Exam 1 v2key 139

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Seattle Central College *

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139

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Chemistry

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May 24, 2024

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CHEM139 Exam 1 v2 W2024 page 1 of 4 CHEM139: Exam 1 v2 Name: Page 1 Page 2 Page 3 Page 4 Exam Total out of 124 Exam Percentage (6) 1. Circle all of the pure substances below: air argon gas tap water steel lead pipe dry ice, CO 2 (s) (12) 2. Consider Figures A-F below: Check all of the statements below that are correct : o a. Figures A, B, and F all represent compounds. o b. Figures A and E both represent liquids. o c. Figures C, D, and F all represent gases. o d. Figures C and D represent mixtures. o e. Figure D represents nitrogen. o f. Figure A and F represent water at different temperatures. (6) 3. Consider figures A to F in problem #2 above. Provide the letter for the molecular level image that represents the following substances at room temperature : (Example i has been done as an example.) B i. NaCl (s) _______ ii. air _______ iii. mercury _______ iv. steam A B C D E F Ky - elements compounds E ex Ar Pb H,0/1) air H20(g) / / y ~ X D E F

CHEM139 Exam 1 v2 W2024 page 2 of 4 (15) 4. Give the corresponding symbol or name for the following elements: (Spelling counts!) a. lead _______ d. P ______________________ g. F ______________________ b. copper _______ e. Se ______________________ h. Cr ______________________ c. iron _______ f. Hg ______________________ i. Ag ______________________ (6) 5. Complete the following table: Isotope Mass number # of protons # of neutrons # of electrons potassium-39 54 Cr barium-138 (6) 6. Check all of the following statements that are CORRECT : o a. Freezing and deposition are physical changes that both result in a solid. o b. Dissolving and precipitating are both examples of physical changes. o c. Air is a homogeneous mixture consisting mostly of oxygen with nitrogen and trace gases. o d. Dissolving table salt in water is a physical change that results in a heterogeneous mixture. o e. The heat from a chemical reaction comes from atoms being created and/or destroyed. o f. Even though the force of gravity on the moon is one-sixth the force of gravity on Earth, an astronaut’s mass on the moon would be the same as his/her mass on Earth. (4) 7. Circle all of the elements below that exist as solids at room temperature: He Br Ca Fe Ar Sr I Hg (4) 8. Indicate the symbol for the element that fits each of the following descriptions: _____ a. The alkali metal with the lowest atomic number _____ c. The noble gas in the 3 rd period _____ b. The alkaline earth metal in the 4 th period _____ d. The only liquid metal at 25°C (5) 9. Check all of the following statements that are true : o a. Protons are positive charged, electrons are negatively charged, and neutrons are neutral. o b. Part of Dalton’s model of the atom was later proven wrong because of subatomic particles. o c. Most the mass of an atom comes from the protons and neutrons in the atomic nucleus. o c. Isotopes of an element have the same number of protons but differ in numbers of electrons. o d In Rutherford’s Alpha-Scattering experiment, most of the alpha particles went through the gold foil without being deflected because the atom is mostly empty space. (3) 10. Consider the relative sizes of an atom and its nucleus. If an atom’s radius is about 0.1 km, what is the radius of the atom’s nucleus in centimeters? ________________ Ab phosphorus fluorine selenium chromium Fe mercury silver 39 19 20 19 54 24 30 24 138 56 82 56 M X X X M 0 & &O Li Ar Ca Ag v X / X 8.1 em the atom is 105 times bigger than nucleus: , 0.1 em

CHEM139 Exam 1 v2 W2024 page 3 of 4 (4) 11. Circle all of the liquids below in which an ice cube (d ice =0.917 g/cm 3 ) would SINK : gasoline (0.743 g/mL) glycerin (1.26 g/mL) ethanol (0.789 g/cm 3 ) beer (d=1.01 g/cm 3 ) (4) 12. Circle all of the elements below with only radioactive and unstable isotopes: Ba Fr Ra U Pb Po I Rn (6) 13. There are only two naturally occurring isotopes for lithium, lithium-6 and lithium-7, which have masses of 6.0151228874 amu and 7.016003434, respectively. Write in complete sentences to explain why the average atomic mass reported on the Periodic Table for lithium is 6.941 amu and not simply the average of these two (~6.516 amu), then indicate which isotope is more abundant. (8) 13. Fill in the blanks: a. 1 g º _______ μ g c. 1 s º _______ ps e. 1 h º ________ s g. 1 gigawatts º _________ watts b. 1 m º _______ cm d. 1 L º _______ cm 3 f. 37.0˚C = ______˚F h. 25.00˚C = ____________ K For the problems below, SHOW ALL WORK and give the answers with the correct units and the correct number of significant figures to receive full credit. CIRCLE YOUR FINAL ANSWER. (6) 15. The volcano reaction involves vinegar and baking soda, which react to form carbon dioxide (CO 2 ), water, and salt. A student adds 2.005 g of baking soda to a beaker with 50.500 g of vinegar , and the resulting mixture contains 47.975 g of water with 1.220 g of carbon dioxide released. Calculate the mass of salt that was also produced by the reaction. dise> diquid > - 00 ⑧ 0 10b 1012 3600 189 100 1000 98.6 298.15 vinegar t baking soda-> CO2+ water- salt t 2.0059 - 1.228g 975g + x M ⊥ an 52.5839 52.585 9 195 he The atomic mass reported on the Periodic Table for each element is the weighted average mass based on percent natural abundance of the naturally occurring isotopes for that element. The mass reported for lithium is 6.941 amu, not 6.516 amu, since lithium-7 is much more abundant than lithium-6. Thus, the atomic mass shown on the Periodic Table for lithium is closer to the mass for lithium-7 since more lithium atoms exist as lithium-7.

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CHEM139 Exam 1 v2 W2024 page 4 of 4 Conversions: 1 mile=1.609 km 1 qt.=946 mL 1 lb.=453.6 g 1 in. º 2.54 cm For the problems below, SHOW ALL WORK and give the answers with the correct units and the correct number of significant figures to receive full credit. CIRCLE YOUR FINAL ANSWER. 16. A box of 96 screws made of steel weigh 1.00 lb., and the density of the screws is 7.95 g/cm 3 . If a (13) student puts 65 screws in a 100-mL graduated cylinder with 50.0 mL of water, calculate the new level of water in the graduated cylinder after the screws are added. 17. A silver-colored ball weighs about 0.1095 oz., and its diameter is 0.325 inches. (14) a. Calculate the ball’s density (in g/cm 3 ). (1 lb. º 16 oz.) V sphere = ! " p r 3 and p = 3.14159 (2) b. The ball is made of ____. (Circle one) Al (2.70 g/cm 3 ) Sn (7.31 g/cm 3 ) Ag (10.5 g/cm 3 ) Extra Credit (6 points): Copper’s two naturally occurring isotopes have atomic masses of 62.9295989 amu and 64.9277929 amu. Use the atomic mass reported on the Periodic Table for copper to determine the fractional abundance (in percent) for each of copper’s naturally occurring isotopes. Copper-63: _________% Copper-65: _________% 65/ was, the big the ene 0.18950z., . 69 = 104375g V = 4r = 4(3.14159)/)in)()] = 0.4543...c d = A I Jams - in re - - Let y = %(b3 -> 1 -x = % (a-15 (62.9295989a)(x) + (64.9277929an)(1 - x) = 63.55 62.9295989x + 64.9277929 - 64.9277929y = 63.55 - 1.9981940y = 63.55 - 64.9277929 = - 1.3777929 69.8 - -- - -1.9981940 x = 0.689519-1.9981940 31.0 -