Selected Exercise Chemistry_The Central Science
Aqueous Reactions and Solution Stoichiometry
4.1 Which of the following schematic drawings best describes
a solution of Li2S04 in water (water molecules
not shown for simplicity)? [Section 4.1]
(a) (b) (c)
Methanol, CH30H, and hydrogen chloride, HCl, are
both molecular substances, yet an aqueous solution of
methanol does not conduct an electrical current, whereas
a solution of HCl does conduct. Account for this difference.
4.3 Aqueous solutions of three different substances, AX, AY,
and AZ, are represented by the three diagrams below.
Identify each substance as a strong electrolyte, weak
electrolyte, or nonelectrolyte. [Section 4.1]
4.4 A 0.1 M solution of acetic acid, CH3COOH, causes the
Ughtbulb in the apparatus of Figure 4.2 to glow about as
brightly as a 0.001 M solution of HBr. How do you account
for this fact? [Section 4.1]
4.5 You are presented with three white solids, A, B, and C,
which are glucose (a sugar substance), NaOH, and
AgBr. Solid A dissolves in water to form a conducting
solution. B is not soluble in water. C dissolves in water
to form a nonconducting solution. Identify A, B, and C.
4.6 We have seen that ions in aqueous solution are stabilized
by the attractions between the ions and the water
molecules. Why then do some pairs of ions in solution
form precipitates? [Section 4.2]
4.7 Which of the following ions will always be a spectator
ion in a precipitation reaction? (a) CC (b) N03-,
(c) NH4 +, (d) S2-, (e) sol-. Explain briefly. [Section 4.2]
4.8 The labels have fallen off two bottles, one containing
Mg(N03)z and the other containing Pb(N03)z. You have
a bottle of dilute H2S04. How could you use it to test a
portion of each solution to identify which solution is
which? [Section 4.2]
4.9 Explain how a redox reaction involves electrons in the
same way that an acid-base reaction involves protons.
[Sections 4.3 and 4.4]
4.10 If you want to double the concentration of a solution,
how could you do it? [Section 4.5]
4.11 When asked what causes electrolyte solutions to conduct
electricity, a student responds that it is due to the
movement of electrons through the solution. Is the student
correct? If not, what is the correct response?
4.12 When methanol, CH30H, is dissolved in water, a nonconducting
solution results. When acetic acid, CH3COOH,
dissolves in water, the solution is weakly conducting and
acidic in nature. Describe what happens upon dissolution
in the two cases, and account for the different results.
4.13 We have learned in this chapter that many ionic solids
dissolve in water as strong electrolytes, that is, as separated
ions in solution. What properties of water facilitate
4.14 What does it mean to say that ions are hydrated when
an ionic substance dissolves in water?
4.15 Specify what ions are present in solution upon dissolving
each of the following substances in water: (a) ZnCI2,
(b) HN03, (c) (NH4)zS04, (d) Ca(OH)z.
4.16 Specify what ions are present upon dissolving each of
the following substances in water: (a) Mgiz, (b) Al(N03)J,
(c) HC104, (d) NaCH3COO.
4.17 Formic acid, HCOOH, is a weak electrolyte. What solute
particles are present in an aqueous solution of this compound?
Write the chemical equation for the ionization
4.18 Acetone, CH3COCH3, is a nonelectrolyte; hypochlorous
acid, HClO, is a weak electrolyte; and ammonium
chloride, NH4Cl, is a strong electrolyte. (a) What are the
solute particles present in aqueous solutions of each
compound? (b) If 0.1 mol of each compound is dissolved
in solution, which one contains 0.2 mol of solute
particles, which contains 0.1 mol of solute particles, and
which contains somewhere between 0.1 and 0.2 mol of
Precipitation Reactions and Net Ionic Equations
4.19 Using solubility guidelines, predict whether each of the
following compounds is soluble or insoluble in water:
(a) NiC12, (b) Ag2S, (c) Cs3P04, (d) SrC03, (e) PbS04.
4.20 Predict whether each of the following compounds is soluble
in water: (a) Ni(OHh, (b) PbBr:z, (c) Ba(N03h,
(d) AlP04, (e) AgCH3COO.
4.21 Will precipitation occur when the following solutions
are mixed? If so, write a balanced chemical equation for
the reaction. (a) Na2C03 and AgN03, (b) NaN03 and
NiS04, (c) FeS04 and Pb(N03)z.
4.22 Identify the precipitate (if any) that forms when the
following solutions are mixed, and write a balanced
equation for each reaction. (a) Ni(N03h and NaOH,
(b) NaOH and K2S04, (c) Na2S and Cu(CH3COO)z.
