Chem. B Midterm Version A Name Student Number All wor must be shown on the eam for partial credit. Points will be taen off for incorrect or no units and for the incorrect number of significant figures. Calculators are allowed. On short answer problems you must show your wor in order to receive credit for the problem. If your cell phone goes off during the eam you will have your eam removed from you. Fundamentals (of 0 possible) Problem (of possible) Problem (of possible) Problem (of 6 possible) Multiple Choice (of 0 possible) Midterm Total (of 00 possible)
Fundamental Questions Each of these fundamental chemistry questions is worth 5 points. You must show wor to get credit. Little to no partial credit will be rewarded. Mae sure to report answers in the correct number of significant figures and with the proper units. ) 5 pts For the following equation CH OH(l) + O (g) CO (g) + H O(l) What is oidized and what is the reducing agent? C - +4 lost electrons CH OH Reducing Agent C was oidized ) 5 pts Given the following reaction mechanism: NO Cl ClO + N O +ClO N O + ClO NO + NOCl NOCl + ClO NO +Cl Write the overall reaction. Identify the intermediate(s) if any in the reaction. Identify the catalyst(s) if any in the reaction. Overall Reaction NO Cl NO + Cl Intermediates N O, ClO, NOCl, and ClO Catalysts None ) 5 pts What is the nd half life for a second order reaction with = s and an initial concentration of M. st ½ life [ o = M nd ½ life [ o = 6 M nd Order Reaction t A A s.0m t 0.0076s [= 6.0 M [=.0 M t 6.0M
4) 5 pts What is E cell for the following reaction at 5 C? I (s)+ Fe(s)Fe + (aq, 0.0M) + I - (aq, 0.0 M) RT E E lnq nf Fe Fe + + e - E =0.44 V I + e - I - Fe + I Fe + + I - Q Fe I E 0.98V E = 0.54 V E =0.98 V J 8.45 K 98K C 96,485 ln 0.0M 0.0M.0V 5) 5 pts Write the balanced equation and determine the cell potential for Pt(s) Cr + (aq),cr + (aq) Cu + (aq) Cu(s) Assume standard conditions. Mae sure to include the states in the balanced equation. V Anode (Cr + Cr + + e - ) E = 0.50 V Cathode Cu + +e - Cu E = 0.4 V Cr + (aq)+cu + (aq) Cr + (aq)+cu(s) E =0.84 6) 5 pts What is K for the following reaction at 5 C? Sn 4+ (aq) + Ag(s) Sn + (aq) + Ag + (aq) E =0.65 V Are there more reactants or products at equilibrium? Sn 4+ + e - Sn + (AgAg + + e - ) RT E lnk nf J 8.45 K 98K 0.65V 96,485 ln K 5 K 9.70 More products C ln K
Short Answer Questions Each of the following short answer questions are worth the noted points. Partial credit will be given. Mae sure to show wor, report answers to the correct number of significant figures and use the proper units. ) pts A metal forms the salt MCl. Electrolysis of the ten salt with a current of 0.700 A for 6.6 h produced.00 g of the metal. What is the ar mass of the metal? Determine the es of electrons It n F 60min 60s t 6.6h 900s h min It 0.700A900s n 0.7 C F 96,485 Because M forms the compound MCl the ion that M forms is M + M + + e - M Determine the es of M M 0.7e 0. 0577M e Determine ar mass M.00g 0.0577M 5.0 g To get full credit for this question you must have shown your wor completely: 4 points for calculating the es of electrons. In order to convert between es of electrons and es of M you needed to have an equation that allowed you to get a e to e ratio M + +e - M. Putting is not showing your wor. I have no idea where these numbers are coming from or what you are converting between. Therefore: points for realizing M formed the ion M + (If you did not put M + on your paper you could only get 4 points even if you got the correct answer. In order to be able to construct the ½ reaction needed to mae the e to e conversion you needed to now the charge on the M) points for the following equation M + +e - M (If you did not put M + +e - M on your paper you could only get 7 points even if you got the correct answer because in order to now the e to e conversion factor you needed to now the ½ reaction) points for the correct answer. 4
