Answer: If we know the empirical formula of a compound,

What is an atomic mass unit? Why is it necessary to introduce such a unit?

What is the mass (in amu) of a carbon-12 atom? Why is the atomic mass of carbon listed as 12.01 amu in the table on the inside front cover of this book?

Explain clearly what is meant by the statement The atomic mass of gold is 197.0 amu.

What information would you need to calculate the average atomic mass of an element?

The atomic masses of 35 17Cl (75.53 percent) and 37 17Cl (24.47 percent) are 34.968 amu and 36.956 amu, respectively. Calculate the average atomic mass of chlorine. The percentages in parentheses denote the relative abundances.

The atomic masses of 6 3Li and 7 3Li are 6.0151 amu and 7.0160 amu, respectively. Calculate the natural abundances of these two isotopes. The average atomic mass of Li is 6.941 amu.

What is the mass in grams of 13.2 amu?

How many amu are there in 8.4 g?

Define the term mole. What is the unit for mole in calculations? What does the mole have in common with the pair, the dozen, and the gross? What does Avogadros number represent?

What is the molar mass of an atom? What are the commonly used units for molar mass?

Earths population is about 7.2 billion. Suppose that every person on Earth participates in a process of counting identical particles at the rate of two particles per second. How many years would it take to count 6.0 3 1023 particles? Assume that there are 365 days in a year

The thickness of a piece of paper is 0.0036 in. Suppose a certain book has an Avogadros number of pages; calculate the thickness of the book in light-years. (Hint: See Problem 1.49 for the definition of light-year.)

How many atoms are there in 5.10 moles of sulfur (S)?

How many moles of cobalt (Co) atoms are there in 6.00 3 109 (6 billion) Co atoms?

How many moles of calcium (Ca) atoms are in 77.4 g of Ca?

How many grams of gold (Au) are there in 15.3 moles of Au?

What is the mass in grams of a single atom of each of the following elements? (a) Hg, (b) Ne

What is the mass in grams of a single atom of each of the following elements? (a) As, (b) Ni

What is the mass in grams of 1.00 3 1012 lead (Pb) atoms?

A modern penny weighs 2.5 g but contains only 0.063 g of copper (Cu). How many copper atoms are present in a modern penny

Which of the following has more atoms: 1.10 g of hydrogen atoms or 14.7 g of chromium atoms?

Which of the following has a greater mass: 2 atoms of lead or 5.1 3 10223 mole of helium.

Calculate the molecular mass or formula mass (in amu) of each of the following substances: (a) CH4, (b) NO2, (c) SO3, (d) C6H6, (e) NaI, (f) K2SO4, (g) Ca3(PO4)2.

Calculate the molar mass of the following substances: (a) Li2CO3, (b) CS2, (c) CHCl3 (chloroform), (d) C6H8O6 (ascorbic acid, or vitamin C), (e) KNO3, (f) Mg3N2.

Calculate the molar mass of a compound if 0.372 mole of it has a mass of 152 g

How many molecules of ethane (C2H6) are present in 0.334 g of C2H6?

Calculate the number of C, H, and O atoms in 1.50 g of glucose (C6H12O6), a sugar.

Dimethyl sulfoxide [(CH3)2SO], also called DMSO, is an important solvent that penetrates the skin, enabling it to be used as a topical drug-delivery agent. Calculate the number of C, S, H, and O atoms in 7.14 3 103 g of dimethyl sulfoxide

Pheromones are a special type of compound secreted by the females of many insect species to attract the males for mating. One pheromone has the molecular formula C19H38O. Normally, the amount of this pheromone secreted by a female insect is about 1.0 3 10212 g. How many molecules are there in this quantity?

The density of water is 1.00 g/mL at 48C. How many water molecules are present in 2.56 mL of water at this temperature?

Describe the operation of a mass spectrometer

Describe how you would determine the isotopic abundance of an element from its mass spectrum.

Carbon has two stable isotopes, 12 6C and 13 6C, and fluorine has only one stable isotope, 19 9F. How many peaks would you observe in the mass spectrum of the positive ion of CF1 4? Assume that the ion does not break up into smaller fragments

Hydrogen has two stable isotopes, 1 1H and 2 1H, and sulfur has four stable isotopes, 32 16S, 33 16S, 34 16S, and 36 16S. How many peaks would you observe in the mass spectrum of the positive ion of hydrogen sulfide, H2S1? Assume no decomposition of the ion into smaller fragments.

Use ammonia (NH3) to explain what is meant by the percent composition by mass of a compound.

Describe how the knowledge of the percent composition by mass of an unknown compound can help us identify the compound.

What does the word empirical in empirical formula mean?

If we know the empirical formula of a compound, what additional information do we need to determine its molecular formula?

Tin (Sn) exists in Earths crust as SnO2. Calculate the percent composition by mass of Sn and O in SnO2.

For many years chloroform (CHCl3) was used as an inhalation anesthetic in spite of the fact that it is also a toxic substance that may cause severe liver, kidney, and heart damage. Calculate the percent composition by mass of this compound.

Cinnamic alcohol is used mainly in perfumery, particularly in soaps and cosmetics. Its molecular formula is C9H10O. (a) Calculate the percent composition by mass of C, H, and O in cinnamic alcohol. (b) How many molecules of cinnamic alcohol are contained in a sample of mass 0.469 g?