4.23 Name the spectator ions in any reactions that may be
involved when each of the following pairs of solutions
(a) Na2C03(aq) and MgS04(aq)
(b) Pb(N03)z(aq) and NazS(aq)
(c) (NH4)JP04(aq) and CaC12(aq)
4.24 Write balanced net ionic equations for the reactions that
occur in each of the following cases. Identify the spectator
ion or ions in each reaction.
(a) Crz(S04)J(aq) + (NH4}zC03(aq) --->
(b) Ba(N03h(aq) + K2S04(aq) --->
(c) Fe(N03h(aq) + KOH(aq) --->
4.25 Separate samples of a solution of an unknown salt are
treated with dilute solutions of HBr, H2SO"' and NaOH.
A precipitate forms in all three cases. Which of the following
cations could the solution contain: K+; Pb2+; Ba2+?
4.26 Separate samples of a solution of an unknown ionic
compound are treated with dilute AgN03, Pb(N03):z,
and BaC12. Precipitates form in all three cases. Which of
the following could be the anion of the unknown salt:
Br-; col-; N03 -?
4.27 You know that an unlabeled bottle contains a solution
of one of the following: AgN03, CaCl:z, or Alz(S04)J.
A friend suggests that you test a portion of the solution
with Ba(N03h and then with NaCI solutions. Explain
how these two tests together would be sufficient to determine
which salt is present in the solution.
4.28 Three solutions are mixed together to form a single solution.
One contains 0.2 mol Pb(CH3COOh, the second
contains 0.1 mol Na2S, and the third contains 0.1 mol
CaC12• (a) Write the net ionic equations for the precipitation
reaction or reactions that occur. (b) What are the
spectator ions in the solution?
4.29 Which of the following solutions has the largest concentration
of solvated protons: (a) 0.2 M LiOH, (b) 0.2 M HI,
(c) 1.0 M methyl alcohol (CH30H)? Explain.
4.30 Which of the following solutions is the most basic?
(a) 0.6 M NH3, (b) 0.150 M KOH, (c) 0.100 M Ba(OH)z.
4.31 What is the difference between (a) a monoprotic acid
and a diprotic acid, (b) a weak acid and a strong acid,
(c) an acid and a base?
4.32 Explain the following observations: (a) NH3 contains
no OH- ions, and yet its aqueous solutions are basic;
(b) HF is called a weak acid, and yet it is very reactive;
(c) although sulfuric acid is a strong electrolyte, an aqueous
solution of H2S04 contains more HS04- ions than
4.33 HO, HBr, and HI are strong acids, yet HF is a weak acid.
What does this mean in terms of the extent to which
these substances are ionized in solution?
4.34 What is the relationship between the solubility rules
in Table 4.1 and the list of strong bases in Table 4.2?
Another way of asking this question is, why is Cd(OHh,
for example, not listed as a strong base in Table 4.2?
4.35 Label each of the following substances as an acid, base,
salt, or none of the above. Indicate whether the substance
exists in aqueous solution entirely in molecular
form, entirely as ions, or as a mixture of molecules
and ions. (a) HF; (b) acetonitrile, CH3CN; (c) NaCI04;
4.36 An aqueous solution of an unknown solute is tested
with litmus paper and found to be acidic. The solution is
weakly conducting compared with a solution of NaCI of
the same concentration. Which of the following substances
could the unknown be: KOH, NH3, HN03,
KClO:z, H3P03, CH3COCH3 (acetone)?
4.37 Classify each of the following substances as a nonelectrolyte,
weak electrolyte, or strong electrolyte in water:
(a) H2S03, (b) C2H50H (ethanol), (c) NH3, (d) KCI03,
4.38 Classify each of the following aqueous solutions as a
nonelectrolyte, weak electrolyte, or strong electrolyte:
(a) HC104, (b) HN03, (c) NH4Cl, (d) CH3COCH3
(acetone), (e) CoS04, (f) CnH220u (sucrose).
4.39 Complete and balance the following molecular equations,
and then write the net ionic equation for each:
(a) HBr(aq) + Ca(OH)z(aq) --->
(b) Cu(OH)z(s) + HCI04(aq) --->
(c) Al(OH)J(s) + HN03(aq) --->
4.40 Write the balanced molecular and net ionic equations
for each of the following neutralization reactions:
(a) Aqueous acetic acid is neutralized by aqueous
(b) Solid chromium(Ill) hydroxide reacts with nitric
(c) Aqueous hypochlorous acid and aqueous calcium
4.41 Write balanced molecular and net ionic equations for
the following reactions, and identify the gas formed in
each: (a) solid cadmium sulfide reacts with an aqueous
solution of sulfuric acid; (b) solid magnesium carbonate
reacts with an aqueous solution of perchloric acid.
