HOMEWORK 2A
1. From the data given in Handout 3 on the class website, determine the pKa of the following acids.
(a) Hydrocyanic acid
(b) Hypochlorous acid (c) Formic acid
2. Determine if solutions of each of the following pairs of solutes constitutes a buffer
(a) Hydrocyanic acid and sodium cyanide
(b) Nitric acid and potassium nitrate.
(c) Ammonia and ammonium chloride.
3. Determine the pH of a solution that is 0.75 M in hypochlorous acid and 0.35 M in sodium
hypochlorite.
4. Determine the pH of a solution prepared by mixing 70.0 mL of a 0.10 M formic acid solution and 30.0
mL of a 0.10 M sodium formate solution.
5. From the data given in Handout 3 on the class website, determine the best weak acid – conjugate base
pair to prepare the following buffers.
(a) A buffer of pH = 3.50
(b) A buffer of pH = 5.00
(c) A buffer of pH = 10.25
6. Calculate the molar ratio of acid to conjugate base in a solution that has a pH of 9.00 and contains the
weak acid hydrocyanic acid and a salt of its conjugate base, sodium cyanide.
HOMEWORK 2B
1. A solution is prepared by mixing 60.0 mL of a 0.10 M acetic acid solution and 40.0 mL of a 0.10 M
sodium acetate solution. Will this be a buffer solution? Calculate the pH. Is this solution acidic or
basic?
2. A solution is prepared by mixing 60.0 mL of a 0.10 M acetic acid solution and 40.0 mL of a 0.10 M
sodium hydroxide solution. Will this be a buffer solution? Calculate the pH. Is this solution acidic or
basic?
3. A solution is prepared by mixing 75.0 mL of a 0.40 M ammonia solution and 25.0 mL of a 0.60 M
ammonium chloride solution. Will this be a buffer solution? Calculate the pH. Is this solution acidic or
basic?
4. A solution is prepared by mixing 75.0 mL of a 0.40 M ammonia solution and 25.0 mL of a 0.60 M
hydrochloric acid solution. Will this be a buffer solution? Calculate the pH. Is this solution acidic or
basic?
5. A solution is prepared by mixing 10.0 mL of a 0.25 M hydrochloric acid solution and 40.0 mL of a
0.20 M potassium chloride solution. Will this be a buffer solution? Calculate the pH. What will be the
concentration of the chloride ions in the solution?
6. A solution is 0.10 M in formic acid and 0.010 M in sodium formate.
(a) Calculate the pH of the solution. Is this solution acidic or basic?
(b) Calculate the final pH if 0.10 gram of sodium hydroxide is added to 1.00 liter of the buffer
solution, assuming the volume does not change.
(c) Calculate the final pH if 1.0 gram of sodium hydroxide is added to 1.00 liter of the buffer solution
instead of 0.10 gram, still assuming the volume does not change.
7. A buffer is prepared by mixing 20.0 mL of a 0.60 M ammonia solution with 10.0 mL of a 1.8 M
ammonium chloride solution.
(a) Calculate the pH of the solution. Is the solution acidic or basic?
(b) Calculate the final pH if 1.0 mL of a 1.0 M hydrochloric acid solution is added to the buffer
solution.
(c) Calculate the final pH if 1.0 mL of a 1.0 M sodium hydroxide solution is added to the buffer
solution instread of the hydrochloric acid solution.
HOMEWORK 2C
1. Novocain (Nvc) is a weak organic base that reacts with water as follows:
Nvc + H2O ⇆ NvcH+ + OHThe base dissociation constant for this reaction, Kb = 9.0 x 10-6. When titrated with nitric acid,
Novocain reacts as follows:
Nvc + HNO3 → NvcH+ + NO3(a) 30.0 mL of a 0.200 M solution of Novocain are titrated with 0.250 M nitric acid. Calculate the
volume of the nitric acid solution required to neutralize the Novocain.
(b) Calculate the pH of the Novocain solution at the beginning of the titration.
(c) Calculate the pH of the resulting solution after 6.0 mL of the nitric acid solution has been added.
