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Vermont Tech CHE1031 CHE1031 Chapter 1 Homework Problem Key Homework problems are organized by topic, in the same order that topics are covered in lecture. Once we cover a topic in lecture, the problems for that topic are due at our next class meeting. If you have questions about which questions are due, please ask! Homework format: Problems must be solved, or written out, in their entirety with all work shown on engineering graph paper. You must label each set in the upper left hand corner with your name, the date and the chapter. Problems must be identified by number and all work must be shown with answers boxed. Be sure your handwriting is legible. 1.1 Science and chemistry 1. What is the difference(s) between science and engineering? Science is the systematic study of the physical world by observation and experimentation; any systematic collection or body of knowledge about a certain subject. Engineering is the practical application of knowledge in the construction of machines, buildings, infrastructure etc. 2. What’s the essential difference between physics and chemistry? [Use any resource you need to pin this down.] Physics is the study of matter and its behavior. Chemistry is the study of the changes matter undergoes. 3. The scientific method is “iterative” in nature. What does iterative mean and how does it apply to the scientific method. Iterative means that a process must be applied again and again (repeatedly) in order to learn and solve a problem. The scientific method involves observing a phenomenon, forming a hypothesis, designing and executing experiments to test the hypothesis, and finally supporting or disproving the hypothesis; supported hypotheses become theories. Most hypotheses are not supported, so scientists must engage the method in an iterative fashion until they develop a hypothesis that can be supported by experimentation. 1.2: What is matter? States of matter 4. In which physical state is matter most: a. Dense solid b. Energetic gas c. most compressible gas 5. What is unusual about the solid physical state of water? [Imagine a pond of water with ice and compare it to a pond of molten steel with solid steel chunks.] Solid ice is less dense than liquid water and floats on liquid it. The solid state of most substances is more dense than the liquid state, and will sink through it. 1 Vermont Tech CHE1031 Pure substance vs. mixture 6. Classify each of the following as a pure substance or as a mixture. If a mixture, is it homogeneous or heterogeneous? a. air mixture; homogeneous b. tomato juice mixture; heterogeneous if you can see pulp c. iodine crystals pure substance; element d. sand mixture of granules, largely silicon dioxide Physical vs. chemical change 7. Label each as a physical or chemical property of Zn: a. Zn is a silver-gray metal. physical b. Zn melts at 420°C. physical c. Zn “disappears” when added to acid, and hydrogen gas is produced. chemical d. Zn has a hardness of 2.5 Mohs. physical 3 e. Zn has a density of 7.13 g/cm . physical f. Zn reacts with oxygen, at elevated temperatures, to produce zinc oxide, ZnO. chemical 8. Identify each as a chemical or physical change: a. the match burns chemical b. the metal gets warmer physical c. water condenses on the metal physical – change of state d. soot is deposited on the metal chemical – soot is formed by combustion 1.3: Measurement, metric units & prefixes Units 9. What exponential notation do the following abbreviations represent: a. d -1 b. c -2 c. f -15 d. μ -6 e. M +6 f. k +3 g. n -9 h. m -3 i. p -12 2 Vermont Tech CHE1031 Density 10. The label fell off a bottle of clear liquid. The lab tech thinks that it’s benzene – a nasty carcinogen – and measures its density to try and confirm this. A 25.0-mL volume of the liquid has a mass of 21.95 g. The density of benzene is 0.8787 g/mL at 15°C. Was the tech right? ρ = m/v = 21.95 g = 0.878 g/mL So density is a match for benzene. 