CHEM 110 Lecture Notes - Lecture 1: Nan, Litre, Conjugate AcidExam


Department
Chemistry
Course Code
CHEM 110
Professor
Xu
Study Guide
Final

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AP Questions: Acids and Bases
1970
(a) What is the pH of a 2.0 molar solution of acetic acid. Ka acetic acid = 1.8x10-5
(b) A buffer solution is prepared by adding 0.10 liter of 2.0 molar acetic acid solution to 0.1 liter of a 1.0 molar sodium hydroxide
solution. Compute the hydrogen ion concentration of the buffer solution.
(c) Suppose that 0.10 liter of 0.50 molar hydrochloric acid is added to 0.040 liter of the buffer prepared in (b). Compute the hydro-
gen ion concentration of the resulting solution.
1972
Given a solution of ammonium chloride, what additional reagent or reagents are needed to prepare a buffer from the ammonium chlo-
ride solution?
Explain how this buffer solution resists a change in pH when:
(a) Moderate amounts of strong acid are added.
(b) Moderate amounts of strong base are added.
(c) A portion of the buffer solution is diluted with an equal volume of water.
1973
A sample of 40.0 milliliters of a 0.100 molar HC2H3O2 solution is titrated with a 0.150 molar NaOH solution. Ka for acetic acid =
1.8x10-5
(a) What volume of NaOH is used in the titration in order to reach the equivalence point?
(b) What is the molar concentration of C2H3O2
- at the equivalence point?
(c) What is the pH of the solution at the equivalence point?
1974 A
A solution is prepared from 0.0250 mole of HCl, 0.10 mole propionic acid, C2H5COOH, and enough water to make 0.365 liter of solu-
tion. Determine the concentrations of H3O+, C2H5COOH, C2H5COO-, and OH- in this solution. Ka for propionic acid = 1.3x10-5
1975 A
(a) A 4.00 gram sample of NaOH(s) is dissolved in enough water to make 0.50 liter of solution. Calculate the pH of the solution.
(b) Suppose that 4.00 grams of NaOH(s) is dissolved in 1.00 liter of a solution that is 0.50 molar in NH3 and 0.50 molar in NH4
+. As-
suming that there is no change in volume and no loss of NH3 to the atmosphere, calculate the concentration of hydroxide ion, af-
ter a chemical reaction has occurred. [Ionization constant at 25ºC for the reaction NH3 + H2O -->NH4
+ + OH-; K = 1.8x10-5]
1977
The value of the ionization constant, Ka, for hypochlorous acid, HOCl, is 3.110-8.
(a) Calculate the hydronium ion concentration of a 0.050 molar solution of HOCl.
(b) Calculate the concentration of hydronium ion in a solution prepared by mixing equal volumes of 0.050 molar HOCl and 0.020
molar sodium hypochlorite, NaOCl.
(c) A solution is prepared by the disproportionation reaction below. Cl2 + H2O --> HCl + HOCl
Calculate the pH of the solution if enough chlorine is added to water to make the concentration of HOCl equal to 0.0040 molar.
1978 D
Predict whether solutions of each of the following salts are acidic, basic, or neutral. Explain your prediction in each case
(a) Al(NO3)3 (b) K2CO3 (c) NaBr
1979 B
A solution of hydrochloric acid has a density of 1.15 grams per milliliter and is 30.0% by weight HCl.
(a) What is the molarity of this solution of HCl?
(b) What volume of this solution should be taken in order to prepare 5.0 liters of 0.20 molar hydrochloric acid by dilution with wa-
ter?

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1979 D
NH4
+ + OH- <=>NH3 + H2O
H2O + C2H5O- <=> C2H5OH + OH-
The equations for two acid-base reactions are given above. Each of these reactions proceeds essentially to completion to the right when
carried out in aqueous solution.
(a) Give the Bronsted-Lowry definition of an acid and a base.
(b) List each acid and its conjugate base for each of the reactions above.
(c) Which is the stronger base, ammonia or the ethoxide ion. C2H5O-? Explain your answer.
1980 A
Methylamine CH3NH2, is a weak base that ionizes in solution as shown by the following equation.
CH3NH2 + H2O <=> CH3NH3
+ + OH-
(a) At 25ºC the percentage ionization in a 0.160 molar solution of CH3NH2 is 4.7%. Calculate [OH-], [CH3NH3
+], [CH3NH2],
[H3O+], and the pH of a 0.160 molar solution of CH3NH2 at 25ºC
(b) Calculate the value for Kb, the ionization constant for CH3NH2, at 25ºC.
(c) If 0.050 mole of crystalline lanthanum nitrate is added to 1.00 liter of a solution containing 0.20 mole of CH3NH2 and 0.20 mole
of its salt CH3NH3Cl at 25ºC, and the solution is stirred until equilibrium is attained, will any La(OH)3 precipitate? Show the cal-
culations that prove your answer. (The solubility constant for La(OH)3, Ksp = 1x10-19 at 25ºC)
1981 D
Al(NO3)3 K2CO3 NaHSO4 NH4Cl
(a) Predict whether a 0.10 molar solution of each of the salts above is acidic, neutral or basic.
(b) For each of the solutions that is not neutral, write a balanced chemical equation for a reaction occurring with water that supports
your prediction.
1982 A
A buffer solution contains 0.40 mole of formic acid, HCOOH, and 0.60 mole of sodium formate, HCOONa, in 1.00 litre of solution.
The ionization constant, Ka, of formic acid is 1.8x10-4.
(a) Calculate the pH of this solution.
(b) If 100. millilitres of this buffer solution is diluted to a volume of 1.00 litre with pure water, the pH does not change. Discuss why
the pH remains constant on dilution.
(c) A 5.00 millilitre sample of 1.00 molar HCl is added to 100. millilitres of the original buffer solution. Calculate the [H3O+] of the
resulting solution.
(d) A 800.-milliliter sample of 2.00-molar formic acid is mixed with 200. milliliters of 4.80-molar NaOH. Calculate the [H3O+] of the
resulting solution.
1983 C
(a) Specify the properties of a buffer solution. Describe the components and the composition of effective buffer solutions.
(b) An employer is interviewing four applicants for a job as a laboratory technician and asks each how to prepare a buffer solution
with a pH close to 9.
Archie A. says he would mix acetic acid and sodium acetate solutions.
Beula B. says she would mix NH4Cl and HCl solutions.
Carla C. says she would mix NH4Cl and NH3 solutions.
Dexter D. says he would mix NH3 and NaOH solutions.
Which of these applicants has given an appropriate procedure? Explain your answer, referring to your discussion in part (a). Ex-
plain what is wrong with the erroneous procedures.
(No calculations are necessary, but the following Ka’s may be helpful: acetic acid, Ka= 1.8x10-5; NH4
+, Ka = 5.6x10-10)
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