STutor™ Sample Questions

STutor™ Sample Questions
These questions below cover a significant cross-section of the Stoichiometry curriculum. The questions have
been solved with STutor, providing a good demonstration of the program’s versatility and depth of subject
matter coverage. The proprietary problem (*.prob) files are stored in …\STutor\Problem_Files. Each .prob file
is named after the corresponding question e.g. the problem file corresponding to question 1 is saved as
Q1.prob. Simply load the files from the folder into the user interface to see how the problem inputs are
entered (see STutor_User_Manual.pdf for details). Evaluate each problem by clicking the “Analyze“button.
This will produce a text script showing calculation steps in detail. Conversely, analyzing each problem in the
practice mode converts the program into an Intelligent Tutor System (ITS) that guides the user to the problem
solution using customized hints and prompts (see the manual for details).
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During a severe air pollution episode, the concentration of lead in air was observed to be 3.01µg Pb/m 3.
How many Pb atoms would be present in a 0.500L sample of this air (the approximate lung capacity of a
human adult)? Answer: 4.37x1012
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a. Determine the number of moles of Na in a 135.0g sample
b. The number of atoms in 245.0Kg sulfur.
c. The mass of one trillion (1.0x1012) atom sample of copper.
Answer: (a). 5.872 mole Na; (b). 4.601x1027 S atoms; (c). 1.1x10-10g Cu
Pottasium-40 is one of the few naturally occurring radioactive isotope elements of low atomic number. Its
percent natural abundance is 0.012%. How many 40K atoms do you ingest by diluting one cup of milk
containing 371mg K? Answer: 6.9x1017 K atoms.
How many Cu atoms are present in a 1.00m length of 20-guage copper wire (a 20-guage Cu wire has a
diameter of 0.03196 inches, 1m = 39.37 inches; density of copper = 8.92 g/cm3)? Answer: 4.38x1022 Cu
atoms.
The volatile liquid, ethyl mercaptan (C2H6S) is one of the most odoriferous substances known. It is used in
natural gas to make gas leaks detectable. How many C2H6S molecules are contained in a 1.0µL sample (d =
0.84g/mL)? Answer: 8.1x1018 molecules.
For the compound, Ge[S(CH2)4CH3]4, determine:
(a). The number of grams of S in 1.000 mole of compound.
(b). The number of C atoms in 33.10g of the compound.
Answer: (a). 128.3g S; (b). 8.212x1023 C atoms
Given the reaction:
SO32- + MnO4- + H+ = SO42- + Mn2+ + H2O
Assume that the only reducing agent present in a particular wastewater is SO32-. If a 25.00mL sample of the
wastewater requires 34.08 mL of 0.01964M KMnO4 for its titration, what is the Molarity of SO32- in the
wastewater? Answer: 0.06693M SO32-.
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Mn2+ (aq) can be determined by titration with MnO4-(aq):
Mn2+ + MnO4- + OH- + H+ = H2O + MnO2 (s) A 25.00mL sample of Mn2+ (aq) requires 34.77 mL of 0.05876M
KMnO4 (aq) for its titration. What is the molarity of Mn2+ in the sample? Answer: 0.1226M.
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Sodium Dithionite, Na2S2O4 is an important reducing agent. One interesting use is the reduction of
chromate ion (CrO42-) in wastewater to solid chromium III hydroxide, Cr(OH)3:
CrO42- + S2O42- + H2O + OH- = Cr(OH)3 (s) + SO32In the treatment of 1.00x102 L of a wastewater solution that is 0.0108M in CrO42-;
(a). What mass of Cr(OH)3 in g would precipitate?
(b). What mass of Na2S2O4 in g would be consumed?
Answer: (a). 111g Cr(OH)3; (b). 282g Na2S2O4.