) pts The reaction 5Br - (aq) + BrO - (aq) + 6H + (aq) Br (l) + H O(l) Is epected to obey the mechanism BrO - (aq) + H + (aq) HBrO (aq) (forward)/ - (bacward) Fast Equilibrium HBrO (aq) + H + (aq) H BrO + (aq) Fast Equilibrium (forward)/ - (bacward) Br - (aq) + H BrO + (aq) (Br-BrO )(aq) + H O(l) Slow (Br-BrO )(aq) + 4H + (aq) + 4Br - (aq) products Fast 4 Write the rate law for this reaction and show what the overall is in terms of elementary reaction s. rate Br HBrO H BrO + is an intermediate therefore, needs to be eliminated from the rate law. Use equilibrium to eliminate the intermediate. HBrO H H BrO HBrO H H BrO Br HBrO H Br H BrO rate HBrO is an intermediate therefore, needs to be eliminated from the rate law. Use equilibrium to eliminate the intermediate. BrO H HBrO BrO H HBrO rate rate Br HBrO H Br BrO H Br BrO H 5
a) 0 pts The following data were obtained for the reaction A+B products [ o (M) [B] o (M) Initial Rate( ) 0.0500 0.00 6.0 0.00 0.00 7 0.00 0.00 4 What is the rate law? y rate [ [ B] Determine reaction order with respect to A Use eperiments and 6.0 0.0500M 7 0.5 log 0.0M y 0.00M 0.0M 0.0500M 0.00M 0.5 log0.500 0.500.50.50 y rate [ [ B] Determine reaction order with respect to B Use eperiments and When the [B] double and the concentration of [ remains the same the rate doubles. Therefore, reaction is st order with respect to [B]..50 rate [ [ B] y b) 6 pts If the rate law was determined to be. rate [ [ B] And the following data was collected [ o (M) [B] o (M) Initial Rate( ) 0.0500 0.00 6.0 What is? Remember to include units.. rate [ [ B] 6.0 0.0500 0.00 0 0. 0. L s. 6
Multiple Choice Questions Each of the following multiple choice questions are worth 5 points. Your answers need to be filled in on the Scantron provided. Note: Your Scantrons will not be returned to you, therefore, for your records, you may want to mar your answers on this sheet. On the Scantron 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 point. Your perm number is placed and bubbled in under the ID number. Do not sip boes or put in a hyphen. In addition, leave bubbles blan under any unused boes. The version number (A) is bubbled in under the test form. Use the following to answer question : For the reaction a A products, select the reaction order(s) that best fit(s) the observations.. A plot of [ vs. t gives a straight line. A) first order in A B) second order in A C) zero order in A D) all of these E) none of these. The reaction profile for the mechanism NO (g) + F (g) NO F(g) + F(g) slow F(g) + NO (g) NO F(g) fast shows A) two maima, the second maimum being the higher. B) one maimum for the second step. C) two maima, both the same height. D) two maima, the first maimum being the higher.. For a reaction in a voltaic cell, both H and S are positive. Which of the following statements is true? A) G > 0 for all temperatures. B) E cell will increase with an increase in temperature. C) E cell will decrease with an increase in temperature. D) E cell will not change when the temperature increases. E) None of the above statements is true. 7
4. All of the following statements with respect to the effect of a catalyst on a reaction are true ecept: A) A catalyst speeds up a reaction by providing an alternate pathway for the reaction. B) When a reaction is catalyzed, both forward and reverse reactions are accelerated. C) When a catalyst speeds up a reaction, the rate law stays the same. D) A catalyst provides a lower activation energy for the reaction. E) A catalyst has no effect on the equilibrium composition of the reaction. 5. A concentration cell is constructed using two Ni electrodes with Ni + concentrations of.6 M (cathode) and 4.95 0 4 M (anode) in the two half-cells. The reduction potential of Ni + is 0. V. Calculate the potential of the cell at 5 C. A) +0.0 V B) +0. V C) 0.0 V D) 0.087 V E) 0. V 6. True of False. This (electrolysis) is when an electric current catalyzes a reaction. A) True B) False 8