(d) Calculate the pH of the resulting solution after 12.0 mL of the nitric acid solution has been added.
(e) Calculate the pH of the resulting solution at the equivalence point.
(f) Calculate the pH of the resulting solution after 30.00 mL of the nitric acid solution has been
added.
(g) Sketch the titration curve for the titration of 0.200 M Novocain with 0.250 M nitric acid. Plot
accurately the pH at the beginning of the titration, and after the addition of 6.00 mL, 12.00 mL,
24.00 mL, and 30.0 mL of the 0.250 M nitric aicd.
(h) The indicator bromcresol green has a pKa of 5.0. Is this indicator suitable for the titration?
2. The titration curve for a weak acid being titrated with a strong base is shown. Indicate the following.
(a) The point on the titration curve
when the solution contains only the
weak acid
(b) The point on the titration curve
when the solution contains only the
weak conjugate base
(c) The point on the titration curve
when the solution contains equal
amounts of the weak acid and its
weak conjugate base
(d) The Ka of the weak acid
(e) From Table 15.8 in the textbook,
determine the best indicator to use
for this titration
HOMEWORK 2D
1. The solubility of silver phosphate in water is 0.0067 grams per liter at 20ºC. Calculate the solubility
product, Ksp, for this salt at 20ºC.
2. Using the solubility product constants for strontium carbonate and silver carbonate, determine which
salt is more soluble in water.
3. At 30ºC, the solubility product, Ksp, for magnesium fluoride is 8 x 10-8.
(a) Calculate the solubility of magnesium fluoride, in moles per liter and grams per liter, in pure
water at 30ºC.
(b) Calculate the solubility of magnesium fluoride, in moles per liter and grams per liter, in a solution
that is 0.050 M NaF at 30ºC.
4. Determine if the solubility of nickel (II) hydroxide will (1) increase, (2) decrease, or (3) remain the
same with the addition of each of the following reagents.
(a) Ni(NO3)2 (aq)
(b) NaOH (aq)
(c) HCl (aq)
(d) NaCl (aq)
5. A solution is made 0.10 M in Mg2+, and 0.10 M in NaOH. Will Mg(OH)2 precipitate?
HOMEWORK 2E
1. Calculate the concentration of silver ions needed to precipitate silver hydroxide in a buffer solution of
pH 13.00.
2. A solution is made 0.10 M in Mg2+, and Na2CO3 is added until the CO32- concentration is 0.0010 M.
Calculate the percentage of Mg2+ ions left in the solution at this point.
3. Iodide ions are slowly added to a solution containing 0.150 M lead (II) ions and 0.250 M silver ions.
(a) What cation will be the first to precipitate?
(b) What will be the concentration of the iodide ions when the first cation starts to precipitate?
(c) What will be the concentration of the first cation when the second cation starts to precipitate?
4. In the precipitation of metal sulfides, selective precipitation can be achieved by adjusting the
hydronium ion concentration. Calculate the pH that ZnS begins to precipitate from a water solution
saturated with H2S (0.077 M) and containing 0.08 M Zn2+.
5. Calculate the solubility of FeS at pH 9.00 and at pH 2.00 in a water solution saturated with H2S (0.077
M). Can you see how its behavior might be useful in analytical separations?
HOMEWORK 2F
1. Find the Chart of the Nuclides on the internet at the web site for the National Nuclear Data Center,
and complete the following data for data concerning all known isotopes of magnesium.
Isotope
Stable or Radioactive
Natural Abundance
Half-Life
2. Complete the following nuclear equations and supply symbols of values for X or x.
(a)
X
(b)
14
(c)
X
(d)
75
(e)
235
(f)
59
86Rn
XC
XNe