All of the substances listed here are fertilizers that contribute nitrogen to the soil. Which of these is the richest source of nitrogen on a mass percentage basis? (a) Urea, (NH2)2CO (b) Ammonium nitrate, NH4NO3 (c) Guanidine, HNC(NH2)2 (d) Ammonia, NH3

Allicin is the compound responsible for the characteristic smell of garlic. An analysis of the compound gives the following percent composition by mass: C: 44.4 percent; H: 6.21 percent; S: 39.5 percent; O: 9.86 percent. Calculate its empirical formula. What is its molecular formula given that its molar mass is about 162 g?

Peroxyacylnitrate (PAN) is one of the components of smog. It is a compound of C, H, N, and O. Determine the percent composition of oxygen and the empirical formula from the following percent composition by mass: 19.8 percent C, 2.50 percent H, 11.6 percent N. What is its molecular formula given that its molar mass is about 120 g?

The formula for rust can be represented by Fe2O3. How many moles of Fe are present in 24.6 g of the compound?

How many grams of sulfur (S) are needed to react completely with 246 g of mercury (Hg) to form HgS?

Calculate the mass in grams of iodine (I2) that will react completely with 20.4 g of aluminum (Al) to form aluminum iodide (AlI3).

Tin(II) fluoride (SnF2) is often added to toothpaste as an ingredient to prevent tooth decay. What is the mass of F in grams in 24.6 g of the compound?

What are the empirical formulas of the compounds with the following compositions? (a) 2.1 percent H, 65.3 percent O, 32.6 percent S, (b) 20.2 percent Al, 79.8 percent Cl.

What are the empirical formulas of the compounds with the following compositions? (a) 40.1 percent C, 6.6 percent H, 53.3 percent O, (b) 18.4 percent C, 21.5 percent N, 60.1 percent K

The anticaking agent added to Morton salt is calcium silicate, CaSiO3. This compound can absorb up to 2.5 times its mass of water and still remains a free-flowing powder. Calculate the percent composition of CaSiO3.

The empirical formula of a compound is CH. If the molar mass of this compound is about 78 g, what is its molecular formula?

The molar mass of caffeine is 194.19 g. Is the molecular formula of caffeine C4H5N2O or C8H10N4O2?

Monosodium glutamate (MSG), a food-flavor enhancer, has been blamed for Chinese restaurant syndrome, the symptoms of which are headaches and chest pains. MSG has the following composition by mass: 35.51 percent C, 4.77 percent H, 37.85 percent O, 8.29 percent N, and 13.60 percent Na. What is its molecular formula if its molar mass is about 169 g?

Use the formation of water from hydrogen and oxygen to explain the following terms: chemical reaction, reactant, product.

What is the difference between a chemical reaction and a chemical equation?

Why must a chemical equation be balanced? What law is obeyed by a balanced chemical equation?

Write the symbols used to represent gas, liquid, solid, and the aqueous phase in chemical equations.

Balance the following equations using the method outlined in Section 3.7: (a) C 1 O2 CO (b) CO 1 O2 CO2 (c) H2 1 Br2 HBr (d) K 1 H2O KOH 1 H2 (e) Mg 1 O2 MgO (f) O3 O2 (g) H2O2 H2O 1 O2 (h) N2 1 H2 NH3 (i) Zn 1 AgCl ZnCl2 1 Ag (j) S8 1 O2 SO2 (k) NaOH 1 H2SO4 Na2SO4 1 H2O (l) Cl2 1 NaI NaCl 1 I2 (m) KOH 1 H3PO4 K3PO4 1 H2O (n) CH4 1 Br2 CBr4 1 HBr

Balance the following equations using the method outlined in Section 3.7: (a) N2O5 N2O4 1 O2 (b) KNO3 KNO2 1 O2 (c) NH4NO3 N2O 1 H2O (d) NH4NO2 N2 1 H2O (e) NaHCO3 Na2CO3 1 H2O 1 CO2 (f) P4O10 1 H2O H3PO4 (g) HCl 1 CaCO3 CaCl2 1 H2O 1 CO2 (h) Al 1 H2SO4 Al2(SO4)3 1 H2 (i) CO2 1 KOH K2CO3 1 H2O (j) CH4 1 O2 CO2 1 H2O (k) Be2C 1 H2O Be(OH)2 1 CH4 (l) Cu 1 HNO3 Cu(NO3)2 1 NO 1 H2O (m) S 1 HNO3 H2SO4 1 NO2 1 H2O (n) NH3 1 CuO Cu 1 N2 1 H2O

On what law is stoichiometry based? Why is it essential to use balanced equations in solving stoichiometric problems?

Describe the steps involved in the mole method.

Which of the following equations best represents the reaction shown in the diagram? (a) 8A 1 4B C 1 D (b) 4A 1 8B 4C 1 4D (c) 2A 1 B C 1 D (d) 4A 1 2B 4C 1 4D (e) 2A 1 4B C 1 D A D C B

Which of the following equations best represents the reaction shown in the diagram? (a) A 1 B C 1 D (b) 6A 1 4B C 1 D (c) A 1 2B 2C 1 D (d) 3A 1 2B 2C 1 D (e) 3A 1 2B 4C 1 2D 8n A D C B

Consider the combustion of carbon monoxide (CO) in oxygen gas: 2CO(g) 1 O2(g) 2CO2(g) Starting with 3.60 moles of CO, calculate the number of moles of CO2 produced if there is enough oxygen gas to react with all of the CO.