25.0 mL 11. The density of titanium metal is 4.51 g/cm3 at 25°C. What mass of Ti displaces 125.0 mL of water at that temperature? m = ρv = (4.51 g/cm3)(125.0 cm3) = 564 g Exact vs. inexact numbers 12. Which are exact numbers? a. Mass of a 16-oz. bag of coffee from Vermont Coffee Company b. Number of students in class c. The temperature of the surface of the sun d. The mass of a postage stamp e. The number of millimeters in a cubic meter of water f. the average height of students at the college inexact exact inexact inexact exact inexact Uncertainty precision & accuracy 13. You are using a graduated cylinder calibrated in one mL intervals. The volume of liquid in your cylinder looks to be halfway between 20 and 21 mL. How would you report this volume with proper uncertainty? 20.5 + 0.5 where the ‘0.5’ after the 20 is the digit of uncertainty, and the + 0.5 is one-half of the instrument’s least count (smallest calibration) and tells the reader about the instrument’s quality. 14. The US government issues monthly statistics for job growth, unemployment, manufacturing productivity, etc. The numbers are usually revised a few weeks after they are first announced. Is the purpose of the revision to increase: a. accuracy; or Revised statistics use complete and checked data. b. precision? Significant figures 15. How many significant figures in each of these numbers: a. 3.774 km 4 2 b. 205 m 3 c. 1.700 cm 4 d. 350.00 K 5 e. 307.080 g 6 3 f. 1.3 x 10 m/s 2 3 Vermont Tech CHE1031 16. The diameter of the Earth at the equator is 7926.381 miles. Round that to 3 sig figs and express it with scientific notation. 7.93x103 miles 17. Express the answer to each problem with the correct number of significant figures. a. 320.5 – (6104.5/2.3) = = 320.5 – 2600 = -2280 (none after decimal) b. ((285.3 x 105) – (1.200 x 103)) x 2.8954 = = (2.99 x 104 – 124)(2.8954) = 8.62x104 c. (0.0045 x 20,000.0) + (281.3 x 12) = = 90. + 3.4 x 103 = 35. x 102 d. 863 x (1255 – (3.45 x 108)) = = (863)(882) = 7.61 x 105 Scientific notation 18. Convert these numbers into scientific notation: a. 25030000 2.503 x 107 b. 0.00000042600 4.2600 x 10-7 1.5: Dimensional analysis Single conversion factor 19. A blue whale has a lung capacity of 5.0 x 103 L. Convert that to gallons. 5.0x103 L 1 gallon = 1.3x103 gallons 3.7854 L With multiple conversion factors 20. In 2007, it’s estimated that 31 billion tons of CO2 was emitted worldwide due to fossil fuel combustion and cement production. Express this mass in grams using a metric prefix without scientific notation. 31x109 tons 2000 lb 1 ton 453.59 g = 2.81x1016 g = 28100000 Gg 1 lb 21. Bamboo can grow up to 60.0 cm per day. Convert that to inches per hour. 60.0 cm 1 in 1 day = 0.984 in/hour 1 day 2.54 cm 24 hr 22. The recommended adult dose of Elixophyllin, an asthma drug, is 6 mg/kg of body weight. What’s the dose (mg) for a 185-lb person? 185 lb 453.59 g 1 kg 6 mg = 503 mg 1 lb 103 g 1 kg 4 Vermont Tech CHE1031 With cubed unit volumes 23. Silicon for computer chips is grown in large cylinder called “boules”. One boule is 300 mm in diameter and 2 m tall. The density of Si is 2.33 g/cm3. Silicon wafers for making integrated circuits are sliced from a 2.0 m boule and are 0.75 mm thick and 300 mm in diameter. a. How many wafers can be cut from a single boule? b. What is the mass of one wafer? a. 2.0 m 1000 mm 1 slice = 2.7 x 103 slices 1m 0.75 mm b. volume of a slice = (h)(πr2) = (0.75 mm)(π)(150 mm/2)2 = 5.3 x 104 mm3 5.3 x 104 mm3 13 cm3 103 mm3 2.33 g = 1.2 x 102 g 1 cm3 24. The concentration of carbon monoxide in an urban apartment is 48 μg/m3. What is the mass (g) of CO in room that measures 11.0 x 11.5 x 20.5 ft? Room volume = (11.0)(11.5)(20.5) = 2.59 x 103 ft3 2.59 x 103 ft3 123 in3 2.543 cm3 13 m3 13 ft3 13 in3 1003 cm3 48 μg 1g = 3.52 x 10-3 g 1 m3 106 μg 5