Chem. 1A Midterm 2 Version A November 9, 2018

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1 First initial of last name Chem. 1A Midterm 2 Version A November 9, 2018 Name: Print Neatly. You will lose 1 point if I cannot read your name or perm number. 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 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 6 possible) Problem 1 (of 17 possible) Problem 2 (of 17 possible) Multiple Choice (of 0 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 Is Cu(OH) 2 (s) + 2HNO (aq) Cu(NO ) 2 (aq) + 2H 2 O(l) a redox reaction? NO If yes, what is reduced? Is Fe 2 O (s) + CO(g) 2Fe(s) + CO 2 (g) a redox reaction? YES If yes, what is the oxidizing agent? Fe 2 O Is P 4 (s) + 10HClO(aq) + 6H 2 O(l) 4H PO 4 (aq) + 10HCl(aq) a redox reaction? YES If yes, what is oxidized? P 2) 6 pts What are the (a) molecular, (b) complete ionic, and (c) net ionic reactions when the following are mixed? If no reaction occurs, write no reaction. Do not forget to include states. Fe(NO ) (aq) and (NH 4 ) 2 SO 4 (aq) No reaction CaCl 2 (aq) and K 2 SO 4 (aq) Molecular CaCl 2 (aq) + K 2 SO 4 (aq) 2KCl(aq) + CaSO 4 (s) Complete Ionic Equation Ca 2+ (aq)+2cl - (aq)+2k + (aq)+so 4 2- (aq) 2K + (aq)+2cl - (aq)+caso 4 (s) Net Ionic Equation Ca 2+ (aq) + SO 4 2- (aq) CaSO 4 (s) ) 6 pts Calculate the pressure exerted by mole of N 2 in a L container at 25.0 C. Use the van der Waals equation. [P + a ( n V )2 ] (V nb) = nrt nrt P = a (V nb) (n V )2 P = L atm ( mol)( mol K )(298.2) L ( L ( mol)(0.091 mol 12.1 atm )) (1.9 atm L mol ) ( mol L )2 = 2

3 4) 6 pts Determine the concentration of NaOH if 10.0 ml of the solution took 11.5 ml of 2.0 M H 2 SO 4 to reach the equivalence point in a titration. 2NaOH(aq) + H 2 SO 4 (aq) Na 2 SO 4 (aq) + 2H 2 O(l) 2 mol NaOH L H 2 SO 4 ( 2.0 mol H 2SO 4 ) ( ) = mol NaOH 1 L H 2 SO 4 1 mol H 2 SO 4 M = n mol = = 4.6 M V L 5) 6 pts Consider the following samples of gas: Select the graphs that show the distribution of speed of the atoms in each sample. Sample Composition Pressure Temperature A 1.0 mol Ar(g) 2.8 atm 279 C B 1.0 mol Ar(g) 1.9 atm 298 C C 1.0 mol Ar(g) 2.6 atm 24 C Sample Composition Pressure Temperature D 2.9 mol Ar(g) 2.6 atm -. C E 2.9 mol Kr(g) 2.5 atm -. C F 2.9 mol Xe(g) 1.1 atm -. C 6) 6 pts A sealed balloon is filled with 1.00 L of helium at 2 C and 1.00 atm. The balloon rises to a point in the atmosphere where the pressure is 220. torr and the temperature is -1 C. What is the change in the volume of the balloon as it ascends form 1.00 atm to a pressure of 220. torr? Need to calculate ΔV V = V F V I Determine V F Find a relationship between P, V, and T (R and n constant) PV = nrt P I V I T I = P FV F T F V F = P IV I T F (1.00 atm)(1.00 L)(242K) = = 2.8 L T I P F (296K)(0.289 atm) Calculate the change in volume V = V F V I = 2.8 L 1.00 L = 1.8 L

