8. Relax and do well.

Transcription

1 CHEM :30 pm Section Exam II ohn II. Gelder October 16, 2002 Name TA's Name Lab Section INSTRUCTIONS: 1. This examination consists of a total of 8 different pages. The last three pages include a periodic table, a solubility table, a Table of Standard Heats of Formation, an Activity Series and some useful equations. All work should be done in this booklet. 2. PRINT your name, TA's name and your lab section number now in the space at the top of this sheet. DO NOT SEPARATE THESE PAGES. 3. Answer all questions that you can and whenever called for show your work clearly. Your method of solving problems should pattern the approach used in lecture. You do not have to show your work for the multiple choice or short answer questions. 4. No credit will be awarded if your work is not shown in problems Point values are shown next to the problem number. 6. Budget your time for each of the questions. Some problems may have a low point value yet be very challenging. If you do not recognize the solution to a question quickly, skip it, and return to the question after completing the easier problems. 7. Look through the exam before beginning; plan your work; then begin. 8. Relax and do well. Page 2 Page 3 Page 4 Page 5 TOTAL SCORES (40) (22) (22) (16) (100)

2 CHEM 1314 EXAM II PAGE 2 (12) 1. Write the chemical formula(s) of the product(s) and balance the following reactions. Identify all products phases as either (g)as, (l)iquid, (s)olid or (aq)ueous. a) 2Al(s) + Fe 2 O 3 (s) Æ Al 2 O 3 (s) + 2Fe(s) b) Na 2 SO 4 (aq) + BaCl 2 (aq) Æ BaSO 4 (s) + 2NaCl(aq) c) 2NaOH(aq) + Cu(NO 3 ) 2 (aq) Æ Cu(OH) 2 (s) + 2NaNO 3 (aq) d) Li 2 CO 3 (s) + 2HCl(aq) Æ 2LiCl(aq) + H 2 O(l) + CO 2 (g) (8) 2. Write the ionic and net ionic chemical equations for 1b). 1b) Ionic equation: 2Na + (aq) + SO 4 2 (aq) + Ba 2+ (aq) + 2Cl (aq) Æ BaSO 4 (s) + 2Na + (aq) + 2Cl (aq) Net Ionic equation: Ba 2+ (aq) + SO 4 2 (aq) Æ BaSO 4 (s) (20) 3. A sample of a pure gaseous hydrocarbon was analyzed by combustion analysis. Results revealed the sample contained grams of carbon (C) and grams of hydrogen (H). a) What is the empirical formula of the compound? g CË ÁÊ 1 mol C 12.0 g C ˆ g HË ÁÊ 1 mol H 1.01 g H ˆ = mol C = mol H Á Ê mol Cˆ Ë : Ë ÁÊ mol H ˆ 1.00 mol C : mol H multiply by 3 (1 C : H ) = 3 C : 8 H C 3 H 8 b) Another sample of this gaseous hydrocarbon with a mass of 4.16 grams contains 5.69 x molecules. i) What is the molar mass of the hydrocarbon? 5.69 x molecules C 3 H 8 Ë ÁÊ 1 mol C 3H x 10 ˆ 23 = mol C molecules C 3 H 3 H 8 8 Á Ê 4.16 g C 3 H 8 ˆ g Ë mole C 3 H 8 = 44.0 mole ii) Using the information from part a) what is the molecular formula of the hydrocarbon? EW * n = MM 44.0 * n = 44.0 n = 1 molecular formula is C 3 H 8

