Exam 2A KEY

Exam 2A KEY - (please print as name appears on UNC roll)...

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Unformatted text preview: (please print as name appears on UNC roll) Chemistry 101 Section 1 2. 3. 4. 5. Use pen or pencil, but only exams written in pen can be regraded. Seat rowl# Exam YAOctober 20, 2010 Directions: 1. Print your name on the first and last pages of the exam. For multiple-choice problems, write your answer (A, B, C, D, E) in the box provided on last page of exam. On numerical problems, show your work including units as you go in order to receive credit for your work and write your answer in the box/line provided (include units). Make sure your significant figures are correct. m D(H20) = 1.00 g/mL 1 mL = 1 cm Honor pledge: I have neither given nor received help on this exam. Signed Worksheet 3 s(H20) = 4.184 Jlg K K= °C + 273.15 D=M V M1V1 = “’1sz KE = 1/2 mv2 AE=q+w q=smAT q=CAT AH = in AHf(products) - Em AHf(reactants) c=Av h=6.626x10'34Js E=hv c=3.00x108mls A = h/mv RH = 1.097 x 107 lm ‘ AE =—han[—2 H7]: —2.18x10"31[~1~2- m nf n. nf n. 1 1 l l' Name "A (please print as name appears on UNC roll) 1. (10 pts) A solution is made by dissolving an unknown amount of sodium oxalate, Na20204, in enough water to make 250.0 mL solution. When a 5.000 mL sample of this is titrated, it requires 25.82 mL of 0.02140 iVl KMnO4(aq) to complete react, according to the reaction below. How many grams of Na20204 were dissolved in the original 250.0 ml. solution? The balanced net ionic equation is: 5 CZO4Z'(aq) + 2 Mn04'(aq) + 16 H+(aq) ~) 2 Mn2*(aq) + 8 H20(|) + 10 002(9) 2.— .OZESZL. .021 m Mmo' emu 9" l =.Z76MQ09 l, Zlmol Adi/104’ .DDGODOL = .zmM NazCzOq [mm @0me or 260.0%) “QQWJDL I.Q?blmol M12904 = . 0mg; IMO; magi)! u}: 290.0% (3.2% l/ .0090? Mel M c 0+ [540 = 4.26 Na 0 z z W..— % 2C2 ‘l ‘1‘ SF 2. (12 pts) Given the following reaction and thermochemical information, answer the following quesfions: iNaHSOAs) 9 2 NaOH(s) + 2 802(9) + 02(9) AH = +806 kJ A) Calculate the enthalpy change whenrogen sulfate is reacted. ' ' 51506] l . M0! = ~0203 soc. ch ., x a) now, me! ammusofi. .bzoaimu WWW 85F C) In a separate experiment, enough reactant is consumed such that 1852 kJ heat also required. What is the mass of sulfur dioxide is produced in this experiment? B) Is this reaction an exothermic reaction or an endothermic one? 30%) 1.189sz X = M0 muse, [meg Name A (please print as name appears on UNC roll) 3. (16 pts) Methylhydrazine (CHsNz, Mle 46.09) is used as a liquid rocket fuel. The combustion of methylhydrazine with oxygen produces N2(g), 002(9), and H200): 2 CH5N2(I) + 5 02(9) —> 2 N2(g) + 2 002(9) + 6 H200) delta H = 4299 kJ A) An unknown amount of methylhydrazine is burned in a bomb calorimeter that has a heat capacity of 22@ he temperature of the calorimeter increases by 15.3 Ceicius degrees. How many grams of methylhydrazine were burned? Z = O + = O 6% Céaglbw = ” cal 'AT" “ 220-04053?) °C Carry; ‘7 "' J -: -- 31ml (ll-lei); x Vnol B) Suppose the previous experiment was repeated but with the addition of 450 9 water in the bomb. What is the heat capacity of the water in this experiment? JSF‘ C=S-m= 4.1343 (490 , 4.; a) C) Without doing calculations, predict whether the change in temperature for the assembly (calorimeter + water) is the same, more or less than it was in the first experiment? Why? ATfWC'al-rllzo will be Legs 44mm aTfixuW cal boa Lilo ads as heat Veeawoir. H20 er Wat W would Wk: 0 Name Z (please print as name appears on UNC roll) 4. (10 pts) Given the following balanced reaction: A) which element is oxidized? FE. B) which substance is the oxidizing agent? 