4.42 Because the oxide ion is basic, metal oxides react readily
with acids. (a) Write the net ionic equation for the following
FeO(s) + 2 HC104(aq) -----> Fe(ClO.J2(aq) + H20(1)
(b) Based on the equation in part (a), write the net ionic
equation for the reaction that occurs between NiO(s)
and an aqueous solution of nitric acid.
4.43 Write a balanced molecular equation and a net ionic
equation for the reaction that occurs when (a) solid
CaC03 reacts with an aqueous solution of nitric acid;
(b) solid iron(II) sulfide reacts with an aqueous solution
of hydrobromic acid.
4.44 As K20 dissolves in water, the oxide ion reacts with
water molecules to form hydroxide ions. Write the molecular
and net ionic equations for this reaction. Based
on the definitions of acid and base, what ion is the base
in this reaction? What is the acid? What is the spectator
ion in the reaction?
4.45 Define oxidation and reduction in terms of (a) electron
transfer and (b) oxidation numbers.
4.46 Can oxidation occur without accompanying reduction?
4.47 Which circled region of the periodic table shown here
contains the most readily oxidized elements? Which
contains the least readily oxidized?
4.48 From the elements listed in Table 4.5, select an element
that lies in region A of the periodic table shown above
and an element that lies in region C. Write a balanced
oxidation-reduction equation that shows the oxidation
of one metal and reduction of an ion of the other.
You will need to decide which element is oxidized and
which is reduced.
4.49 Determine the oxidation number for the indicated element
in each of the following substances: (a) S in 502,
(b) C in COC12, (c) Mn in Mn04 -, (d) Br in HBrO, (e) As
in As4, (f) 0 in K202.
4.50 Determine the oxidation number for the indicated element
in each of the following compounds: (a) Ti in Ti02,
(b) Sn in SnC13 -, (c) C in C20l-, (d) N in N2H4, (e) N in
HNOz, (f) Cr in Cr20l-.
4.51 Which element is oxidized and which is reduced in the
(a) N2(g) + 3 H2(g) -----> 2 NH3(g)
(b) 3 Fe(N03)z(aq) + 2 Al(s) ----->
3 Fe(s) + 2 Al(N03)J(aq)
(c) Cl2(aq) + 2 Nal(aq) -----> I2(aq) + 2 NaCl(aq)
(d) PbS(s) + 4 H202(aq) -----> PbS04(s) + 4 HzO(l)
4.52 Which of the following are redox reactions? For those
that are, indicate which element is oxidized and which
is reduced. For those that are not, indicate whether they
are precipitation or acid-base reactions.
(a) Cu(OH)z(s) + 2 HN03(aq) ----->
Cu(N03)z(aq) + 2 H20(1)
(b) Fe203(s) + 3 CO(g) -----> 2 Fe(s) + 3 C02(g)
(c) Sr(N03)z(aq) + H2S04(aq) ----->
SrS04(s) + 2 HN03(aq)
(d) 4 Zn(s) + 10 H+(aq) + 2 N03 -(aq) ----->
2+(aq) + NzO(g) + 5 HzO(I)
4.53 Write balanced molecular and net ionic equations
for the reactions of (a) manganese with dilute sulfuric
acid; (b) cluomium with hydrobromic acid; (c) tin with
hydrochloric acid; (d) aluminum with formic acid,
4.54 Write balanced molecular and net ionic equations for
the reactions of (a) hydrochloric acid with nickel; (b) dilute
sulfuric acid with iron; (c) hydrobromic acid with
magnesium; (d) acetic acid, CH3COOH, with zinc.
4.55 Using the activity series (Table 4.5), write balanced chemical
equations for the following reactions. If no reaction
occurs, simply write NR. (a) Iron metal is added to a
solution of copper(II) nitrate; (b) zinc metal is added to
a solution of magnesium sulfate; (c) hydrobromic acid is
added to tin metal; (d) hydrogen gas is bubbled through
an aqueous solution of nickel(II) chloride; (e) aluminum
metal is added to a solution of cobalt(ll) sulfate.
4.56 Based on the activity series (Table 4.5), what is the outcome
(if any) of each of the following reactions?