4
2X
X

XN
19
+
0
XU
+
1
XCo
+
2
XAs
+
+
XF
-1e
0n
1X
222
0
XX
-1β
+
0

X
-
+1β
+
32X
 x 0n +
1

60
XCo
94
36X
+
139
XX
X
XX
+
3. Write equations for each of the following nuclear processes.
(a) beta positive decay by 12051Sb
(b) beta minus decay by 3516S
(c) alpha decay by 22688Ra
(d) electron capture by 74Be
4. What type of decay would you expect from each of the following radioisotopes?
(a)
12
B
(b)
55
Ni
(c)
243
Am
Decay Mode
HOMEWORK 2G
1. Radioactive Na with a half-life of 14.8 hours is injected into an animal in a tracer experiment. How
many days will it take for the radioactivity to fall to 10.0% of its original intensity?
2. If 1.000 g of 99Mo decays by β- emission to 0.125 g in 200. hours, what is the half-life of 99Mo?
3. A sample of a radioisotope shows an activity of 100. disintegrations per minute. After 1.0 hour, the
activity decreases to 77 disintegrations per minute. Determine the half-life of the radioisotope.
4. A sample of wood from an Egyptian mummy case gives 9.6 cpm g-1 of carbon of 14C disintegrations.
How old is the mummy case?
5. In a sample of uranite ore from the Black Hills of South Dakota, the mass of 206Pb is 22.8% the mass
of the 238U present. Estimate a minimum age for the earth from this information.
6. Calculate the binding energy per nucleon for the following nuclear species.
(a)
(b)
37
17Cl (m = 36.96590 u)
208
82Pb (m = 207.9766 u)
HOMEWORK 2R
1. Identify which of the following will result in a buffer solution when equal volumes of the two
solutions are mixed.
(a)
(b)
(c)
(d)
(e)
(f)
(g)
0.10 M KNO3 and 0.10 M HNO3
0.10 M NaNO2 and 0.10 M HNO2
0.20 M NaOH and 0.10 M HNO2
0.10 M NaOH and 0.20 M HNO2
0.10 M HCl and 0.10 M NH3
0.20 M HCl and 0.10 M NH3
0.10 M HCl and 0.20 M NH3
2. Hypobromous acid has a Ka of 2.5 x 10-9.
(a) Calculate the pH of a 0.25 M hypobromous acid solution.
(b) Calculate the percent ionization of hypobrous acid.
(c) Calculate the pH of a solution that is 0.25 M in hypobromous acid and 0.45 M in sodium
hypobromite.
3. At 15°C, hypochlorous acid has a Ka of 2.9 x 10-8.
(a) Calculate the pH of a 0.45 M hypochlorous acid solution.
(b) Calculate the pH of a solution in which 100.0 mL of the 0.50 M hypochlorous acid solution is
mixed with 200.0 mL of a 0.30 M in sodium hypochlorite solution.
(c) Calculate the pH if 0.010 moles of NaOH is added to the buffer solution in (b).
(d) Calculate the pH if 0.010 moles of HCl is added instead to the buffer solution in (b).
(continued on next page)
4. A buffer is prepared by mixing 60. mL of a 0.50 M ammonia solution with 40. mL of a 0.90 M
ammonium chloride solution. The solution is divided into to equal 50. mL portions
(a) Calculate the pH of the buffer solution.
(b) If 5 mL of a 1.0 M hydrochloric acid solution is added to the first 50. mL portion of the buffer,
what will be its final pH?
(c) If 5 mL of a 1.0 M sodium hydroxide solution is added to the second 50. mL portion of the buffer,
what will be its final pH?
5. Determine the volume of 0.50 M hydrofluoric acid that must be mixed with 50.0 mL of 0.30 M
sodium hydroxide to produce a buffer with pH = 4.00.
6. Given the following Ka values:
H2CO3 + H2O ⇆ H3O+ + HCO3HCO3- + H2O ⇆ H3O + + CO32-
Ka1 = 4.3 x 10-7
Ka2 = 5.6 x 10-11
A pH = 10.00 buffer is to be prepared by mixing 100.0-mL of 0.50 M sodium bicarbonate with the
correct volume of 2.0 M sodium hydroxide. Calculate the volume of the sodium hydroxide solution
needed to prepare the buffer.
7. A 20.0 mL sample of 0.10 M hydrocyanic acid solution is to be titrated with a 0.20 M sodium
hydroxide solution.
(a) Calculate the volume of 0.20 M sodium hydroxide to reach the endpoint of the titration.
(b) Calculate the pH of the hydrocyanic acid solution before the titration.
(c) Calculate the pH of the solution after 1.0 mL of the sodium hydroxide solution was added.
(d) Calculate the pH of the solution after 5.0 mL of the sodium hydroxide solution was added.
(e) Calculate the pH of the solution after 10.0 mL of the sodium hydroxide solution was added.
(f) Calculate the pH of the solution after 15.0 mL of the sodium hydroxide solution was added.
(g) Calculate the pH of the solution after 19.0 mL of the sodium hydroxide solution was added.
(h) Calculate the pH of the solution after 20.0 mL of the sodium hydroxide solution was added.
(i) From the list of indicators in Figure 15.8, what would be the best indicator for this titration?
8. Answer the following questions concerning the titration
of acid HY with sodium hydroxide, using the curve to
the right.