Silicon tetrachloride (SiCl4) can be prepared by heating Si in chlorine gas: Si(s) 1 2Cl2(g) SiCl4(l) In one reaction, 0.507 mole of SiCl4 is produced. How many moles of molecular chlorine were used in the reaction?

Ammonia is a principal nitrogen fertilizer. It is prepared by the reaction between hydrogen and nitrogen. 3H2(g) 1 N2(g) 2NH3(g) In a particular reaction, 6.0 moles of NH3 were produced. How many moles of H2 and how many moles of N2 were reacted to produce this amount of NH3?

Certain race cars use methanol (CH3OH, also called wood alcohol) as a fuel. The combustion of methanol occurs according to the following equation: 2CH3OH(l) 1 3O2(g) 2CO2(g) 1 4H2O(l) In a particular reaction, 9.8 moles of CH3OH are reacted with an excess of O2. Calculate the number of moles of H2O formed.

The annual production of sulfur dioxide from burning coal and fossil fuels, auto exhaust, and other sources is about 26 million tons. The equation for the reaction is S(s) 1 O2(g) SO2(g) How much sulfur (in tons), present in the original materials, would result in that quantity of SO2?

When baking soda (sodium bicarbonate or sodium hydrogen carbonate, NaHCO3) is heated, it releases carbon dioxide gas, which is responsible for the rising of cookies, donuts, and bread. (a) Write a balanced equation for the decomposition of the compound (one of the products is Na2CO3). (b) Calculate the mass of NaHCO3 required to produce 20.5 g of CO2

If chlorine bleach is mixed with other cleaning products containing ammonia, the toxic gas NCl3(g) can form according to the equation: 3NaClO(aq) 1 NH3(aq) 3NaOH(aq) 1 NCl3(g) When 2.94 g of NH3 reacts with an excess of NaClO according to the preceding reaction, how many grams of NCl3 are formed?

Fermentation is a complex chemical process of wine making in which glucose is converted into ethanol and carbon dioxide: C6H12O6 2C2H5OH 1 2CO2 glucose ethanol Starting with 500.4 g of glucose, what is the maximum amount of ethanol in grams and in liters that can be obtained by this process? (Density of ethanol 5 0.789 g/mL.)

Each copper(II) sulfate unit is associated with five water molecules in crystalline copper(II) sulfate pentahydrate (CuSO4 ? 5H2O). When this compound is heated in air above 1008C, it loses the water molecules and also its blue color: CuSO4 ? 5H2O CuSO4 1 5H2O If 9.60 g of CuSO4 are left after heating 15.01 g of the blue compound, calculate the number of moles of H2O originally present in the compound.

For many years the recovery of goldthat is, the separation of gold from other materialsinvolved the use of potassium cyanide: 4Au 1 8KCN 1 O2 1 2H2O 4KAu(CN)2 1 4KOH What is the minimum amount of KCN in moles needed to extract 29.0 g (about an ounce) of gold?

Limestone (CaCO3) is decomposed by heating to quicklime (CaO) and carbon dioxide. Calculate how many grams of quicklime can be produced from 1.0 kg of limestone.

Nitrous oxide (N2O) is also called laughing gas. It can be prepared by the thermal decomposition of ammonium nitrate (NH4NO3). The other product is H2O. (a) Write a balanced equation for this reaction. (b) How many grams of N2O are formed if 0.46 mole of NH4NO3 is used in the reaction?

The fertilizer ammonium sulfate [(NH4)2SO4] is prepared by the reaction between ammonia (NH3) and sulfuric acid: 2NH3(g) 1 H2SO4(aq) (NH4)2SO4(aq) How many kilograms of NH3 are needed to produce 1.00 3 105 kg of (NH4)2SO4?

A common laboratory preparation of oxygen gas is the thermal decomposition of potassium chlorate (KClO3). Assuming complete decomposition, calculate the number of grams of O2 gas that can be obtained from 46.0 g of KClO3. (The products are KCl and O2.)

Define limiting reagent and excess reagent. What is the significance of the limiting reagent in predicting the amount of the product obtained in a reaction? Can there be a limiting reagent if only one reactant is present?

Give an everyday example that illustrates the limiting reagent concept.

Consider the reaction 2A 1 B C (a) In the diagram here that represents the reaction, which reactant, A or B, is the limiting reagent? (b) Assuming complete reaction, draw a molecularmodel representation of the amounts of reactants and products left after the reaction. The atomic arrangement in C is ABA. A B

Consider the reaction N2 1 3H2 2NH3 Assuming each model represents 1 mole of the substance, show the number of moles of the product and the excess reagent left after the complete reaction. H2 N2 NH3

Nitric oxide (NO) reacts with oxygen gas to form nitrogen dioxide (NO2), a dark-brown gas: 2NO(g) 1 O2(g) 2NO2(g) In one experiment 0.886 mole of NO is mixed with 0.503 mole of O2. Calculate which of the two reactants is the limiting reagent. Calculate also the number of moles of NO2 produced.