10. § (a). A piece of iron wire weighing 0.1568g is converted to Fe2+ (aq) and requires 26.24 mL of a KMnO4 (aq)
solution for its titration. What is the Molarity of KMnO4 (aq) given the following equation:
Fe2+(aq) + MnO4-(aq) + H+(aq) = Fe3+(aq) + Mn2+(aq) + H2O?
(b). Assume that the KMnO4 (aq) described above were standardized by the reaction with As2O3 instead of
iron wire. If a 0.1256g sample that is 99.97% As2O3 by mass had been used in the titration, what volume of
the KMnO4 (aq) would have been required?
As2O3 + MnO4- + H+ + H2O = H3AsO4 + Mn2+
Answer: (a). 0.02140 M KMnO4; (b). 23.73 mL KMnO4
11. §A 4.04 x 2.17 x 0.0235 in3 piece of Aluminum foil is dissolved in excess HCl (aq). What mass of H2 (g) is
produced assuming the density of Al is 2.70g/cm3, given the following reaction: Al + HCl = AlCl3 + H2?
Answer: 1.02g H2
12. §What volume in mL of a KMnO4 (aq) solution containing 12.6g KMnO4/L must be used to convert 9.13g KI
to I2 given: KMnO4 + KI + H2SO4 = K2SO4 + MnSO4 + I2 + H2O.
Answer: 138 mL.
13. §Iron ore is impure Fe2O3. When Fe2O3 is heated with an excess of carbon (coke), iron metal is produced.
From a sample of ore weighing 812Kg, 486Kg of pure iron is obtained. What is the % Fe 2O3 by mass in the
ore sample? Fe2O3 + C = Fe + CO2. Answer: 85.6% Fe2O3.
14. §A side reaction in the manufacture of rayon from wood pulp is:
CS2 + NaOH = Na2CS3 + Na2CO3 + H2O
(a). How many moles of Na2CO3 is produced by allowing 1.00mole each of CS2 and NaOH to react?
(b). What mass of Na2CS3 in grams is produced in the reaction of 88.0mL of liquid CS2 (d = 1.26g/mL) and
3.12 mole NaOH.
Answer: (a). 0.167mole Na2CO3; (b). 150g Na2CO3
15. §The decomposition of Sodium Azide, NaN3 at high temperatures produces N2 (g). Together with the
necessary devices to initiate reaction and trap the Na metal formed, this reaction is used in air bag safety
systems. What volume of N2 (g) measured at 735mmHg and 26oC is produced when 70.0g NaN3 is
decomposed?
2NaN3 = 2Na + 3N2
Answer: 41.1L
16. §A particular coal sample contains 2.12% S by mass. When coal is burned, the sulfur is converted to SO2 (g).
What volume of SO2 (g) measured at 25oC and 738mmHg is produced by burning 3.5x106 Ibs of this coal?
S + O2 = SO2.
Answer: 2.6x107 L SO2
17. §1.50L H2S (g) measured at 23.0oC and 735mmHg is mixed with 4.45L O2 (g) measured at 26.1oC and
751mmHg, is burned: H2S (g) + O2 (g) = SO2 (g) + H2O;
How much SO2(g) in moles is produced? Answer: 0.0597 moles SO2;
18. §A 2.92g sample of a KCl-KClO3 mixture is decomposed by heating and produces 89.8 mL O2 (g) measured
at 21.8oC and 727mmHg. What is the mass percent of KClO3 in the mixture? (Hint: KCl is unchanged):
KClO3 (s) = KCl (s) + O2 (g). Answer: 9.93% KClO3
19. *When a mixture of silver metal and sulfur is heated, silver sulfide is formed:
Ag (s) + S8 (s) = Ag2S (s).
What mass of Ag2S is produced from a mixture of 2.0g of Ag and 2.0g S8?
Answer: 2.3g
20. *The compound cisplatin, Pt(NH3)2Cl2, has been extensively studied as a potential anti-tumor agent.
Cisplatin is synthesized as follows:
K2PtCl4 (aq) + NH3 (aq) = Pt(NH3)2Cl2 (s) + KCl (aq)
What mass of cisplatin can be made from 65g of K2PtCl4 and sufficient NH3? What mass of KCl is also
produced?
