PRINT NEATLY Alias Name_________________ Real Name (Optional) ___________________ ____ ____ ____ ____ ____ ____ ____ ____ ____ ____ Total Score:_____ _____________________________________________________________ Chemistry 1201 Section 4 Spring 1999 Professor Russo Exam #3 Type of exam: Take-home. You can work with anyone on this exam, including me! You better know how to do these problems, though. You will probably see similar problems again. Due: Tuesday, February 23 at the beginning of class. 100 points. Show your work neatly. We will not grade papers that just show an answer, nor can we assign partial credit if we don't see the work. ________________________________________________________________________ Question #1. (BLB Text 2.16) Fill in the table. 70 Symbol Ga Protons 23 Neutrons 28 Electrons 45 34 136 79 Atomic No. 86 Mass No. 197 Question #2. (BLB Text 2.56 --Oh dear, yet another density problem! But this density is unusual). Using the mass of the proton from Table 2.1 and assuming its diameter is 1.0 x 10-15 m, calculate the density of a proton in g/cm3. About what fraction of water is actually empty space? __________________ Put the density here Chem 1201 Sec. 4 __________________ Put the empty fraction here Exam #3 Page 1 PRINT NEATLY Alias Name_________________ Real Name (Optional) ___________________ Question #3. (based on BLB Text 2.61; see the FAQ page on the website for help. This question is phrased more directly than the one in your book, but it is essentially the same problem. It is a very important, basic type of problem since this is how much of what we know about chemical matter was determined). Butane contains 82.8 % carbon by weight and hydrogen as the only other element. For example, a 2.503 g sample of butane contains 2.072 g of carbon. Determine the empirical formula of butane. Hint: another hydrocarbon called acetylene is found to contain 92.3% carbon by mass. Of all hydrocarbons, acetylene has the highest percentage of carbon. __________________ Put your answer here Question #4. (BLB 6.8a) What is the frequency of the radiation whose wavelength is 1.73 nm? What kind of radiation do we call this? ___________________ Put the frequency here Chem 1201 Sec. 4 Exam #3 __________________ Put the type of radiation here Page 2 PRINT NEATLY Alias Name_________________ Real Name (Optional) ___________________ Question #5. (based on BLB #6.14) What is the smallest increment of energy in calories that can be emitted or absorbed at a wavelength of 146 nm? __________________________ Put your answer here Question #6. (BLB 6.20) A certain photographic film requires a minimum radiation energy of 80 kJ/mol to cause exposure. What is the longest wavelength, in meters, of radiation that possesses the necessary energy to expose the film? Could the film be used for infrared photography? ______________________ Put Longest Wavelength Here Yes, OK No, Not OK Circle One Question #7. (BLB Text 6.32b) The hydrogen atom can absorb light of wavelength 1282 nm. Determine the initial and final values of n associated with their absorption. nfinal:__________ Chem 1201 Sec. 4 Exam #3 ninitial_________ Page 3 PRINT NEATLY Alias Name_________________ Real Name (Optional) ___________________ Question #8. (BLB Text 6.36) When an electron in an electron microscope is accelerated through 100 V, it attains a speed of 5.93 x 106 m/s. Determine the characteristic wavelength of this electron in Å. Is that wavelength comparable to the size of atoms? ____________________ Write wavelength here Yes, comparable No, not Circle One Question #9. (similar to BLB 6.75, which was not assigned--sorry). The little red laser pointer that I use in class produces about 5 mW at 670 nm. How many photons will it emit in 15 s? Express your answer in mol. __________________ Put your answer here Question #10 (BLB 6.77). Chorophyll absorbs blue light, = 460 nm, and emits red light, = 660 nm. Calculate the net energy change in the chlorophyll system (in kilojoules) when a mole of 460-nm photons is absorbed and a mole of 660-nm photons is emitted. ________________________ Put Answer Here Chem 1201 Sec. 4 Exam #3 Page 4