8. Relax and do well.

Transcription

1 CHEM and Name Exam III John III. Gelder TA's Name November 5, 2000 Lab Section INSTRUCTIONS:. This examination consists of a total of 9 different pages. The last three pages include a periodic table, some useful equations, a table of standard heats of formation and a solubility table. 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 3, 4a, 4b, 4c, and 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 (26) (20) (27) (27) (00)

2 CHEM 34 EXAM III PAGE 2 (2). 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) Pb(NO 3 ) 2 (aq) + Na 2 S(aq) PbS(s) + 2NaNO 3 (aq) b) C 5 H 2 (aq) + 6O 2 (g) 5CO 2 (g) + 6H 2 O(l) c) 2NaOH(aq) + H 2 SO 4 (aq) Na 2 SO 4 (aq) + 2H 2 O(l) d) Ba(OH) 2 8H 2 O(s) + NH 4 SCN(s) Ba(SCN) 2 (aq) + 0H 2 O(l) + 2NH 3 (g) (4) 2. Write the ionic and net ionic chemical equations for c). c) Ionic equation: 2Na + (aq) + 2OH (aq) + 2H + (aq) + SO 4 2 (aq) 2Na + (aq) + SO4 2 (aq) + 2H2 O(l) Net Ionic equation: 2Na + (aq) + 2OH (aq) + 2H + (aq) + SO 4 2 (aq) 2Na + (aq) + SO4 2 (aq) + 2H2 O(l) 2OH (aq) + 2H + (aq) 2H 2 O(l) OH (aq) + H + (aq) H 2 O(l) calorimeter containing 75.0 g of water at 24.5 C. The heat capacity of the calorimeter is 0.5 J C -. Determine the final temperature of the system. Note: The specific heat of aluminum is J g - C -. q Al, hot = ( q water + q calorimeter ) mass Al S.H. Al T Al, hot = ( mass water S.H. water T water + HC calorimeter T calorimeter ) 225 g J g - C - (T f C) = ( 75.0 g 4.84 J g - C - (T f 24.5 C) J C - (T f 24.5 C)) J C - (T f C) = ( 33.8 J C - (T f 24.5 C) J C - (T f 24.5 C)) J C - (T f C) = ( J C - (T f 24.5 C)) J C - (T f ) 9845 J = ( J C - (T f ) 7945 J)) J C - (T f ) = J J (T f ) = J C- = 52.8 C

3 CHEM 34 EXAM III PAGE 3 (20) 4. A hydrogen atom emits a photon of light with a wavelength of.875 x 0 6 m. a) Calculate the frequency of this photon. c x 0 8 m s x 0 6 m =.60 x 0 4 Hz (cps or s - ) b) Calculate the energy of the photon. E = h x 0-34 J s).60 x 0 4 s - =.06 x 0-9 J c) Determine the initial energy level of the electron if the final energy level the electron has is n = 3. E = 2.8 x 0 8 J n 2 f n 2 i In the above equation E is.06 x 0-9 J. We must add the negative sign because the photon is emitted by the atom as the electron falls from a higher energy level to a lower energy level..06 x 0-9 J = 2.8 x 0 8 J 3 2 f.06 x 0-9 J 2.8 x 0 8 = = J 3 2 f n 2 i n 2 i = 9 n 2 i n 2 = = i n 2 = 6.0 and n = 4 d) Draw and label an energy level diagram for the hydrogen atom and show the transition for the electron as determined in c.

4 CHEM 34 EXAM III PAGE 4 (0) 5. Calculate H for the following reaction, SiO 2 (s) + 4HF(g) SiF 4 (g) + 2H 2 O(g) H rxn = H f (products) - H f (reactants) H rxn = H f(sif 4 ) + 2 H f (H 2 O) ( H f(sio 2 ) + 2 H f(hf)) H rxn = 90.9 kj kj ( 64.9 kj kj) H rxn = 95. kj (2) 6. Write the electron configuration and indicate the number of unpaired electrons for each of the following in their ground state, i. Cr 6 unpaired electrons s 2 2s 2 2p 6 3s 2 3p 6 4s 3d 5 or [Ar]4s 3d 5 ii. I 0 unpaired electrons s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 0 4p 6 5s 2 4d 0 5p 6 or [Kr]5s 2 4d 0 5p 6 iii. Es 5 unpaired electrons s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 0 4p 6 5s 2 4d 0 5p 6 6s 2 4f 4 5d 0 5p 6 7s 2 5f 0 6d or [Rn]7s 2 5f 0 6d (5) 7. Draw the orbital diagram for the valence electrons for phosphorus in its ground state The electron configuration for phosphorus is s 2 2s 2 2p 6 3s 2 3p 3. There are five valence electron in phosphorus. 3s 3p

