Exam 1A_Chem 107_ChrisF - Key - Spring 2023

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Feb 20, 2024

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Chemistry 107 Exam #1 A 2/23/2023 Directions: You have the entire class period to complete this exam. Use the back of the page for additional scratch paper if needed and indicate “more work on back” on the front of the page Write clearly and show ALL work. If no work is shown, no credit will be given. Budget your time. If you get stuck, go to the next question. Box in your final answer. Name: ________________________________ Multiple Choice Component: / 30 Short Answer / Worked Problem # Problems Component: 1) / 9 2) / 4 3) / 4 4) / 20 5) / 3 6) / 10 7) / 6 8) / 7 9) / 7 ____________________________________ Total: / 100 KEY

MULTIPLE CHOICE / TRUE/FALSE SECTION: Circle the correct letter for each question (there is only one correct answer per question). Be sure to completely erase any mistakes. You may use this exam paper for scratch. (2.5 pts each, 30 pts total) 1. The odds of winning the Powerball grand prize are about 292.2 million to 1. Based on this, your % chance of winning is . . . a) 0.0003422 % b) 0.0000003422 % c) 0.0000000003422 % d) 0.0000002922 % e) 0.0000000002922 % 2. What would be the uncertainty for the digital measurement recorded in the picture to the right? a) ± 0.05 in. b) ± 0.005 in. c) ± 0.01 in. d) ± 0.001 in. e) None of the above. 3. The uncertainty for the analog device to the right is . . . a) ± 0.5 mL b) ± 0.05 mL c) ± 0.1 mL d) ± 0.01 mL e) ± 0.001 mL 4. When recording measurements on analog devices, you should record significant figures according to . . . a) the largest division. b) the smallest division. c) the smallest division, plus at least one extra digit. d) the smallest division, plus at least two extra digits. e) none of the above. 5. The correct number of significant figures in the number 0.000 74600 is: a) 3 b) 4 c) 5 d) 7 e) 8 6. In the metric system, which unit of measure would have 10 0 for its magnitude? a) TL b) g c) GB d) ns e) kJ Digital devices always record to ± 1 of the last sig. fig. Analog devices always record to ± half of the closest division (0.1 mL in this case). Thus, (0.1 mL x ½) = ± 0.05 mL 100 x 10 x 292.2 1 6 = The base unit alone (i.e., g) is the only metric unit with 10 0 for its magnitude. 0.0000003422 % Remember, leading zeros are NEVER significant. This includes zeros immediately to the right of the decimal.

7. Which of the following represents a hypothesis (this a theory yet to be proven by experiments)? a) Sodium reacts with water to form sodium hydroxide and hydrogen gas. b) Nitrogen gas is a fairly inert substance. c) Nickel has a silvery sheen. d) When a substance combusts, it combines with air. e) When wood burns, heat is given off. 8. Which of the following represents a physical property? a) Sodium metal is extremely reactive with chlorine gas. b) Mercury is a silvery liquid at room temperature. c) Aluminum has a tendency to "rust." d) Butane is highly flammable. e) Argon has an unreactive nature. 9. The Plum-Pudding model of the atom was incorrect because . . . a) it did not take into account neutrons within the nucleus. b) it assumed that protons and electrons occupied the same volume. c) it assumed that electrons were homogeneous throughout the atom. d) it assumed that protons were homogeneous throughout the atom. e) all of the above. 10. The number, 0.0058200 x 10 9 , in proper scientific notation and with the correct significant figures is . . . a) 5.82 x 10 6 b) 5.8200 x 10 12 c) 5.82 x 10 -3 d) 5.8200 x 10 8 e) None of these 11. What answer should be reported, with the correct number of significant figures, for the following calculation? (433.621 – 333.9) x 11.900 a) 1.19 x 10 3 b) 1.187 x 10 3 c) 1.1868 x 10 3 d) 1.18680 x 10 3 e) 1.186799 x 10 3 12. The average distance between nitrogen and oxygen atoms is 115 pm in a compound called nitric oxide. What is this distance in millimeters? a) 1.15 × 10 -8 mm b) 1.15 × 10 -7 mm c) 1.15 × 10 13 mm d) 1.15 × 10 17 mm e) 1.15 × 10 -4 mm pm 10 mm 10 x pm 115 -3 -12 = 1.15 x 10 2 x 10 -9 km = 1.15 x 10 -7 mm 5.8200 x 10 -3 x 10 9 km = 5.8200 x 10 6 Note: Answer has 3 S.F.’s because (433.621 – 333.9) = 99.7 Note: Option (d) is the only choice that tries to explain WHY something happens.

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Free Response. Print clearly AND show all work or receive no points. (70 points total) 1. (9 points) Significant Figures What are the different kinds of “zeros” that need to be considered when determining the number of significant figures in a measurement? Make up any number and use it to illustrate an example of each type of zero (i.e., circle each type of zero in the number and label it). Which type of zero is never significant? 2. (4 points) The Metric System What are the two components of any metric unit? Give an example of a metric unit and indicate both components. 3. (4 points) Units and Significant Figures Perform each of the following calculations to the correct number of significant figures and units: (a) (100.36 g)(4.184 J / g °C)(65.10 °C – 64.73 °C) = (100.36 g)(4.184 J / g °C)( 0.37 °C ) = 155.37 J ===> 160 J (b) = 1.7 x 10 -23 nm The three different kinds of zeros when considering significant figures are: 1) leading zeros ( never significant) 2) trapped zeros 3) trailing zeros For example, all three types of zeros are shown in the following number: 0.056300782000 leading zeros trapped zeros trailing zeros Note: Answer has 2 sig. figs. because 0.37 °C has only two sig. figs.! The two components of a metric unit are: 1) metric prefix 2) base unit For example, picojoules has the following unit: pJ prefix base unit ) 6 . 15 )( 1000 1 )( 5 . 2 ( ) 10 )( 1 1 )( 10 626 . 6 ( 1 9 2 2 34 − − − ms g kg g m nm J s m kg s J x