(a) Which indicator would be best for the titration:
thymol blue, bromcresol purple, or
thymolphthalein?
(b) What is the Ka of the acid HY?
(c) Where on the titration curve would you find all HY
in the solution?
(d) Where on the titration curve would you find half
HA and half Y- in the solution?
(e) Where on the titration curve would you find all Yin the solution?
(continued on next page)
9. Answer the following questions concerning the titration
of acid H2X with hydroxide, using the curve to the
right.
(a) What is the Ka1 of the acid H2X?
(b) What is the Ka2 of the acid H2X?
(c) Where on the titration curve would you find all
H2X in the solution?
(d) Where on the titration curve would you find half
H2X and half HX- in the solution?
(e) Where on the titration curve would you find all
HX- in the solution?
(f) Where on the titration curve would you find half HX- and half X2- in the solution?
(g) Where on the titration curve would you find all X2- in the solution?
10. Sketch a titration curve for each of the following titrations. For each, identify the pH before the
titration, at the half-neutalization point, and at the equivalence point.
(a) 0.10 M nitric acid being titrated with 0.10 M potassium hydroxide
(b) 0.10 M hydrofluoric acid being titrated with 0.10 M potassium hydroxide..
(c) 0.10 M ammonia being titrated with 0.10 M hydrochloric acid.
11. The solubility of chromium (III) fluoride in water is 0.0075 grams per liter at 20ºC. Calculate the
solubility product, Ksp, for this salt at 20ºC.
12. Using the solubility product constants, determine the more soluble salt in each pair
(a) lead (II) bromide and silver hydroxide
(b) iron (II) carbonate and silver phosphate
13. At 20ºC, the solubility product, Ksp, for lead (II) bromide is 4.6 x 10-6.
(a) Calculate the solubility of lead (II) bromide in moles per liter and grams per liter in pure water at
20ºC.
(b) Calculate the solubility of lead (II) bromide in moles per liter and grams per liter in a solution that
is 0.10 M Pb(NO3)2 at 20ºC.
14. The solubility product, Ksp, for silver sulfate is 1.2 x 10-5. If 20.0 mL of a 0.10 M silver nitrate solution
is added to 30.0 mL of a 0.20 M sodium sulfate solution, does a precipitate of silver sulfate form?
15. Calculate the concentration of silver ions needed to precipitate silver sulfate in a solution that is 0.25
M in sodium sulfate.
16. A solution is made 0.10 M in Pb2+, and NaCl is added until the Cl- concentration is 0.050 M. Calculate
the percentage of Pb+ ions left in the solution at this point.
(continued on next page)
17. Chromate ions are slowly added to a solution containing 0.100 M barium ions and 0.100 M silver
ions.
(a) What cation will be the first to precipitate?
(b) What will be the concentration of the chromate ions when the first cation starts to precipitate?
(c) What will be the concentration of the first cation when the second cation starts to precipitate?
18. Calculate the pH that MnS begins to precipitate from a water solution that is saturated with H2S (0.077
M) and containing 0.10 M Mn2+.
19. Calculate the solubility of MnS (a) at pH 10.00 and (b) at pH 1.00 in a water solution that is saturated
with H2S (0.077 M).
20. The following reaction produces the orange dichromate ion:
Ag2Cr2O7 (s) ⇆ 2Ag+ (aq) + Cr2O72- (aq)
The absorbances of five standard dichromate ion solutions were measured with a spectrometer in a
1.00 cm cuvet at 495 nm, and a plot of the absorbance of each solution against their concentrations is
given below, including the equation for the calibration line.
To determine the solubility product constant
for silver dichromate, an equilibrium solution
was prepared by mixing 10.00 mL of 0.700 M
AgNO3 with 15.00 mL of 0.250 M K2Cr2O7.
The absorbance of this solution was measured
in a 1.0 cm cuvet with a spectrometer set at a
wavelength of 495 nm, and found to be 0.171.
(a) Calculate the initial concentrations of
Ag+ and Cr2O72- in the equilibrium
solution.
(b) Determine the equilibrium concentration
of Cr2O72- in the equilibrium solution.
(c) Calculate the value for the Ksp of
Ag2Cr2O7.
21. Predict the type of nuclear decay for each of the following radioisoptopes.
(a)
13
(b)
69
(c)
7N
30Zn
209
84Po
22. Write equations for each of the following nuclear processes.
(a) beta positive decay by 15065Tb
(b) beta minus decay by 12853I
(c) alpha decay by 22089Ac
(d) electron capture by 5026Fe
(e) spontaneous fission of 23994Pu
(continued on next page)
23. Complete the following nuclear equations.
(a)
238
(b)
40
XNp
XAr
1
+
+
2
0n
1X
 x10n +