(a) Mn(s) + NiC12(aq) ----->
(b) Cu(s) + Cr(CH3COO)J(aq) ----->
(c) Cr(s) + NiS04(aq) ----->
(d) Pt(s) + HBr(aq) ----->
(e) Hz(g) + CuClz(aq) ----->
4.57 The metal cadmium tends to form Cd2+ ions. The following
observations are made: (i) When a strip of zinc metal
is placed in CdCI2(aq), cadmium metal is deposited on
the strip. (ii) When a strip of cadmium metal is placed
in Ni(N03h(aq), nickel metal is deposited on the strip.
(a) Write net ionic equations to explain each of the observations
made above. (b) What can you conclude
about the position of cadmium in the activity series? (c)
What experiments would you need to perform to locate
more precisely the position of cadmium in the activity
4.58 (a) Use the following reactions to prepare an activity series
for the halogens:
Br2(aq) + 2 Nal(aq) --> 2 NaBr(aq) + I2(aq)
Cl2(aq) + 2 NaBr(aq) --> 2 NaCl(aq) + Br2(aq)
(b) Relate the positions of the halogens in the periodic
table with their locations in this activity series. (c) Predict
whether a reaction occurs when the following reagents
are mixed: Cl2(aq) and KI(aq); Br2(aq) and LiCl(aq).
Solution Composition; Molarity
4.59 (a) Is the concentration of a solution an intensive or an
extensive property? (b) What is the difference between
0.50 mol HCl and 0.50 M HCI?
4.60 (a) Suppose you prepare 500 mL of a 0.10 M solution of
some salt and then spill some of it. What happens to
the concentration of the solution left in the container?
(b) Suppose you prepare 500 mL of a 0.10M aqueous solution
of some salt and let it sit out, uncovered, for a long
time, and some water evaporates. What happens to the
concentration of the solution left in the container? (c) A
certain volume of a 0.50 M solution contains 4.5 g of a salt.
What mass of the salt is present in the same volume of a
2.50 M solution?
4.61 (a) Calculate the molarity of a solution that contains
0.0250 mol NH4Cl in exactly 500 mL of solution.
(b) How many moles of HN03 are present in 50.0 mL of
a 2.50 M solution of nitric acid? (c) How many milliliters
of 1.50 M KOH solution are needed to provide 0.275 mol
4.62 (a) Calculate the molarity of a solution made by dissolving
0.750 grams of Na2S04 in enough water to form
exactly 850 mL of solution. (b) How many moles of
KMn04 are present in 250 mL of a 0.0475 M solution?
(c) How many milliliters of 11.6 M HCl solution are
needed to obtain 0.250 mol of HCl?
4.63 The average adult human male has a total blood volume
of 5.0 L. If the concentration of sodium ion in this average
individual is 0.135 M, what is the mass of sodium
ion circulating in the blood?
4.64 A person suffering from hyponatremia has a sodium ion
concentration in the blood of 0.118 M and a total blood
volume of 4.6 L. What mass of sodium chloride would
need to be added to the blood to bring the sodium ion
concentration up to 0.138 M, assuming no change in
4.65 The concentration of alcohol (CH3CHzOH) in blood,
called the "blood alcohol concentration" or BAC, is
given in units of grams of alcohol per 100 mL of blood.
The legal definition of intoxication, in many states of the
United States, is that the BAC is 0.08 or higher. What is
the concentration of alcohol, in terms of molarity, in
blood if the BAC is 0.08?
4.66 The average adult male has a total blood volume of
5.0 L. After drinking a few beers, he has a BAC of 0.10
(see Exercise 4.65). What mass of alcohol is circulating in
4.67 Calculate (a) the number of grams of solute in 0.250 L of
0.175 M KBr, (b) the molar concentration of a solution
containing 14.75 g of Ca(N03)z in 1.375 L, (c) the volume
of 1.50 M Na3P04 in milliliters that contains 2.50 g of
4.68 (a) How many grams of solute are present in 50.0 mL of
0.488 M K2Cr207? (b) If 4.00 g of (NH4)zS04 is dissolved
in enough water to form 400 mL of solution, what is the
molarity of the solution? (c) How many milliliters of
0.0250 M CuS04 contain 1.75 g of solute?
4.69 (a) Which will have the highest concentration of potassium
ion: 0.20 M KCI, 0.15 M K2Cr04, or 0.080 M K3P04?
(b) Which will contain the greater number of moles of
potassium ion: 30.0 mL of 0.15 M K2Cr04 or 25.0 mL of
0.080 M K3P04?
4.70 1n each of the following pairs, indicate which has the
higher concentration of Cl- ion: (a) 0.10 M CaC12 or
0.15 M KCI solution, (b) 100 rnL of 0.10 M KCI solution
or 400 rnL of 0.080 M LiCI solution, (c) 0.050 M HCl
solution or 0.020 M CdC12 solution.
