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Chem. 1A Final Name__________________________________________ Student Number _________________________________ All work must be shown on the exam for partial credit. Points will be taken off for incorrect or no units and for the incorrect number of significant figures. A non graphing calculator is allowed. On short answer 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 48 possible) Problem 1 (of 22 possible) Problem 2 (of 14 possible) Problem 3 (of 14 possible) Problem 4 (of 14 possible) Problem 5 (of 14 possible) Problem 6 (of 26 possible) Multiple Choice (of 48 possible) Extra Credit (of 4 possible) Finial Total (of 200 possible) 1 Fundamental Questions Each of these fundamental chemistry questions is worth 4 points. You must show work to get credit. Little to no partial credit will be rewarded. Make sure to report answers in the correct number of significant figures and with the proper units. 1) 4 pts What is the equilibrium expression for the following reaction? 2HCl(g) + I2(s) 2HI(g) + Cl2(g) HI 2 Cl 2 K HCl 2 2) 4 pts What is the conjugate base of H3PO4? What is the conjugate acid of KOH? H2PO4H2O 3) 4 pts What is the formula of magnesium bromide? What is the name of N2O3? MgBr2 dinitrogen trioxide 4) 4 pts Write a balanced chemical reaction for the following process. Potassium reacts with water to give potassium hydroxide and hydrogen. 2K(s) + 2H2O(l) 2KOH(aq) + H2(g) 5) 4 pts How many protons, neutrons, and electrons in 59Fe and 64Cu-? 59 Fe p = 26, e- = 26, and n = 33 64 Cu- p = 29, e -= 30, and n = 35 6) 4 pts Calculate the pH of 0.25 M Ba(OH)2. Ba(OH)2 is a strong base [Ba(OH)2]=2[OH-] 2NaOH(aq) + H2SO4(aq) Na2SO4(aq) + 2H2O OH 20.25M 0.50M pOH logOH log0.50M 0.30 pH 14.00 pOH 14.00 0.30 13.70 7) 4 pts What is the molar solubility of Mg(OH)2? Ksp = 2.06×10-13 K sp [ Mg 2 ][OH ] 2 [ Mg 2 ] S [OH ] 2 S K sp S [2 S ] 2 4 S 3 S 3 K sp 4 3 2.06 10 13 mol 3.72 10 5 4 L 2 8) 4 pts On the followin ng periodic taable indicatee the locationn of the metaals, non nmetals, metaalloids. Also o label whicch group is thhe noble gasses, alkaline eartth metals, alk kali metals, halides, h and transition m metals. 9) 4 pts How w many widg gets are in 2.3×10-20 molles? 6.022 10 0 23 widgets 1. 4 10 4 widgets 2.3 10 20 mol 1mol m 10) 4 pts If th he equilibriu um constant K for the reeaction A(aq)) ⇌ B(aq) is 22 at a giveen tem mperature, an nd if [A] = 0.10 M and [B B] = 2.0 M iin a reactionn mixture at thaat temperaturre, is the reacction at chem mical equilibbrium? If noot, in which direection will th he reaction proceed p to reeach equilibrrium? B 2.0 20 Q A 0.10 QK Thereffore there aree too many rreactants andd the reaction will proceeed to the prod ducts (right)). 11) 4 pts Callculate the pH of a solutiion that is 0..60 M HF annd 1.00 M K KF A pH pK K a log HA pK a log K a log 7.2 10 4 3.144 1.00 pH 3.14 log 3.36 0.60 12) 4 pts If 10.0 1 mL of 2.5 2 M SrCl2 is i diluted to 500. mL whhat is the final con ncentration of o Cl ions? M 1V1 M 2V2 2.5M 10 1 .0mL M 2 500.mL M 2 0.050M SrCl2 0.050molSrCl 2mo m olCl 2 0.10M Cl SrCl2 1LS 1molSSrCl2 3 Short Answer Questions Each of the following short answer questions are worth the noted points. Partial credit will be given. Make sure to show work, report answers to the correct number of significant figures and use the proper units. 1a) 12 pts The equilibrium constant K for the reaction H2(g) + I2(g) ⇌ 2HI(g) is 54.3 at 430°C. At the start of the reaction there are 0.713 mole of H2, 0.984 mole of I2, and 0.886 mole of HI in a 2.40 L reaction chamber. Calculate the concentrations of the gases at equilibrium. H2 I2 HI Initial (mol) 0.713 0.984 0.886 Initial (M) 0.297 0.410 0.369 Determine which way the reaction will proceed HI 2 0.369 2 1.12 Q H 2 I 2 0.2970.410 Since Q<K the reaction will proceed toward the products H2 I2 HI Initial (M) 0.297 0.410 0.369 Change -x -x +2x Equilibium 0.297-x 0.410-x 0.369+2x K HI 2 0.369 2 x 2 54.3 H 2 I 2 0.297 x 0.410 x 4 x 2 1.48 x 0.136 54.3( x 2 0.707 x 0.122) 4 x 2 1.43x 0.136 54.3 x 2 38.4 x 6.62 50.3x 2 39.8 x 6.48 0 x 2 b b 2 4ac 39.8 39.8 