2294475-CHEM-Chapter-9-Review-Questions-139-odd

2294475-CHEM-Chapter-9-Review-Questions-139-odd - March 16,...

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Unformatted text preview: March 16, 2008 CHEM: Ch. 9. Review: Questions 1-39 (odd) Jonathan Sterling CHEM: Ch. 9. Review: Questions 1-39 (odd) 1. Mole Ratio a. Explain the concept of mole ratio as used in reaction-stoichiometry problems. A mole ratio is the proportion of the numbers of moles of one substance to that of another. b. What is the source of this value? This value is found in the chemical equations. 3. Molar Mass a. What is molar mass? The molar mass is the proportion of mass in grams to amount in moles, or amount in moles to mass in grams. b. What is its rle in reaction stoichiometry? The molar mass is used to convert between grams and moles. 5. Distinguish between the limiting reactant and the excess reactant in a chemical reaction. The excess reactant is the one where there is more than needed to react with the limiting reactant; at the end of a reaction, there will be leftover of the excess reactant. 7. What is the percent yield of a reaction? The percent yield is 9. Given the chemical equation 2 , determine to two decimal places the molar masses of all substances involved, and then write them as conversion factors. Substance Molar Mass Conversion Factor I am not sure at all what this book means by "conversion factor" 105.998 in this context. Does it want me to five a conversion factor 74.09 between each of them? Because that would end up being 16 40.00 different conversion factors, which would be no fun. Anyway, the 100.09 molar mass is a conversion factor already. 11. Ethane Combustion a. If 4.50 of ethane, , undergo combustion according to the unbalanced equation , how many moles of oxygen are required? 2 7 4 6 is the balanced equation. 7.00 4.50 15.8 2.00 b. How many moles of each product are formed? 9.00 and 13.5 are formed. 13. Sodium chloride is produced from its elements through a synthesis reaction. What mass of each reactant would be required to produce 25.0 ? The balanced equation for this reaction is the following: 2 2 . 2.00 22.990 25.0 575 2.00 1.00 1.00 70.906 25.0 886.325 2.00 1.00 15. Iron is generally produced from iron ore through the following reaction in a blast furnace: . 100. 1 March 16, 2008 CHEM: Ch. 9. Review: Questions 1-39 (odd) Jonathan Sterling a. If 4.00 are available to react, how many moles of are needed? The balanced equation is 3 2 3 . 1000 1.00 3.00 4.00 75.1 1.00 159.863 1.00 b. How many moles of each product are formed? 1000 1.00 2.00 50.0 4.00 1.00 159.863 1.00 1000 1.00 3.00 4.00 75.1 1.00 159.863 1.00 17. Nitrogen combines with oxygen in the atmosphere during lightning flashes to form nitrogen monoxide, , which then reacts further with to produce nitrogen dioxide, . a. What mass of is formed when reacts with 384 ? The balanced equation is: 2 2 1.00 2.00 46.005 384 1.10 10 31.998 1.00 1.00 b. How many grams of are required to react with this amount of ? 1.00 2.00 30.006 384 720 31.998 1.00 1.00 19. The metathesis reaction between silver nitrate and sodium bromide produces silver bromide, a component of photographic film. a. If 4.50 react, what mass of sodium bromide is required? The balanced equation is: 1.00 102.894 4.50 463 1.00 1.00 b. What mass of silver bromide is formed? 1.00 187.77 4.50 845 1.00 1.00 , is produced through the following reaction of salicylic acid, 21. Aspirin, anhydride, : . ? a. What mass of aspirin (in kg) could be produced from 75.0 75.0 , and acetic b. What mass of acetic anhydride (in kg) would be required? 75.0 1.00 1.00 102.088 1.00 1.00 1.00 180.158 1.00 1.000 1000. 13.5 7.66 c. At 20C, how many litres of acetic acid would be formed? The density of acetic acid is 1.05 . 75.0 1.00 1.00 60.052 1.00 1.00 1.05 1.000 1000. 4.29 1.000 1000. 23. For each reaction specified in Problem 22, determine the amount in moles of excess reactant that remains. a. (2.0 , 2.5 ) 1.0 2.5 2.0 0.50 1.0 b. 2 (2.5 , 6.0 ) 2 March 16, 2008 CHEM: Ch. 9. Review: Questions 1-39 (odd) Jonathan Sterling 2.0 1.0 1.0 c. 2 3 6 , (4.0 , 6.5 ) 3 4.0 0.50 6.5 2 25. Limiting Reactant in a Single-Replacement Reaction a. If 2.50 and 5.50 are available to react by single replacement, identify the limiting reactant. 