Chemistry 1 Second Lecture Exam Fall Abbasi Khajo Kruft Levine Mathias Mathias/Ortiz Metlitsky Rahi Sanchez-Delgado Vasserman

Transcription

1 Page 1 of 9 Chemistry 1 Second Lecture Exam Fall 2011 Name Circle the name of your recitation/lab instructor(s) Abbasi Khajo Kruft Levine Mathias Mathias/Ortiz Metlitsky Rahi Sanchez-Delgado Vasserman Before you begin the exam, write your name on this page and read all these instructions. Answer all questions in these pages. No scrap paper allowed Show all work. Express answers with the proper units and to the correct number of significant figures. You have 90 minutes. Do not spend too much time on one question. There are questions on BOTH SIDES of most pages. This exam has 9 pages and 5 sheets. Make sure you have all of them. If you need more space, use page 2 or the last page. Calculators may be inspected to make sure they do not contain a cheating sheet. Graphing calculators are not allowed. Use of cell phones is prohibited and will be considered as cheating. PERIODIC CHART OF THE ELEMENTS IA IIA IIIA IVA VA VIA VIIA 0 1 H Li Be B C N O H F He Ne Na Mg Al Si P S Cl Ar K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr Rb Sr Y Zr Nb Mo Tc (98) 44 Ru Rh Pd Ag Cd In Sn Sb Te I Xe Cs Fr (223) 56 Ba Ra * La # Ac Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po (209) 85 At (210) 86 Rn (222) * Lanthanides # Actinides 58 Ce Th Pr Pa Nd U Pm (145) 93 Np Sm Pu (244) 63 Eu Am (243) 64 Gd Cm (247) 65 Tb Bk (247) 66 Dy Cf (251) 67 Ho Es (254) 68 Er Fm (257) 69 Tm Md (257) 70 Yb No (255) 71 Lu Lr (256)

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3 NAME CONSTANTS Page 3 of 10 R = L atm mol 1 K 1 1 atm = 760 torr c = m/s h = J s 1. (3 pts) Which one of the following sets of quantum numbers is allowed as the quantum numbers of an electron in an atom? (a) n = 2, l = 1, m l = 1, m s = ½ (b) n = 0, l = 0, m l = 0, m s = ½ (c) n = 2, l = 2, m l = 2, m s = ½ (d) n = 5, l = 3, m l = 2, m s = ½ (e) n = 4, l = 2, m l = 1, m s = 1 (f) n = 2, l = 1, m l = 2, m s = ½ 2. (5 pts) Give the complete ground-state electron configuration of each of the following (do not use the inert-gas abbreviation but list ALL the electrons) (a) P (atomic number 15) (b) Ni (atomic number 28) 3. (2 pts) How many valence electrons (also called outer or high-energy electrons) does a P atom (question 2a) have in its ground state? (This is the same number as is shown in the dot formula for P.) 4. (2 pts) For a 5f electron: (a) Give the value of the quantum number n (b) give the value of the quantum number l

4 Page 4 of (3 pts) Read this buret to the nearest 0.01 ml (no credit if your answer is to the nearest 0.1 ml). Do not spend too much time on this you are allowed to be slightly in error. 6. (6 pts) State whether each of the following sentences is true or false. (a) If a highly competent chemistry professor dissolves moles of sucrose in liters of water, the sucrose molarity in this solution is M. (b) In a sample of N 2 gas held at constant temperature, all the molecules move at the same speed. (c) In the hydrogen atom, the electron moves on a circular orbit around the nucleus. (d) In the hydrogen atom, the 2s and 2p subshells have the same energy but they have different energies in atoms with more than one electron. 7. (2 pts) Give the name of the scientist who did each of the following. Choose your answers from Einstein, Weinstein, Schopenhauer, Heisenberg, Eisenberg Pauli, Bohr, de Broglie, Maxwell, Planck, Schrödinger, Hindemith.,. (a) He was the first person to propose that electrons have wave properties. (b) He discovered the equation that when solved gives the correct energy levels and the wave functions for electrons in all atoms and molecules. 8. (3 pts) f H for C 3 H 8 O(l) is the enthalpy change for a certain chemical reaction. Write this chemical reaction. You must include s, l, g for each substance. (In one case, you can get extra credit by writing something that is not s, l, or g.)