Answer: (a). 47g cisplatin; (b). 23g HCl
21. CH4 burns in O2 producing CO2 and H2O (g). A 1.22L CH4 cylinder at 15oC, registers a pressure of 328KPa. (a)
What volume of O2 at 100KPa and 298K will be required to react completely with all the CH4? (b). How
many grams of H2O (g) are produced?
CH4 + O2 = CO2 + H2O. Answer: (a). 8.28L; (b) 6.02g H2O
22. ¶What is the Molarity of K+ in an aqueous solution that contains 63.3ppm K3Fe(CN)6? Assume that the
density of the aqueous solution is essentially that of water i.e. 1.00g/mL.
Answer: 5.77x10-4M K+
23. How many grams of HCl are consumed in a reaction of 425g of a mixture containing 35.2% MgCO 3 and
64.8% Mg(OH)2 by mass; given the following equations? (Hint: Solve the problem in two parts)
MgCO3 + HCl = MgCl2 + H2O + CO2
Mg(OH)2 + HCl = MgCl2 + H2O
Answer: 473.8g HCl
24. §Vinegar is a dilute aqueous solution of acetic acid (HC2H3O2) produced by the bacterial fermentation of
apple cider, wine or other carbohydrate material. The legal minimum acetic acid content of vinegar is 4%
by mass. A 5.00mL sample of a particular vinegar was titrated with 38.08mL of 0.1000M NaOH (aq). Does
this sample exceed the minimum limit? (Vinegar has a density of about 1.01g/mL).
HC2H3O2 + OH- = C2H3O2- + H2O. Answer 4.53% HC2H3O2
25. §For the reaction:
Ca(OH)2 + 2HCl = CaCl2 + 2H2O;
(a). What mass of Ca(OH)2 in grams is required to react completely with 485 mL of 0.886M HCl?
(b). What mass of Ca(OH)2 in kilograms is required to react with 465L of an HCl solution that is 30.12% HCl
by mass and has a density of 1.15g/mL?
Answer: (a) 15.9g Ca(OH)2; (b) 164Kg Ca(OH)2
26. §Lithophone is a brilliant white pigment used in water-based interior paints. It is a mixture of BaSO4 and
ZnS produced by the reaction: BaS + ZnSO4 = ZnS + BaSO4.
What mass of Lithophone in grams is produced in the reaction of 275 mL of 0.350M ZnSO 4 and 325mL of
0.280M BaS? (Hint: Solve this problem in two parts)
Answer: 30.1 g Lithophone
27. §A 1.562g sample of the hydrocarbon C7H16 is burned in excess oxygen. What mass of (a) CO2, and (b) H2O,
should be obtained?
Answer: (a) 4.802g CO2; (b) 2.247g H2O
28. *The reusable booster rockets of the US space shuttle employ a mixture of Aluminum and Ammonium
Perchlorate for fuel. A possible equation for the reaction is:
Al + NH4ClO4 = Al2O3 + AlCl3 + NO + H2O.
What mass of NH4ClO4 in Kg, should be used in the fuel mixture for every Kg of Al?
Answer: 4.4Kg NH4ClO4.
29. How many milliliters of 3.00M H2SO4 are required to react with 4.35g of solid containing 23.2% Ba(NO3)2 if
the reaction is Ba2+ + SO42- --> BaSO4(s)? Hint: figure out all the mole relationships (a challenging
question!)
Answer: 1.29mL H2SO4 solution
30. A 2.50 mL sample of low-fat milk was treated with sodium oxalate, and the precipitate was filtered and
dissolved in H2SO4. This solution required 6.81 mL of 4.56x10-3 M KMnO4 to reach the end point.
(a) Calculate the Molarity of Ca2+ in the milk.
(b) What is the concentration of Ca2+ in g/L?