2 The balanced equation is: 2 1.00 5.50 2.75 2.00 Since there are only 2.50 , copper is the limiting reactant, because with that quantity of will be reacted. copper, only 2.50 b. Determine the amount in moles of excess reactant remaining. Silver nitrate is the excess reactant. 2.00 5.50 2.50 0.50 1.00 c. Determine the amount in moles of each product formed. 1.00 2.50 2.50 1.00 2.00 2.50 5.00 1.00 d. Determine the mass of each product formed. 1.00 136.019 2.50 350 1.00 1.00 2.00 107.87 2.50 539 1.00 1.00 27. The energy used to power one of the Apollo lunar missions was supplied by the following overall 3 6 2 8 . For the phase of the mission reaction: 2 when the lunar module ascended from the surface of the moon, a total of 1200. of were available to react with 1000. and 4500. . a. For this portion of the flight, which of the allocated components was used up first? 6.0 2.5 Because approximately 19980 are needed to react with 1200. , whereas there are only 1000. available, was between the two, the limiting reactant. Next, it will be determined whether or is the limiting reactant: 1000. 1200. 1000. 1.000 1.000 30.030 1.000 2.000 19980 b. From that, we know that is the limiting reactant of the entire reaction. This means that the dinitrogen tetraoxide was used up first in the reaction. How much water, in kilograms, was put into the lunar atmosphere through this reaction? 4500. 1000. 1.000 1.000 92.010 8.000 3.000 18.015 1.000 1.000 1000. 3250. 1000. 1.000 1.000 60.099 3.000 1.000 49920 29. From the theoretical and percentage yields given below, determine the actual yields: a. theoretical yield: 12.0 ; percent yield: 90.0% 3 March 16, 2008 CHEM: Ch. 9. Review: Questions 1-39 (odd) Jonathan Sterling 12.0 100 12.0 b. theoretical yield: 8.50 ; percent yield: 70.0% 8.50 100 90.0 100 12.0 10.0 90.0 0.900 8.50 c. theoretical yield: 3.45 ; percent yield: 48.0% 3.45 100 70.0 100 8.50 5.95 70.0 0.700 48.0 100 3.45 3.45 0.480 1.66 31. Magnesium is obtained from sea water. is added to sea water to precipitate . The precipitate is filtered and reacted with to produce . The is electrolyzed to . If 185.0 are recovered from 1000. , what is the percentage produce and yield for this reaction? The balanced equation is: . The theoretical yield is the following: 1.000 1.000 24.305 1000. 255.3 95.211 1.000 1.000 Therefore, the percent yield will be: 185.0 100 72.46% 255.3 33. Coal gasification is a process that converts coal into methane gas. If this reaction has a percent yield of 85.0%, how much methane can be obtained from 1250 ? The balanced equation is 2 2 . The theoretical yield is the following: 1.00 1.00 16.043 1250 835 12.011 2.00 1.00 Therefore, the actual yield can be found as follows: 85.0 835 100 835 710 35. Builders and dentists must store plaster of Paris, 835 100 85.0 0.850 , in airtight containers to prevent 48.0 it from absorbing water vapour from the air and changing to gypsum, 2 . How many litres of water evolve when 5.00 2 are heated at 110C to produce plaster of Paris? 4 March 16, 2008 CHEM: Ch. 9. Review: Questions 1-39 (odd) Jonathan Sterling At 110C, the density of 0.581 5.00 2 2 is 2.32 2.32 1.00 18.015 1.00 , and the density of water vapour is 2 4 . . 2 1000. 1.00 3.00 2.00 The balanced equation is: 2 3 2 2 37. The chemical equation is a good source of information concerning a reaction. Explain the relationship that exists between the actual yield of a reaction produce and the chemical equation of the produce. As the experiment becomes more and more accurate, the division of the actual yield by the theoretical yield (given by the coefficients in the chemical equation) approaches 1. I am not sure if this was the answer that was looked for, though. 39. In the lab, you run an experiment that appears to have a percent yield of 115%. Propose reasons for this result. Can an actual yield ever exceed a theoretical yield? The only reason for a result like that, that I can think of, is that the resulting substance contains something other than the target, thereby skewing the results. The reason percent yields are always less than 100% is that in experiments, it is almost impossible not to lose any of the substance at all, I think, and that there is always a degree of human error. As far as I know, an actual yield should never exceed its theoretical yield. 2 2 1.00 0.581 1.00 172.205 1.000 1000. 2 2 3.13 5 ...
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