450.36.48 2a 250.3 x 0.562 or 0.229 x = .229 M because concentration must be positive H 2 0.297 x 0.297 0.229 0.068M I 2 0.410 x 0.410 0.229 0.181M HI 0.369 2 x 0.369 20.229 0.827M 1b) 10 pts When the equilibrium is disturbed, in which direction will the reaction proceed? Circle the correct answer. H2(g) + I2(g) ⇌ 2HI(g) exothermic Remove HI Reduce the volume Increase the temperature Add Ne Add H2 Reactants Reactants Reactants Reactants Reactants Products Products Products Products Products No Change No Change No Change No Change No Change 4 2) 14 pts A 20.0 L stainless steel container was charged with 2.00 atm of hydrogen gas and 3.0 atm of oxygen gas. A spark ignites the mixture, producing H2O. What is the pressure in the tank at 25°C? 2H2(g) + O2(g) 2H2O(l) What was given V 2.00 L PH 2 2.00atm PO2 3.00atm This is a limiting reagent problem Find an expression for the number of moles of H2 PV nRT nH 2 PH 2V nO2 PO2 V 2.00atmV RT RT Find an expression for the number of moles of O2 PV nRT RT 3.00atmV RT Find the number of moles of O2 needed to fully react 2.00atm V RT moles of H2 2.00atm V molH 1molO2 1.00atm V molO 2 2 RT RT 2molH 2 3.00atm V moles of O , H is the limiting reagent Since we have 2 2 RT Calculate the moles of O2 used (calculated above) 1.00atm V molO 2 RT Calculate the moles of O2 left over 3.00atm V 1.00atm V 2.00atm V RT RT RT Calculate the total moles present at the end of the reaction 2.00atm V ntot nO2 RT Calculate the final pressure PV nRT 2.00atm V RT RT ntot RT 2.00atm P V V 5 3) 14 1 pts A 43.29 mL sam mple of soluttion containiing Fe2+ ionss is titrated w with a 0.02 239 M KmN NO4 solution.. It requiredd 20.97 mL oof KMNO4 ssolution to oxid dize all of th he Fe2+ ions to t Fe3+ by thhe following reaction. M MnO4-(aq q) + Fe2+(aq)) acidic Mn2+(aq) + F Fe3+(aq) (unbbalanced) 2+ What was the co oncentration n of Fe ionss in the sampple solution?? MnO4-(aq) + Fe2+(aq) ( Mn2++(aq) + Fe3+((aq) Balancce using the ½ reaction m method Reduction ½ reaction(M Mn +7 +22) Mn nO4-(aq) M Mn2+(aq) Mn nO4-(aq) M Mn2+(aq) + 44H2O Mn nO4 (aq) + 8H H+(aq) + 5e- Mn2+(aq)) + 4H2O(l) Oxidation ½ reaction (F Fe +1 +33) Fe2+(aq) Fe3 +(aq) + eMn nO4-(aq) + 8H H+(aq) + 5e- Mn2+(aq)) + 4H2O(l) 5(F Fe2+(aq) F Fe3+(aq) + e-) + 2+ MnO M 4 (aq) + 8H 8 (aq) +5F Fe (aq) M Mn2+(aq) + 44H2O(l) + 5F Fe3+(aq) 2 molMnO4 5molFe L 0.0239moolKMnO4 1m m 1L 0.000251molFe2 20.97mL LKMnO4 MnO4 1 mo olKMnO 1LKM 1 m olMnO 1000mL 4 4 4) 14 1 pts Calcullate the molaarity of Fe2+ 1L V 43.29mL m 0.043299L L 1000mL n 0.00251mol M 0.0580M V 0.04329L Draaw the follow wing titration n plots. a) Strong g acid (analyte) Strong baase (titrant) b) Weak acid (analytee) Strong baase (titrant) Mak ke sure to cleearly label th he equivalennce points onn both plots. For plot b also label l the region with the maximum bbuffering, w where =pKa, the bu uffer region, where the pH H only depeends on [HA], and wheree pH= the pH only dep pends on [A-]. a) bb) 6 5) 14 pts A sample of a compound of Cl and O reacts with an excess of H2 to give 0.233 g of HCl and 0.403 g of H2O. Determine the empirical formula of the compound. ClxOy + H2 HCl + H2O Determine the moles of Cl (All of the Cl in ClxOy goes to HCl) 1mol HCl 1mol Cl 0.233 g HCl 0.00639mol Cl 36.46 g HCl 1mol HCl Determine the moles of O (All of the O in ClxOy goes to H2O) 1mol H 2O 1mol O 0.403g H 2O 0.0224mol O 18.02 g H 2O 1mol H 2O Divide through by smallest number (0.00881) Chlorine 0.00639 mol 1.00 0.00639 mol Oxygen 0.0224 mol 3.51 0.00639 mol ClO3.5 Turn to whole number (multiple by 2) Cl2O7 6a) 12 pts Determine the acid base properties of the following salts. Circle the correct answer. KBr Al(NO3)3 BaCl2 C5H5NHF 6b) 14 pts Acid Acid Acid Acid Base Base Base Base Neutral Neutral Neutral Neutral What is the the pH of 0.10 M NaCN? NaCN is a basic salt CN-(aq) + H2O(l) HCN(aq) + OH-(aq) HCN Ka = 6.2×10-10 K 1.0 10 14 HCN OH Kb w 1.6 10 5 10 K a 6.2 10 CN HCN OHCNInitial (M) 0.10 0 0 Change -x +x +x Equilibrium 0.10-x x x HCN OH CN xx 0.10 x 1.6 10 5 Assume 0.10-x = 0.10 xx 0.10 1.6 10 5 x 0.0013 Check assumption 0.0013 100 % 1.3% good 0.10 7 pOH log OH log 