Answer: (a) 0.00621M Ca2+; (b) 0.249 g Ca2+ / L Milk
31. 69.32g of an unknown monoprotic acid is dissolved in a 250mL volumetric flask. If 5.00 mL of this solution
is transferred into a conical flask and titrated to equivalence with 36.86mL of 0.1066M NaOH, what is the
molecular weight of the unknown acid.
Answer: 353 g/mole (H+)
32. Only one isotope of this element occurs in nature. One atom of this isotope has a mass of 9.123 x 10 -23g.
Identify the element and give its atomic weight.
Answer: 54.94 g/mole, Mn – Manganese
33. Chlorophyll (essential for the process of photosynthesis) contains Mg to the extent of 2.72% by mass.
Assuming one Mg atom per chlorophyll molecule, what is the molecular mass of chlorophyll?
Answer: 894 g/mole (chlorophyll).
34. In rhombic sulfur, S atoms are joined into S8 molecules. If the density of rhombic sulfur is 2.07g/cm3,
determine for a crystal of volume 2.10 x 10-3 cm3; (a) the number of moles of S8; (b) the total number of S
atoms. Answer: 1.69 x 10-5 moles S8; (b) 8.14 x 1019 atoms S
35. When ammonium carbonate is heated, three gases are produced by its decomposition. (NH4)2CO3(s) =
2NH3 (g) +CO2 (g) + H2O (g). What total volume of gas is produced, measured at 453 oC and 1.04 atm, if
52.0 g of ammonium carbonate is heated? (Hint: solve this problem in three parts). Answer: 124L
36. How many kilograms of limestone should be added for every kilogram of iron ore processed in a blast
furnace if the limestone is 93.00% pure and the iron ore contains 10.60% SiO 2 by mass?
(Note: SiO2 + CaCO3 = CaSiO3 + CO2). Answer: 0.1899 Kg (limestone)/ Kg (iron ore) or 18.99% limestone
37. The reaction below can be used as a laboratory method of preparing small quantities of Cl2. If a 62.6 g
sample that s 98.5 % K2Cr2O7, by mass, is allowed to react with 325 mL of HCl with a density of 1.15 g/mL
and 30.1 % HCl by mass, how many grams of Cl2 are produced?
Cr2O72- + Cl- + H+ → Cr3+ + Cl2 + H2O. Answer: 44.7g Cl2
38. A 3.33 gram sample of iron ore is transformed to a solution of iron (II) sulfate, and this solution is titrated
with 0.150 M potassium dichromate. If it required 41.4 mL of potassium dichromate solution to titrate the
iron (II) sulfate solution, what is the percentage of iron in the ore? Fe+2 (aq) + Cr2O7-2(aq) + H+ = Fe+3 (aq) +
Cr+3 (aq) + H2O (unbalanced). Answer: 62.5% Fe2+
39. Turquoise is given by the following molecular formula: CuAl6(PO4)4(OH)8.4H2O
a. What is the total number of atoms in a 5.00 g sample of turquoise?
b. What mass of turquoise (in mg) contains 3.75 x 1022 atoms of oxygen?
Answer: (a). 3.70 x 1021 atoms; (b) 1810mg
40. How many grams of manganese dioxide are produced in the reaction of 224mL of 0.0465 M potassium
permanganate and 356mL of 0.0677 M potassium cyanide, which react in a basic solution according to the
unbalanced equation: MnO4- + CN- + H2O = MnO2 + OCN- + OHAnswer: 0.906g MnO2
41. In a titration, 25cm3 of 0.100M KOH is pipetted into a conical flask. Sulphuric acid (H2SO4) is run in from the
burette and it was found that 19.8cm3 were required to react exactly. Calculate the concentration of the
H2SO4 (Hint: first write and balance the equation). Answer: 0.063M H2SO4
42. 0.9733g of FeCl2, 1.661g of FeCl3, and 3.000g of KCN are added together to produce the following
equation FeCl2 + FeCl3 + KCN = KCl + Fe4[Fe(CN)6]3. Balance the reaction and calculate the amount in
grams of (a) KCl and (b) Fe4[Fe(CN)6]3 produced. Answer: (a). 3.435g KCl; (b). 2.199g Fe4[Fe(CN) 6]3.