5 CHEM 34 EXAM III PAGE 5 Multiple Choice: (27 points) Print the letter (A, B, C, D) which corresponds to the answer selected. 8. A 9. B 0. D. B 2. A 3. C 4. C 5. B 6. D ONLY THE ANSWERS IN THE AREA ABOVE WILL BE GRADED. Select the most correct answer for each question. Each question is worth 3 points. 8. Which of these species has a standard enthalpy of formation equal to zero? A) F 2 (g) B) F(g) C) HF(aq) D) F (aq) 9. Which electron configuration is not allowed for either a neutral atom or an ion in its ground state? A) s 2 2s 2 2p 3 B) s 2 2s 2p 6 C) s 2 2s 2 2p 6 3s 2 3p 6 3d 3 D) s 2 2s 2 2p 6 3s 2 3p 6 4s 3d 0 0. Which principal quantum number transition in a hydrogen atom will release the greatest amount of energy? A) 3 B) 6 4 C) 3 5 D) 4 2. Which element in its ground state has the greatest number of unpaired electrons? A) V (atomic number 23) B) Fe (atomic number 26) C) In (atomic number 49) D) As (atomic number 33) 2. In a bomb calorimeter, reactions are carried out at A) constant volume B) constant pressure C) constant temperature D) atm pressure and 0 C 3. Which is a possible set of quantum numbers for a valence electron in phosphorus? n l m l m s A) 2 0 +/2 B) C) 3 - +/2 D) 3 2 -/2

6 CHEM 34 EXAM III PAGE 6 4. Carbon reacts with oxygen according to this equation 2C(s) + O 2 (g) 2CO(g) H = 220 kj I. The reaction is exothermic II. H f of CO is 220 kj III. The combustion of 0.5 mol of carbon produces 55 kj of heat energy A) I only B) I and II C) I and III D) I, II and III 5. Given the reactions Reaction H (kj mol - ) Mg(s) + 2HCl(aq) MgCl 2 (aq) + H 2 (g) 467 MgO(s) + 2HCl(aq) MgCl 2 (aq) + H 2 O(l) 5 and the H f for H 2 O(l) is 286 kj mol, -, the H f for MgO is, A) 904 kj B) 602 kj C) 36 kj D) 30.0 kj 6. Which of the following processes/reactions is not exothermic? A) CH 4 (g) + 2O 2 (g) CO 2 (g) + 2H 2 O(g) B) 2H 2 (g) + O 2 (g) 2H 2 O(g) C) H 2 O(g) H 2 O(l) D) SO 2 (s) SO 2 (l)

7 CHEM 34 EXAM III PAGE IA H Li 6.94 IIA 4 Be Na Mg IIIA IVA VA VIA VIIA B C N O F 9 0 Ne 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 Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe (98) Cs Ba La Periodic Table of the Elements Hf Al Si P S Cl VIIIA 2 Ta W Re 75 Os Ir Pt Au Hg 80 Tl Pb Bi Po At Rn (209) (20) Fr Ra Ac (223) (26) (262) (263) He Ar (222) Lanthanides Actinides Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu (45) Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr (244) (243) (247) (247) (25) (252) (257) (258) (259) (260) Useful Information E n = 2.8 x 0 8 J n 2 r n = x 0 8 n 2 cm h = x 0 34 J s E = 2.8 x 0 8 J n 2 f n 2 λ = c E = hν c = 3.00 x 0 i ν 8 m s J Specific heat of H 2 O(s) = 2.09 g C Specific heat of H J 2O(l) = 4.84 g C J Specific heat of H 2 O(g) =.84 g C Heat of fusion of H 2O(s) = 6.0 kj mol Heat of vaporization of H 2 O(l) = kj mol R = L. atm mol. K or R = 8.34 J 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 = Σ n H f (products) - Σ m H f (reactants)

8 CHEM 34 EXAM III PAGE 8 Table of Standard Heats of Formation Substance H f Substance H f and State (kj/ mol) and State (kj/ mol) C(s) (graphite) 0 HNO 3 (aq) C(s) (diamond) 2 HNO 3 (l) HCl(g) CH 4 (g) 75 HBr(g) CH 3 OH(g) -20 HI(g) 26.5 CH 3 OH(l) -239 I 2 (g) H 2 CO(g) -6 O 2 (g) 0 CCl 4 (l) O(g) 249 HCOOH(g) -363 O 3 (g) 43 HCN(g) 35. CS 2 (g) 7.4 N 2 (g) 0 CS 2 (l) 89.7 NH 3 (g) -46 C 2 H 2(g) 227 NH 3 (aq) -80 C 2 H 4 (g) 52 NH 4 + (aq) -32 CH 3 CHO(g) -66 N 2 H 3 CH 3 (l) 54 C 2 H 5 OH(l) -278 N 2 H 4 (l) 50.6 C 2 H 5 O 2 N(g) -533 NO(g) C 2 H 6 (g) NO 2 (g) 33.8 C 3 H 6 (g) 20.9 N 2 O(g) 82.0 C 3 H 8 (g) -04 N 2 O 4 (g) 9.6 C 4 H 0 (g) -26 N 2 O 4 (l) 20 CH 2 = CHCN(l) 52 CH 3 COOH(l) -484 S 2 Cl 2 (g) -8 C 6 H 2 O 6 (s) -275 SO 2 (g) TiO 2 (s) -945 H 2 S(g) Cl 2 (g) 0 SOCl 2 (g) -23 Cl 2 (aq) -23 Cl - (aq) -67 SiCl 4 (g) -657 SiO 2 (s) SiF 4 (g) HF(g) -273 H(g) 27 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

9 CHEM 34 EXAM III PAGE 9 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