Lethal Theory

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53 Lethal TheoryEyal Weizman The maneuver conducted by units of the Israeli Defense Forces (IDF) in Nablus in April 2002 was described by its commander, Brigadier General Aviv Kokhavi, as inverse geometry, the reorganization of the urban syntax by means of a series of microtactical actions. During the battle, soldiers moved within the city across hundred-meter-long “over- ground-tunnels” carved through a dense and contiguous urban fabric.

• possibility of military training for palestinians
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• Publié par: sewyeng
• Nombre de lectures: 20
• Langue: English

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Chemistry 60/68 Mock Exam #2 ANSWERS pp. 1

Los Angeles City College Chemistry 60/68 Mock Exam #2ANSWER KEY Professor Torres Multiple Choice 1. …C 10 H 12 O 4 S(s) + …O 2 (g)→ …CO 2 (g) + …SO 2 (g) + …H 2 O(g) When the equation above is balanced and all coefficients are reduced to their lowest whole-number terms, the coefficient for O 2 (g) is A.6 B.7 C.12 D.14 2. Whichof the following does NOT dissolve in water? A.KCl B.(NH 4 ) 2 S C.Ba(NO 3 ) 2 D.AgCl 3. Whensolutions of barium nitrate and potassium sulfate are mixed, a white precipitate forms.What is the formula of the precipitate? A.BaSO 4 B.Ba 2 SO 4 C.KNO 3 D.K(NO 3 ) 2 4. Chemicalsubstances written to the left of an arrow in a chemical equation are called A.coefficients B.products C.reactants D.subscripts 5. Anyreaction in which a compound breaks down to form two or more simpler substances is called A.Synthesis B.Decomposition C.Single Replacement D.Metathesis

Chemistry 60/68 Mock Exam #2 ANSWERS pp. 2

- 6. Whichof the following produces Brions when dissolved in water? A.Br 2 B.PCl 3 C.NaBr D.Hg 2 Br 2 For Questions 7 – 14, consider the diagram shown below:

B C A D E eaction Cooinate 7. Whichletter represents the enthalpy change of theforwarddirection?D 8. Whichletter represents the activation energy of thereversereaction?C 9. Whichletter represents the transition state of theforwardreaction?B 10. Whichletter represents the activation energy of theforwardreaction?A 11. Whichletter represents the enthalpy change of thereversereaction?D 12. Whichletter represents the transition state of thereversereaction?B 13. MARK“A” for TRUE or “B” for FALSE: Theforwardreaction is an example of an endothermic reaction.A 14. MARK“A” for TRUE or “B” for FALSE: Thereversereaction is an example of an endothermic reaction.B 15. Whichof the following represents the synthesis of HF(g) from hydrogen gas and fluorine gas, an exothermic process? A.H 2  +F 2  +energy→ 2HF B.2HF→ H 2  +F 2  +energy C.H 2 F + 2 → 2HF+ energy D.2H + 2F→+ energy 2HF

Chemistry 60/68 Mock Exam #2 ANSWERS pp. 3

16. Themolar mass of C 3 H 8 O is A.29.02 amu B.53.03 amu C.66.08 amu D.60.09 amu 17. 6.0g of nitrogen (N 2 ) contains A.6.0 atoms of N 23 B.1.26 x 10atoms of N C.0.21 mole of N 23 D.1.26 x 10molecules of N 2 18. Whatis the percent composition of zinc chloride, ZnCl 2 ? A.52.02% Zn, 47.97% Cl B.47.97% Zn, 52.02% Cl C.64.86% Zn, 35.17% Cl D.35.17% Zn, 64.86% Cl 19. Considerthe following reaction: 2C 2 H 4 + 6O 2 → 4CO 2 + 4H 2 manyO. How  gramsof O 2 are required for the complete reaction of 45 g of C 2 H 4 ? 2 A.1.5 x 10 B.51.4 C.112.5 D.288 20. Ina REDOX reaction, A.reduction is the loss of electrons, and oxidation is the gain of electrons. B.no electrons are transferred. C.oxidation is the loss of oxygen, and reduction is the gain of electrons. D.oxidation is the loss of electrons, and reduction is the gain of electrons. Free Response 21. Themolecular formula of aspartame, the artificial sweetener marketed as ® NutraSweet ,is C 14 H 18 N 2 O 5 .  A.Determine the number of moles of aspartame in an 882 mg sample. 27  B.Determine the mass (in g) of aspartame in 9.34 x 10molecules.