Ammonia and sulfuric acid react to form ammonium sulfate. (a) Write an equation for the reaction. (b) Determine the starting mass (in g) of each reactant if 20.3 g of ammonium sulfate is produced and 5.89 g of sulfuric acid remains unreacted

Propane (C3H8) is a component of natural gas and is used in domestic cooking and heating. (a) Balance the following equation representing the combustion of propane in air: C3H8 1 O2 CO2 1 H2O (b) How many grams of carbon dioxide can be produced by burning 3.65 moles of propane? Assume that oxygen is the excess reagent in this reaction

Consider the reaction MnO2 1 4HCl MnCl2 1 Cl2 1 2H2O If 0.86 mole of MnO2 and 48.2 g of HCl react, which reagent will be used up first? How many grams of Cl2 will be produced?

Why is the theoretical yield of a reaction determined only by the amount of the limiting reagent?

Why is the actual yield of a reaction almost always smaller than the theoretical yield?

Hydrogen fluoride is used in the manufacture of Freons (which destroy ozone in the stratosphere) and in the production of aluminum metal. It is prepared by the reaction CaF2 1 H2SO4 CaSO4 1 2HF In one process, 6.00 kg of CaF2 are treated with an excess of H2SO4 and yield 2.86 kg of HF. Calculate the percent yield of HF.

Nitroglycerin (C3H5N3O9) is a powerful explosive. Its decomposition may be represented by 4C3H5N3O9 6N2 1 12CO2 1 10H2O 1 O2 This reaction generates a large amount of heat and many gaseous products. It is the sudden formation of these gases, together with their rapid expansion, that produces the explosion. (a) What is the maximum amount of O2 in grams that can be obtained from 2.00 3 102 g of nitroglycerin? (b) Calculate the percent yield in this reaction if the amount of O2 generated is found to be 6.55 g.

Titanium(IV) oxide (TiO2) is a white substance produced by the action of sulfuric acid on the mineral ilmenite (FeTiO3): FeTiO3 1 H2SO4 TiO2 1 FeSO4 1 H2O Its opaque and nontoxic properties make it suitable as a pigment in plastics and paints. In one process, 8.00 3 103 kg of FeTiO3 yielded 3.67 3 103 kg of TiO2. What is the percent yield of the reaction?

Ethylene (C2H4), an important industrial organic chemical, can be prepared by heating hexane (C6H14) at 8008C: C6H14 C2H4 1 other products If the yield of ethylene production is 42.5 percent, what mass of hexane must be reacted to produce 481 g of ethylene?

When heated, lithium reacts with nitrogen to form lithium nitride: 6Li(s) 1 N2(g) 2Li3N(s) What is the theoretical yield of Li3N in grams when 12.3 g of Li are heated with 33.6 g of N2? If the actual yield of Li3N is 5.89 g, what is the percent yield of the reaction?

Disulfide dichloride (S2Cl2) is used in the vulcanization of rubber, a process that prevents the slippage of rubber molecules past one another when stretched. It is prepared by heating sulfur in an atmosphere of chlorine: S8(l) 1 4Cl2(g) 4S2Cl2(l) What is the theoretical yield of S2Cl2 in grams when 4.06 g of S8 are heated with 6.24 g of Cl2? If the actual yield of S2Cl2 is 6.55 g, what is the percent yield?

Gallium is an important element in the production of semiconductors. The average atomic mass of 69 31Ga (68.9256 amu) and 71 31Ga (70.9247 amu) is 69.72 amu. Calculate the natural abundances of the gallium isotopes.

Rubidium is used in atomic clocks and other precise electronic equipment. The average atomic mass of 85 37Rb (84.912 amu) and 87 37Rb (86.909 amu) is 85.47 amu. Calculate the natural abundances of the rubidium isotopes

The following diagram represents the products (CO2 and H2O) formed after the combustion of a hydrocarbon (a compound containing only C and H atoms). Write an equation for the reaction. (Hint: The molar mass of the hydrocarbon is about 30 g.) CO2 H2O

Consider the reaction of hydrogen gas with oxygen gas: 2H2(g) 1 O2(g) 2H2O(g) H2 O2 H2O Assuming complete reaction, which of the diagrams shown next represents the amounts of reactants and products left after the reaction? (a) (b) (c) (d)

Ethylene reacts with hydrogen chloride to form ethyl chloride: C2H4(g) 1 HCl(g) C2H5Cl(g) Calculate the mass of ethyl chloride formed if 4.66 g of ethylene reacts with an 89.4 percent yield

Write balanced equations for the following reactions described in words. (a) Pentane burns in oxygen to form carbon dioxide and water. (b) Sodium bicarbonate reacts with hydrochloric acid to form carbon dioxide, sodium chloride, and water. (c) When heated in an atmosphere of nitrogen, lithium forms lithium nitride. (d) Phosphorus trichloride reacts with water to form phosphorus acid and hydrogen chloride. (e) Copper(II) oxide heated with ammonia will form copper, nitrogen gas, and water.

