Chem. 1C Midterm 2 Version B May 17, 2017

Transcription

1 First initial of last name Chem. 1C Midterm 2 Version B May 17, 2017 Name: rint Neatly. You will lose 1 point if I cannot read your name or perm number. erm Number: All work must be shown on the exam for partial credit. oints will be taken off for incorrect or missing units. Calculators are allowed. Cell phones may not be used as calculators. On fundamental and challenge 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 36 possible) roblem 1 (of 12 possible) roblem 2 (of 22 possible) Multiple Choice (of 30 possible) Midterm Total (of 100 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 Determine the crystal field splitting of the d-orbitals for a square planer complex. The location of the ligands are seen in the picture on the left and the d orbitals are seen in the picture on the right. z y d yz d xy d Z 2 x d xz d x 2 y 2 Highest Energy dx 2 -y 2 dz 2 dxy Lowest Energy dyz dxz 2a) 1 pts Identify the type of structural isomerism that exists in each of the following pairs of compounds: [Co(NO 2)(NH 3) 5]Br 2 and [Co(ONO)(NH 3) 5]Br 2 Linkage Isomers 2b) 1 pts [CrCl(NH 3) 5]Br and [CrBr(NH 3) 5]Cl Coordination Isomer 2c) 4 pts Can [MA 2B 4] have stereoisomers, where M is a transition metal and A/B are ligands? If so draw them and label the type of stereoisomers. Make sure to use appropriate notation to show bonds going into or out of the board. Geometric Isomers 3) 6 pts 135. mg of an unknown protein are dissolved in enough solvent to make 5.00 ml of solution. The osmotic pressure of this solution is measured to be atm at 25.0 C. Calculate the ar mass of the protein. Round your answer to 3 significant digits. π imrt M n solute n protein V Solvent L atm (1)( n protein L atm )( )(298.2K) L K n protein g g M

3 4) 6 pts Three bottles of aqueous solutions are discovered in an abandoned lab. The solutions are green, yellow, and purple. It is known that three complex ions of chromium(iii) were commonly used in the lab: [Cr(H 2O) 6] 3+, [Cr(NH 3) 6] 3+, and [Cr(H 2O) 4Cl 2] +. Determine the likely identity of each of the colored solutions Color of Solution Color Absorbed Energy Yellow Violet Highest Energy Green Red Lowest Energy urple Yellow Order of crystal field splitting from lowest to highest: Cl - < H 2O < NH 3 Yellow Solution [Cr(NH 3) 6] 3+, urple Solution [Cr(H 2O) 6] 3+, Green Solution [Cr(H 2O) 4Cl 2] + 5) 6 pts An aqueous antifreeze solution is 40.0% ethylene glycol (C 2H 6O 2) by mass. The density of the solution is 1.05 g. Calculate the arity, ality, and e cm 3 fraction of the ethylene glycol. Molarity, ality, and e fraction are intrinsic properties (do not depend on sample size), therefore, assume sample size of 100. g. 40 g of C 2H 6O 2 and 60 g H 20 M n C2H6O2 V solution n C2 H 6 O 2 40 g ( 1 ) g V solution 100 g ( 1 cm3 ) ( 1 ml 1 L 1.05 g 1 cm3) ( M 6.76 M L m n C2H6O2 m H n 2O C2H6O kg 10.7 kg χ n C 2H6O2 +n H2O n H2 O 60 g ( 1 ) g χ ml ) L 6) 6 pts Circle the correct response for each of the following: The solubility of gases in liquids increases as temperature: increases decreases The solubility of gases in liquids increases as pressure: increases decreases Which will be more strongly hydrated? Na + K + Which of the following is more soluble in CCl 4? C 6H 6 C 6H 5OH 3