Chemistry 60/68 Mock Exam #2 ANSWERS pp. 4

 C.How many oxygen atoms are present in 4.33 mg of aspartame?  A.mol aspartameg xmol = 0.00300mol aspartame = 882 mgx 1 1000 mg294 g 27 B.mass aspartame = 9.34 x 101 molmolecules xgx 294 23  6.02x 10molec. 1mol 6  =4.56 x 10g aspartame 23 C.oxygen atoms =molex 1 mol x 5 mol O x 6.022 x 101 g4.33 mg x  1000mg 294g 1mol cpd1 mol O 19 = 4.43 x 10atoms O 22. Considerthe unbalanced chemical equation shown below: 2Al(l) + Cr 2 O 3 (s) + heat→ Al 2 O 3 (s) +2Cr(l)  A.What mass of aluminum is needed to reduce 10.0 kg of  chromium(III)oxide to produce chromium metal?  B.How many molecules of chromium metal are produced?  A.g Al = 10.0 kg Cr 2 O 3 x 1 mol Crx 1000 g 2 O 3 x 2 mol Alx 27g  1kg 152g 1mol 1mol Al 3  =g Al3.55 x 10 B.molec. Cr = 10.0 kg Cr 2 O 3  xx 11000 gmol Cr 2 O 3  x2 mol Cr  1kg Cr 2 O 3  152 g Cr 2 O 3 mol Cr 1 2 O 3 23  x6.022 x 10molecules Cr  1mol Cr 25  =7.92 x 10molecules Cr 23. FIGUREIT OUT!One of the common organic chemistry reactions worth mentioning involves the synthesis of aspirin (C 9 H 8 O 4 ) from salicylic acid (C 7 H 6 O 3 ) and acetic anhydride (C 4 H 6 O 3 balanced reaction proceeds as). The follows: H H O O C OH O CH O C 3 HC C HC C C + C C + C H CO CH 3 3 HC C OH HC C O H C OH 3 OH C C C C H H O O Suppose a student obtained an 84.5% yield of aspirin during her experiment. Determine the minimum volume of acetic anhydride (note: density acetic

Chemistry 60/68 Mock Exam #2 ANSWERS pp. 5

anhydride = 1.080 g/mL) that this student would have to use in order to produce 152 kg of aspirin.  [***NOTE:asp = aspirin; AA = acetic anhydride] 84.5% = 100% x (152 kg/X) X = 180. kg asp mL AA = 180. kg aspx 1000g aspx 1mol aspx 1mol AAx 102g AAx LAA  1kg asp180 g asp1 mol asp1 mol AA1.080 g 4  =9.44 x 10mL acetic anhydride (AA) 24. Considerthe various descriptions below.Predict the product(s) where  appropriate,balance the overall reactions, and include net ionic equations if  applicable.Write NR if no reaction occurs.  A.Solid magnesium turnings are mixed with chlorine gas. Mg(s) + Cl 2 (g)→ MgCl 2 (s)  B.Solid manganese is reacted with hydrobromic acid. + +2 Mn(s) + 2H(aq)→(aq) + H Mn 2 (g)  C.Iron metal is added to a solution of aluminum phosphate. cannot replace Al!NR! Fe  D.Aqueous ammonium sulfide is mixed with aqueous lead(II) nitrate. -2 +2 S (aq) + Pb(aq)→ PbS(s)  E.Aqueous radium chloride is mixed with aqueous copper(I) sulfate. +2 -+ -2 (aq) + SORa (aq)+ Cl (aq) + Cu 4 (aq)→RaSO 4 (s) + CuCl(s)  F.Aqueous scandium(III) chloride is mixed with aqueous nickel(II)  nitrate. NR! Bothproducts are soluble, and all spectator ions cross  out!  G.Bromine gas is reacted with aqueous sodium iodide. - - Br 2 (g) + 2I(aq)→+ I 2Br (aq) 2 (g)  H.TNT, a powerful organic explosive with the formula C 7 H 5 (NO 2 ) 3 ,  iscombusted to form molecular nitrogen as well as other expected  products. 4C 7 H 5 (NO 2 ) 3  +21O 2 → 6N 2  +28 CO 2 10H + 2 O + heat

