Chemistry 1100 Atoms & Molecules Winter Semester 2005, Dr. Rainer Glaser For text answers: 1. Read the entire question! Try to understand the question. Do not jump to any conclusion as to what the question might be about because you know something about a word in the question. 2. Answer the question! There are no points for information provided but not asked for. 3. Be brief and concise. No need to fill the entire space provided. ften a few good words are all that is needed. Practice Examination Chapter 1 andout on Tuesday, 2/8/05. Name: Answer Key Question 1. oney, who shrunk the nitrogen? 25 Question 2. What s that stuff? 15 Question 3. ey, what s smelling so good? 20 Total 60 1
Question 1. oney, who shrunk the nitrogen [concentration]? (25 points) Table 1.2 from the text is reproduced below and additional columns were added for you to fill in as part of this problem. Note that the compositions are given in percent by volume. Substance Mol. Mass Inhaled Air (%) Exhaled Air (%) Nitrogen, N 2 28 78.0 75.0 xygen, 2 32 21.0 16.0 Argon, Ar 40 0.9 0.9 Carbon Dioxide, C 2 44 0.04 4.0 Water, 2 18 0.0 4.0 ther 0.06 0.1 (a) In column 1, for each compound provide its chemical formula after the comma after the compound name. (5 points) Added in red. (b) In column 2, for each compound provide its molecular mass in grams/mol. The mass of Argon is provided. f course, we know that 1 mol is 6.023 10**(23) molecules. Provide the exponent and note that 10 2 = 10**(2). (5 points). Added in blue. (c) Compute how much of inhaled air and of exhaled air are ther gases and enter the result in the table. (2 points) Added in green. (d) Suppose you want to do an experiment to study effects of air composition on the sleepiness of mice. You need to fill 1 m 3 of volume (which is _1000_ dm 3 or _1000_ liters) with air of composition 25% oxygen and 75% nitrogen. ow would you do this? (3 points) 250 liter of oxygen gas 750 liter of nitrogen gas 2
(e) The nitrogen content of inhaled air is said to be 78% and that of exhaled air is said to be 75%. Can this be right? What happened to nitrogen? (5 points) We exhale a lot more water than we inhale. The table is not entirely correct in saying that there is no water in inhaled air. Normal inhaled air contains a lot of water and this is true especially in places like Missouri with humid climates. In any case, we exhale a lot more water than we inhale. The main reason is that we drink a lot of water and we loose a good portion in liquid form (sweat, urine) but also a good portion by exhaling (that is why we make clouds literally when we breathe out in cold weather). Nitrogen is an inert gas with regard to inhalation / exhalation, that is, the body does not do anything with it. Any inert gas inhaled with X percent by volume will be exhaled with Y percent by volume, with X > Y, because we are exhaling more gas overall than we inhale. We exhale more because of the added water. We could say all this using the term particle density : The particle density was changed because the total number of particles is increased. (f) The argon content of inhaled and exhaled air is said to be 0.9%. Can this be true? If you think it is true, then explain why. If it cannot be true, then explain why it cannot be true. [int: ne of the numbers is wrong. 1 extra point for saying which one is wrong.] (5 points) The number for exhaled argon MUST be smaller than the inhaled number. Like dinitrogen, argon is inert with regard to inhalation / exhalation. Since water is added to the exhaled air, the percentage of each inert component will have to go down in exhaled air. Note what happens to oxygen. (a) Some is unused. (b) Some is used in internal oxidation. If the oxygen ends up in a carbon dioxide, then the number of molecules is preserved. If the oxygen ends up in water, then we get two molecules of water for each molecule of oxygen. This is another reason why we breath out more than we breathe in. 3
Question 2. What s that stuff? (15 points) For each of the following substances, mark whether it is pure ( yes or no ), whether it contains atoms or molecules, and write down what atoms, and or ions, and/or molecules the mixture contains (give names or formulas, completeness is not required for complex mixtures, we just want to see that you got the idea). (-1 for each wrong box) Substance Pure? Atoms, and/or Ions, and/or Molecules? What s that stuff? What atoms, ions, and molecules? Water Ice Yes Molecules 2 Dry Ice Yes Molecules C 2 Rock Salt Yes Ions Na + Cl - Perrier (or any other naturally sparkling water) No Atoms, Ions, & Molecules 2, C 2, Na +, Cl -, etc. Natural Gas No Molecules, some atoms Mostly C 4 some 2, C 2 6 Gasoline (lead-free, without ethanol) No Molecules Isomers of C 8 18 and C 7 16 4
Question 3. ey, what s smelling so good? (20 points) Combustion is the oldest sign of civilization. Those of you who attended Saturday Morning Science know that Australopithecus enjoyed the benefits of wood fire some 1.5 million years ago. We still use combustion every day; sometimes we like complete combustion and sometimes incomplete combustion. Whenever we are interested in energy production, then we want the combustion to be as complete as possible. The art in the kitchen is to oxidize the food just a little and that creates the superb flavors. The definition of a complete combustion is that every atom in a fuel is converted into its most oxidized form: Carbon to carbon dioxide, hydrogen to water, nitrogen to nitrogen dioxide, sulfur to sulfur dioxide (not usually the sulfur trioxide). (a) For each of the following fuel molecules, provide the molecular sum formula after the comma after the name (see example butane), provide sum formulas for all the products and balance all equations. (4 points each) The Camping Gas Butane, C 4 10 C 4 10 + 6.5 2 4 C 2 + 5 2 The Gasoline Component Isooctane, C 8 18 C 8 18 + 12.5 2 8 C 2 + 9 2 5
The Sugar Glucose, C 6 12 6 C C 2 C 6 12 6 + 6 2 6 C 2 + 6 2 A Fat Molecule, C 54 98 6 C 16 31 C 16 31 C 16 31 C 54 98 6 + 75.5 2 54 C 2 + 49 2 An Amino Acid, C 5 11 2 NS N 2 C 5 11 2 NS + 8.75 2 3 C S 2 C 2 C C C 5 C 2 + 5.5 2 + N 2 + S 2 6