exam2_Key - EV EXAM#2 CHE 214_Fall 200 Name I(10 points...

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Unformatted text preview: EV EXAM #2 CHE 214_Fall 200? Name: I. (10 points) ENCIRCLE ALL CORRECT ANSWERS (there ma be more than one correct answer in W Q delS {67’ each GS 1. For a given chemical reaction, th ormation of products under common laboratory conditions (constant temperature and pressure) will be favored by: ENCIRCLE ALL CORRECT ANSWERS negative value of AH b) negative value of AS @egaflve value or AG negative value of K Given the dissolution reaction for the salt Cu4(OI-I)6(SO4) in water: Cu4(OH)6(SO4) s <==> 4Cu2?‘ + 60H' + 303‘ Kg: 2.3 x 1069' Which of the following statements islare TRUE about the solubility of Cu4(0H)5(SO4) @Solubility will increase when a strong acid is added in the solution @ Solubility will decrease when Cu2+ is added in the solution c) Solubility will increase when SO42” is added in the solution d) Solubility will increase when more solid Cu4(OH)6(SO4) is added into a saturated solutiori of this salt. The following are required for a primary standard in titration reactions, EXCEPT: 21) Should be at least 99.9% pure M b) Should not decompose under ordinary storage @Should change in color when equivalence point is reached Should be stable when dried by heating or vacuum The pH of a solution containing 5.56 x 10'5 molar KOH which is a strong base is: a) 4.25 (9,934 c 5.56 d) can not be calculated without the Ka or Kb being given Consider the analysis of a mixture containing 0.250 moles Cl' and 0.750 moles of Br‘ by titration with A g*. The endpoint is determined by monitoring the Ag” concentration using an electrode to measure pAg“. The Ksp of AgBr is 5.0 x 10'”, while the Ksp of AgCl is 1.8 x 10"". Which of the following statements is NOT TRUE. . a) Co-precipitation of AgCl with AgBr may result even before the solubility of the more soluble salt has not been reached b) AgBr will precipitate first c) The first endpoint will require 0.750 moles Ag“, while the second endpoint will require _ 0.250 moles Ag+ @‘lone of the above EQUILIBRIUM CONSTANT S (3 pts) 1. Write K of the reaction below: 8105+ 2Cr+3+ 4H20 # Br‘ + (320.3 + gH+ \W US“); 3 [CH 33 L ACID-BASE EQUILIBRIUM 1. (2 points) Identify the Lewis Acid and the Lewis Base in the following reaction: BF3 + NH3 69 F3B-NH3 m Gate 2. (2 points) Identify the conjugate acid-base pairs in the following reaction: on [email protected] = 92 E+©+ PROBLEM SOLVING: SHOW ALL SOLUTIONS TO GET FULL POINTS (ROUND OFF FINAL ANSWER TO PROPER NUMBER OF SIGNIFICANT FIGURES) l. (10 points) Standardization Sulfamic acid (MW: 97.095) is a primary standard that can be used to standardize NaOI-I. +H3NSO3' + OH“ ------ > Hstoa- + H20 ' (sulfamic acid) What is the molarin of a sodium hydroxide solution if 41.54 mL react with 0.439? g of sulfamic acid? 0 o m “JV“; coca : m r 0.00 quggg ' ‘i’r-Ois 3/...01 [email protected] [0W3 <— O‘OWQWS Ml: 2. (18 points) A solution of NaOl-I is added to a solution containing a mixture of 0.300 molar Niido- 0. 300 molar A]3+ and 0.300 molar Be“. Given: Tfl/m 0L W9 Ksp: Ni(OH)2 = 6.0 X 10"“ PM a] b Ksp: Al(OH)3 = 2.0 x 10'32 Ksp: sewn)2 = 7.0 x 10-32 " .22 0a WW” -0 3' for” ,1. .2 moor/ed :. whom; :1) Write the dissolution reaction and the equilibrium constant expression (Ksp) for the 3 insoluble 5 above. 