7#$  $\\\\\j< x, *\L: NAME _________________ Chemistry 142 Third Exam Spring, 1995 Constants: c = 2.998 x 108 m sec-1 h = 6.626 x 10-34 J sec To = 273.2 K R = 8.314 J mol-1K-1 R = 0.08206 L atm mol-1 K-1 NA = 6.023 x 1023 mol-1 Kw = 1.0 x 10-14 M2 F = 96,400 C/mole You must show all work for full credit. Please report all answers with the correct number of significant figures and units. 1) Define: oxidizing agent 2) Define: buffer capacity 3) The following reactants are mixed in equal molar portions. Predict if the resulting solution will be acidic, basic, neutral, or if there is not enough information given to tell for sure. HCl(aq) + Ca(OH)2 (aq) --> ? 4) Given the two following half reactions, Ni2+ (aq) + 2e - Ni(s) Eo = -0.25 V Hg2+ (aq) + 2e - Hg(l) Eo = +0.86 V calculate Eocell for the following reaction: Hg2+ (aq) + Ni(s) Ni2+ (aq) + Hg(l) 5) Consider the following half reactions: Cl2 (aq) + 2e - 2 Cl- (aq) Eo = +1.36 V Sn2+ (aq) + 2e- Sn(s) Eo = -0.137 V Al3+ (aq) + 3e - Al(s) Eo = -1.66 V (a) Which species wants to be oxidized the most? ___________________ (b) Which species will reduce Cl2? ______________________________ 6) We have 100. mL of a 0.10 M solution of CH3COOH. How many grams of NaCH3COO (fwt. 83. g/mol ) must be added to make a buffer solution of pH = 5.00? Ka (CH3COOH) = 1.8 x 10 -5 M. 7) The Ka for the dissociation of hypoiodous acid (HIO) is 2.00 x 10-11 M. What is the pKb for its conjugate base? 8) We have 500. mL of a 0.10 M NH3 solution. We add 1.0 mL of 10.0 M HCl. What is the pH of the resulting solution? pKb (NH3) = 4.75 9) We have 200. mL of 0.10 M HClO solution. pKa (HClO) = 7.46 a) What is the pH of the resulting solution after 25 mL of 0.40 M NaOH is added? b) What is the pH of the resulting solution after 50 mL of 0.40 M NaOH is added? 10) Consider an electrochemical cell where the following reaction takes place: 2 Au3+ (aq) + 3 Zn(s) 2 Au(s) + 3 Zn2+ (aq) Draw the cell labeling the parts (anode, cathode, etc.). Indicate which direction electrons will flow in the cell. 11) Eo for the following redox reaction is +1.05 V. 2 Ag+ (aq) + Ni(s) 2 Ag(s) + Ni2+ (aq) What is DGo and K for this reaction? 12) Determine the cell potential for Cu(s) + Pt2+ (aq) Cu2+ (aq) + Pt(s) where [Cu2+] = 0.85 M and [Pt2+] = 0.0070 M using the following standard reduction potentials. Pt 2+ (aq) + 2e - Pt(s) Eo = +1.20 V Cu2+ (aq) + 2e - Cu(s) Eo = +0.34 V CH142:Exam III  initials _______ uv a bif only job   ? @ @ @ @ @ ?@@0 0`_π H@?  8 H #{   ?????????KLMZ[acderv}~w  &(67PQvw{ &'@AUWcd{|@      V@Ad+-DE=>BC     i k r s v x   3 4 O Q ` a y z @ @   M)4ALxrz]eMdlm13456789:;<MNOPQRST$$$$ $hh$ $$ $ $ OTUVWXYZ Q R S T U V W X Y Z [ \ F w x y z { | } ~  " # $ % & ' ( ) * + , Q Y  ? G !#@$$$$M   @ lZ AP6@ I $$#&@ T   &p&r9HH(EG(HH(d'@=/RBH-:LaserWriter 8 ChicagoNew YorkGenevaMonaco Zapf DingbatsPalatinoTimes HelveticaCourierSymbol DeltaSymbol&p Espy Sans&rEspy Sans Bold9 eWorld Tight111ERRQ*1S     Q   :Exam#3-Spring-1995College Use OnlyCollege Use Only