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AP Chemistry by Satellite Lectureguide
Student Edition
Acid - Base Equilibria
Chapter 15

Objectives

Following your study of this chapter, you should be able to

  1. define the terms Arrhenius acid and Arrhenius base.
  2. write the autoionization reaction for water and the equilibrium expression for the autoionization reaction.
  3. define pH and pOH and be able to calculate the pH or pOH of an aqueous solution of an acid or a base.
  4. write ionization equations for Arrhenius acids and bases.
  5. define the terms Bronsted-Lowry acid and Bronsted-Lowry base.
  6. describe the difference between a strong acid and a weak acid.
  7. describe the difference between a strong base and a weak base.
  8. calculate the pH of a solution of a strong acid or a strong base.
  9. estimate the magnitude of the equilibrium constant for a strong acid or strong base given the initial concentration of the strong acid or base and the pH of the solution.
  10. calculate the magnitude of the equilibrium constant for a weak acid or weak base given the initial concentration of the weak acid or base and the pH of the solution.
  11. calculate the pH of a solution of a weak acid or weak base given the initial concentration of the acid or base and the equilibrium constant.
  12. calculate the pH of a solution containing a polyprotic acid.
  13. define the term salt and determine what salt is formed in a neutralization reaction between a strong acid and a strong base, a strong acid and a weak base and a weak acid and a strong base.
  14. write the hydrolysis reaction which occurs when a salt of a weak acid and a strong base is added to water and determine the magnitude of the equilibrium constant for the reaction.
  15. write the hydrolysis reaction which occurs when a salt of a strong acid and a weak base is added to water and determine the magnitude of the equilibrium constant for the reaction.
  16. calculate the pH of a salt solution given the initial concentration of the salt.
  17. explain how the strength of an acid is related to its molecular structure in the hydrogen halides and the oxyacids.


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1. Define the terms Arrhenius acid and Arrhenius base.


In the space below, list some examples of Arrhenius acids and Arrhenius bases.

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2a. Write the autoionization reaction for water and the equilibrium expression for the autoionization reaction.


b. What is the magnitude of the equilibrium constant at 25 ºC for the autoionization reaction of water?


c. What are the concentrations of H+ and OH- at 25 ºC in pure water?


IMAGE SCSIMG/SCH1505.gif


d. The [H+] in a particular aqueous solution is 1.0 x 10-4 M. Calculate the [OH-] for this solution.


Ans: [OH-] = 1.0 x 10-10 M


e. The [OH-] in a particular aqueous solution is 1.0 x 10-5 M. Calculate the [H+] for this solution.


Ans: [H+] = 1.0 x 10-9 M

f. The [H+] in a particular aqueous solution is 6.0 M. Calculate the [OH-] for this solution.


Ans: [OH-] = 1.7 x 10-15 M


3a. Define pH and pOH for aqueous solutions of acids or bases.


b. Indicate the range of pH which characterizes an acidic solution and the range which characterizes a basic solution.


IMAGE SCSIMG/SCH1506.gif


c. Calculate the pH and pOH of a solution with a [H+] = 3.68 x 10-8 M.


Ans: pOH = 6.57


d. Calculate the [H+] and [OH-] of a solution with a pH = 4.22.


Ans: [H+] = 6.03 x 10-5 M

4a. Based on the lecture demonstration complete the following table.

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b. Write the ionization equations which support the experimental observations listed above.


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5a. Define the terms Bronsted-Lowry acid and Bronsted-Lowry base.


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c. Identify the conjugate bases for each of the following acids.
i) NH4+


ii) H3PO4


iii) H2O


d. Identify the conjugate acid for each of the following bases.
i) Br-


ii) HSO4-


iii) H2O


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6a. In 5b above which acid is stronger, HCl or H3O+? What experiment could be performed to determine which is stronger?


b. Describe the difference between a strong acid and a weak acid.


c. Give four examples of strong acids and four examples of weak acids.