38
XCl
98
40X
+
+
136
XX
X
XX
24. Calculate the binding energy per nucleon for the following nuclear species.
(a)
(b)
10
5B (m = 10.012939 u)
200
80Hg (m = 199.99834
u)
25.Which one of the following nuclei would be expected to have a higher binding energy per nucleon?
(a)
8
4Be
(b)
65
Zn
(c)
235
U
26. Radioactive fluorine-18, with a half-life of 110. minutes, is used for imaging in PET scans. How many
hours will it take for the radioactivity of the fluorine-18 to fall to 10.0% of its original intensity?
27. A sample of vanadium-42 shows an activity of 100. disintigrations per second. After one minute, the
activity decreases to 83 disintigrations per second. Determine the half-life of vanadium-42.
28. A sample of bone gives 12.4 cpm g-1 of carbon of 14C disintegrations. How old is the bone?
HOMEWORK 2R ANSWERS
1. b, d, g
2. (a) 4.60
(b) 0.01%
(c) 8.86
3. (a) 3.94
(b) 7.62
(c) 7.78
4. (a) 9.18
(b) 8.89
(c) 9.44
7. (a) 10. mL
(b) 5.10
(c) 8.25
(d) 9.21
(e) 11.01
(f) 12.46
(g) 12.66
(h) 12.70
(b) 1 x 10-2
(c) (d) (e) below to the left
(d) 7.46
5. 34 mL
6. 9.0 mL
(i) alizarin yellow
8. (a) bromcresol purple
(continued on next page)
9. (a) 1 x 10-2
(b) 3 x 10-7
10. (a)
(c) (d) (e) (f) (g) below to the right
(b)
1.00, 1.48, 7.00
(c)
2.09, 3.14, 7.92
11. 6.1 x 10-16
12. (a) PbBr2
(b) Ag3PO4
13. (a) 0.010 M, 3.8 g/L
(b) 0.0034 M, 1.2 g/L
14. Yes
15. 6.9 x 10-3 M
16. 6.4%
17. BaCrO4
(b) 8.x 10-10 M
18. 5.74
19. (a) 3.0 x 10-10 M
(b) 3.0 x 108 M
20. (a) 0.280 M Ag+, 0.150 M Cr2O72(b) 0.018 M Cr2O72(c) 4.6 x 10-6
(continued on next page)
(c) 0.094 M
11.12, 9.26, 5.28
21. (a) beta positive decay or electron capture
(b) beta minus decay
(c) alpha decay or spontaneous fission

22. (a)
150
65Tb
(b)
128
53I
(c)
220
89Ac
(d)
50
(e)
239
23. (a)
238
(b)
40

150
128
54Xe

87Fr
-

-1e
94Pu

Y
93Np
+
18Ar
+
+
1
2
ZX
0n
1H
+
0
+
Zn
26. 6.09 hours
27. 3.7 minutes
28. 1,740 years
-
4
2α
25Mn
239 – Y – N
 510n +

+
50
38
(b) 7.766 MeV/nucleon
65
+1β
-1β
24. (a) 6.475 MeV/nucleon
25.
0
+
+
216
0
26Fe
64Gd
17Cl
94 – ZX
98
+
40Zr
4
2
α
+ N 10n
+
136
53I