4 x 10-7), an addictive compound obtained in a species of poppy and used as an analgesic
e.a solution containing 0.0099 g of KOH (FW = 56 g/mol) dissolved into enough water to give 0.150 L of solution
7.Calculate the [H3O+] and [OH-] for a solution that has a pOH of 6.40.
8.In the titration of 50.00 mL of 0.125 M NaOH with 0.200 M HCl, calculate (a) the pH at the point in the titration at which 31.25 mL of HCl has been added and (b) the pH at the point in the titration at which 20.00 mL of HCl has been added.
9.Short Answer
a.What is a buffer solution and what are the necessary components of a buffer solution?
b.Is it ever possible for a solution of a weak acid, such as acetic acid, to have a lower pH than a solution of a strong acid, such as hydrochloric acid? (Think about this before answering.) Explain!
Answers for Fall 1999 Acid-Base Exam Questions
1.a. neutral
b. basic
c. acidic
d. acidic
2.a. neutral
b. basic
c. acidic
3.CH3NH2 + HF CH3NH3+ + F-, conjugate pairs (acid/base) = HF/F-, CH3NH3+/CH3NH2
4.a. 2S2O32- + Ag+ Ag(S2O3)23-
base acid
b. NaHCO3 + NaOH H2O + Na2CO3
acid base
c. BCl3 + Cl- BCl4-
acid base
5.Ba(OH)2 > (CH3)2NH > (CH3)2NH + (CH3)2NHCl > NaI > HOBr > HClO4
highest pHlowest pH
6.a. pH = 12.21, pOH = 1.79
b. pH = 13.65, pOH = 0.35
c. pH = 1.12, pOH = 12.8
d. pH = 10.34, pOH = 3.66
e. pH = 11.07, pOH = 2.93
7.[H3O+] = 2.5 x 10-8 M, [OH-] = 4.0 x 10-7 M
8.a. pH = 7
b. pH = 12.51
9.a. A buffer is a solution that has the ability to resists changes in pH. Necessary components are a weak acid and its salt, or a weak base and its salt.
b. Yes. The pH and [H3O+] is not only dependent on acid strength, but also on concentration. As an example, a strong acid solution with an analytical concentration of 10-6 M will have a lower [H3O+] and a higher pH than a weak acid (Ka = 10-5) with an analytical concentration of 10-1 M.
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