5 Pt W'f’gjtfl . mm. :3 N“‘3+ 2W kip [Nrfl’ltom P b) Calculate the concentration of 0H required to precipitate each of thcions, 0.300 molar Ni2+ 0.300 molar Al“, and 0.300 molar Bez”. 5‘15}an ‘ffit—cfl C) Based on your calculations above, which metal hydroxide will precipitate first, second, last? “(0747—3 7:? 19+ “ix {fly}— @ 303»); "h"? 2N9 4vrf+ (61471 i? hr} 40 P7}— d) Will precipitate form if you mix 50.00 mL of 1.00 x 10'3M NaOH and 50.00 mL of 001. x 10'3 M of Ni”? (Assume total volume is exactly 100.00 mL) - W [Niill {0H,1fi”: [($13 oomL><Lemmta) M] [(89% 5°“)(Iomo'5 10° 0o ML 100 m) 3i ,- 3. (30 points) A 30.00 mL solution containing 0.1168 M Na2C204 was titrated with 0.25 88 M La(ClO4)3 to precipitate lanthanum oxalate (Ksp: 1.0 x 10'”). La2(C204)3 (s) -.——"" 2 La+3 + '3 czofit'2 Ksp=l.0 x 10-25 ’Z“ “3% 4— l-bMo“ 5 a) What is the equilibrium constant (K) for the titration reaction below? 2 La3+ + 302042“ ------ > La2(C204)3 m Titrant unknown lanthanum oxalate 25 ___.l_ _ l - _ Ito KID (3 K: k I i M) N0357- m (D (D b) Calculate the molar solubility of lanthanum oxalate in a solution that is contaminated with 1.0 x 10—3 M oxalate ions? w LLa*’12EC;Oq"§3 @3 @ :- CDC); C3w/vt l-owaZD (D </—\ aflaw 5x <~c< NC) xio"3® l «4” (mac :4"; (lb Noc‘i) G) i E) X: L‘Afii‘flr,fi_ .. go “a 4.0 NO” ._ ' 7C {0 c) Where will lanthanum oxalate be more soluble, in pure water or in a solution containing oxalate ions? Why? (no calculations necessary). i/ r: G d) What volu f 0.2588 M La(CIO4)3 ' re uired each the equivalence point? 1. I 3.309. mmit C309 SQJ (—3000 "‘L) O'IIBSM 0%quI New L553 75b 33%: P Bison; mHLe 90;“ Q g G . + r: . 3 @ ZLOJB K mhqu-P La“? 3 how}: Li W ”mi N 55ft 2-336, h—MLK I.‘ C, 026 L L533 0. M -“ ' M c) Find the concentration of La+3 and pLaz'+ when 10.00 mL of La(ClO4)3 have been added (HINT: is this before equivalence point, at equivalence point, or afier equivalence point?) ‘9" [043% ML {S “(i-U Elton/ale.” PFJ‘Q Q Vbilkki L61”) 2': f) Findchnn‘ation of La+3 and 1:!La3+ when 9.00 mL of La(ClO4)3 have been added (HINT: is this before equivalence point, at equivalence point, or after equivalence point?) C) QOOmL f9 We eguivaflmcp Pt' X : 2,3292mmé Adagilzgf} ” 3-49593thh0‘90 . 0104*“? ' 0 CD 1 ‘ ' - . «€9- 0 ® wreadeal C104“ 1 '3 : 3,50 mm 5.493%mm Ci 4 . CD"- '«OQWOéMmWEL. [61042-1 1 0.2 :O'SMmofi: _:. 0,0002“ “1 mrxiwf [50.004 906m: 06‘" 0 1 4 a , 45" +5 _ LOKID'“ U035} [C104 1 “ LO “0 _;, [L0 i ” lefloflQérfissg)?’ W W G) O [Lots] : .14.?6'5XIO’Q‘: 74?le (D 4 8;?"fj’ PLO‘A- w ill/2H CD 4 3'”? if? @ met 0;an 4. (25 points) A cyanide solution with a volume of 16.75 rnL was treated with 30.00 mL of Ni+2 solution (containing excess Ni”) to convert the cyanide into tetracyanonickelate (II): Titration reaction: 4 CN‘ ' + Ni+2 —> Ni(CN)4 2' f The excess Ni+2 was then titrated with 12 63 mL of 0. 01509 M ethylenediaminetetracetic acid (EDTA): Ni+2 + EDTA —) Ni(EDTA)2' Ni(CN)42' does not react with EDTA. If 40. 00 mL of EDTA were required to react with 30. 00 mL of the original Ni+2 solution, calculate the molarity of CN in the 16.75 mL cyanide sample. ((D_’wai_ (Ni) . .304)th Vthh' ...
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