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 How many grams of silver chloride can be prepared by the reaction of ml of 0.20 M silver nitrate with ml of 0.15 M calcium chloride? Calculate the concentrations of each ion remaining in solution after precipitation is complete. 2AgNO (aq) + CaCl 2 (aq) 2AgCl(s) + Ca(NO ) 2 (aq) This is a limiting reagent problem Calculate the moles of AgNO ml AgNO ( 1 L ) 1000 ml (0.20 mol AgNO ) = mol AgNO 1 L AgNO Calculate the moles of CaCl ml CaCl 2 ( 1 L ) 1000 ml (0.15 mol CaCl ) = mol CaCl 1 L CaCl 2 2 Calculate the number of moles of CaCl 2 needed to fully react AgNO mol AgNO ( 1 mol CaCl 2 ) = mol CaCl 2 mol AgNO 2 Since we have mol of CaCl 2 the AgNO is the limiting reagent. AgNO (aq) (L.R) CaCl 2 (aq) AgCl(s) Ca(NO ) 2 I (mol) C (mol) -2x= x= x= x=0.010 F (mol) x = 0 x = Calculate the grams of AgCl produced g AgCl mol AgCl ( ) = 2.9 g AgCl 1 mol AgCl Calculate the concentration of the all the ions. Final Volume of Solutions 1 L ml ml = ml ( ) = L Calculate the concentration of Ag + ion M Ag + all went into forming AgCl Calculate the concentration of Cl - ions 1000 ml c = n = M Cl from the CaCl 2 V L Calculate the concentration of Ca 2+ ions = 2(0.005 mol) c = n V CaCl 2 - Calculate the concentration of NO ions c = n V = mol mol L = 2(0.010 mol) L = M Ca 2+ from the Ca(NO ) 2 and = 0.10 M NO from the Ca(NO ) 2 4

5 2) 17 pts Metallic molybdenum can be produced from the mineral molybdenite (MoS 2 ). The mineral is first oxidized in air to molybdenum trioxide and sulfur dioxide. Molybdenum trioxide is then reduced to metallic molybdenum using hydrogen gas. The balanced equations are MoS 2 (s) + 7 O 2 2(g) MoO (s) + 2SO 2 (g) MoO (s) + H 2 (g) Mo(s) + H 2 O(l) Calculate the volume of air and hydrogen gas at 17 C and 1.00 atm that are necessary to produce kg of pure molybdenum from MoS 2. Assume air contains 21% oxygen by volume and assume 100% yield for each reaction. What was given P = 1.00 atm m = kg Mo g M Mo = mol n = kg Mo ( 1000 g 1 kg T = 17 = = 290. K Calculate the moles of O 2 ) ( 1 mol Mo g Mo mol O 2 ) = 10,400 mol Mo 10,400 mol Mo ( 1 mol MoO ) ( 7 2 ) = 6,400 mol O 1 mol Mo 1 mol MoO 2 Calculate the volume of O 2 PV = nrt V = nrt L atm (6,400 mol)( = mol K )(290. K) = L P 1.00 atm Calculate the volume of air L = V air (0.21) V air = L Calculate the moles of H 2 10,400 mol Mo ( mol H 2 ) = 1,200 mol H 1 mol Mo 2 Calculate the volume of H 2 V = nrt L atm (1,200 mol)( = mol K )(290. K) = L P 1.00 atm 5

6 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. A sample of an unknown gas effuses in 8.2 minutes. An equal volume of krypton in the same apparatus at the same temperature and pressure effuses in 4.0 minutes. What is the likely identity of the gas? Helpful Information:,,, and a. Br 2 b. Ne c. Ar d. UF 6 2. Balance the following equation in basic solution and determine the coefficient of OH - and its location (right side or left side) in the equation: Ce(s) + PO 4 - (aq) HPO 2- (aq) + Ce(OH) (s) a., left b., right c. 5, right d. 5, left. You dissolve g of NH 4 NO in ml of solution (call this solution A). You take 20.0 ml of solution A and add water until the total volume is 75.0 ml (call this solution B). You take 15.0 ml of solution B and add 25.0 ml of water to it (call this solution C). You mix 10.0 ml of solution B and 10.0 ml of solution C (call this solution D). What is the concentration of ammonium nitrate in solution D? a M b M c M d M 6

7 4. Given a cylinder of fixed volume filled with 1 mol of argon gas, which of the following is correct? (Assume all gases obey the ideal gas law.) a. If the temperature of the cylinder is changed from 25 C to 50 C, the pressure inside the cylinder will double. b. If a second mole of argon is added to the cylinder, the ratio T/P will remain constant. c. A cylinder of identical volume filled with the same pressure of helium must contain more atoms of gas because He has a smaller atomic radius than argon. d. Two of these are correct. e. None of these is correct. 5. For the following device where would the Hg level be? (P ex = 0.5 atm) a. 2. m b. 0.7 m c. 0.8 m d. 1.9 m 6. Which gas is the most dense at 1 atm and 25ºC a. nitrogen monoxide b. nitrogen dioxide c. hydrogen cyanide d. carbon monoxide e. hydrogen sulfide D,B,D,E,D,B 7

Chem. 1A Midterm 2 Version B November 9, 2016

Chem. 1A Midterm 2 Version B November 9, 2016 Chem. 1A Midterm 2 ersion B November 9, 2016 First initial of last name Name: Print Neatly. You will lose 1 point if I cannot read your name or perm number. Perm Number: All work must be shown on the exam