0.0013 2.89 pH 14.00 pOH 14.00 2.89 11.11 Multiple Choice Questions Each of the following multiple choice questions are worth 4 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 mark 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 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. The acids HC2H3O2 and HF are both weak, but HF is a stronger acid than HC2H3O2. HCl is a strong acid. Order the following according to base strength. A) C2H3O2– > F– > H2O > Cl– B) F– > C2H3O2– > H2O > Cl– C) C2H3O2– > F– > Cl– > H2O D) Cl– > F– > C2H3O2– > H2O E) none of these 2. Consider a solution of 2.0 M HCN and 1.0 M NaCN (Ka for HCN = 6.2 10–10). Which of the following statements is true? A) The pH will be below 7.00 because the concentration of the acid is greater than that of the base. B) The buffer will be more resistant to pH changes from addition of strong acid than to pH changes from addition of strong base. C) The solution is not a buffer because [HCN] is not equal to [CN–]. D) [OH–] > [H+] E) All of these statements are false. 3. In the reaction Zn + H2SO4 ZnSO4 + H2, which element, if any, is oxidized? A) Sulfur B) Oxygen C) Hydrogen D) Zinc E) none of these 8 4. Given: K P4(s) + 6Cl2(g) 4PCl3(l) Calculate the equilibrium constant for the following reaction. 1 2PCl3(l) 3Cl2(g) + P4(s) 2 A) 1/K2 B) 1/K C) K1/2 D) –K1/2 E) 1/K1/2 5. A plot of the Maxwell distribution against speed for different molecules shows that A) light molecules have a very narrow range of speeds. B) light molecules have a lower average speed. C) heavy molecules have a higher average speed. D) heavy molecules travel with speeds close to their average values. E) heavy molecules have a wide range of speeds. 6. The following Kp values were collected for a system. KP=6.8 10-4 T=25 C -4 KP=1.9 10 T=400 C Is the reaction endothermic of exothermic? A) Endothermic B) Exothermic 7. What is the relationship between K and Kp for the reaction below? 2HgO(s) 2Hg(l) + O2(g) A) K = RTKp B) K = (RT)2Kp C) Kp = (RT)2K D) Kp = K E) Kp = RTK 8. Consider the reaction between 50.0 mL of 0.200 M sodium hydroxide and 75.0 mL of 0.100 M HCl. Which of the following statements is correct? A) The NaOH is the limiting reactant. B) After the reaction, the concentration of Na+ is equal to the concentration of Cl-. C) After the reaction, the concentration of Na+ is still 0.200 M because Na+ is a spectator ion. D) After the reaction, the concentration of Na+ is greater than the concentration of OH-. E) None of these are correct. 9 9. High concentrations of aqueous solutions of potassium sulfide and nickel(II) nitrate are mixed together. Which statement is correct? A) No precipitate forms. B) NiS will precipitate from solution. C) No reaction will occur. D) Both KNO3 and NiS precipitate from solution. E) KNO3 will precipitate from solution. 10. Which of the following statements concerning equilibrium is not true? A) The equilibrium constant is independent of temperature. B) The value of the equilibrium constant for a given reaction mixture is the same regardless of the direction from which equilibrium is attained. C) A system that is disturbed from an equilibrium condition responds in such a way as to restore equilibrium. D) Equilibrium in molecular systems is dynamic, with two opposing processes balancing one another. E) A system moves spontaneously toward a state of equilibrium. 11. Which of the following is not the correct chemical formula for the compound named? A) Zn3P2 zinc phosphide B) HCl hydrogen chloride C) CaBr2 calcium bromide D) LiOH lithium hydroxide E) Fe2SO4 iron(II) sulfate 12. Consider the following statements: 1. Real gases act more like ideal gases as the temperature increases. 2. When n and T are constant, a decrease in P results in a decrease in V. 3. At 1 atm and 273 K, every molecule in a sample of a gas has the same speed. 4. At constant T, CO2 molecules at 1 atm and H2 molecules at 5 atm have the same average kinetic energy. Which of these statements is true? A) 1 and 2 B) 2 and 4 C) 3 and 4 D) 2 and 3 E) 1 and 4 10 Answer Key 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. A D D E D B E D B A E E 11