Industrially, nitric acid is produced by the Ostwald process represented by the following equations: 4NH3(g) 1 5O2(g) 4NO(g) 1 6H2O(l) 2NO(g) 1 O2(g) 2NO2(g) 2NO2(g) 1 H2O(l) HNO3(aq) 1 HNO2(aq) What mass of NH3 (in g) must be used to produce 1.00 ton of HNO3 by the above procedure, assuming an 80 percent yield in each step? (1 ton 5 2000 lb; 1 lb 5 453.6 g.)

A sample of a compound of Cl and O reacts with an excess of H2 to give 0.233 g of HCl and 0.403 g of H2O. Determine the empirical formula of the compound.

How many grams of H2O will be produced from the complete combustion of 26.7 g of butane (C4H10)?

A 26.2-g sample of oxalic acid hydrate (H2C2O4 ? 2H2O) is heated in an oven until all the water is driven off. How much of the anhydrous acid is left?

The atomic mass of element X is 33.42 amu. A 27.22-g sample of X combines with 84.10 g of another element Y to form a compound XY. Calculate the atomic mass of Y

How many moles of O are needed to combine with 0.212 mole of C to form (a) CO and (b) CO2?

A research chemist used a mass spectrometer to study the two isotopes of an element. Over time, she recorded a number of mass spectra of these isotopes. On analysis, she noticed that the ratio of the taller peak (the more abundant isotope) to the shorter peak (the less abundant isotope) gradually increased with time. Assuming that the mass spectrometer was functioning normally, what do you think was causing this change?

The aluminum sulfate hydrate [Al2(SO4)3 ? xH2O] contains 8.10 percent Al by mass. Calculate x, that is, the number of water molecules associated with each Al2(SO4)3 unit.

The explosive nitroglycerin (C3H5N3O9) has also been used as a drug to treat heart patients to relieve pain (angina pectoris). We now know that nitroglycerin produces nitric oxide (NO), which causes muscles to relax and allows the arteries to dilate. If each nitroglycerin molecule releases one NO per atom of N, calculate the mass percent of NO available from nitroglycerin

The carat is the unit of mass used by jewelers. One carat is exactly 200 mg. How many carbon atoms are present in a 24-carat diamond?

An iron bar weighed 664 g. After the bar had been standing in moist air for a month, exactly one-eighth of the iron turned to rust (Fe2O3). Calculate the final mass of the iron bar and rust

A certain metal oxide has the formula MO where M denotes the metal. A 39.46-g sample of the compound is strongly heated in an atmosphere of hydrogen to remove oxygen as water molecules. At the end, 31.70 g of the metal is left over. If O has an atomic mass of 16.00 amu, calculate the atomic mass of M and identify the element.

An impure sample of zinc (Zn) is treated with an excess of sulfuric acid (H2SO4) to form zinc sulfate (ZnSO4) and molecular hydrogen (H2). (a) Write a balanced equation for the reaction. (b) If 0.0764 g of H2 is obtained from 3.86 g of the sample, calculate the percent purity of the sample. (c) What assumptions must you make in (b)?

One of the reactions that occurs in a blast furnace, where iron ore is converted to cast iron, is Fe2O3 1 3CO 2Fe 1 3CO2 Suppose that 1.64 3 103 kg of Fe are obtained from a 2.62 3 103 -kg sample of Fe2O3. Assuming that the reaction goes to completion, what is the percent purity of Fe2O3 in the original sample?

Carbon dioxide (CO2) is the gas that is mainly responsible for global warming (the greenhouse effect). The burning of fossil fuels is a major cause of the increased concentration of CO2 in the atmosphere. Carbon dioxide is also the end product of metabolism (see Example 3.13). Using glucose as an example of food, calculate the annual human production of CO2 in grams, assuming that each person consumes 5.0 3 102 g of glucose per day. The worlds population is 7.2 billion, and there are 365 days in a year.

Carbohydrates are compounds containing carbon, hydrogen, and oxygen in which the hydrogen to oxygen ratio is 2:1. A certain carbohydrate contains 40.0 percent carbon by mass. Calculate the empirical and molecular formulas of the compound if the approximate molar mass is 178 g.

Which of the following has the greater mass: 0.72 g of O2 or 0.0011 mole of chlorophyll (C55H72MgN4O5)?

Analysis of a metal chloride XCl3 shows that it contains 67.2 percent Cl by mass. Calculate the molar mass of X and identify the element.

Hemoglobin (C2952H4664N812O832S8Fe4) is the oxygen carrier in blood. (a) Calculate its molar mass. (b) An average adult has about 5.0 L of blood. Every milliliter of blood has approximately 5.0 3 109 erythrocytes, or red blood cells, and every red blood cell has about 2.8 3 108 hemoglobin molecules. Calculate the mass of hemoglobin molecules in grams in an average adult.

Myoglobin stores oxygen for metabolic processes in muscle. Chemical analysis shows that it contains 0.34 percent Fe by mass. What is the molar mass of myoglobin? (There is one Fe atom per molecule.)

Calculate the number of cations and anions in each of the following compounds: (a) 0.764 g of CsI, (b) 72.8 g of K2Cr2O7, (c) 6.54 g of Hg2(NO3)2.