4.71 Indicate the concentration of each ion or molecule present
in the following solutions: (a) 0.25 M NaN03,
(b) 1.3 X 10-2 M MgS04, (c) 0.0150 M Ct;H120IV (d) a mixture
of 45.0 mL of 0.272 M NaCI and 65.0 mL of 0.0247 M
()zC03. Assume that the volumes are additive.
4.72 Indicate the concentration of each ion present in the solution
formed by mixing (a) 42.0 rnL of 0.170 M NaOH
and 37.6 rnL of 0.400 M NaOH, (b) 44.0 rnL of 0.100 M
and Na2S04 and 25.0 mL of 0.150 M KCI, (c) 3.60 g KCl
in 75.0 rnL of 0.250 M CaC12 solution. Assume that the
volumes are additive.
4.73 (a) You have a stock solution of 14.8 M NH3. How many
milliliters of this solution should you dilute to make
1000.0 mL of 0.250 M NH3? (b) If you take a 10.0-mL
portion of the stock solution and dilute it to a total volume
of 0.500 L, what will be the concentration of the
4.74 (a) How many milliliters of a stock solution of 10.0 M
HN03 would you have to use to prepare 0.450 L of
0.500 M HN03? (b) If you dilute 25.0 mL of the stock solution
to a final volume of 0.500 L, what will be the
concentration of the diluted solution?
4.75 (a) Starting with solid sucrose, C12H22011, describe how
you would prepare 250 mL of a 0.250 M sucrose solution.
(b) Describe how you would prepare 350.0 mL of
0.100 M C12H22011 starting with 3.00 L of 1.50 M
4.76 (a) How would you prepare 175.0 mL of 0.150 M AgN03
solution starting with pure solute? (b) An experiment
calls for you to use 100 mL of 0.50 M HN03 solution. All
you have available is a bottle of 3.6 M HN03. How
would you prepare the desired solution?
[4.77] Pure acetic acid, known as glacial acetic acid, is a liquid
with a density of 1 .049 g/mL at 25 °C. Calculate the molarity
of a solution of acetic acid made by dissolving
20.00 mL of glacial acetic acid at 25 oc in enough water
to make 250.0 mL of solution.
[4.78] Glycerol, C3H803, is a substance used extensively in the
manufacture of cosmetics, foodstuffs, antifreeze, and
plastics. Glycerol is a water-soluble liquid with a density
of 1.2656 g/L at 15 oc. Calculate the molarity of a solution
of glycerol made by dissolving 50.000 mL glycerol
at 15 oc in enough water to make 250.00 mL of solution.
Solution Stoichiometry; Titrations
4.79 What mass of KCl is needed to precipitate the silver ions
from 15.0 mL of 0.200 M AgN03 solution?
4.80 What mass of NaOH is needed to precipitate the Cd2+
ions from 35.0 mL of 0.500 M Cd(N03)z solution?
4.81 (a) What volume of 0.115 M HCI04 solution is needed to
neutralize 50.00 mL of 0.0875 M NaOH? (b) What volume
of 0.128 M HCI is needed to neutralize 2.87 g of
Mg(OH)z? (c) If 25.8 mL of AgN03 is needed to precipitate
all the o- ions in a 785-mg sample of KCl (forming
AgCI), what is the molarity of the AgN03 solution?
(d) If 45.3 mL of 0.108 M HCl solution is needed to neutralize
a solution of KOH, how many grams of KOH
must be present in the solution?
4.82 (a) How many milliliters of 0.120 M HCl are needed to
completely neutralize 50.0 mL of 0.101 M Ba(OH)z solution?
(b) How many milliliters of 0.125 M H2S04 are
needed to neutralize 0.200 g of NaOH? (c) If 55.8 mL of
BaCI2 solution is needed to precipitate all the sulfate ion
in a 752-mg sample of Na2S04, what is the molarity of
the solution? (d) If 42.7 mL of 0.208 M HCl solution is
needed to neutralize a solution of Ca(OH)z, how many
grams of Ca(OHh must be in the solution?
4.83 Some sulfuric acid is spilled on a lab bench. You can
neutralize the acid by sprinkling sodium bicarbonate on
it and then mopping up the resultant solution. The sodium
bicarbonate reacts with sulfuric acid as follows:
2 NaHC03(s) + HzS04(aq) ->
NazS04(aq) + 2 HzO(I) + 2 COz(g)
Sodium bicarbonate is added until the fizzing due to the
formation of C02(g) stops. If 27 mL of 6.0 M HzS04 was
spilled, what is the minimum mass of NaHC03 that
must be added to the spill to neutralize the acid?
