Chem 1C Midterm 2 Practice Test 1

Transcription

1 Chem 1C Midterm 2 Practice Test 1 First initial of last name Name Perm Number All work must be shown on the exam for partial credit. Points will be taken off for incorrect or missing units. Calculators are allowed. Cell phones may not be used for 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) Problem 1 (of 17 possible) Problem 2 (of 17 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 rewarded. Make sure to include the correct units on your answers. 1a) 2 pts What is the chemical formula and coordination number of pentaamminesulfatocobalt(iii) chloride? 1b) 4 pts What is the name and coordination number of Na[Co(NO2)2(en)2] 2a) 4 pts When pure methanol is mixed with water, the solution gets cold to the touch. Draw a graph showing the vapor pressure as a function of the mole fraction of water, χ H2 O. 2b) 2 pts Is this an ideal solution? What does this tell you about the interactions between CH3OH and H2O? 3) 6 pts Calculate the freezing and boiling points of an aqueous solution that is 5.5% NaNO3 by mass. 2

3 4a) 1 pts Identify the type of structural isomerism that exists in each of the following pairs of compounds: [Co(NO2)(NH3)5]Br2 and [Co(ONO)(NH3)5]Br2 4b) 1 pts [CrCl(NH3)5]Br and [CrBr(NH3)5]Cl 4c) 4 pts Can [MA2B4] have stereoisomers, where M is a transition metal and A/B are ligands? If so draw them and label the type of stereoisomers that they are? If bonds are going into or out of the board use appropriate notation. 5) 6 pts There are three unlabeled beakers with different colored solutions (yellow, blue, and orange). It is known that each beaker contains one soluntion that is one of the following: [CoF6] 3-, [Co(NH3)6] 3+, and [Co(CN)6] 3-. Based on the colors of the three solutions, which of the complex ions is present in each of the beakers. You must give evidence for your selection. 6) 6 pts 189. 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 molar mass of the protein. Round your answer to 3 significant digits. 3

4 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) 17 pts The vapor pressure of carbon tetrachloride CCl4, is atm and the vapor pressure of chloroform, CHCl3, is atm at 316K. A solution is prepared from equal masses of these two compounds at this temperature. Calculate the mole fraction of the chloroform in the vapor above the solution. If the vapor above the original solution is condensed and isolated into a separate flask, what would the vapor pressure of chloroform be above this new solution? 4

5 2) 17 pts Ammonia and potassium iodide solutions were added to an aqueous solution of Cr(NO 3 ) 3. A solid was isolated (compound A) and the following data was collected: 1. When g of compound A was strongly heated in excess O g of CrO 3 was formed. 2. In a second experiment it took ml of 0.100M HCl to titrate completely the NH 3 present in g of compound A. 3. Compound A was found to contain 73.53% iodine by mass. 4. The freezing point of water was lowered by 0.64 C when g of compound A was dissolved in g of H 2 O (K f = 1.86 kg mol What is the formula of the compound? What is the structure of the complex ion present? [Hints: Cr 3+ is expected to be six-coordinate with NH 3 and (possibly) I - acting as ligands. The I - ions will be the counter ions if needed. 5

6 Multiple Choice Questions Each of the following multiple choice questions are worth 5 points. Your answers need to be filled in on your ParSCORE 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. On the ParSCORE you need to fill in your 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. In addition, leave bubbles blank under any unused boxes. The version number (A) is bubbled in under the test form. 1. A salt solution sits in an open beaker. Assuming constant temperature and pressure, the vapor pressure of the solution A) stays the same over time. B) increases over time. C) We need to know the temperature and pressure to answer this. D) decreases over time. E) We need to know which salt is in the solution to answer this. 2. Which metal ion has a d 6 electron configuration? A) Fe 3+ B) Co 3+ C) Ni 2+ D) Mn Fluoride ion ranks low in the spectrochemical series and produces a weak crystal field in complex ions. Based on this information, predict the number of unpaired electrons in [CrF6] 3. A) 0 B) 5 C) 2 D) 1 6

7 4. Rank the following compounds according to increasing solubility in water. I. CH3 CH2 CH2 CH3 II. CH3 CH2 O CH2 CH3 III. CH3 CH2 OH IV. CH3 OH A) I < II < IV < III B) III < IV < II < I C) I < II < III < IV D) I < III < IV < II 5. The color of a transition metal complex results from A) stretching vibrations. B) transition of an electron between d orbitals. C) nuclear magnetic resonance. D) bending vibrations. E) transition of an electron between an s orbital and a p orbital. 6. A solution containing g of NaCl per liter has a density of g/ml. What is the molality of the solution? A) m B) m C) m D) m 7