12.2 USING MOLES Supplemental Practice Problems,

 

Solve the following problems. The reactions may not be balanced.

1. If 20.0 g of magnesium react with excess hydrochloric acid, how many grams of magnesium chloride are produced?

Mg(s) + HCl(aq) à MgCl2(aq) + H2(g)

 

 

 

2. How many grams of chlorine gas must be reacted with excess sodium iodide if 10.0 g of sodium chloride are needed?

NaI(aq) + Cl2(g) à NaCl(aq) + I2(s)

 

 

 

3. How many grams of oxygen are produced in the decomposition of 5.00 g of potassium chlorate?

KClO3(s)à KCl(s) + O2(g)

 

 

 

4. What mass of copper is required to replace silver from 4.00 g of silver nitrate dissolved in water?

Cu(s) + AgNO3(aq) à Cu(NO3)2(aq) + Ag(s)

 

 

 

5. If excess ammonium sulfate reacts with 20.0 g of calcium hydroxide, how many grams of ammonia are produced?

(NH4)2SO4(aq) + Ca(OH)2(s) à CaSO4(s) + NH3(s) + H2O(l)

 

 

 

6. If excess sulfuric acid reacts with 30.0 g of sodium chloride, how many

grams of hydrogen chloride are produced?

NaCl(aq) + H2SO4(aq) à HCl(g) + Na2SO4(aq)

 

 

 

7. How much silver phosphate is produced if 10.0 g of silver acetate react with excess sodium phosphate?

AgCH3COO(aq) + Na3PO4(aq) à Ag3PO4(s) + NaCH3COO(aq)

 

 

 

8. How many grams of sodium hydroxide are needed to completely neutralize 25.0 g of sulfuric acid?

NaOH(aq) + H2SO4(aq) à Na2SO4(s) + H2O(g)

Assume the volumes given are at STP unless other conditions are specified.

 

 

 

9. Calculate the number of moles contained in each of the following gas

volumes.

a. 5.00 X 104 mL H2

 

b. 1.000 X 103 mL N2

 

c. 6500 mL SO2

 

d. 15 000 mL NH3

 

e. 2500 mL O2

 

f. 2.000 X 103 mL CO2

 

10. Calculate the mass of each of the following volumes of gas.

a. 2.00 X 104 L CH4

 

b. 1500.0 mL Cl2

 

c. 70.0 mL SO3

 

d. 3.000 X 102 L N2O

 

e. 3.0 X 103 L N2

 

f. 3500.0 mL H2S

 

11. Calculate the volume in L of each of the following.

a. 4.0 mol Br2

 

b. 200.0 g H2S

 

c. 25.5 g SO2

 

d. 600.0 g Cl2

 

e. 2.50 mol NH3

 

f. 50.0 g NO2

 

g. 7.00 mol O2

 

h. 10.0 g HCl

 

Assume that all volumes are at STP.

12. How many mL of hydrogen are produced if 4.00 g zinc react with excess hydrochloric acid?

Zn(s) + 2HCl(aq) à ZnCl2(aq) + H2(g)

 

 

 

13. If excess chlorine gas reacts with a solution containing 20.0 g of potassium bromide, how many milliliters of bromine gas can be produced?

2KBr(aq) + Cl2(g) à 2KCl(aq) + Br2(g)

 

 

 

14. How many grams of copper(II) oxide can be reduced to copper metal with 10.0 L of H2?

CuO(s) + H2(g) à Cu(s) + H2O(g)

 

 

15. Calculate the mL of oxygen that can be produced by the electrolysis of 5.00 g of water.

2H2O(l) à 2H2(g) + O2(g)

 

 

16. In the reaction between aluminum and oxygen, how many grams of aluminum are required to react with 5.00 L of oxygen?

4Al(s) + 3O2(g) à 2Al2O3(s)

 

 

17. In the electrolysis of water, 75.0 mL of oxygen gas are produced. How many mL of hydrogen are produced?

2H2O(l) à 2H2(g) + O2(g)

 

 

18. If an electric discharge produces 20.0 mL of ozone, O3, how many milliliters of oxygen are required?

3O2(g) à 2O3(g)

 

 

19. Ammonia can be produced by the Haber process. If 60.0 L of NH3 are produced, how many L of hydrogen and nitrogen are necessary?