43. A 0.20g sample of a monobasic acid requires 8.0 cm3 of 0.40M sodium hydroxide for the complete
reaction? What is the relative molecular mass of the acid? Answer: 63 g/mole (H+).
44. A water supply has become contaminated with alcohol (COH4). To determine the extent of the
contamination, one needs to determine the number of moles of alcohol / kg of H2O in a solution of 6.00
grams COH4 in 100.0g of H2O. The result should have 3 significant figures.
Answer: 1.87 moles (COH4)/Kg (H2O)
45. ¶Seawater contains an average of 1.08 x 103 ppm of Na+ and 270 ppm SO42-. Calculate the molar
concentrations of Na+ and SO42- given that the average density of seawater is 1.02g/mL.
Answer: (a). 0.0479M Na+; (b). 0.0287M SO4246. A 7.88% (w/w) Fe(NO3)3 solution has a density of 1.062 g/mL. Calculate (a) the molar analytical
concentration of Fe(NO3)3 in this solution; and (b) the grams Fe(NO3)3 contained in each liter of this
solution. Answer: (a). 0.346M Fe(NO3)2; (b) 83.7g/L
47. What mass of solid La(IO3)3 is formed when 50.0mL of 0.150M La3+ are mixed with 75.0mL 0f 0.202M
IO3-? Answer: 3.35g La(IO3)3
48. If you were to take the mineral hematite (Fe2O3) and cause a reaction with carbon, you could produce
iron metal. Can you calculate and tell me how many grams of iron are present in a gram of hematite? Your
result should have 5 significant figures. (Here are two hints to help you: the molecular weight of Fe is
55.847 g Fe / mol Fe and the molecular weight of Fe2O3 is 159.692 g Fe2O3 / mol Fe2O3.).
Answer: 0.69943g Fe/g Fe2O3
49. The chemical method of analysis in determination of the blood alcohol content (%BAC) is:
K2Cr2O7 + H2SO4 + C2H5OH ---> Cr2(SO4)3 + K2SO4 + CH3COOH + H2O. During a Breathalyzer Test it was
determined that 1.70mg of K2Cr2O7 was consumed by the above reaction. Calculate the number of
milligrams of ethanol in the test sample. Answer: 0.399mg C2H5OH
50. 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 40.00 mL of glacial acetic acid at 25°C in enough
water to make 150.0 mL of solution. Answer: 4.658M Acetic Acid
51. To analyze an iron containing compound, you convert all the iron into Fe2+ in aqueous solution and then
titrate the solution with standardized KMnO4. MnO4- + Fe2+ + H+ --> Mn2+ + Fe3+ + H2O (a) Balance
this equation (b) A 0.956g sample of iron-compound requires 22.25 mL of 0.0123 M KMnO4 for titration to
the equivalence point. What is the mass percent of iron in the sample? Answer: 7.99% Fe
52. The iron concentration of an acidic mine waste was determined by reducing all Fe present to Fe 2+, and
then titration using a standard dichromate solution. A 100.00 mL sample of acid mine waste was titrated
with 0.0376 mol/L Cr2O72-. The titration volume was 7.13 mL. The unbalanced equation is as follows:
Fe2+ + Cr2O72- + H+ --> Fe3+ + Cr3+ + H2O. Calculate the iron concentration in mg/L (ppm).
Answer: 898ppm
53. In an experiment ammonium iron (II) sulfate hexahydrate FeSO4 (NH4)2 SO4.6H2O is used to prepare the
stock solution of iron. How much of this salt is required to prepare 500.0 mL of stock which has an iron
concentration of 40.00 mg/L? Answer: 0.1404g FeSO4 (NH4)2 SO4.6H2O
54. §The mineral spodumene has the formula Li2O.Al2O3.4SiO2. Given the percentage of Lithium-6 atoms in
naturally occurring Lithium is 7.40%, how many lithium-6 atoms are present in a 426-g sample of
spodumene? Answer 1.02 x 1023 6Li atoms.
