winter 2011 first

winter 2011 first - CHEM14A YOUR NAME .... .. Instructor:...

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Unformatted text preview: CHEM14A YOUR NAME .... .. Instructor: Dr. Laurence Lavelle WINTER 2001 IST MIDTERM (Total number of pages = 7) (Total points = 50) (Total time = 50 mins) “Carefully remove last page which is your Periodic Table." YOUR DISCUSSION SECTION .................................... .. WRITE IN PEN (Show all your work on this paper.) Constants and Formulas Planck constant, h = 6.63 x 10'34 J - s Avogadro constant, NA = 6.02 x 1023 mol'1 Rydberg constant, R = 3.29 x 1015 Hz Gas constant, R = 8.314 J.K“.mol'1 Mass of electron, me = 9.1 x 10‘31 kg Speed of light, c = 3.0 x 108 m.s‘1 0°C=273.15 K 1L=1dm3 1atm= 101.325 kPa TC=3.14 h2n2 E=hv E=pc En=m2 p=mv En=- £6213 A:% I c=}\,v [AH]|NITIAL ACID - _ 2 _ Solution to AX2 + BX + C = o is X = ______B +/ 4AC 01) A) B) C) D) E) Exactly 4.35 g of compound X are put into a combustion chamber. Combustion yieldsflg carbon dioxide and 4.82 9 water. /‘0- 467' What is the empirical formula of compound X ? (3pt) Mass spectrometry shows that compound X has a mass of 145.8 1- 1.2 g mol“. What is the molecular formula of compound X ? (1 pt) (1 pt) Write the balanced reaction for the combustion of compound X. if we repeat the combustion experiment with exactly 5.00 g of owgen gas and 5.00 g of compound X which will be the limiting reactant ? (2pt) The reaction in part (D) above produced 3.56 g of carbon dioxide. What was the percent yield of carbon dioxide in this experiment ? (3pt) Chemistry 14A Winter 2001, Dr. L. Lavelle Midterm #1 Question #1 Scoring Key Solutions were not penalized twice for the same error being carried through. In these situations the answers to later parts were recalculated based on the answers for the earlier parts. Part (A) o 1 point—Correct moles/mass of C and H from C0; and H20 — Either 0.238 moles C or 2.86 g C — Either 0.535 moles H or 0.539 g H — No penalty if 9.52 g C02 used (instead of 10.47 g C02 corrected) 0 1 point—getting the correct mass of O with the right method (subtracting mass C and mass H from mass X = 4.35 g) — Either 0.950 g 0 or 0.0594 moles O o l point—solving for the correct ratios and empirical formula - C4H90 - No penalty for a mistake in either of the first two parts, but answers needed to be consistent (i.e. forgot to calculate mass of 0, accepted C4H9) Part (B) 1 point—using correct methodology of (MW (given) / FW (calculated) = multiplier No penalty for moderate rounding errors (i.e. CHI-14,19 C2H4), but penalized extreme rounding (CM-)Cg) o Penalized 1 point if empirical formula that was NOT whole numbers 0 l point—correctly balanced reaction - Needed to have used the molecular formula determined in (B) o Needed to have compound X as a reactant and C02 and H20 on products Part (D) 0 1 point-—calculating the correct moles of Oug) and compound X (from part (B)) — 0.156 moles 02 — Penalized if used 0 (MW = 16.00) and did not correct for it later 0 1 point—using stoichiometric ratios from balanced or unbalanced reaction in (C) — 2nd point based on correct logic Part (E) o 1 point—getting the equation “Percent yield = Actual yield / Theoretical yield” 0 1 point—using their limiting reagent (right or wrong) from part (D) o 1 point—doing the calculation correctly 02 A) Calculate the wavelength of the radiation emitted by a hydrogen atom when an electron makes a transition from n = 3 to n = 2. (6pt) .. » K . 4 (.7 ’34‘ K -/ _, £3 , j : X/o Irgzzww y : _z.¢ZX/agz fizz ~§¢5X/;MT . 4E: £3 -EL : Zof/r/i’qf AE : [1V : AC (I a: :c : [({Jx/;Z;‘7_5)[ZpX/ojm.f’) 5 3‘02 x/a'mf = 1-51! mm (2%) : ifén/n B) Of the following sets of four quantum numbers (n, l, m., ms) identify the ones that cannot exist for an electron in an atom and explain why not. (4pt) (M a) {2, 2, -1,+1/2} (Wt) { 14:2 AMMMZu 650/ [7:2 jMO:///7~flm) b) {6, 0, 0, +1/2} (w) a“ 49-67%?! W OS A) Each second a lamp produces 9.8 x 102° photons with a wavelength of 434nm. How much energy is produced from the radiation at this wavelength ? (5pt) 5 : A v : Ac 6 4,1) (I B) The energy required to break a C---C bond in a molecule is 348 kJ.mol". Will visible light be able to break this bond ? (5pt) I . . m M f¢¢m flab/{A MV/nem' / A ’flwrg wwwfl/rwfl “aim (@511 fly / j (m a/MJ /.’,’ MW Wiwflék flé : WWMMc-cw.) //?W % 562’ W; Q4) Write the Lewis structures for the following reactive species found to contribute to the destruction of the ozone layer and indicate which are radicals. (1 Opt) a) chlorine monoxide , CIO :d—b': arr [1% 7% (Md b) dichloroperoxide, Cl—O—O—Cl .i/éé——-f§—-0w—/ééz c) chlorine nitrate, CION02 (the central 0 atom is attached to the Cl atom and to the N atom of the N02 group) /é'—/r/70" (74%) on \ " v.0; d) chlorine peroxide, Cl—O—O «75L él- 0'2 (M/ '. I. W [4,29 6 05 Which M2+ ions are predicted to have the following ground-state electron configurations. (10pt) A) [Ar]3d7 662+ B) [Ar]3d1 C) [Kr14ci‘05s2 Snzf D) {16:34.63 [717’] 34/0 Eff (17%) E) [Ar]3d‘°4s24p5 m” (m9 ...
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This note was uploaded on 02/08/2012 for the course CHEM 14A 142042200 taught by Professor Lavelle during the Spring '10 term at UCLA.

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winter 2011 first - CHEM14A YOUR NAME .... .. Instructor:...

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