AP Chemistry Assessment 2

Transcription

1 AP Chemistry Assessment 2 DATE OF ADMINISTRATION: January 8 January 12 TOPICS COVERED: Fundatinal Tpics, Reactins, Gases, Thermchemistry, Atmic Structure, Peridicity, and Bnding. MULTIPLE CHOICE KEY AND CROSSWALK Questin Number Crrect Answer Essential Knwledge Learning Objective Science Practice Q1 C 2.D Q2 D 1.C Q3 A 1.C Q4 A 1.B Q5 A 3A-3C Q6 D 1.A Q7 B 1.D Q8 D 1.D Q9 C 5.B Q10 B 3.A Q11 B 2.D Q12 C 5.B Q13 A 3.A Q14 C 3.A Q15 B 1.A Prir knwledge Q16 C 3.A Q17 D 2.C Q18 A 2.A Q19 C 2.A Q20 B 2.C Cpyright 2017 Natinal Math + Science Initiative, Dallas, Texas. All rights reserved. Visit us nline at 1

2 Q21 B 2.D Q22 D 1.C Q23 B 2.C Q24 C 2.A Q25 C 2.D A Rubric Q26 2.C A Rubric Q27 5.C Q28 Rubric 1.A FREE RESPONSE SCORING GUIDELINES AND CROSSWALK CH 4 (g) + 2 Cl 2 (g) CH 2 Cl 2 (g) + 2 HCl(g) 26. Methane gas reacts with chlrine gas t frm dichlrmethane and hydrgen chlride, as represented by the equatin abve. (a) A 25.0 g sample f methane is placed in a reactin vessel cntaining 2.58 ml f Cl2(g). (i) Identify the limiting reactant when the methane and chlrine gases are cmbined. Justify yur answer with a calculatin. Cl 2 is the limiting reactant 25.0 g CH 4 1 ml CH g CH 4 1 ml CH 2 Cl 2 1 ml CH 4 =1.56 ml CH 2 Cl ml Cl 2 1 ml CH 2 Cl 2 2 ml Cl 2 =1.29 ml CH 2 Cl 2 1 pint fr the crrect claim 1 pint fr prper justificatin (ii) Calculate the ttal number f mles f CH2Cl2(g) in the cntainer after the limiting reactant has been ttally cnsumed ml CH 2 Cl 2 is prduced when 2.58 ml f Cl 2 is cnsumed. 1 pint cnsistent with part a(i); wrk may be shwn in part a(i) r prper explanatin in part (ii) Cpyright 2017 Natinal Math + Science Initiative, Dallas, Texas. All rights reserved. Visit us nline at 2

3 Initiating mst reactins invlving chlrine gas invlves breaking the Cl Cl bnd, which has a bnd energy f 242 kj ml 1. (b) Calculate the amunt f energy, in jules, needed t break a single Cl Cl bnd. 242 kj ml f bnds 1000 J 1ml bnds 1 kj bnds = J/bnd 1 pint fr crrect answer (c) Wuld a red laser, wavelength f 656 nanmeters, supply the needed energy t break the Cl Cl bnd? Justify yur answer. Red light des nt have enugh energy t break the Cl Cl bnd since the red phtn nly cntains 3.03x10-19 J. E = hc λ 1 pint fr claim that red light wuld nt be enugh 1 pint fr supprting evidence E = ( Js)( m/s)(10 9 nm/m) (656 nm) E = J (d) (i) Draw the Lewis structure fr dichlrmethane, CH2Cl2(g), in the bx prvided. H 1 pint fr a crrect Lewis structure H C Cl Cl (ii) Identify the mlecular structure fr this mlecule. tetrahedral 1 pint fr a crrect mlecular structure Cpyright 2017 Natinal Math + Science Initiative, Dallas, Texas. All rights reserved. Visit us nline at 3

4 (e) Cnsider the fllwing Bltzmann distributin curve representing the prducts f this reactin. Identify the peak that represents HCl. Explain yur reasning. Number f Mlecules HCl HCl shuld be assigned t the peak with greater number f particles with greater speed (the lwest peak n this graph) Speed (m/s) 1 pint fr identificatin f the crrect peak Bth f the prducts are at the same temperature and pssess the same average kinetic energy; hwever, CH 2 Cl 2 has a mass f 84.9 g/ml while HCl has a mass f 36.5 g/ml. The greater the mass, the slwer the particles because KE = ½ mv 2 1 pint fr apprpriate reasning 27. Prpane, C 3, is a hydrcarbn that is cmmnly used as fuel fr cking. (a) Write a balanced equatin fr the cmplete cmbustin f prpane gas, which yields CO 2 (g) and H 2 O(l). C O 2 3 CO H 2 O 1 pint fr crrect reactants and prducts 1 pint fr crrect balancing Cpyright 2017 Natinal Math + Science Initiative, Dallas, Texas. All rights reserved. Visit us nline at 4