4.84 The distinctive odor of vinegar is due to acetic acid,
CH3COOH, which reacts with sodium hydroxide in the
CH3COOH(aq) + NaOH(aq) ->
HzO(l) + NaCzHPz(aq)
If 3.45 mL of vinegar needs 42.5 mL of 0.115 M NaOH to
reach the equivalence point in a titration, how many
grams of acetic acid are in a 1.00-qt sample of this vinegar?
4.85 A sample of solid Ca(OH)z is stirred in water at 30 oc
until the solution contains as much dissolved Ca(OH)z
as it can hold. A 100-mL sample of this solution is withdrawn
and titrated with 5.00 x 10-2 M HBr. It requires
48.8 mL of the acid solution for neutralization. What is
the molarity of the Ca(OH)z solution? What is the solubility
of Ca(OH)z in water, at 30 oc, in grams of Ca(OH)z
per 100 mL of solution?
4.86 ln a laboratory, 6.82 g of Sr(N03)z is dissolved in enough
water to form 0.500 L of solution. A 0.100-L sample is
withdrawn from this stock solution and titrated with a
0.0245 M solution of Na2Cr04. What volume of Na2Cr04
solution is needed to precipitate all the Sr2+(aq) as
4.87 A solution of 100.0 mL of 0.200 M KOH is mixed with a
solution of 200.0 mL of 0.150 M NiS04. (a) Write the
balanced chemical equation for the reaction that occurs.
(b) What precipitate forms? (c) What is the limiting reactant?
(d) How many grams of this precipitate form?
(e) What is the concentration of each ion that remains in
4.88 A solution is made by mixing 12.0 g of NaOH and
75.0 mL of 0.200 M HN03. (a) Write a balanced
equation for the reaction that occurs between the
solutes. (b) Calculate the concentration of each ion
remaining in solution . (c) Is the resultant solution
acidic or basic?
[4.89] A 0.5895-g sample of impure magnesium hydroxide
is dissolved in 100.0 mL of 0.2050 M HCI solution.
The excess acid then needs 19.85 mL of 0.1020 M
NaOH for neutralization. Calculate the percent by
mass of magnesium hydroxide in the sample, assuming
that it is the only substance reacting with the
[4.90] A 1.248-g sample of limestone rock is pulverized and
then treated with 30.00 mL of 1 .035 M HCl solution.
The excess acid then requires 11.56 mL of 1.010 M NaOH
for neutralization. Calculate the percent by mass of calcium
carbonate in the rock, assuming that it is the only
substance reacting with the HCl solution.
4.91 Explam why a titration experiment is a good way to
measure the unknown concentration of a compound
4.92 The accompanying photo shows the reaction between a
solution of Cd(N03)z and one of Na2S. What is the identity
of the precipitate? What ions remam in solution? Write
the net ionic equation for the reaction.
4.93 Suppose you have a solution that might contain any or
all of the following cations: Ni2+, Ag+, Sr2+, and Mn2+
Addition of HCl solution causes a precipitate to form.
After filtering off the precipitate, H2S04 solution is
added to the resultant solution and another precipitate
forms. This is filtered off, and a solution of NaOH is
added to the resulting solution. No precipitate is observed.
Which ions are present in each of the precipitates?
Which of the four ions listed above must be
absent from the original solution?
4.94 You choose to investigate some of the solubility guidelines
for two ions not listed in Table 4.1, the chromate
ion (Crol-) and the oxalate ion (C2ol-). You are given
O.Ql M solutions (A, B, C, D) of four water-soluble salts:
When these solutions are mixed, the following observations
(a) Write a net ionic equation for the reaction that occurs
in each of the experiments. (b) Identify the precipitate
formed, if any, in each of the experiments. (c) Based on
these limited observations, which ion tends to form the
more soluble salts, chromate or oxalate?
4.95 Antacids are often used to relieve pain and promote
healing in the treatment of mild ulcers. Write balanced
net ionic equations for the reactions between the HCl(aq)
in the stomach and each of the following substances
used in various antacids: (a) Al(OHh(s), (b) Mg(OH)z(s),
(c) MgC03(s), (d) NaAl(C03)(0H)z(s), (e) CaC03(s).
