First letter of last name Chem. 1B Midterm 1 Practice Test 2 Name Print Neatly. You will lose 1 point if I cannot read your name or perm number. Student Number If you are sitting next to someone with the same version of the test, you will be moved and lose 5 points. All work must be shown on the exam for partial credit. Points will be taken off for incorrect or no 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
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 your answer includes the proper units. 1) 6 pts Calculate the ph of 0.25 M Ba(OH)2. 2) 6 pts Given the following equilibrium constants at 427 C Na2O(s) 2Na(l) + ½O2(g) K 1 = 2 10 25 NaO(g) Na(l) + ½O2(g) K 2 = 2 10 5 Na2O2(s) 2Na(l) + O2(l) K 3 = 5 10 29 NaO2(s) Na(l) + O2(g) K 4 = 3 10 14 Determine the value for the equilibrium constant for 2NaO(g) Na2O2(s) 3) 6 pts The ph of a 0.78 M solution of barbituric acid (HC4H3N2O3) is measured to be 2.06. Calculate the acid dissociation constant Ka of barbituric acid. Round your answer to 2 significant digits. 2
4) 6 pts What is the equilibrium expression for the following reaction? 2HCl(g) + I2(s) 2HI(g) + Cl2(g) 5) 6 pts If the equilibrium constant K for the reaction A(aq) 2B(aq) is 22 at a given temperature, and if [A] = 0.10 M and [B] = 2.0 M in a reaction mixture at that temperature, is the reaction at chemical equilibrium? If not, in which direction will the reaction proceed to reach equilibrium? 6) 6 pts What is the conjugate base of H2PO4 -? What is the conjugate acid of KOH? 3
Challenge Questions Each of the following short answer questions are worth the noted points. Partial credit will be given. Make sure to show your work and include the proper units on your answer. 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. 1b) 5 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 Reactants Products No Change Reduce the volume Reactants Products No Change Increase the temperature Reactants Products No Change Add Ne Reactants Products No Change Add H 2 Reactants Products No Change 4
2a) 8 pts Determine the acid base properties of the following salts. Circle the correct answer. KBr Acid Base Neutral Al(NO 3) 3 Acid Base Neutral BaCl 2 Acid Base Neutral C 5H 5NHF Acid Base Neutral 2b) 9 pts What is the the ph of 0.10 M NaCN? NaCN is a basic salt 5
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 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. Given: P4(s) + 6Cl2(g) 4PCl3(l) K Calculate the equilibrium constant for the following reaction. A) 1/K 2 B) 1/K C) K 1/2 D) K 1/2 E) 1/K 1/2 2PCl3(l) 3Cl2(g) + 1 2 P4(s) 3. The following Kp values were collected for a system. KP=6.8 10-4 T=25 C KP=1.9 10-4 T=400 C Is the reaction endothermic of exothermic? A) Endothermic B) Exothermic 6
4. What is the relationship between K and Kp for the reaction below? 2HgO(s) 2Hg(l) + O2(g) A) K = RTKp B) K = (RT) 2 Kp C) Kp = (RT) 2 K D) Kp = K E) Kp = RTK 5. The ph of a 0.10 M solution of a weak base is 9.82. What is the Kb for this base? A) 6.6 10-4 B) 2.1 10-4 C) 4.3 10-8 D) 2.0 10-5 E) None of the above 6. Which of the following indicates the most acidic solution? A) [H + ] = 0.3 M B) [OH ] = 0.5 M C) poh = 5.9 D) ph = 1.2 E) [H + ] = 1.0 10 4 M 7