CHM 1046 PRE-TEST 2 June 12, 1996 This test is take-home and open book, and it is intended that all members of the group contribute to completing it. Only one copy is to be submitted by the group, and all members who participated should sign their names below. Test is due at the beginning of class on Monday, June 17. List names in alphabetical order! _______________________ _______________________ _______________________ _______________________ _______________________ _______________________ Points 1. The equilibrium constant, Kp, for the following reaction at 480oC is 0.0752. 2 Cl2(g) + 2 H20(g) þ 4 HCl(g) + 02(g) (2)(a)Write the expression for Kp. (2)(b)Calculate Kc for the reaction. (R = 0.08205 L-atm/mol-K) (4)(c)A mixture of 0.20 moles of Cl2, 0.10 moles of H20, 0.075 moles of HCl(g) and 0.075 moles of of oxygen are placed in a 1.00 L container which is heated to 480oC. Will the reaction proceed to the left or to the right? Show the calculations your reasoning is based on. (2)(d)After the reaction comes to equilibrium, the volume of the container is increased to 1.5 L. Will the equilibrium shift to the left or right? (2)(e)After the reaction comes to equilibrium, the temperature is raised from 480oC to 600oC. Will the equilibrium shift to the left or right? (þH for the reaction = +114 kJ/mol.) (10)2.Kc for the following reaction is 61 at 700 K. A 1.00 L container containing a starting concentration of only 0.05 moles of HBr is heated to 700 K. When the reaction comes to equilibrium, what will be the concentrations of H2, Br2 and HBr? H2(g) + Br2(g) þ 2 HBr(g) (4)3. A container is filled with 0.83 M ammonia, 0.35 M oxygen, 0.65 M nitrogen, and 1.34 M water vapor at a temperature of 300 oC. For the following reaction, Q under these conditions is smaller than K. Express the final concentration of each species in terms of x, where x is the change in the nitrogen concentration. 4 NH3(g) + 3 O2(g) þ 2 N2(g) + 6 H2O(g) ammonia oxygen nitrogen water Final con- centration: _________ _________ _________ _________ (6)4. For each of the following pH values, circle the [H+] that is written to the correct number of significant figures. pH [H+] 5.61 2 x 10-6 2.5 x 10-6 2.45 x 10-6 2.455 x 10-6 4.2 6 x 10-5 6.3 x 10-5 6.31 x 10-5 6.310 x 10-5 10.9 1 x 10-11 1.3 x 10-11 1.26 x 10-11 1.259 x 10-11 5. Calculate the [H+], pH, [OH-], and pOH of the following solutions: (8) (a) 0.028 M HCl (8) (b) 0.17 M NaOH (12)6.HClO is a weak acid with a Ka of 3.0 x 10-8. Calculate the [H+] and pH of a 0.55 M solution of HClO. (6)7. A 0.10 M solution of a weak acid has a pH of 3.50. What is the Ka for the acid? 8. Methylamine (CH3NH2) is a weak base with a Kb of 4.4 x 10-4. (4) (a) Calculate the Ka for methylammonium ion (CH3NH3+). (10) (b) Calculate the [OH-] and [H+] of a solution of 0.16 M methylamine. (12)9.Formic acid (HCOOH) has a Ka of 1.8 x 10-4. Sodium formate will therefore hydrolyze in aqueous solution to produce some formic acid and hydroxide ion. Calculate the [OH-] and pH of a solution of 0.15 M sodium formate. (8)10.In each of the following pairs of compounds, circle the stronger acid. (a) HClO2 and HClO3 (b) HCOOH and ClCOOH (c) H2S and H2Se (d) HSO3- and HSO4-