7a. In Exercise 5b above, which base is stronger, NH3 or OH-? What experiment could be performed to determine which is stronger?


b. Describe the difference between a strong base and a weak base.


c. Give four examples of strong bases and four examples of weak bases.


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8a. Based on the lecture demonstration, complete the following table.


IMAGE SCSIMG/SCH1513.gif


b. How does the measured concentration of the H+ compare to the concentration of HCl?


c. Briefly describe the qualitative relationship between the concentration of a strong acid and its pH.


d. How does the measured concentration of the OH- compare to the concentration of NaOH?


e. Briefly describe the qualitative relationship between the concentration of a strong base and its pH.


f. Calculate the pH of a 0.450 M HCl solution.


Ans: pH = 0.347


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g. Calculate the pH of a 0.710 M KOH solution.


Ans: pH = 13.85

9a. The chemical equation which describes how HCl dissociates in aqueous solution is,

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In the demonstration performed earlier, the initial concentration of HCl is 0.100 M. In the space provided below (ICE Table), enter the initial concentration of HCl, H+ and Cl-. Based on the measured pH of this solution, calculate and enter the equilibrium concentration of H+.


IMAGE SCSIMG/SCH1516.gif


b. Calculate the change in [H+].


c. Using the balanced chemical equation and the calculated change in [H+], calculate the change in HCl and Cl-.


d. Calculate the equilibrium concentration of HCl and Cl-.


e. Estimate the equilibrium constant for the dissociation of HCl(aq).


IMAGE SCSIMG/SCH1517.gif


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10a. The chemical equation which describes how HC2H3O2 dissociates in aqueous solution is,

IMAGE SCSIMG/SCH1519.gif


In the demonstration performed earlier, the initial concentration of HC2H3O2 is 0.100 M. In the space provided below (ICE Table), enter the initial concentration of HC2H3O2, H+ and C2H3O2-. Based on the measured pH of this solution, calculate and enter the equilibrium concentration of H+.


IMAGE SCSIMG/SCH1520.gif

b. Calculate the change in [H+].


c. Using the balanced chemical equation and the calculated change in [H+], calculate the change in HC2H3O2 and C2H3O2-.


d. Calculate the equilibrium concentration of HC2H3O2 and C2H3O2-.


e. Estimate the equilibrium constant for the dissociation of HC2H3O2(aq).


IMAGE SCSIMG/SCH1521.gif


f. Calculate the magnitude of the equilibrium constant for benzoic acid, HC7H5O2, if a 0.100 M solution has a pH = 2.59.


Ans: Ka = 6.8 x 10-5


g. Write a general chemical equation which describes how a weak base, BOH(aq), dissociates in aqueous solution and setup the ICE table.


h. Calculate the magnitude of the equilibrium constant for an aqueous solution of ammonia, if a 0.100 M solution has a pH = 11.13.


Ans: Kb = 1.8 x 10-5


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11a. Calculate the pH of a solution which is 0.53 M HC6H4NO2 (nicotinic acid). Ka = 1.4 x 10-5


Ans: pH = 2.6


b. Calculate the pH of a solution which is 0.712 M CH3NH2 (methylamine). Kb = 4.4 x 10-4


Ans: pH = 12.25


IMAGE SCSIMG/SCH1523.gif


Problem Set #26
AP Chemistry by Satellite Name___________________________________


ALL work must be shown in all problems for full credit.

PS26.1. For aqueous solutions of the following substances, write the dissociation reaction and indicate whether the substance behaves as an Arrhenius acid or base.

a) HF(aq)

b) HC6H5O(aq)

c) Ba(OH)2(aq)

d) LiOH(aq)

e) H2O(aq)

f) H2CO3(aq)

PS26.2. Calculate the pH and pOH in each of the following aqueous solutions. In each case, indicate whether the solution is acidic or basic.