55. §What mass of the food preservative butylated hydroxyanisole (BHA), C11H16O2, should be burned to
produce 0.5000g CO2 in combustion analysis? Answer: 0.1862g BHA.
56. The production capacity for acrylonitrile (C3H3N) in the United States is over 2 million pounds per year.
Acrylonitrile, the building block for polyacrylonitrile fibers and a variety of plastics, is produced from
gaseous propylene, ammonia, and oxygen. C3H6 (g) + NH3(g) + O2(g) = C3H3N(g) + H2O(g). After balancing the
equation, calculate the mass of acrylonitrile that is produced from a mixture of 1.29 kg of propylene, 1.88
kg of ammonia, and 2.74 kg of oxygen. Answer: 1.63Kg C3H3N
57. Gasoline (C7H16) has a density of 0.685 kg/liter. How many liters of oxygen at 37 °C and 950 mmHg are
needed to burn 15 liters of gasoline? Answer: 2.3 x 104 L O2
58. Aluminum can be determined gravimetrically by reaction with a solution of 8-hydroxyquinoline (C9H7NO).
The net ionic equation is: Al3+ + C9H7NO → Al(C9H6NO)3 + H+. A mass of 0.1248 g of Al(C9H6NO)3 was
obtained by precipitating all of the Al3+ from a solution prepared by dissolving 1.8571 g of a mineral. What
is the mass percent of aluminum in the mineral sample? Answer: 0.3947%
59. A test solution of aluminum nitrate must be made that is 20.0 g/L in the salt. If 1500.0 mL of the solution is
desired, (a) how many grams of the solute must be used? (b) What is the Molarity of the solution?
Answer: (a). 30.0 g, (b). 0.0940 M
60. The bromide ion concentration in a solution may be determined by the precipitation of silver bromide.
Ag+(aq) + Br-(aq) = AgBr(s) A student finds that 23.43 mL of 0.7370 M silver nitrate is needed to precipitate
all of the bromide ion in a 10.00-mL sample of an unknown. What is the molarity of the bromide ion in the
student's unknown? Answer: 1.727M Br61. *Hemoglobin is the protein that transports oxygen in mammals. Hemoglobin is 0.342% Fe by mass, and
each hemoglobin molecule contains four iron atoms. Calculate the molar mass of hemoglobin.
Answer: 6.53 x 104 g/mole hemoglobin
62. *Vitamin B12, cyanocobalamin, is essential for human nutrition. It is concentrated in animal tissue but not
in higher plants. Although nutritional requirements for the vitamin are quite low, people who abstain
completely from animal products may develop a deficiency anemia. Cyanocobalamin is the form used in
vitamin supplements. It contains 4.34% cobalt by mass. Calculate the molar mass of cyanocobalamin,
assuming there is one atom of cobalt in every molecule of cyanocobalamin.
Answer: 1.36 x 103 g/mole cyanocobalamin
63. A 0.783 g sample of an ore of iron is dissolved in acid and converted to Fe (II). The sample is oxidized by
38.50 mL of 0.161 M Ce(SO4)2. The cerium IV ion is reduced to Ce (III). Write the balanced equation for this