3H2(g) + N2(g) à 2NH3(g)

 

 

20. How many mL of chlorine gas are required to produce 50.0 mL of hydrogen chloride gas?

H2(g) + Cl2(g) à 2HCl(g)

 

 

21. The residue from the complete decomposition of potassium chlorate is found to contain 1.80 g of potassium chloride. Determine the following:

 

a. grams of KClO3 originally present

 

b. grams of oxygen produced

 

c. milliliters of oxygen at STP

 

22. If 20.0 g of NaOH react with 30.0 g of H2SO4 to produce Na2SO4, which

reactant is limiting?

2NaOH(aq) + H2SO4(aq) à Na2SO4(aq) + 2H2O(l)

 

 

23. If 5.00 g of copper metal react with a solution containing 20.0 g of AgNO3 to produce silver metal, which reactant is limiting?

Cu(s) + 2AgNO3(aq) à Cu(NO3)2(aq) + 2Ag(s)

 

 

24. What reactant is limiting if 3.00 L of Cl2 at STP react with a solution containing 25.0 g of NaBr to produce Br2?

 

 

25. If 20.0 g of KOH react with 15.0 g of (NH4)2SO4, calculate the L of NH3 produced at STP.

 

 

26. Magnesium acetate can be prepared by a reaction involving 15.0 g of

iron(III) acetate with either 10.0 g of MgCrO4 or 15.0 g of MgSO4. Which

reaction will give the greatest yield of Mg(CH3COO)2? How many grams of Mg(CH3COO)2 will be produced?

2Fe(CH3COO)3(aq) + 3MgCrO4(s) à3Mg(CH3COO)2(aq) + Fe2(CrO4)3(s)

 

 

2Fe(CH3COO)3(aq) + 3MgSO4(s) à 3Mg(CH3COO)2(aq) + Fe2(SO4)3(s)

 

 

27. If 14.7 g of sodium peroxide (Na2O2) react with water to produce sodium hydroxide and oxygen gas, how many L of oxygen are produced at 22°C and 1.12 X 105 Pa?

 

 

28. How many L of chlorine gas measured at 18.5°C and 98.0 kPa can be produced by the electrolysis of 62.3 g NaCl to give sodium metal and chlorine gas?

 

 

29. How many L of nitrogen measured at 21.5°C and 9.55 X 104 Pa are required to react with excess calcium carbide, CaC2, to produce 100.0 g of calcium cyanamid, CaCN2, and carbon?

 

 

30. How many grams of iron metal must react with excess steam to produce 10.0 L of hydrogen collected over water at 20.0°C and 9.90 X 104 Pa? The other product is iron(II,III) oxide, Fe3O4 (Fe3O4 is actually FeO . Fe2O3).

 

 

31. What is the molecular mass of sulfur dioxide, SO2, if 300.0 mL of the gas has a mass of 0.855 g at STP?

 

 

32. A sample of hydrogen iodide, HI, has a mass of 2.28 g and occupies

400.0 mL at STP. What is the molecular mass of this compound?

 

 

33. If 0.179 g of methane, CH4, occupy 0.250 L, what is the molecular mass of methane if the volume is given at standard conditions?

 

 

34. From the volume, temperature, and pressure, calculate the number of moles for each gas listed using the ideal gas equation.

a. 750.0 mL O2 at 27°C and 99.0 kPa

 

 

b. 3.00 L CO2 at -15°C and 103.0 kPa

 

 

35. Calculate the volume each gas will occupy under the conditions listed using the ideal gas equation.

a. 3.00 mol H2 at 24°C and 100.5 kPa

 

 

b. 150.0 g Cl2 at -12.5°C and 98.5 kPa

 

 

36. The density of a sample of phosphorus trifluoride, PF3, is 3.90 g/L. What is the molecular mass of this gas at STP?

 

 

37. Calculate the mass percent of each element of the following compounds.

a. Fe2O3

 

b. Ag2O

 

c. HgO

 

d. Na2S

 

 

38. Determine the mass percent of sodium in sodium sulfate, Na2SO4.

 

 

39. Urea, CO(NH2)2, and ammonia, NH3, are two compounds used as a source of nitrogen in fertilizers. Calculate the mass percent of nitrogen in each.