4 Challenge roblems Each of the following short answer questions are worth the noted points. artial credit will be given. You must show your work to get credit. Make sure to include proper units on your answer. 1a) 6 pts entane (C 5H 12) and hexane (C 6H 14) combine to form an ideal solution. At 25 C the vapor pressure of the pentane and hexanes are 511 and 150. torr, respectively. A solution is prepared by mixing 25 ml of pentane (density 0.63 g ). What is the vapor pressure of this ml ml solution? solution χ C5 H 12 C5 H 12 + χ n C5 H solution 12 n C6 H n Calculate es of C 5H 12 m C5 H 12 Vd C5 H 12 (25 cm 3 g ) (0.63 cm3) 16 g 16 g C 5 H 12 ( 1 C 5H 12 ) 0.22 C g C 5 H 12 5H 12 Calculate es of C 6 H 14 m Vd (45 cm 3 g ) (0.66 cm3) 30. g 30. g C 6 H 14 ( 1 C 6H 14 ) 0.35 C g C 6 H 14 6H 14 + n solution + + n 0.22 solution (511 torr) (150. torr) 290 torr b) 6 pts What is the e fraction of pentane in the vapor that is in equilibrium with the solution? We need to calculate the e fraction of pentane in the vapor phase. You cannot use the e fraction that was calculated in part (a) because that is the e fraction in the liquid phase. In the gas phase V nrt n V RT χ C5 H 12 + n C5 H 12 V RT total V RT C 5 H 12 total C5 H torr χ C5 H torr torr 0.22 (511 torr)

5 2a) 2 pts What is the name of (NH 4) 3[Co(CN) 6]? ammonium hexacyanocobaltate(iii) 2b) 2 pts What is the electron configuration for Cobalt? Co [Ar]4s 2 3d 7 2c) 2 pts What is the electron configuration for the cobalt ion in (NH 4) 3[Co(CN) 6]? Co 3+ [Ar]3d 6 2d) 4 pts Is this complex paramagnetic or diamagnetic? You must draw out the energy level diagram to get credit. e g t 2g Diamagnetic 2e) 6 pts The octahedral crystal field splitting energy of (NH 4) 3[Co(CN) 6] is 306 kj. What is the color of the complex ion? 306 kj ( 1 J ) (1000 complexes 1 kj ) J m s ) λ hc ( J s)( m 391 nm E J This complex absorbs in the violet range therefore the complex appears yellow 2f) 6 pts 1.0 g of (NH 4) 3[Co(CN) 6] is added to 100. ml of water. What is the freezing point of the solution? The density of water is 1.00 g. ml T imk f 1.0g (NH 4 ) 3 [Co(CN) 6 ] ( 1 (NH 4) 3 [Co(CN) 6 ] ) g m n solute m m solvent kg T (4)(0.037 m) (1.86 kg ) 0.28 T f T f T

6 Multiple Choice Questions On the arscore 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 (B) under the test form. Note: Your arscore 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. For each of the following solutions, would you expect it (with respect to Raoult's law) to be relatively ideal, to show a positive deviation, or to show a negative deviation? 1. acetone (C 3H 6O) and water A) negative deviation B) positive deviation C) relatively ideal 2. What is the boiling point of an aqueous solution that contains 20.0 g of NaCl and 40.0 g of CaF 2 that were dissolved in 1.00 L of water? Helpful Information: k b of water is 0.51 and the density of water is A) 99.6 C B) C C) C D) C E) None of the above 3. In the following closed system what happens to the liquid level in the beaker with the salt water? A) Goes up B) Remains the same C) Goes down Water Salt Water 6

7 4. A liquid-liquid solution is called an ideal solution if I. it obeys V nrt. II. it obeys Raoult's law. III. solute-solute, solvent-solvent, and solute-solvent interactions are very similar. IV. solute-solute, solvent-solvent, and solute-solvent interactions are quite different. A) II, III B) I, II, IV C) I, II, III D) I, II E) II, IV 5. Using the data below, calculate the vapor pressure of chloroform over a chloroform-benzene solution at 25 C, which contains 50.0 g of CHCl 3 and 50.0 g of C 6H 6. Assume that the solution behaves ideally. benzene (C 6H 6) chloroform (CHCl 3) Vapor pressure at 25 C 94.4 torr torr A) 148 torr B) 172 torr C) 125 torr D) 68.0 torr E) None of the above 6. Give the number of geometric isomers for the octahedral compound [MA 2B 2C 2], where A, B, and C represent ligands. A) 2 B) 1 C) 5 D) 3 E) None of the above A,D,A,A,D,C 7