ICE Week 7

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					CHAPTER 17
1. What is meant by the term “buffer capacity”?



2. Which would form a buffer?
(a) HCl and CH3COOH

(b) NaH2PO4 and Na2HPO4

(c) H2CO3 and NaHCO3




3. Which would form a buffer?
(a) NaOH and NaCl

(b) NaOH and NH3

(c) Na3PO4 and Na2HPO4




8. A strong acid is titrated with a strong base, such as KOH.
Describe the changes in the composition of the solution as the
titration proceeds: prior to the equivalence point, at the
equivalence point, and beyond the equivalence point.
9. Repeat the description for Question 8, but use a weak acid
rather than a strong one.




Henderson Hasselbach
Consider the ionization of a weak acid HA which has some pKa.
It is often convenient to be able to relate the pH of a solution
of a weak acid to the pKa of the acid and the extent of
ionization. The reaction would be
                        HA  H+ + A-
The acid dissociation constant (Ka) for this reaction would be
given by the equation



This equation can be rearranged to isolate the hydrogen ion
concentration on the left, because, remember, we want an
equation relating the pH of the solution to the pKa and the
extent of ionization of the weak acid. The rearranged form of
the equation is




By definition, log 1/ [H+] = pH, and log 1/Ka = pKa, so that by
taking the log of the equation above, we get the equation
This is the well-known Henderson-Hasselbalch equation that is
often used to perform the calculations required in preparation
of buffers for use in the laboratory, or other applications.



17. Without doing calculations, determine the pH of a buffer
made from equimolar amounts of these acid-base pairs.
(a) Nitrous acid and sodium nitrite




(b) Ammonia and ammonium chloride




(c) Formic acid and potassium formate




20. Select from Table 17.1 a conjugate acid-base pair that
would be suitable for preparing a buffer solution with pH
equal to
(a) 3.45

(b) 5.48

(c) 8.32
(d) 10.15
21. To buffer a solution at a pH of 4.57, what mass of sodium
acetate should you add to 500 mL of a 0.150 M solution of
acetic acid?




22. How many grams of ammonium chloride would have to be
added to 500 mL of 0.10 M solution to have a pH of 9.00?




23. A buffer solution can be made from benzoic acid and
sodium benzoate How many grams of the acid would you have
to mix with 14.4 g of the sodium salt to have a liter of a
solution with a pH of 3.88?
28. If added to 1 L of 0.20 M NaOH, which of these would
form a buffer?
(a) 0.10 mol acetic acid
(b) 0.30 mol acetic acid
(c) 0.20 mol HCl
Explain your answers.




38. It required 22.6 mL of 0.0140 M solution to titrate a
25.0-mL sample of HCl to the equivalence point. Calculate the
molarity of the HCl solution.




39. It took 12.4 mL of 0.205 M solution to titrate 20.0 mL of
a sodium hydroxide solution to the equivalence point. Calculate
the molarity of the original NaOH solution.
30. Calculate the pH change when 1.0 mL of 1.0 M NaOH is
added to 0.100 L of a solution of
(a) 0.10 M acetic acid and 0.10 M sodium acetate.



(b) 0.010 M acetic acid and 0.010 M sodium acetate.




(c) 0.0010 M acetic acid and 0.0010 M sodium acetate.
45. The titration of 50.00 mL of 0.150 NaOH with 0.150 M
HCl is carried out in a chemistry laboratory. Calculate the pH
of the solution after these volumes of the titrant have been
added:
(a) 0.00 mL




(b) 25.00 mL




(c) 49.9 mL




(d) 50.00 mL




(e) 50.1 mL




(f) 75.00 mL
Use the results of your calculations to plot a titration curve
for this titration. On the curve indicate the position of the
equivalence point.
46. The titration of 50.00 mL of 0.150 HCl with 0.150 M
NaOH is carried out in a chemistry laboratory. Calculate the
pH of the solution after these volumes of the titrant have
been added:
(a) 0.00 mL




(b) 25.00 mL




(c) 49.9 mL




(d) 50.00 mL




(e) 50.1 mL
(f) 75.00 mL

				
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