PracticeMidterm4C

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Chemistry

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Feb 20, 2024

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Page 1 of 6 Chemistry 1A, Section 4 Practice Midterm #4C (90 min, closed book) Name:__________________________________ SID:___________________________________ GSI Name:________________ Useful Equations and constants: E = h ν λν = c E kin (e-) = h ν − binding energy A = ε l c 1 eV = 1.6021 × 10 -19 J 1 J = 1 kg·m 2 /s 2 h = 6.63 × 10 -34 J·s c = 3.0 × 10 8 m/s N A = 6.02 x 10 23 particles/mol 183

Name_____________________GSI__________ Page 2 of 5 Consider the following elements: Ca, Fe, Ga, and Se 1. The electron configuration for Fe is A) [Ar] 3d 6 4s 2 B) [Ar] 4s 2 3d 5 C) [Ar] 3d 8 2. How many nodes does the 3d orbital have? A) 2 B) 3 C) 4 3. Choose the best explanation for why the ionization energy of Ga is LESS than the ionization energy of Ca . A) The ionization energy decreases across a row due to increasing effective nuclear charge . B) The ionization energy increases across a row due to increasing effective nuclear charge . C) The effective nuclear charge for Ga is smaller because there are more electrons in the n=3 shell. 4. For which element is the total energy required to remove 3 electrons the greatest? A) Fe B) Ca C) Ga 5. How many electrons are in the n=3 level in Se A) 6 B) 8 C) 18 6. Which quantum numbers describe the outermost electron in Ga A) shell=4 subshell = p orientation=p z spin = + ½ B) shell=3 subshell = d orientation=d xy spin = −½ C) shell=3 subshell = p orientation=p x spin = + ½ 184

Name_____________________GSI__________ Page 3 of 5 A fellow Chem 1A student takes a trip to an art museum and decides to review the concepts of light and color. What follows are his thoughts about what he is observing. Circle the sentence that is correct. 7. As I walk in the door, I notice that the museum lights are very dim. There is also a sign that says: “No flash photography in the museum.” I’ve heard that bright light makes the paint fade. A) I bet that happens because the light energy can cause vibrations in the paint pigment molecules, which cause the red pigments to get hotter than the blue pigments. B) It seems that red paint fades more than blue because red paint absorbs shorter wavelength blue light. C) High intensity light is effective in breaking chemical bonds . 8. Here’s a sculpture done like a neon sign. The description says that when you put an electric current through the neon gas, it glows with a characteristic color A) This must be because electrons move from energy levels close to the nucleus to energy levels farther away as they emit the light. B) A characteristic energy is needed to ionize the atoms. You only see colors that are not absorbed. C) The electric current moves an electron to an excited state. When the electron returns to the ground state it emits a specific wavelength of visible light. 9. Another room has a collection of photographs. The sign says that they were taken indoors without a flash. White objects appear yellow. A) This is because the filament in the light bulb in the room was not hot enough to emit equal intensities of all visible light. B) This is because the light bulb in the room emited light in the infrared region of the spectrum. C) This is because violet light is absorbed by the white objects. 10. If you walk too near to the paintings, an alarm sounds. I notice that there is a beam of red light (700 nm) crossing in front of the paintings shining onto a photocell. The alarm sounds if you block the light from striking the photocell. What must be true of the light striking the photocell? A) Light of 500 nm will not eject electrons to complete the circuit. B) Light of 750 nm will eject electrons provided the intensity is high enough. C) More intense light of 700 nm will eject electrons with greater kinetic energy. D) None are true. 185

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Name_____________________GSI__________ Page 4 of 5 Plastic sleeves made out of polypropylene can protect photographs from damage by light. To test how well the polypropylene sheet protector blocks harmful light, a Chem 1A student collected absorbance spectra using a UV/Vis spectrometer. The student cut several small strips of the plastic and measured 1-5 layers stacked on top of one another. The data she gathered are shown below. 11. When the absorbance at 273 nm is plotted versus thickness of the plastic sheet a linear graph is obtained (shown above right). What is the slope of the line for this plot? A) ε l B) ε c C) l c 12. The Chem 1A student found a cheaper supplier of polypropylene sheet protectors. She determined the sample absorbance at 273 nm to be 1.23. What is the thickness of the sheet? A) 3.73 mm B) 0.44 mm C) 1.23 mm 13. Based on the spectra shown above, what color are the sheet protectors? A) colorless B) yellow C) white 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 200 400 600 800 Absorbance Wavelength (nm) Polypropylene UV/Vis Spectra 5 Layers 4 Layers 3 Layers 2 Layers 1 Layer y = 2.7287x + 0.0167 R² = 0.9995 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 0 0.1 0.2 0.3 0.4 0.5 0.6 Absorbance Plastic Sheet Thickness (mm) Polypropylene Sheet Protectors 186

Name_____________________GSI__________ Page 5 of 5 The first 4 electron energy levels in hydrogen, H, and helium cation, He + are provided in the table. Use the data to answer the questions below. Energy level Hydrogen, H Helium cation, He + n=1 -1312 kJ/mol -5248 kJ/mol n=2 -328 kJ/mol -1312 kJ/mol n=3 -146 kJ/mol -583 kJ/mol n=4 -82 kJ/mol -328 kJ/mol 14. Which spectrum represents the photoelectron spectrum of He + ? A) B) C) 15. Which spectrum represents the lowest energy absorption line of H (g) at room temperature? A) B) C) 16. How much energy is required to ionize He + ? A) 5248 kJ/mol B) 1312 kJ/mol C) 3936 kJ/mol 17. Which ion releases the most energy when an electron attaches: H, He, He + ? A) He because it is a noble gas. B) H because the added electron will fill the 1s shell. C) He + because it has the highest effective nuclear charge. D) H because it is more electronegative than He and He + . 18. What happens to the electron in the ground state of hydrogen atoms, H, if you shine light of energy 1061 kJ/mol on a sample? A) The electron has enough energy to move to the n=2 shell. The excess energy is released as kinetic energy. B) The electron does not have enough energy to move to the n=2 shell. Nothing happens. C) The energy does not correspond to the energy difference between n=1 and n=2. The light is transmitted. D) The energy is large enough to ionize the electron from the n=2 shell. D) HF satisfies the octet rule, but CH does not. 2000 4000 6000 2000 4000 6000 2000 4000 6000 2000 4000 6000 2000 4000 6000 2000 4000 6000 187

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