IMAGE SCSIMG/SCH1524.gif


PS26.3. Calculate the [H+] and [OH-] in each of the following aqueous solutions.


a) pH = 7.41


b) pH = 11.0


c) pOH = 0.230


d) pOH = 7.00


e) pH = 14.9


f) pH = -0.543


IMAGE SCSIMG/SCH1525.gif


PS26.4. For each of the following acids, write the formula for the conjugate base.

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PS26.5. For each of the following bases, write the formula for the conjugate acid.


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PS26.6. For the following compounds, write the reaction with water and indicate the Bro/nsted acids, bases, the conjugate acid and conjugate base.


a) HCl(g)
b) NH3(g)
c) HCN(g)
d) HC6H5O(s)
e) CH3CH2NH2(l)


PS26.7. Determine the equilibrium constant for the following solutions. (Show your work clearly!)


a) 0.100 M HC2H3O2 whose pH = 2.87.


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PS26.7. (Continued)

b) 0.812 M NH3 whose pH = 11.58.


c) 0.500 M B whose pH = 10.67.


d) 0.0751 M HA whose pH = 4.00.


IMAGE SCSIMG/SCH1529.gif


PS26.8. Given the following substances and their initial concentration:


Answer the following,

i) identify each as an acid, base or neutral substance.

ii) list the Ka value for each acid and Kb value for each base.

iii) identify each substance as strong or weak.

iv) calculate the [H+] and the pH of each of the solutions.

v) rank all substances from strongest acid...weakest acid...neutrals..

...weakest base...strongest base.


a) 0.100 M HNO3


b) 55.5 M H2O


c) 0.100 M NaOH


d) 0.100 M C2H5NH2


e) 0.100 M HF


f) 0.100 M HNO2


g) 0.100 M CH3NH2


h) 0.100 M C5H5N


i) 0.100 M HC6H5O


j) 0.100 M Ba(OH)2


k) 0.00491 M HF


l) 0.100 M HOCl


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PS26.8. (Continued)


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12. Write the dissociation equations which describe the behavior of a polyprotic acid with the general formula, H2A.


a. Carbonic acid, H2CO3, is a diprotic acid.


i) Write the two dissociation reactions showing the diprotic behavior.


ii) If the initial concentration of H2CO3 is 0.100 M, calculate [H+]. In your calculation, assume only the first dissociation occurs. (Note: The equilibrium constant for the first dissociation, Ka1, is 4.3 x 10-7.)


Ans: [H+] = 2.07 x 10-4 M


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iii) Now consider the second dissociation equation for which Ka2 = 5.6 x 10-11. What is the initial concentration of [HCO3-]? What is the initial concentration of [H+]? Calculate the final [H+] assuming the second dissociation occurs.


Ans: [H+ ]total = 2.07 x 10-4 M


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13a. Define the term salt.


b. Based on the lecture demonstration, complete the following table.

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c. Predict the product of the neutralization reactions,

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d. In general, what is the acid-base property of any salt formed in the reaction between a strong acid and a strong base?


e. In general, what is the acid-base property of any salt formed in the reaction between a strong acid and a weak base?


f. In general, what is the acid-base property of any salt formed in the reaction between a weak acid and a strong base?


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14a. Write the dissociation equation which describes what happens when NaC2H3O2(s) is added to water.


b. Write the equation which describes the acidic character of Na+(aq). Write the equilibrium expression and estimate Ka for Na+(aq).


c. Write the equation which describes the basic character of C2H3O2-(aq). Write the equilibrium expression and calculate the Kb for C2H3O2-(aq).


d. Which of the two ions, Na+(aq) or C2H3O2-(aq), affects the pH of the solution? Explain why.


e. Predict the products when KCN(s) is added to water. Will the pH of the solution formed when the salt is added to water be greater or less than 7?


