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Problem 88b
What are the empirical formulas of substances with the following mass percent compositions? (b) Ilmenite (a titanium-containing ore): 31.63% O, 31.56% Ti, 36.81% Fe
Problem 88c
What are the empirical formulas of substances with the following mass percent compositions? (c) Sodium thiosulfate (photographic 'fixer'): 30.36% O, 29.08% Na, 40.56% S
- Ferrocene, a substance proposed for use as a gasoline additive, has the percent composition 5.42% H, 64.56% C, and 30.02% Fe. What is the empirical formula of ferrocene?
Problem 89
- What is the empirical formula of stannous fluoride, the first fluoride compound added to toothpaste to protect teeth against decay? Its mass percent composition is 24.25% F, 75.75% Sn.
Problem 90
Problem 91a
What are the empirical formulas of each of the following substances? (a) Ibuprofen, a headache remedy: 75.69% C, 15.51% O, 8.80% H
Problem 91b
What are the empirical formulas of each of the following substances? (b) Magnetite, a naturally occurring magnetic mineral: 72.36% Fe, 27.64% O
Problem 91c
What are the empirical formulas of each of the following substances? (c) Zircon, a mineral from which cubic zirconia is made: 34.91% O, 15.32% Si, 49.77% Zr
- An unknown liquid is composed of 5.57% H, 28.01% Cl, and 66.42% C. The molecular weight found by mass spectrometry is 126.58. What is the molecular formula of the compound?
Problem 92
- An unknown liquid is composed of 34.31% C, 5.28% H, and 60.41% I. The molecular weight found by mass spectrometry is 210.06. What is the molecular formula of the compound?
Problem 93
- Combustion analysis of 45.62 mg of toluene, a commonly used solvent, gives 35.67 mg of H2O and 152.5 mg of CO2. What is the empirical formula of toluene?
Problem 94
- Coniine, a toxic substance isolated from poison hemlock, contains only carbon, hydrogen, and nitrogen. Combus-tion analysis of a 5.024 mg sample yields 13.90 mg of CO2 and 6.048 mg of H2O. What is the empirical formula of coniine?
Problem 95
Problem 96
Cytochrome c is an iron-containing enzyme found in the cells of all aerobic organisms. If cytochrome c is 0.43% Fe by mass, what is its minimum molecular weight?
- Nitrogen fixation in the root nodules of peas and other leguminous plants is carried out by the molybdenum-containing enzyme nitrogenase. What is the molecular mass of nitrogenase if the enzyme contains two molybdenum atoms and is 0.0872% Mo by mass?
Problem 97
- Disilane, Si2Hx, is analyzed and found to contain 90.28% silicon by mass. What is the value of x?
Problem 98
- A certain metal sulfide, MS2, is used extensively as a high-temperature lubricant. If MS2 is 40.06% sulfur by mass, what is the identity of the metal M?
Problem 99
- Combustion analysis of a 31.472 mg sample of the widely used flame retardant Decabrom gave 1.444 mg of CO2. Is the molecular formula of Decabrom C12Br10 or C12Br10O?
Problem 100
- The stimulant amphetamine contains only carbon, hydrogen, and nitrogen. Combustion analysis of a 42.92 mg sample of amphetamine gives 37.187 mg of H2O and 125.75 mg of CO2. If the molar mass of amphetamine is less than 160 g/mol, what is its molecular formula?
Problem 101
Problem 101a
Heating elemental cesium and platinum together for two days at 973 K gives a dark red ionic compound that is 57.67% Cs and 42.33% Pt. (a) What is the empirical formula of the compound?
- Describe the path of a neutral molecule in the mass spectrometer. Why is ionization a necessary first step?
Problem 102
- Why are high precision and accuracy in molecular mass measurement needed for identifying the formula of molecules made in the lab?
Problem 103
- The molecular weight of an organic compound was found by mass spectrometry to be 70.042 11. Is the sample C5H10, C4H6O, or C3H6N2? Exact masses of elements are: 1.007 825 (1H); 12.000 00 (12C); 14.003 074 (14N); 15.994 915 (16O).
Problem 104
- The mass of an organic compound was found by mass spectrometry to be 58.07746. Is the sample C4H10, C3H6O, or C2H6N2? Exact masses of elements are: 1.007825 (1H); 12.00000 (12C); 14.003074 (14N); 15.994915 (16O).
Problem 105
Problem 106a
(a) Combustion analysis of 50.0 mg of benzene, a commonly used solvent composed of carbon and hydrogen, gives 34.6 mg of H2O and 169.2 mg of CO2. What is the empirical formula of benzene?
Problem 106b
b) Given the mass spectrum of benzene, identify the molecular weight and give the molecular formula.
- (a) Combustion analysis of 150.0 mg of 1,2,3,benzenetriol, a compound composed of carbon, hydrogen, and oxy-gen, gives 64.3 mg of H2O and 314.2 mg of CO2. What is the empirical formula of 1,2,3,benzenetriol?
Problem 107
Problem 108
The molecular weight of ethylene glycol is 62.0689 when calculated using the atomic weights found in a standard periodic table, yet the molecular weight determined experimentally by high-resolution mass spectrometry is 62.0368. Explain the discrepancy.
- Assume that gasoline has the formula C8H18 and has a density of 0.703 g/mL. How many pounds of CO2 are produced from the complete combustion of 1.00 gal of gasoline?
Problem 110
- Compound X contains only carbon, hydrogen, nitrogen, and chlorine. When 1.00 g of X is dissolved in water and allowed to react with excess silver nitrate, AgNO3, all the chlorine in X reacts and 1.95 g of solid AgCl is formed. When 1.00 g of X undergoes complete combustion, 0.900 g of CO2 and 0.735 g of H2O are formed. What is the empirical formula of X?
Problem 111
- A pulverized rock sample believed to be pure calcium carbonate, CaCO3, is subjected to chemical analysis and found to contain 51.3% Ca, 7.7% C, and 41.0% O by mass. Why can't this rock sample be pure CaCO3?
Problem 112
- A certain alcoholic beverage contains only ethanol (C2H6O) and water. When a sample of this beverage undergoes com-bustion, the ethanol burns but the water simply evaporates and is collected along with the water produced by combus-tion. The combustion reaction is When a 10.00 g sample of this beverage is burned, 11.27 g of water is collected. What is the mass in grams of ethanol, and what is the mass of water in the original sample?
Problem 113