Chemistry 60/68 Mock Exam #2 ANSWERS pp. 6

25. Twohydrocarbons have the percent composition 92.25% C and 7.75% H. A.Obtain the empirical formula corresponding to this composition. B.One of the compounds has a molecular weight of 52.03 amu; the other has a molecular weight of 78.05 amu.Obtain the molecular formulas of both compounds. A.You can figure this part out yourself!Convert the percentages (i.e. grams) of carbon and hydrogen to moles, and divide by the smallest number to obtain the empirical formula CH. B.The first compound has a molecular formula of C 4 H 4 ; the second compound has the molecular formula C 6 H 6 . 26. Aspace shuttle uses aluminum metal and ammonium perchlorate to form  aluminumoxide, aluminum chloride, nitrogen monoxide, and water in its reusable  boosterrockets. Thereaction mixture contains 5.75 g of Al and 7.32 g of  NH 4 ClO 4 . Al + NH 4 ClO 4 → Al 2 O 3  +AlCl 3  +NO + H 2 O  A.Balance the aforementioned chemical equation.  B.Determine the theoretical yield (in g) of aluminum chloride, AlCl 3 .  CLEARLYidentify both the LIMITING REAGENT and the  EXCESSREAGENT. C.How much (in g) of which reactant is left unreacted? D.If 1.87 g of aluminum chloride is formed, what is the percentage yield of this reaction?  A.3Al + 3NH 4 ClO 4 → Al 2 O 3  +AlCl 3 3NO + 6H + 2 O AlClB. g 3 = 5.75 g Al x 1 mol Al x 1 mol AlCl 3 x 133 g AlCl 3  27g Al3 mol Al1 mol AlCl 3  =9.44 g AlCl 3 from Al g AlCl 3 = 7.32 g NH 4 ClO 4 x 1 mol x 1 mol AlCl 3 133 g x  117.5g 3mol NH 4 ClO 4  1 mol AlCl 3 = 2.76 g AlCl 3 from NH 4 ClO 4 ⇐ LIMITING!  Therefore,the LIMITING REAGENT is NH 4 ClO 4 and the  EXCESSREAGENT is Al. reacted Al = 2.76 g AlClC. g 3 x 1 mol AlCl 3 x 3 mol Al x 27 g Al 133 g1 mol AlCl 3 1 mol Al  =1.68 g reacted Al

Chemistry 60/68 Mock Exam #2 ANSWERS pp. 7

 Therefore,g unreacted Al = 5.75 total Al g – 1.68 g Al used  =4.07 g unreacted Al  D.Percentage Yield = 100% (Actual Yield/Theoretical Yield)  =100% (1.87 g/2.76 g)  =68.0% yield + 2+2+ 27. Asolution contains one or more of the following ions: Ag, Ca, and/or Cu.  Whensodium chloride is added to the solution, no precipitate forms.When  sodiumsulfate is added to the solution, a white precipitate occurs.The precipitate  isfiltered off, and sodium carbonate is added to the remaining solution, producing  aprecipitate. Determinewhich ion(s) is/are present in the original solution?  Brieflyexplain your reasoning, and write net ionic equations for the formation of  eachof the precipitates observed. When sodium chloride is added to the solution, no precipitate forms: This +  statementconfirms that NO Agis present since AgCl(s) would precipitate  accordingto our solubility rules! When sodium sulfate is added to the solution, a white precipitate occurs: This +2  statementimplies that Cais present due to formation of the calcium sulfate  precipitate.The net ionic equation is as follows: +2 -2 Ca (aq)+ SO 4 (aq)→ CaSO 4 (s) …and sodium carbonate is added to the remaining solution, producing a +2  precipitate: Thisstatement implies that Cuis present due to formation of  thecopper(II) carbonate precipitate.The net ionic equation is as follows: +2 -2 Cu (aq)+ CO 3 (aq)→ CuCO 3 (s) 2+ 2+  Therefore,the unknown contains both Ca ion and the Cuion.