reaction and determine the percent of iron in the ore. Answer: 44.2% Fe
64. A certain gas with a density of 1.65g/L occupies a container at 27oC and exerts a pressure of 734 torr.
What is the formula mass of the gas? Answer: 42g/mol
65. What is the maximum mass of calcium hydrogen phosphate, CaHPO4, that can form from the mixture of
12.50 kg of a solution that contains 84.0% H3PO4, 25.00 kg of Ca(NO3)2, 25.00 L of 14.8 M NH3, and an
excess of CO2 and H2O? 3H3PO4 + 5Ca (NO3)2 + 10NH3 + 2CO2 + 2H2O → 10NH4NO3 + 2CaCO3 + 3CaHPO4
Answer: 12.4 Kg CaHPO4
66. How many grams of baking soda (NaHCO3) must be used to produce 45mL of CO2 gas at 190 degrees
Celsius and 101.3 kPa in a pan muffin? Answer: 0.20g baking soda
67. A student collects 41.4mL of O2 at 745mm and 26oC by water displacement. The water level inside and
outside the collection tube are equal. How many moles of O2 are present? Answer - 0.0016 moles.
68. How many grams of sodium hydrogen carbonate, NaHCO3, must be heated to produce 2.50 L of carbon
dioxide measured at 22.5 degrees C and 97.5 kPa? The other products are sodium carbonate and water.
Answer: 16.7g NaHCO3
69. The equation for removing hydrogen sulfate from sour natural gas is: H2S(g)+O2(g)=>H2O+S(s)
Let's say a processing plant has a nominal capacity of 0.5 metric tons of sulfur per day, and that the input
sour gas has a content of 3% by mass. How would one go about calculating the mass (in Kg) of natural gas
that this plant could process each day? Answer: 1.77 x 104 Kg sour gas
70. Ammonia reacts with sulfuric acid to form ammonium sulfate. What mass of ammonium sulfate can be
produced from 75.0 kL of ammonia at 10 oC and 110 KPa? Answer: 232Kg (NH4)2SO4.
71. How many milliliters of 3.60 M H2SO4 are required to react with 2.00 g of solid containing 40.0 wt%
Ba(NO3)2 if the reaction is as shown; Ba2+ + SO42-  BaSO4(s)? Answer: 0.850mL
72. 168 L of concentrated nitric acid (62.4% by mass, density 1.46 g/cm3) was spilt on a road. Sodium
carbonate was spread on the spill to neutralize the acid. How many kilograms of sodium carbonate are
needed? Answer: 129Kg Na2CO3
73. My car has a 13.7 gallon tank. Assuming that gasoline is entirely made from octane (C8H18), how many
pounds of CO2 would be produced from my car (due to combustion) each time I use a tank of gas given
that the density of octane is 0.855g/mL? Answer: 301 pounds O2
74. A student measures 10.00mL of unknown solution of Fe 2+ into an erlenmeyer flask and dilutes with 90mL
of 1.0M HCl acid. He then titrates this sample with 0.001975M of dichromate solution. If 29.79mL of
potassium dichromate solution is needed to reach the end point, what is the concentration of Fe2+ in the
original solution? The governing reaction is as follows: Cr2O72- + 6Fe2+ + 14H+ = 2Cr3+ + 6Fe3+ + 7H20 .
Hint: The acid is for pH adjustment. Answer: 0.03530M Fe2+
Combination Problems:
(a). Determine the empirical formula of a compound with the following composition by mass: 60.0 % C, 8.0 %
H and 32.0 % O. (b). If 100 mg of this compound is neutralized with exactly 10.0 mL of 0.0500 M NaOH in a
reaction with a 1:1 stoichiometry, what is the molecular formula of this compound? Answers: (a) C5H8O2 (b)
C10H16O4
(b). A 33.5g sample of iron is heated, producing 46.3 g of iron oxide. What is the empirical formula of the
oxide? Verify your answer by confirming the weight of Fe and O2 in the oxide. Answer: Fe3O4
References
§
General Chemistry: Principles and Modern Applications by R.H. Petrucci and D.S. Harwood; 6 th edition;
MacMillan Publishing Company, 1993
*Chemical Principles by Stephen S. Zumdahl; D.C Heath and Company, 1992
¶
Analytical Chemistry: An Introduction by D.A Skoog, D.M. West, and F.J. Holler; 6 th Edition; Saunders
College Publishing, 1994