4. (20 points) Measurements, scientific notation, significant figures, metric conversions, chemical symbols and isotopes. Note: Each question regarding the picture below is independent from the previous question. (a) (8 points) What is the diameter (in cm) of the atom depicted above according to the attached metric ruler (note: the ruler has units of pm)? You may use a piece of scratch paper to visually make your measurement. Express your answer in proper scientific notation with the correct number of significant figures. 434 pm x 10 -12 cm 10 −𝟐 pm = (b) (4 points) How many petagrams of electrons are contained in the atom above? (mass of electron = 9.109 x 10 -28 g) 10 electrons x 9.109 x 10 -28 g electron x 10 𝟎 Pg 10 15 g = There are 10 electrons in the atom above. 9.109 x 10 -42 Pg 600 500 300 400 200 100 700 800 900 pm pm e - ●    ● ● ● ● ●  ●    e - e - e - e - e - e - e - e - According to the ruler, the atom’s diameter is ~434 p m. The smallest increment on the ruler is to every 10 picometers (pm, not Pm!!). Therefore, we record the measurement to the 1 pm (one more digit of precision beyond the smallest increment). 4.34 x 10 2 x 10 -12 x 10 2 cm = 4.34 x 10 -8 cm e - Note:  = proton ● = neutron e - = electron

(c) (4 points) Write the complete chemical symbol for the Bohr orbit diagram in the above figure. (d) (4 points) Would the isotope pictured above indicate the most common isotope of the element? Answer yes or no and explain your choice. 5. (3 points) The Periodic Table Fill out the table below by writing in the name of the element symbols and determine if they are a metal, non-metal or metalloid. Element Symbol Element Name Metal, non- metal, or metalloid? Ba barium metal B boron metalloid Br bromine non-metal N 14 7 3- Yes, the average atomic mass of nitrogen is 14.007 g/mol. The nearest whole number to this is 14 (this means that the most common isotope of nitrogen has 7 protons + 7 neutrons). The isotope pictured also has 7 neutrons.

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6. (10 points) Classification of Matter At the bottom of this page is a list of ten items with a number. Fill in the blank boxes in the diagram below by matching the correct number of the item into the appropriate box. There is only one way to correctly fill in all boxes. To be clear, you should only be placing numbers into the blank boxes. Place the item numbers below in the correct boxes above 1. Salt water. 2. Liquid and gaseous bromine in a close vessel. 3. Pure substance. 4. Copper tubing. 5. Compound. 6. Sugar cubes. 7. Element. 8. Mixture. 9. Water with Ice Cubes. 10. Oil floating on water. 9 2 3 4 5 6 8 7 1 10

7. (6 points) Unit Conversions Our Earth’s circumference at the equator is 4.00000750 x 10 7 m (this is the distance around the Earth). Given that the Earth makes one full revolution in a single day, what is the speed of Earth’s rotation in units of miles per hour. (Note: 1 mile = 1.609 km.) Hint: Hours in a day??? 8. (7 points) Unit Conversions In the year 1869, the largest gold nugget in history, called the “Welcome Stranger”, was found in Victoria, Australia. It weighed in at 220 lbs. and was eventually melted down. How much would this gold nugget be worth in today’s dollars? Note that there are 453.59 grams in a pound, 28.350 grams in an ounce and there are 1.0971 ounces in a troy ounce. Lastly, as of last week, the price of a troy ounce of gold was going for $1835.34. ( 1835.34 dollars 1 troy oz. ) ( 1 troy oz. 1.0971 oz. ) ( 1 oz. 28.350 g ) ( 453.59 g 1 lb. ) ( 220 lbs. ) = Start by writing all unit conversions: 1 mile = 1.609 km 10 3 m = 10 0 km (from metric table) 1 day = 24 hrs. (this is just common knowledge that everyone should know) 1 day = 4.00000750 x 10 7 m Then write what unit is in the desired answer: mi / hr. Start by using the conversion ratio with the desired unit on top and cancel unwanted units from there: 1035.84201 mi/hr 5.888 x 10 6 dollars ====> $5.9 million Start by writing all unit conversions: 1 lbs. = 453.59 g 1 oz. = 28.350 g 1 troy oz. = 1.0971 oz. 1 troy oz. = 1835.34 dollars Then write what unit is in the desired answer: dollars??? Then write any other information: 220 lbs. was the mass of the gold nugget Start by using the conversion ratio with the desired unit on top and cancel unwanted units from there: day 1 m 10 x 4.00000750 hrs. 24 day 1 m 10 km 10 km 1.609 mile 1 7 3 0 =                            

9. (7 points) Energy Flow and Density A miner finds a shiny rock that is suspected of being gold. The rock is determined to have a volume of 0.746 cm 3 and a density of 19.3 g/cm 3 . A separate experiment shows that the temperature of the rock rises from 25 °C to 52 °C upon absorption of 174 J of heat. Is the shiny rock made of pure gold? Answer yes or no and explain your choice. (Note: C pure gold = 0.128 J / g °C for comparison). Use: q = mCΔT and solve for C. 0.4476 J / g °C ====> 0.45 J / g °C No, the rock cannot be pure gold because the specific heat of the rock (0.45 J / g °C) does not come close to matching the specific heat of pure gold (0.128 J / g °C) ( ) ( ) C 25 - 52 cm g 19.3 x cm 0.746 J 174 T - T m q T m q C 3 3 i f substance unknown =        = =  =

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