[4.96] Salts of the sulfite ion, sol-, react with acids in a way
similar to that of carbonates. (a) Predict the chemical
formula, and name the weak acid that forms when the
sulfite ion reacts with acids. (b) The acid formed in part
(a) decomposes to form water and a gas. Predict the
molecular formula, and name the gas formed. (c) Use a
source book such as the CRC Handbook of Chemistry and
Physics to confirm that the substance in part (b) is a gas
under normal room-temperature conditions. (d) Write
balanced net ionic equations of the reaction of HC!(aq)
with (i) Na2S03(aq), (ii) Ag2S03(s), (iii) KHS03(s), and
[4.97] The commercial production of nitric acid involves the
following chemical reactions:
4 NH3(g) + 5 02(g) -----> 4 NO(g) + 6 H20(g)
2 NO(g) + 02(g) -----> 2 N02(g)
3 N02(g) + H20(1) -----> 2 HN03(aq) + NO(g)
(a) Which of these reactions are redox reactions? (b) In
each redox reaction identify the element undergoing
oxidation and the element undergoing reduction.
4.98 Use Table 4.5 to predict which of the following ions can
be reduced to their metal forms by reacting with zinc:
(aq), (b) Pb2+
(aq), (c) Mg2+(aq), (d) Fe2+
(e) Cu2+(aq), (f) Al3+(aq). Write the balanced net ionic
equation for each reaction that occurs.
[4.99] Lanthanum metal forms cations with a charge of 3+.
Consider the following observations about the chemistry
of lanthanum: When lanthanum metal is exposed to air,
a white solid (compound A) is formed that contains lanthanum
and one other element. When lanthanum metal
is added to water, gas bubbles are observed and a different
white solid (compound B) is formed. Both A and B
dissolve in hydrochloric acid to give a clear solution.
When either of these solutions is evaporated, a soluble
white solid (compound C) remains. If compound C is
dissolved in water and sulfuric acid is added, a white
precipitate (compound D) forms. (a) Propose identities
for the substances A, B, C, and D. (b) Write net ionic
equations for all the reactions described. (c) Based on the
preceding observations, what can be said about the position
of lanthanum in the activity series (Table 4.5)?
4.100 A 35.0-mL sample of 1.00 M KBr and a 60.0-mL sample
of 0.600 M KBr are mixed. The solution is then heated to
evaporate water until the total volume is 50.0 mL. What
is the molarity of the KBr in the final solution?
4.101 Using modern analytical techniques, it is possible to detect
sodium ions in concentrations as low as 50 pgjmL.
What is this detection limit expressed in (a) molarity of
Na+, (b) Na+ ions per cubic centimeter?
4.102 Hard water contains Ca2+, Mg2+, and Fe2+, which interfere
with the action of soap and leave an insoluble coating
on the insides of containers and pipes when heated.
Water softeners replace these ions with Na + If 1500 L of
hard water contains 0.020 M Ca2+ and 0.0040 M Mg2+,
how many moles of Na + are needed to replace these ions?
4.103 Tartaric acid, H2C4H406, has two acidic hydrogens. The
acid is often present in wines and precipitates from solution
as the wine ages. A solution containing an unknown
concentration of the acid is titrated with NaOH.
It requires 24.65 mL of 0.2500 M NaOH solution to
titrate both acidic protons in 50.00 mL of the tartaric acid
solution. Write a balanced net ionic equation for the
neutralization reaction, and calculate the molarity of the
tartaric acid solution.
4.104 The concentration of hydrogen peroxide in a solution is
determined by titrating a 10.0-mL sample of the solution
with permanganate ion.
2 Mn04 -(aq) + 5 H202(aq) + 6 H+(aq) --->
2 MnZ+(aq) + 5 02(g) + 8 H20(!)
If it takes 14.8 mL of 0.134 M Mn04- solution to reach
the equivalence point, what is the molarity of the hydrogen
[4.105] A solid sample of Zn(OHh is added to 0.350 L of 0.500
M aqueous HBr. The solution that remains is still acidic.
It is then titrated with 0.500 M NaOH solution, and it
takes 88.5 mL of the NaOH solution to reach the equivalence
point. What mass of Zn(OHh was added to the
4.106 (a) By titration, 15.0 mL of 0.1008 M sodium hydroxide
is needed to neutralize a 0.2053-g sample of an organic
acid. What is the molar mass of the acid if it is monoprotic?
(b) An elemental analysis of the acid indicates that it
is composed of 5.89% H, 70.6% C, and 23.5% 0 by mass.
What is its molecular formula?
4.107 A 3.455-g sample of a mixture was analyzed for barium
ion by adding a small excess of sulfuric acid to an aqueous
solution of the sample. The resultant reaction produced
a precipitate of barium sulfate, which was
collected by filtration, washed, dried, and weighed. If
0.2815 g of barium sulfate was obtained, what was the
mass percentage of barium in the sample?