9‘; C) what are the spectator ions? H + 2 HN03(aQ) + 2 Fe(N03)2(aCl) + C|2(Q) —> 2 Fe(N03)3(aq) + 2 HC|(aq) +2 0 +3 "l 5. (6 pts) What mass of MgCIz (MM: 95.21) must be added to 235 mL of 0.206 M KCI to produce a solution with a concentration of 0.250 M Ci'? Assume no volume change. Mimi amt: ,mi. .206mlCJ":-_ i - _ \Hfif I _+..._=.=L_:——-—— 0484 (mo Cl mastude 16% [fleet/3191‘: .OGSSIMolCl“ Wei-acid. (.DQ88*.04€4 ml) =. 0104 imolCl“ . Z .010 il‘J’llelMClZ‘QWI =3 2 4M 2mm“ Wag“; Lag 35:: 6. (5 pts) Write the balanced chemical reaction for which AH corresponds to the molar heat of formation, AHf, of solid aluminum acetate. MK) ‘I' 'I‘ q/Z “may? Name Z 5 (please print as name appears on UNC roll) 7. (18 pts) Below are the n=1 through n=4 energy levels for the Bohr Model of the hydrogen atom. From left to right, draw and label arrows that identify the following transitions, within these four levels. ' A) the emission of radiation from the n=3 state to ground state. B) the absorption of radiation with the highest frequency. c: lmegf A6 n=4 n=3 n: n=1 0) Calculate AE (in J) for the transition in Part A. AE= -— 2J8M048J I l ’ '2. 3 48 I 3 -l File l0 J . ' .. . ' . gsr’ D) Calculate 7t. (m m) forthe transntlon depicted In Part B. 814“, . AB: ’2.I8X(D’I8J —-_L]= 2 4; I: . q.?3xlo’em A“ "'°/Ae=qusxio’8m E) In what region (UV, vis, lR) of the electromagnetic spectrum does the radiation in Part B occur? mm F) What is the total number of emission lines, considering only these four quantum levels? Lie-‘26 3-47 2 2—? i 5,», Name ( i (please print as name appears on UNC roll) Questions 8-12 5 ts each : 8. Which combination will produce a precipitate? El NaCH3000(aq) and NH4Cl(aq) ) KOH(aq) and Mg<N03)2(aq) MCDl-l); AgN03(aq) and Ca(CH3C00)2(aq) D) NaOH(aq) and HCl(aq) - E) KCI(aq) and Ba(N03)2(aq) 9. What is the molarity of a NaOH solution if 28.2 mL of a 0.355 M H2804 solution is required to - — ’ - a 25.0 mL sample of the NaOH? .A 0.801 *3) 0.315 QWOH"? H2302) ---—-—> ZLLO-l" [0&2504} 8531333 .0230). .369 mol ll 3 Nth-0H ' E) 0400 L limo! (4250‘, .QQQDL. 10. Calculate AE for a process in which a gas absorbs 42 J of heat and does 14 J of work on the surroundings (i.e. the gas expands)? +42.) .- A) —56 J J D) +42 J E) +56 J 11. Find AH (in kJ) for the reaction IFS (g) —> IF3_(g)+ F2(g) given the following information: __’ V1.15? +7q5 1F (9) -> IF(9) + F (g) delta H = +390 kJ __ 1F:Q)+ 2 BOA) 9 |2F5(g) delta H = -745 kJ VWQ +g-—> [F3 340 A) +1135 B) +35 l * lFa -—-> [iii-F2 +395 C) -355 C@ E) -1135 12. If the de Broglie wavelength of an electron is 1.07 nm, what is its velocity? The mass of an electron is 9.11 x 10'28 g. Q) 8.10 mls V: ii = (5,192;p x(Dflg*J. S 0)) 31121mxlio4m/s WA (D'al ( D’q } ' * k4) l- N IM '-‘ 0.80xio‘m/g E) 3.09 x 109 m/s Name I Z k (please print as name appears on UNC roll) m “an I. a ossible - ...
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Exam 2A KEY - (please print as name appears on UNC roll)...

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