5 Page 5 of (6 pts) Box A and Box B have the same volume, the same temperature and the same pressure. Box A contains only CH 4 gas. Box B contains only C 2 H 6 (g). For each of the following quantities, state for which box (A or B) the gas has the greater value of the quantity. If the quantity has the same value in both boxes, write "same." (a) Number of molecules (b) Density (c) Average molecular speed (d) Average molecular kinetic energy 10. (10 pts) Complete and balance each of these reactions. If no reaction occurs, write no reaction and do not write any products. Do not write net ionic reactions here. Some solubility (a) HNO 3 (aq) + Mg(s) (Mg is above H in the activity series). (b) Ca(OH) 2 (aq) + HNO 3 (aq) (c) K 2 CO 3 (aq) + HCl(aq) (Write the final products.) (d) Zn(s) + Ni(NO 3 ) 2 (aq) (Zn is above Ni in the activity series and Ni is above Cu in this series.) (e) Cu(s) + Zn(NO 3 ) 2 (aq) 11. (4 pts) For any two of the reactions in Question 10, find the net ionic reaction. Do only two reactions.

6 Page 6 of (2 pts) A student dissolves a certain number of moles of Fe 2 (SO 4 ) 3 in water and adds water until the solution s volume is L. The Fe 2+ molarity in this solution is 0.60 M. How many moles of Fe 2 (SO 4 ) 3 did the student dissolve? 13. (3 pts) How many glucose molecules are there in 125 ml of a 1.50 M aqueous glucose solution? (Glucose is a nonelectrolyte.) 14. (2 pts) The lowest three energy levels in the H atom are shown at the right. (Note the unequal spacing.) Which one of the following transitions will involve the lowest-frequency photon?: (a) n = 1 to n = 2 (b) n =1 to n = 3 (c) n = 2 to n = 3 n = 3 n = 2 n = (2 pts) The curves at the right show the distribution of speeds in nitrogen gas at two temperatures. Which curve (A or B) is for the higher temperature?

7 16. (3 pts) H at 25 C is 283 kj for the reaction CO(g) + ½ O 2 (g) CO 2 (g). Find H at 25 C for 2CO 2 (g) 2CO(g) + O 2 (g) Page 1 of (6 pts) If ml of NaOH(aq) is needed to titrate ml of M H 2 SO 4 (aq) to the neutralization point in the reaction 2 NaOH(aq) + H 2 SO 4 (aq) Na 2 SO 4 (aq) + 2 H 2 O find the NaOH(aq) molarity. 18. (6 pts) If a large excess of Al is added to 425 ml of a M HNO 3 (aq) solution, find the mass of H 2 produced in the reaction 2Al + 6HNO 3 (aq) 2Al(NO 3 ) 3 + 3H 2

8 19. (5 pts) For the reaction Page 8 of 10 2 NO(g) + O 2 (g) 2 NO 2 (g) H = kj at 25 C. (a) Calculate the amount of heat transferred when 333 g of NO(g) reacts with O 2 (g) at 25 C and 1 atm. (b) Does this heat flow into the system or does it flow to the surroundings? (c) Is this reaction exothermic or endothermic? 20. (3 pts) If 8675 J of heat flows into g of water initially at 20.0 C, find the final temperature of the water. The specific heat of water is 4.18 J g 1 K (6 pts) Find the molecular weight of a gas if g of the gas in a 7045 cm 3 container at 20 C exerts a pressure of 698 torr. (See the constants at the top of page 3.) 22. (6 pts) H at 25 C is 1790 kj for the reaction C 3 H 6 O(l) + 4O 2 (g) 3 CO 2 (g) + 3 H 2 O(l). Given these H f values at 25 C: 394 kj/mol for CO 2 (g), 286 kj/mol for H 2 O(l), and 0 for O 2 (g), find H f for C 3 H 6 O(l).

9 Page 9 of (6 pts) What volume of H 2 (g) at 27 C and 1.08 atm is produced when 45.3 g of Al reacts as follows: 2Al + 6HNO 3 (aq) 2Al(NO 3 ) 3 + 3H (4 pts) The lowest two energy levels of an electron in certain atom (that is NOT the hydrogen atom) are: J J Find the frequency and the wavelength of the light emitted when an electron in this atom goes from the upper level shown in the figure to the lower level. Please note that this problem is NOT about the hydrogen atom and you must NOT use the formula for the energy levels of the hydrogen atom to solve this problem. See the constants on page 2.

10 Page 10 of 10 Extra credit EC1 (1/2 pt) The name of the person who keeps track of Prof. Levine's mistakes in lecture is (a) Michael (b) Emily (c) Renata (d) Amy (e) Louisa (f) Mary (g) Nobody keeps track of Prof. Levine's mistakes. EC2 (1 pt) Give the symbol (one or two letters) of an element with atomic number less than 36 that has 6 unpaired electrons in its ground electronic state. EC3 (1 pt) Consider three energy levels in a certain atom (not the H atom), which we label as levels A, B, and C. We know that the energies of these levels increase from A to B to C, so that EA EB EC. When an electron goes from level C to level A it emits a photon of wavelength 425 nm and when an electron goes from C to B, it emits a photon of wavelength 823 nm. Find the wavelength of the photon emitted when an electron goes from level B to level A. One nm = 10-9 m.