A mixture of NaBr and Na2SO4 contains 29.96 percent Na by mass. Calculate the percent by mass of each compound in the mixture

Consider the reaction 3A 1 2B S 3C. A student mixed 4.0 moles of A with 4.0 moles of B and obtained 2.8 moles of C. What is the percent yield of the reaction?

Balance the following equation shown in molecular models. 1 1

Aspirin or acetyl salicylic acid is synthesized by reacting salicylic acid with acetic anhydride: C7H6O3 1 C4H6O3 C9H8O4 1 C2H4O2 salicylic acid acetic anhydride aspirin acetic acid (a) How much salicylic acid is required to produce 0.400 g of aspirin (about the content in a tablet), assuming acetic anhydride is present in excess? (b) Calculate the amount of salicylic acid needed if only 74.9 percent of salicylic acid is converted to aspirin. (c) In one experiment, 9.26 g of salicylic acid is reacted with 8.54 g of acetic anhydride. Calculate the theoretical yield of aspirin and the percent yield if only 10.9 g of aspirin is produced

Calculate the percent composition by mass of all the elements in calcium phosphate [Ca3(PO4)2], a major component of bone.

Lysine, an essential amino acid in the human body, contains C, H, O, and N. In one experiment, the complete combustion of 2.175 g of lysine gave 3.94 g CO2 and 1.89 g H2O. In a separate experiment, 1.873 g of lysine gave 0.436 g NH3. (a) Calculate the empirical formula of lysine. (b) The approximate molar mass of lysine is 150 g. What is the molecular formula of the compound?

Does 1 g of hydrogen molecules contain as many H atoms as 1 g of hydrogen atoms?

Avogadros number has sometimes been described as a conversion factor between amu and grams. Use the fluorine atom (19.00 amu) as an example to show the relation between the atomic mass unit and the gram

The natural abundances of the two stable isotopes of hydrogen (hydrogen and deuterium) are 1 1H: 99.985 percent and 2 1H: 0.015 percent. Assume that water exists as either H2O or D2O. Calculate the number of D2O molecules in exactly 400 mL of water. (Density 5 1.00 g/mL.)

A compound containing only C, H, and Cl was examined in a mass spectrometer. The highest mass peak seen corresponds to an ion mass of 52 amu. The most abundant mass peak seen corresponds to an ion mass of 50 amu and is about three times as intense as the peak at 52 amu. Deduce a reasonable molecular formula for the compound and explain the positions and intensities of the mass peaks mentioned. (Hint: Chlorine is the only element that has isotopes in comparable abundances: 35 17Cl: 75.5 percent; 35 17Cl: 24.5 percent. For H, use 1 1H; for C, use 12 1C.)

In the formation of carbon monoxide, CO, it is found that 2.445 g of carbon combine with 3.257 g of oxygen. What is the atomic mass of oxygen if the atomic mass of carbon is 12.01 amu?

What mole ratio of molecular chlorine (Cl2) to molecular oxygen (O2) would result from the breakup of the compound Cl2O7 into its constituent elements?

Which of the following substances contains the greatest mass of chlorine? (a) 5.0 g Cl2, (b) 60.0 g NaClO3, (c) 0.10 mol KCl, (d) 30.0 g MgCl2, (e) 0.50 mol Cl2.

A compound made up of C, H, and Cl contains 55.0 percent Cl by mass. If 9.00 g of the compound contain 4.19 3 1023 H atoms, what is the empirical formula of the compound?

Platinum forms two different compounds with chlorine. One contains 26.7 percent Cl by mass, and the other contains 42.1 percent Cl by mass. Determine the empirical formulas of the two compounds.

The following reaction is stoichiometric as written C4H9Cl 1 NaOC2H5 C4H8 1 C2H5OH 1 NaCl but it is often carried out with an excess of NaOC2H5 to react with any water present in the reaction mixture that might reduce the yield. If the reaction shown was carried out with 6.83 g of C4H9Cl, how many grams of NaOC2H5 would be needed to have a 50 percent molar excess of that reactant?

Compounds containing ruthenium(II) and bipyridine, C10H8N2, have received considerable interest because of their role in systems that convert solar energy to electricity. The compound [Ru(C10H8N2)3] Cl2 is synthesized by reacting RuCl3 ? 3H2O(s) with three molar equivalents of C10H8N2(s), along with an excess of triethylamine, N(C2H5)3(l), to convert ruthenium(III) to ruthenium(II). The density of triethylamine is 0.73 g/mL, and typically eight molar equivalents are used in the synthesis. (a) Assuming that you start with 6.5 g of RuCl3 ? 3H2O, how many grams of C10H8N2 and what volume of N(C2H5)3 should be used in the reaction? (b) Given that the yield of this reaction is 91 percent, how many grams of [Ru(C10H8N2)3]Cl2 will be obtained?