5 (b) (i) Calculate the vlume f air at 30 C and 1.00 atmsphere that is needed t burn cmpletely 10.0 grams f prpane. Assume that air is 21.0 percent O2 by vlume at sea level g C 3 1 ml C g C 3 5 ml O 2 1 ml C 3 = 1.14 ml O 2 V O2 = nrt (1.14 ml)( L atm/ml K)(303 K) = P 1.00 atm V O2 = 28.3 L V air = 28.3 L 0.21 =135 L f air 1 pint fr mles f xygen 1 pint fr crrect substitutin and calculatin using ideal gas equatin 1 pint fr vlume f xygen in air (b) (ii) If the reactin were perfrmed at a higher altitude, wuld the vlume f air needed t cmpletely react the prpane be greater than, less than r equal t the calculated vlume at sea level? Explain. The vlume f air needed will be greater than the calculated value at sea level. The amunt f xygen present is less than 21%; dividing by a smaller value will result in a larger vlume. 1 pint fr a crrect claim with apprpriate reasning (c) The heat f cmbustin f prpane is 2,220.1 kj/ml. Calculate the heat f frmatin, ΔH f, f prpane given that ΔH f f H2O(l) = kj/ml and ΔH f f CO2(g) = kj/ml. Δ H cmb = [ Δ H f (CO + Δ H 2 ) f (H 2 O )] [ Δ H f (C + Δ H 3 ) f (O 2 )] = [3(-393.5) + 4(-285.3)] - [X+ 0] X = ΔH cmb = kj/ml 1 pint fr crrect substitutin using cefficients 1 pint fr crrect answer with sign and significant digits (d) Assuming that all f the heat evlved in burning 30.0 grams f prpane is transferred t 8.00 kilgrams f water (specific heat = 4.18 J/g C), calculate the increase in temperature f water. Cpyright 2017 Natinal Math + Science Initiative, Dallas, Texas. All rights reserved. Visit us nline at 5

6 q released = 30.0 g C 3 1 ml kj g 1ml = 1514 kj heat released by prpane = heat absrbed by water q absrbed = ( m)(c p )(ΔT) 1,514,000 J = ( 8000 g)(4.18 J/g. C)(ΔT) ΔT = 45.3 C 1 pint fr kj released by prpane 1 pint fr crrect temperature change Answer the fllwing questins relating t gravimetric analysis. 28. A student is assigned the task f determining the number f mles f water in ne mle f MgCl 2 n H 2 O. The student cllects the data shwn in the fllwing table. Mass f empty cntainer Initial mass f sample and cntainer Mass f sample and cntainer after first heating Mass f sample and cntainer after secnd heating Mass f sample and cntainer after third heating g g g g g (a) Explain why the student can crrectly cnclude that the hydrate was heated a sufficient number f times in the experiment. A negligible change in mass between the secnd and third heating indicates that all f the water has been remved. 1 pint fr crrect explanatin (b) Use the data abve t (i) calculate the ttal number f mles f water lst when the sample was heated, and g hydrate + cntainer g anhydrate + cntainer g water = ml water 1 pint fr crrect calculatin f mles f water Cpyright 2017 Natinal Math + Science Initiative, Dallas, Texas. All rights reserved. Visit us nline at 6

7 (ii) determine the frmula f the hydrated cmpund g anhydrate + cntainer g cntainer g MgCl 2 = ml MgCl 2 1 pint fr crrect frmula with apprpriate calculatin rati is 1:6; therefre, the frmula is MgCl 2 6H 2 O (c) A different student heats the hydrate in an uncvered crucible, and sme f the slid spatters ut f the crucible. What effect will the spattering have n the calculated mass f the water lst by the hydrate? Justify yur answer. Splattering will result in a greater lss f mass that is calculated as water, this will prduce a higher water/salt rati 1 pint fr crrect claim with prper justificatin Cpyright 2017 Natinal Math + Science Initiative, Dallas, Texas. All rights reserved. Visit us nline at 7