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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
Problem 114
A mixture of FeO and Fe2O3 with a mass of 10.0 g is con-verted to 7.43 g of pure Fe metal. What are the amounts in grams of FeO and Fe2O3 in the original sample?
Problem 115
A compound of formula XCl3 reacts with aqueous AgNO3 to yield solid AgCl according to the following equation: When a solution containing 0.634 g of XCl3 was allowed to react with an excess of aqueous AgNO3, 1.68 g of solid AgCl was formed. What is the identity of the atom X?
- When eaten, dietary carbohydrates are digested to yield glu-cose (C6H12O6), which is then metabolized to yield carbon dioxide and water: Balance the equation, and calculate both the mass in grams and the volume in liters of the CO2 produced from 66.3 g of glucose, assuming that 1 mol of CO2 has a volume of 25.4 L at normal body temperature.
Problem 116
Problem 117a
A copper wire having a mass of 2.196 g was allowed to react with an excess of sulfur. The excess sulfur was then burned, yielding SO2 gas. The mass of the copper sulfide produced was 2.748 g. (a) What is the percent composition of copper sulfide?
Problem 117b
A copper wire having a mass of 2.196 g was allowed to react with an excess of sulfur. The excess sulfur was then burned, yielding SO2 gas. The mass of the copper sulfide produced was 2.748 g. (b) What is its empirical formula?
- Element X, a member of group 5A, forms two chlorides, XCl3 and XCl5. Reaction of an excess of Cl2 with 8.729 g of XCl3 yields 13.233 g of XCl5. What is the atomic weight and the identity of the element X?
Problem 118
- A mixture of XCl3 and XCl5 weighing 10.00 g contains 81.04% Cl by mass. How many grams of XCl3 and how many grams of XCl5 are present in the mixture?
Problem 119
Problem 120
Ammonium nitrate, a potential ingredient of terrorist bombs, can be made nonexplosive by addition of diammo-nium hydrogen phosphate, (NH4)2HPO4. Analysis of such a NH4NO3 - (NH4)2HPO4 mixture showed the mass percent of nitrogen to be 30.43%. What is the mass ratio of the two components in the mixture?
- Window glass is typically made by mixing soda ash (Na2CO3), limestone (CaCO3), and silica sand (SiO2) and then heating to 1500 °C to drive off CO2 from the (Na2CO3) and CaCO3. The resultant glass consists of about 12% Na2O by mass, 13% CaO by mass, and 75% SiO2 by mass. How much of each reactant would you start with to prepare 0.35 kg of glass?
Problem 121
- An unidentified metal M reacts with an unidentified halogen X to form a compound MX2. When heated, the compound decomposes by the reaction: When 1.12 g of MX2 is heated, 0.720 g of MX is obtained, along with 56.0 mL of X2 gas. Under the conditions used, 1.00 mol of the gas has a volume of 22.41 L. (a) What is the atomic weight and identity of the halogen X?
Problem 122
- Ethylene glycol, commonly used as automobile antifreeze, contains only carbon, hydrogen, and oxygen. Combustion analysis of a 23.46 mg sample yields 20.42 mg of H2O and 33.27 mg of CO2. What is the empirical formula of ethylene glycol? What is its molecular formula if it has a molecular weight of 62.0?
Problem 123