Heating 2.40 g of the oxide of metal X (molar mass of X 5 55.9 g/mol) in carbon monoxide (CO) yields the pure metal and carbon dioxide. The mass of the metal product is 1.68 g. From the data given, show that the simplest formula of the oxide is X2O3 and write a balanced equation for the reaction

A compound X contains 63.3 percent manganese (Mn) and 36.7 percent O by mass. When X is heated, oxygen gas is evolved and a new compound Y containing 72.0 percent Mn and 28.0 percent O is formed. (a) Determine the empirical formulas of X and Y. (b) Write a balanced equation for the conversion of X to Y

The formula of a hydrate of barium chloride is BaCl2 ? xH2O. If 1.936 g of the compound gives 1.864 g of anhydrous BaSO4 upon treatment with sulfuric acid, calculate the value of x

It is estimated that the day Mt. St. Helens erupted (May 18, 1980), about 4.0 3 105 tons of SO2 were released into the atmosphere. If all the SO2 were eventually converted to sulfuric acid, how many tons of H2SO4 were produced?

Cysteine, shown here, is one of the 20 amino acids found in proteins in humans. Write the molecular formula and calculate its percent composition by mass. S H C O

Isoflurane, shown here, is a common inhalation anesthetic. Write its molecular formula and calculate its percent composition by mass. F C O Cl H

A mixture of CuSO4 ? 5H2O and MgSO4 ? 7H2O is heated until all the water is lost. If 5.020 g of the mixture gives 2.988 g of the anhydrous salts, what is the percent by mass of CuSO4 ? 5H2O in the mixture?

When 0.273 g of Mg is heated strongly in a nitrogen (N2) atmosphere, a chemical reaction occurs. The product of the reaction weighs 0.378 g. Calculate the empirical formula of the compound containing Mg and N. Name the compound.

A mixture of methane (CH4) and ethane (C2H6) of mass 13.43 g is completely burned in oxygen. If the total mass of CO2 and H2O produced is 64.84 g, calculate the fraction of CH4 in the mixture.

Leaded gasoline contains an additive to prevent engine knocking. On analysis, the additive compound is found to contain carbon, hydrogen, and lead (Pb) (hence, leaded gasoline). When 51.36 g of this compound are burned in an apparatus such as that shown in Figure 3.6, 55.90 g of CO2 and 28.61 g of H2O are produced. Determine the empirical formula of the gasoline additive.

Because of its detrimental effect on the environment, the lead compound described in Problem 3.148 has been replaced by methyl tert-butyl ether (a compound of C, H, and O) to enhance the performance of gasoline. (This compound is also being phased out because of its contamination of drinking water.) When 12.1 g of the compound are burned in an apparatus like the one shown in Figure 3.6, 30.2 g of CO2 and 14.8 g of H2O are formed. What is the empirical formula of the compound?

Suppose you are given a cube made of magnesium (Mg) metal of edge length 1.0 cm. (a) Calculate the number of Mg atoms in the cube. (b) Atoms are spherical in shape. Therefore, the Mg atoms in the cube cannot fill all of the available space. If only 74 percent of the space inside the cube is taken up by Mg atoms, calculate the radius in picometers of a Mg atom. (The density of Mg is 1.74 g/cm3 and the volume of a sphere of radius r is 4 3r 3 .)

A certain sample of coal contains 1.6 percent sulfur by mass. When the coal is burned, the sulfur is converted to sulfur dioxide. To prevent air pollution, this sulfur dioxide is treated with calcium oxide (CaO) to form calcium sulfite (CaSO3). Calculate the daily mass (in kilograms) of CaO needed by a power plant that uses 6.60 3 106 kg of coal per day

Air is a mixture of many gases. However, in calculating its molar mass we need consider only the three major components: nitrogen, oxygen, and argon. Given that one mole of air at sea level is made up of 78.08 percent nitrogen, 20.95 percent oxygen, and 0.97 percent argon, what is the molar mass of air?

(a) Determine the mass of calcium metal that contains the same number of moles as 89.6 g of zinc metal. (b) Calculate the number of moles of molecular fluorine that has the same mass as 36.9 moles of argon. (c) What is the mass of sulfuric acid that contains 0.56 mole of oxygen atoms? (d) Determine the number of moles of phosphoric acid that contains 2.12 g of hydrogen atoms

A major industrial use of hydrochloric acid is in metal pickling. This process involves the removal of metal oxide layers from metal surfaces to prepare them for coating. (a) Write an equation between iron(III) oxide, which represents the rust layer over iron, and HCl to form iron(III) chloride and water. (b) If 1.22 moles of Fe2O3 and 289.2 g of HCl react, how many grams of FeCl3 will be produced?

Octane (C8H18) is a component of gasoline. Complete combustion of octane yields H2O and CO2. Incomplete combustion produces H2O and CO, which not only reduces the efficiency of the engine using the fuel but is also toxic. In a certain test run, 1.000 gal of octane is burned in an engine. The total mass of CO, CO2, and H2O produced is 11.53 kg. Calculate the efficiency of the process; that is, calculate the fraction of octane converted to CO2. The density of octane is 2.650 kg/gal.

Industrially, hydrogen gas can be prepared by reacting propane gas (C3H8) with steam at about 4008C. The products are carbon monoxide (CO) and hydrogen gas (H2). (a) Write a balanced equation for the reaction. (b) How many kilograms of H2 can be obtained from 2.84 3 103 kg of propane?