IMAGE SCSIMG/SCH1539.gif


15a. Write the dissociation equation which describes what happens when NH4Cl(s) is added to water.


b. Write the equation which describes the acidic character of NH4+(aq). Write the equilibrium expression and calculate Ka for NH4+(aq).


c. Write the equation which describes the basic character of Cl-(aq). Write the equilibrium expression and estimate Kb for Cl-(aq).


d. Which of the two ions, NH4+(aq) or Cl-(aq), affects the pH of the solution? Explain why.


e. Predict the products when CH3NH3NO3(s) is added to water. Will the pH of the solution formed when the salt is added to water be greater or less than 7?


IMAGE SCSIMG/SCH1540.gif


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16a. Write a general chemical equation which describes how the salt of a weak acid and strong base behaves in aqueous solution.


b. Calculate the pH of a 0.700 M NaC2H3O2. Ka(HC2H3O2) = 1.8 x 10-5


Ans: pH = 9.29


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16c. Write a general chemical equation which describes how the salt of a weak base and strong acid behaves in aqueous solution.


b. Calculate the pH of a 0.392 M CH3NH3NO3. Kb(CH3NH2) = 4.4 x 10-4


Ans: pH = 5.52d


IMAGE SCSIMG/SCH1543.gif


17a. Explain the general trend in acid strength observed in hydrides of Group IVA through VIIA.


b. Explain the trend in acid strength observed in the oxyacids of Groups IVA through VIIA.


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Problem Set #27
AP Chemistry by Satellite Name___________________________________


ALL work must be shown in all problems for full credit..


PS27.1. Ascorbic acid, H2C6H6O6, is a diprotic acid.
a) The equilibrium constant for the first dissociation is Ka1 = 8.0 x 10-5. Assuming the initial concentration of H2C6H6O6 is 0.100 M, calculate [H+] assuming only the first dissociation occurs.


b) Now consider the second dissociation equation for which Ka2 = 1.6 x 10-12. What is the initial concentration of [HC6H6O6-]? What is the initial concentration of [H+]? Calculate the final [H+] assuming the second dissociation occurs.


PS27.2. Calculate the pH of a 0.100 M H2S. Calculate the [S2-] in the solution.


IMAGE SCSIMG/SCH1545.gif


PS27.3. Predict the products of the following neutralization reactions.


a) HCl(aq) + NaOH(aq)
b) HNO3(aq) + Ba(OH)2(aq)
c) NaOH(aq) + H2CO3(aq)
d) NH3(aq) + H2SO4(aq)
e) HC6H5O(aq) + NaOH(aq)
f) HCN(aq) + KOH(aq)

PS27.4. Given a solution containing the following ions (neglect the counter-ion for the moment), write a reaction (with water) and indicate whether the ion acts as an acid or as a base.


a) F-(aq)
b) ClO2-(aq)
c) NO2-(aq)
d) NH4+(aq)
e) CH3NH3+(aq)
f) C2H5NH3+(aq)

PS27.5. Can you make any generalizations about the acid-base character of the ions in Problem #27.4? If so, state them.


PS27.6. Indicate an acid and a base which could react, in a neutralization reaction, to form each of the following salts. In some cases water will be present as another product.


a) KC2H3O2(aq)
b) KClO(aq)
c) C2H5NH3NO3(aq)
d) NH4Cl(aq)
e) KCl(aq)
f) (NH4)2SO4(aq)

PS27.7. If each salt in Problem 27.6 is added to water, indicate whether the resulting solution is acidic, basic or neutral.


IMAGE SCSIMG/SCH1546.gif


PS27.8. Calculate the pH of the following salt solutions

a) 0.355 M KClO


b) 0.777 M NH4Cl


c) 0.0345 M KCl


d) 0.411 M KC2H3O2


IMAGE SCSIMG/SCH1547.gif


PS27.8. (Continued)


e) 1.00 M NaHSO4


PS27.9. In the series of oxyacids, XOH, OXOH, and O2XOH, list the acids in order of increasing acid strength. Justify your answer.


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