3 CHEM 1314 EXAM II PAGE 3 (22) 4a. In an experiment liquid hexane, C 6 H 14 (l), is completely combusted to produce CO 2 (g) and H 2 O(l), according to the equation. 2C 6 H 14 (l) + 19O 2 (g) Æ 12CO 2 (g) + 14H 2 O(l) The H for this reaction is 8.39 x 10 3 k. Calculate H f for C 6 H 14 (l). DH rxn = SDH f (products) - SDH f (reactants) DH rxn = 12DH f (CO 2 ) + 14DH f (H 2 O(l)) - 2DH f (C 6 H 14 ) 2DH f (C 6 H 14 ) = 12DH f (CO 2 ) + 14DH f (H 2 O(l)) - DH rxn 2DH f (C 6 H 14 ) = (12 mol Ë ÁÊ k mol ˆ + 14 mol Ë ÁÊ k mol ˆ )- (-8390 Ë ÁÊ k mol ˆ ) -336 k mol DH f (C 6 H 14 ) = 2 mol = -168 k b) A 1.25 g sample of hexane is combusted in a bomb calorimeter according to the reaction in part a). The bomb calorimeter has a heat capacity of 1850 C and holds 4.00 kg of water. The initial temperature of the water in the bomb calorimeter is C. Calculate the final temperature of the water and the calorimeter after the reaction is complete g C 6 H 14 Ë ÁÊ 1 mol C 6 H g ˆ Ë ÁÊ 8.39 x x 10 3 k 2 mol C 6 H 14 ˆ q rxn = (q water + q calorimeter ) -61,000 = ((4,000 g)( ,000 = ( ,000 = (18590 g. C ) T C T) C ) T C T) C ) T ) T = 3.28 C Tf = C C = C = 61`.0 k

4 CHEM 1314 EXAM II PAGE 4 (22) 5. To remove ozone, O 3, from air, an air sample is passed through an aqueous solution of sodium iodide. The reaction that occurs is described in the equation O 3 (g) + 2NaI(aq) + H 2 O(l) Æ O 2 (g) + I 2 (s) + 2NaOH(aq) 2.35 grams of ozone are required to completely react with all of the NaI in a 400. ml of solution. a) how many grams of NaI are in the solution? 2.35 g O Á Ê 1 mol O 3 3 Ë 48.0 g O 3 ˆ Ë ÁÊ 2 mol NaI 1 mole O 3 ˆ Ë ÁÊ 150 g NaI 1 mole NaI ˆ = 14.7 g NaI b) what was the concentration of the NaI solution before the reaction started? Á Ê mol NaIˆ Ë L = M c) How many grams of I 2 are formed in the reaction? 2.35 g O Á Ê 1 mol O 3 3 Ë 48.0 g O 3 ˆ Ë ÁÊ 1 mol I 2 1 mole O 3 ˆ Ë ÁÊ 254 g I 2 1 mole I 2 ˆ = 12.4 g I 2

5 CHEM 1314 EXAM II PAGE 5 (10) 6. Carbon monoxide can react with iron(iii) oxide as described in the following equation Fe 2 O 3 (s) + 3CO(g) Æ 2Fe(s) + 3CO 2 (g) How many grams of Fe(s) are formed when 18.8 grams of Fe 2 O 3 (s) are combined with 11.1 grams of CO(g)? 18.8 g Fe 2 O Á Ê 1 mol Fe 2 O 3 3 Ë 160 g Fe 2 O 3 ˆ = mol Fe 2 O g CO Ë ÁÊ 1 mol CO 28.0 g CO ˆ = mol NaI (moles Fe 2 O 3 ) initial (moles CO) required (moles CO) initial Conclusion mol mol Fe 2 O Á Ê 3 mol CO 3 Ë 1 mol Fe 2 O 3 ˆ = mol CO mol CO required, and mol of CO available initially. Therefore CO is in excess and Fe 2 O 3 is the limiting reagent mol Fe 2 O Á Ê 2 mol Fe 3 Ë 1 mol Fe 2 O 3 ˆ Ë ÁÊ 55.8 g Fe 1 mol Fe ˆ = 13.2 g Fe (6) 7. Write the chemical formula(s) of the product(s) and balance the following reactions. Identify all products phases as either (g)as, (l)iquid, (s)olid or (aq)ueous. If no reaction occurs write NR. a) Zn(s) + Cu2+(aq) Æ Zn2+(aq) + Cu(s) b) CaCl 2 (aq) + Pb(s) Æ NR c) Sn(s) + AgNO 3 (aq) Æ Sn(NO 3 ) 2 (aq) + Ag(s)