 

 

40. Calculate the percentage of each of the following in the compound sodium sulfate decahydrate, Na2SO4 .10 H2O.

a. Na

 

b. S

 

c. O

 

d. H2O

 

 

41. Write the empirical formula for each of the following.

a. C6H6 (benzene)

 

b. C2H2 (ethyne)

 

c. C6H12O6 (glucose)

 

d. C4H10 (butane)

 

e. P4O10

 

f. SO3

 

g. N2O4

 

h. NO2

 

i. Ag2C4H4O6

 

j. K2S4

 

42. Calculate the empirical formula for compounds with the following compositions.

a. Fe 63.5%, S 36.5%

 

b. Mn 63.1%, S 36.9%

 

c. K 26.6%, Cr 35.4%, O 38.0%

 

43. Calculate empirical formulas for the following two compounds containing sodium, sulfur, and oxygen.

a. Na 32.4%, S 22.6%, O 45.0%

 

b. Na 29.1%, S 40.5%, O 30.4%

 

44. Calculate the empirical formulas for the following three iron ores.

a. Fe 77.7%, O 22.3%

 

b. Fe 72.4%, O 27.6%

 

c. Fe 70.0%, O 30.0%

 

45. There are two oxides of phosphorus. Both oxides can exist in different forms depending on the temperature and the pressure. Calculate the empirical and molecular formulas from the following data.

a. P 56.4%, O 43.6%, molecular mass 220 u

 

b. P 43.7%, O 56.3%, molecular mass 284 u

 

46. The formula mass of a compound is 92 u. Analysis of the compound shows that there are 0.608 g of nitrogen and 1.388 g of oxygen. What is the molecular formula of this compound?

 

 

SECTION REVIEW

1. Molten iron and carbon monoxide are produced in a blast furnace by the reaction of iron(III) oxide and coke (carbon). If 25.0 kg of pure Fe2O3 are used, how many moles of iron can be produced?

 

 

 

2. Ammonia gas produced as a by-product in an industrial reaction can be reacted with sulfuric acid in order that the gas does not escape into the atmosphere. The product, ammonium sulfate, can be used as a fertilizer. Determine how many kilograms of acid are required to produce 1000.0 kg of (NH4)2SO4.

 

 

 

3. Coal gasification is a process that is carried out industrially in a series of steps. The net reaction involves coal (carbon) reacting with water to form methane, CH4, and carbon dioxide. How many kilograms of methane can be produced from 1.00 X 103 kg of coal?

 

 

 

4. A source of acid rain is automobile exhaust. Nitric oxide, formed in an internal combustion engine, reacts with oxygen in the air to produce nitrogen dioxide. The NO2 reacts with water to form nitric acid. It is determined that the average car produces 1.00 X 104 L of exhaust gas per mile driven. Assume that the average concentration of NO2 in auto exhaust is 0.10 ug/L and that traffic surveys have shown an average of 2.00 X 106 vehicle miles driven per day. From this data, determine the kilograms of nitric acid that could be produced annually.

2NO2 + H2Oà HNO2 + HNO3

 

 

 

5. Photosynthesis is a complex process composed of many steps. The initial reactants are carbon dioxide and water and the final products are glucose and oxygen gas. If a plant needs to make 30.0 g of glucose, C6H12O6, through the process of photosynthesis, how many grams of water are required?

 

 

 

6. One mole of He has a mass of 4.0026 g and 1.000 L of He (at STP) has a mass of 0.1787 g. Calculate the molar volume of helium.

