Chem. 1A Final Practice Test 1

Transcription

1 Chem. 1A Final Practice Test 1 All work must be shown on the exam for partial credit. Points will be taken off for incorrect or no units. Calculators are allowed. Cell phones may not be used for calculators. On short answer problems you must show your work in order to receive credit for the problem. If your cell phone goes off during the exam you will have your exam removed from you. Fundamentals (of 72 possible) Problem 1 (of 10 possible) Problem 2 (of 27 possible) Problem 3 (of 15 possible) Problem 4 (of 16 possible) Multiple Choice (of 60 possible) Extra Credit Final Total (of 200 possible) 1

2 Fundamental Questions Each of these fundamental chemistry questions is worth 6 points. You must show work to get credit. Little to no partial credit will be awarded. Make sure to include the correct units on your answers. 1) 6 pts Calculate the de Broglie wavelength associated with a 145 g baseball traveling at the speed of 168 km. Do we need to use quantum mechanics h to describe the properties of a baseball and why. 2a) 3 pts How many orbitals can have the quantum numbers: n=3 2d 2b) 3 pts How many electrons can have the quantum numbers: 4d 4f xyz 3) 6 pts A 2.5 ml bubble is released at a depth of 178 feet in a lake where the total pressure is 6.4 atm and the temperature is 4 o C. What is the volume (ml) of the bubble at the surface when the pressure is 758 torr and 20. o C? 2

3 4) 6 pts What are the electron configurations for: Tl Se - 5) 6 pts Study the following sketch of a molecular orbital (MO) in a homonuclear diatomic molecule. This MO was formed by combining a 3p atomic orbital for each of the atoms. * The dark dots in this sketch are the nuclei What is the symbol for this MO? Is this a bonding or antibonding MO? What is the energy of this MO, compared to the energy of a 3p orbital on one of the separate atoms? (circle one) Higher Lower The Same Not Enough Info 6a) 1 pts What is the Lewis symbol for Ga: 6b) 2.5 pts What is the Lewis structure of CaCl 2 : 6c) 2.5 pts What is the Lewis structure of H 2 CO: 3

4 7) 6 pts A solution is prepared by dissolving 25.0 g of ammonium sulfate in enough water to make a ml sample of stock solution. A 10.0 ml sample of this stock solution is added to 50.0 ml of water. Calculate the concentration of ammonium ions in the final solution. 8) 6 pts Calculate the wavelength of the line in the absorption line spectrum of hydrogen caused by the transition of the electron from an orbital with n=8 to an orbital with n=10. 9) 6 pts a) How many protons, electrons, and neutrons does 127 I have b) Give an example of two species that are isotopes of each other. 4

5 10) 6 pts Write the net ionic equation that occurs when the following are mixed. If no reaction occurs write no reaction: a) sliver nitrate and potassium chloride b) barium chloride and ammonium sulfate 11) 6 pts How are the local electron model and molecular orbital theory similar? How are they different? (75 words or less) 12) 6 pts A robot spacecraft returned samples from the planetesimal Aleks, located in the outer Solar System. Mass-spectroscopic analysis produced the following data on the isotopes of tin in these samples: Isotope Mass Relative (amu) Abundance 114 Sn % 115 Sn % Use these measurements to complete the entry for tin in the Periodic Table that would be used on Aleks. Round your entry for the atomic mass to 5 significant digits. Caution: your correct answer will have the same format but not necessarily the same numbers as the entry for tin in the Periodic Table we use here on Earth. You must show your work to get credit. Sn 5

6 Challenge Problems Each of the following short answer questions are worth the noted points. Partial credit will be given. You must show your work to get credit. Make sure to include proper units on your answer. 1) 10 pts Photodissociation of water H 2 O(l)+ hν H 2 (g) + ½O 2 (g) has been suggested as a source of hydrogen. The H rxn for the reaction, calculated from thermochemical data, is kj per mole of water decomposed. Calculate the maximum wavelength (in nm) that would provide the necessary energy. In principle is it feasible to use sunlight as a source of energy for this process? 6

7 2a) 9 pts For the following structure make sure that the formal charges are minimized. 1) Identify the electronic structure of XeO 3. 2) Identify the molecular structure of XeO 3. 3) Identify the bond angles XeO 3. 4) Identify the polarity of XeO 3. 5) What method did you use to determine these answers? 2b) 9 pts 1) What is the hybridization of all of the atoms in COCl 2? 2) Determine the number of σ and π bonds in COCl 2? 3) What orbital(s) overlap to make the bond(s) in this molecule? If there are any lone pair(s) of electrons what type of orbitals are they in? 4) What method did you use to determine these answers? 2c) 9 pts 1) What is the full electron configuration F 2 (include core electrons)? 2) What is the bond order for F 2? What does this tell you about the bond? 3) Is F 2 diamagnetic or paramagnetic? 4) What method did you use to determine these answers? 7

8 3) 15 pts A g sample of a compound containing C, H, and O is burned in oxygen, producing g of CO 2 and g of H 2 O. Determine the empirical formula of the compound. 8