[4.108] A tanker truck carrying 5.0 X 10
kg of concentrated
sulfuric acid solution tips over and spills its load. If the
sulfuric acid is 95.0% H2S04 by mass and has a density
of 1.84 g/mL, how many kilograms of sodium carbonate
must be added to neutralize the acid?
4.109 A sample of 5.53 g of Mg(OHh is added to 25.0 mL of
0.200 M HN03. (a) Write the chemical equation for the
reaction that occurs. (b) Which is the limiting reactant in
the reaction? (c) How many moles of Mg(OHh, HN03,
and Mg(N03h are present after the reaction is complete?
4.110 A sample of 1.50 g of lead(ll) nitrate is mixed with
125 mL of 0.100 M sodium sulfate solution. (a) Write the
chemical equation for the reaction that occurs. (b) Which
is the limiting reactant in the reaction? (c) What are the
concentrations of all ions that remain in solution after the
reaction is complete?
4.111 A mixture contains 76.5% NaCI, 6.5% MgC12, and
17.0% Na2S04 by mass. What is the molarity of Cl- ions
in a solution formed by dissolving 7.50 g of the mixture
in enough water to form 500.0 mL of solution?
[4.112] The average concentration of bromide ion in seawater is
65 mg of bromide ion per kg of seawater. What is the
molarity of the bromide ion if the density of the seawater
is 1.025 g/mL?
[4.113] The mass percentage of chloride ion in a 25.00-mL sample
of seawater was determined by titrating the sample
with silver nitrate, precipitating silver chloride. It took
42.58 mL of 0.2997 M silver nitrate solution to reach the
equivalence point in the titration. What is the mass percentage
of chloride ion in the seawater if its density is
1 .025 g/mL?
4.114 The arsenic in a 1 .22-g sample of a pesticide was converted
to As043- by suitable chemical treatment. It was
then titrated using Ag + to form Ag3As04 as a precipitate.
(a) What is the oxidation state of As in As04
(b) Name Ag3As04 by analogy to the corresponding
compound containing phosphorus in place of arsenic.
(c) If it took 25.0 mL of 0.102 M Ag+ to reach the equivalence
point in this titration, what is the mass percentage
of arsenic in the pesticide?
[4.115] The newest U.S. standard for arsenate in drinking water,
mandated by the Safe Drinking Water Act, required that
by January 2006, public water supplies must contain no
greater than 10 parts per billion (ppb) arsenic. If this arsenic
is present as arsenate, As04
-, what mass of sodium
arsenate would be present in a 1 .00-L sample of
drinking water that just meets the standard?
[4.116] The safe drinking water standard for arsenic (which is
usually found as arsenate, see 4.115) is 50 parts per billion
(ppb) in most developing countries. (a) How many
grams of sodium arsenate are in 55 gallons of water, if
the concentration of arsenate is 50 ppb? (b) In 1993,
naturally occurring arsenic was discovered as a major
contaminant in the drinking water across the country
of Bangladesh. Approximately 12 million people in
Bangladesh still drink water from wells that have higher
concentrations of arsenic than the standard. Recently, a
chemistry professor from George Mason University was
awarded a $1 million Grainger Challenge Prize for Sustainability
for his development of a simple, inexpensive
system for filtering naturally occuring arsenic from
drinking water. The system uses buckets of sand, cast
iron, activated carbon, and wood chips for trapping arsenic-
containing minerals. Assuming the efficiency of
such a bucket system is 90% (meaning, 90% of the arsenic
that comes in is retained in the bucket and 10%
passes out of the bucket), how many times should water
that is 500 ppb in arsenic be passed through to meet the
50 ppb standard?
[4.117] Federal regulations set an upper limit of 50 parts per million
(ppm) of NH3 in the air in a work environment [that
is, 50 molecules of NH3(g) for every million molecules in
the air]. Air from a manufacturing operation was drawn
through a solution containing 1.00 x 102 mL of O.D105 M
HCI. The NH3 reacts with HCI as follows:
NH3(aq) + HCl(aq) NH4Cl(aq)
After drawing air through the acid solution for 10.0 min
at a rate of 10.0 L/min, the acid was titrated. The remaining
acid needed 13.1 mL of 0.0588 M NaOH to
reach the equivalence point. (a) How many grams of
NH3 were drawn into the acid solution? (b) How many
ppm of NH3 were in the air? (Air has a density of
1.20 g/L and an average molar mass of 29.0 g/mol
under the conditions of the experiment.) (c) Is this manufacturer
in compliance with regulations?
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