 

 

 

7. What is the molecular mass of a gas if 5.75 g of the gas occupy a volume of 3.50 L? The pressure was recorded as 9.525 X 104 Pa and the temperature is 52°C.

 

 

 

8. How many milliliters of hydrogen at STP are produced by the reaction of 0.750 g of sodium metal with excess water?

2Na(s) + 2H2O(l) à 2NaOH(aq) + H2(g)

 

 

 

9. What mass of magnesium will react with excess hydrochloric acid to produce 5.00 X 102 mL of H2 at STP?

Mg(s) + 2HCl(aq) à MgCl2(aq) + H2(g)

 

 

 

10. When lead(II) sulfide is burned in air, lead(II) oxide and sulfur dioxide are produced. If 20.0 L of sulfur dioxide were produced, how many liters of oxygen gas were required to react with the lead(II) sulfide?

2PbS(s) + 3O2(g) à 2PbO(s) + 2SO2(g)

 

 

 

11. In a reaction involving carbon monoxide and iron(III) oxide, the products are iron metal and carbon dioxide. If 84.75 L of carbon dioxide are produced, how many L of carbon monoxide are required?

 

 

 

12. Hydrogen burns to give water. If 200.0 mL of H2 reacts with 150.0 mL of O2, what volume of water vapor is produced? How many milliliters of gas remain unreacted and what gas remains? Assume that all volumes are measured at any given temperature above the normal boiling point of water.

 

 

 

13. How many grams of sodium hydrogen carbonate, NaHCO3, must be heated to produce 2.50 L of carbon dioxide measured at 22.5°C and 97.5 kPa? The other products are sodium carbonate and water.

 

 

 

14. If 3.20 g of aluminum react with excess hydrochloric acid, how many mL of hydrogen collected over water at 20.0°C and 99.5 kPa are produced?

 

 

 

15. A sample of gas has a mass of 1.248 g and occupies 300.0 mL at STP. What is the molecular mass of this gas?

 

 

 

16. From the volume, temperature, and pressure data given, calculate the number of moles and the mass in grams for each gas listed using the ideal gas equation.

a. 2000.0 mL NH3 at 10.0°C and 105.0 kPa

 

b. 5.00 L SO2 at 21.0°C and 100.0 kPa

 

17. Calculate the volume each gas will occupy under the conditions listed using the ideal gas equation.

a. 5.00 mol CH4 at 27.0°C and 97.2 kPa

 

b. 200.0 g NH3 at 12.0°C and 104.5 kPa

 

18. The sugar substitute sodium benzosulfimide (sodium saccharin) has a sweetness of about 500 times that of sucrose. Calculate the percentage of sodium and carbon in the sweetener. Its formula is

 

 

 

19. Copper phthalocyanine is a complex organic molecule possessing a brilliant greenish blue color. Millions of pounds are produced yearly to color products such as plastics, automobile finishes, rubber goods, and printing inks.

Determine the percent carbon in copper phthalocyanine that has the formula Cu(C8H4N2)4.

 

 

20. Write the empirical formula for each of the following.

a. C6H14

 

b. CO2

 

c. N2F4

 

d. C3H6Cl2

 

e. C5H10O2

 

f. P3N3Cl6

 

21. Two compounds are analyzed and found to contain:

a. 0.89 g K, 1.18 g Cr, 1.27 g O

 

b. 1.03 g K, 0.69 g Cr, 0.84 g O

 

Determine the empirical formulas for these two compounds.

22. A fat is composed, in part, of long chains of carbon and hydrogen atoms. In a reaction with a strong base, a fat forms a soap and glycerol. What is the empirical formula of a fat containing 76.5% C, 11.3% O and 12.2% H, if it has a molecular mass of 847 u?

 

 

 

23. Citric acid, an organic acid found in lemons and other citrus fruits, contains 37.5% carbon, 58.3% oxygen, and 4.20% hydrogen. What is the empirical formula of citric acid if it has a molecular mass of 192 u?