6 CHEM 1314 EXAM II PAGE IA 1 H Periodic Table of the Elements VIIIA IIA IIIA IVA VA VIA VIIA Li Be B C O 9 10 N F Ne Na Mg Al Si S P Cl Ar IIIB IVB VB VIB VIIB VIII IB IIB K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr Rb 38 Sr 39 Y 40 Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe (98) Cs 56 Ba 57 La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn (209) (210) (222) 87 Fr 88 Ra 89 Ac Rf Db Sg Bh Hs Mt (223) (261) (262) (266) (264) (269) (268) (271) (272) (277) (285) (289) He Lanthanides Actinides Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu (145) Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr (244) (243) (247) (247) (251) (252) (257) (258) (259) (260) Useful Information Specific heat of H 2 O(s) = 2.09 g C Specific heat of H 2O(l) = g C Specific heat of H 2 O(g) = 1.84 g C Heat of fusion of H 2O(s) = 6.01 k mol Heat of vaporization of H 2 O(l) = k mol R = L. atm mol. K or R = mol. H = E + nrt K q(heat flow) = mass specific heat T q reaction = (q calorimeter + q solution ) q reaction = (q calorimeter + q water ) H rxn = S n H f (products) - S m H f (reactants)

7 CHEM 1314 EXAM II PAGE 7 Table of Standard Heats of Formation Substance H f Substance H f and State (k/mol) and State (k/mol) C(s) (graphite) 0 HCl(g) C(s) (diamond) 2 HBr(g) CO(g) HI(g) 26.5 CO 2 (g) I 2 (g) CH 4 (g) 75 O 2 (g) 0 CH 3 OH(g) -201 O(g) 249 CH 3 OH(l) -239 O 3 (g) 143 H 2 CO(g) -116 CCl 4 (l) N 2 (g) 0 HCOOH(g) -363 NH 3 (g) -46 HCN(g) NH 3 (aq) -80 CS 2 (g) NH 4 + (aq) -132 CS 2 (l) 89.7 N 2 H 3 CH 3 (l) 54 C 2 H 2(g) 227 N 2 H 4 (l) 50.6 C 2 H 4 (g) 52 NO(g) CH 3 CHO(g) -166 NO 2 (g) C 2 H 5 OH(l) -278 N 2 O(g) 82.0 C 2 H 5 O 2 N(g) -533 N 2 O 4 (g) 9.16 C 2 H 6 (g) N 2 O 4 (l) 20 C 3 H 6 (g) 20.9 HNO 3 (aq) C 3 H 8 (g) -104 HNO 3 (l) C 4 H 10 (g) -126 NH 4 ClO 4 (s) -295 CH 2 = CHCN(l) 152 CH 3 COOH(l) -484 S 2 Cl 2 (g) -18 C 6 H 12 O 6 (s) SO 2 (g) H 2 S(g) Cl 2 (g) 0 SOCl 2 (g) -213 Cl 2 (aq) -23 Cl - (aq) -167 SiCl 4 (g) -657 SiO 2 (s) SiF 4 (g) H 2 (g) 0 H(g) 217 TiO 2 (s) H + (aq) 0 TiCl 4 (g) -763 OH - (aq) -230 H 2 O(l) -286 ZnO(s) -348 H 2 O(g) -242 ZnS(s) -206

8 CHEM 1314 EXAM II PAGE 8 Activity Series Half-Reaction Metal Reaction Gold Au e Æ Au Platinum Pt e Æ Pt Mercury Hg e Æ Hg Silver Ag + + e Æ Ag Copper Cu e Æ Cu Hydrogen 2H + + 2e Æ H 2 Lead Pb e Æ Pb Tin Sn e Æ Sn Nickel Ni e Æ Ni Cobalt Co e Æ Co Iron Fe e Æ Fe Chromium Cr e Æ Cr Zinc Zn e Æ Zn Manganese Mn e Æ Mn Aluminum Al e Æ Al Magnesium Mg e Æ Mg Sodium Na + + e Æ Na Calcium Ca e Æ Ca Barium Ba e Æ Ba Potassium K + + e Æ K Lithium Li + + e Æ Li Solubility Table Ion Solubility Exceptions NO 3 soluble none ClO 4 soluble none Cl soluble except Ag +, Hg 2+ 2, *Pb 2+ I soluble except Ag +, Hg 2+ 2, Pb 2+ SO 2 4 soluble except Ca 2+, Ba 2+, Sr 2+, Hg 2+, Pb 2+, Ag + CO 3 2 insoluble except Group IA and NH 4 + PO 3 4 insoluble + except Group IA and NH 4 - OH insoluble except Group IA, *Ca 2+, Ba 2+, Sr 2+ S 2 insoluble except Group IA, IIA and NH + 4 Na + soluble none NH + 4 soluble none K + soluble none *slightly soluble

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