9 4) 16 pts The reaction below can be used as a laboratory method of preparing small quantities of Cl 2 (g). If a 62.6 g sample that is 98.5% K 2 Cr 2 O 7 by mass is allowed to react with 325 ml of HCl(aq) with a density of 1.15 m gl and 30.1% HCl by mass, how many grams of Cl 2 (g) are produced? Cr 2 O 7 2- (aq) + Cl - (aq) Cr 3+ (aq) + Cl 2 (g) (unbalanced) 9

10 Multiple Choice Questions On the ParScore form, you need to fill in your answers, perm number, test version, and name. Failure to do any of these things will result in the loss of 1 point. Your perm number is placed and bubbled in under the ID number. Do not skip boxes or put in a hyphen; unused boxes should be left blank. Bubble in your test version (A) under the test form. Note: Your ParScore form will not be returned to you, therefore, for your records, you may want to mark your answers on this sheet. Each multiple-choice question is worth 5 points. 1. True or False? The equation 2C 2 H 6 + 7O 2 4CO 2 + 6H 2 O is an oxidation-reduction reaction. A) True; the carbon is reduced and the oxygen is oxidized. B) True; the carbon is oxidized and the hydrogen is reduced. C) True; the oxygen is reduced and the hydrogen is oxidized. D) False E) True; the carbon is oxidized and oxygen is reduced. 2. When aqueous solutions of silver nitrate and potassium chromate are mixed, the blood-red precipitate silver chromate is formed. If 10.0 ml of 0.25 M aqueous silver nitrate is mixed with 15.0 ml of 0.14 M aqueous potassium chromate, what is the total concentration of ions in the solution after the precipitate is formed? A) 0.25 M B) 0.39 M C) 0.14 M D) 0.30 M E) none of these 10

11 3. Consider the following gas samples: Sample A S 2 (g) n = 1 mol T = 800 K P = 0.20 atm Sample B O 2 (g) n = 2 mol T = 400 K P = 0.40 atm Which one of the following statements is false? A) Assuming identical intermolecular forces in the two samples, sample A should be more nearly ideal than sample B. B) The root-mean-square velocity of molecules in sample A is twice as large as the root-mean-square velocity of molecules in sample B. C) The average kinetic energy of the molecules in sample A is twice the average kinetic energy of the molecules in sample B. D) The volume of sample A is twice the volume of sample B. E) The fraction of molecules in sample A having a kinetic energies greater than some high fixed value is larger than the fraction of molecules in sample B having kinetic energies greater than that same high fixed value. 4. Indium has atomic number 49 and atomic mass g. Naturally occurring indium contains a mixture of indium-112 and indium-115 in an atomic ratio of approximately A) 94/6. B) 6/94. C) 75/25. D) 25/ Which of the following statements is false? A) A 2p orbital is more penetrating than a 2s; that is, it has a higher electron density near the nucleus and inside the charge cloud of a 1s orbital. B) An orbital can accommodate at most two electrons. C) In the usual order of filling, the 6s orbital is filled before the 4f orbital. D) The spin quantum number of an electron must be either +1/2 or 1/2. E) The electron density at a point is proportional to ψ 2 at that point. 6. For the elements Rb, F, and O, the order of increasing electronegativity is A) O < F < Rb. B) Rb < F < O. C) F < Rb < O. D) Rb < O < F. E) none of these 11

12 7. Which of the following statements is true? A) Only three quantum numbers are needed to uniquely describe an electron. B) Ni has 2 unpaired electrons in its 3d orbitals. C) We can determine the exact location of an electron if we know its energy. D) An electron in a 2s orbital can have the same n, l, and m l quantum numbers as an electron in a 3s orbital. E) In the building up of atoms, electrons occupy the 4f orbitals before the 6s orbitals. 8. Which of the following exhibits the correct orders (increasing) for atomic radius and ionization energy, respectively? A) F, S, O, and O, S, F B) S, F, O, and S, F, O C) F, O, S, and S, O, F D) S, O, F, and F, O, S E) none of these 9. From the following list of observations, choose the one that most clearly supports the conclusion that electrons have wave properties. A) the photoelectric effect B) cathode "rays" C) diffraction D) the emission spectrum of hydrogen E) the scattering of alpha particles by metal foil 10. Which of the following has the smallest radius? A) Br - B) Sr 2+ C) Rb + D) Se 2- E) Kr 11. Which of the following statements is true? A) Antibonding MOs have electron density mainly outside the space between the two nuclei. B) Electrons are never found in an antibonding MO. C) All antibonding MOs are higher in energy than the atomic orbitals of which they are composed. D) None of these statements is true. E) Two of these statements are true. 12

13 12. Complete the Lewis structure for the following molecule. CH 3 O CH 3 CH C C N This molecule has sigma bonds and pi bonds. A) 6, 3 B) 13, 2 C) 4, 5 D) 11, 5 E) None of the above 13