In a natural product synthesis, a chemist prepares a complex biological molecule entirely from nonbiological starting materials. The target molecules are often known to have some promise as therapeutic agents, and the organic reactions that are developed Interpreting, Modeling & Estimating 3.166 While most isotopes of light elements such as oxygen and phosphorus contain relatively equal numbers of protons and neutrons, recent results indicate that a new class of isotopes called neutron-rich isotopes can be prepared. These neutron-rich isotopes push the limits of nuclear stability as the large number of neutrons approach the neutron drip line. They may play a critical role in the nuclear reactions of stars. An unusually heavy isotope of aluminum ( 43 13Al) has been reported. How many more neutrons does this atom contain compared to an average aluminum atom? 3.167 Without doing any detailed calculations, arrange the following substances in the increasing order of number of moles: 20.0 g Cl, 35.0 g Br, and 94.0 g I. 3.168 Without doing any detailed calculations, estimate which element has the highest percent composition by mass in each of the following compounds: (a) Hg(NO3)2 (b) NF3 (c) K2Cr2O7 (d) C2952H4664N812O832S8Fe4 along the way benefit all chemists. The overall synthesis, however, requires many steps, so it is important to have the best possible percent yields at each step. What is the overall percent yield for such a synthesis that has 24 steps with an 80 percent yield at each step?

What is wrong or ambiguous with each of the statements here? (a) NH4NO2 is the limiting reagent in the reaction NH4NO2(s) N2(g) 1 2H2O(l) (b) The limiting reagents for the reaction shown here are NH3 and NaCl. NH3(aq) 1 NaCl(aq) 1 H2CO3(aq) NaHCO3(aq) 1 NH4Cl(aq)

(a) For molecules having small molecular masses, mass spectrometry can be used to identify their formulas. To illustrate this point, identify the molecule that most likely accounts for the observation of a peak in a mass spectrum at: 16 amu, 17 amu, 18 amu, and 64 amu. (b) Note that there are (among others) two likely molecules that would give rise to a peak at 44 amu, namely, C3H8 and CO2. In such cases, a chemist might try to look for other peaks generated when some of the molecules break apart in the spectrometer. For example, if a chemist sees a peak at 44 amu and also one at 15 amu, which molecule is producing the 44-amu peak? Why? (c) Using the following precise atomic masses 1 H (1.00797 amu), 12C (12.00000 amu), and 16O (15.99491 amu)how precisely must the masses of C3H8 and CO2 be measured to distinguish between them?

Potash is any potassium mineral that is used for its potassium content. Most of the potash produced in the United States goes into fertilizer. The major sources of potash are potassium chloride (KCl) and potassium sulfate (K2SO4). Potash production is often reported as the potassium oxide (K2O) equivalent or the amount of K2O that could be made from a given mineral. (a) If KCl costs $0.55 per kg, for what price (dollar per kg) must K2SO4 be sold to supply the same amount of potassium on a per dollar basis? (b) What mass (in kg) of K2O contains the same number of moles of K atoms as 1.00 kg of KCl?

A 21.496-g sample of magnesium is burned in air to form magnesium oxide and magnesium nitride. When the products are treated with water, 2.813 g of gaseous ammonia are generated. Calculate the amounts of magnesium nitride and magnesium oxide formed.

A certain metal M forms a bromide containing 53.79 percent Br by mass. What is the chemical formula of the compound?

A sample of iron weighing 15.0 g was heated with potassium chlorate (KClO3) in an evacuated container. The oxygen generated from the decomposition of KClO3 converted some of the Fe to Fe2O3. If the combined mass of Fe and Fe2O3 was 17.9 g, calculate the mass of Fe2O3 formed and the mass of KClO3 decomposed.

A sample containing NaCl, Na2SO4, and NaNO3 gives the following elemental analysis: Na: 32.08 percent; O: 36.01 percent; Cl: 19.51 percent. Calculate the mass percent of each compound in the sample

A sample of 10.00 g of sodium reacts with oxygen to form 13.83 g of sodium oxide (Na2O) and sodium peroxide (Na2O2). Calculate the percent composition of the mixture

While most isotopes of light elements such as oxygen and phosphorus contain relatively equal numbers of protons and neutrons, recent results indicate that a new class of isotopes called neutron-rich isotopes can be prepared. These neutron-rich isotopes push the limits of nuclear stability as the large number of neutrons approach the neutron drip line. They may play a critical role in the nuclear reactions of stars. An unusually heavy isotope of aluminum ( 43 13Al) has been reported. How many more neutrons does this atom contain compared to an average aluminum atom?

Without doing any detailed calculations, arrange the following substances in the increasing order of number of moles: 20.0 g Cl, 35.0 g Br, and 94.0 g I.

Without doing any detailed calculations, estimate which element has the highest percent composition by mass in each of the following compounds: (a) Hg(NO3)2 (b) NF3 (c) K2Cr2O7 (d) C2952H4664N812O832S8Fe4

Consider the reaction 6Li(s) 1 N2(g) 2Li3N(s) Without doing any detailed calculations, choose one of the following combinations in which nitrogen is the limiting reagent: (a) 44 g Li and 38 g N2 (b) 1380 g Li and 842 g N2 (c) 1.1 g Li and 0.81 g N2

Estimate how high in miles you can stack up an Avogadros number of oranges covering the entire Earth

The following is a crude but effective method for estimating the order of magnitude of Avogadros