Chemistry 2 Exam Roane State Academic Festival. Name (print neatly) School

Transcription

1 Name (print neatly) School There are fifteen question on this exam. Each question is weighted equally. n the answer sheet, write your name in the space provided and your answers in the blanks provided. There is also a bonus question. It will be used as a tie breaker and will be assigned partial credit. Therefore, for this bonus question show your work VERY NEATLY in the space provided on the answer sheet. When you are finished bring you answer sheets to the front and exit quietly. Please refrain from discussing the exam in the hallway since others may still be working NTE: If there are units associated with the answer, full credit with NT be given without the units mole = particles R = L atm mol K 760 torr 1 atm 1. How many molecules are there in 52.0 g of NH 3? 2. In the following reaction is not balanced. For the real reaction 57.0 g of UH 3 are formed. How many grams of hydrogen are needed to produce this 57.0 g of product? U(s) + H (g) UH (s) What volume of 1.00 M KH solution would contain 52.0 g of KH? 4. What volume of M NaH is required to reach the second endpoint of ml of a M H3P 4 solution? The reaction is: 2NaH + H P Na HP + 2H What is the volume of a gas, originally at 650 torr with a volume of 57.0 L, if it were compressed and the pressure increased to 1500 torr? 6. Calculate the normality of an unknown acid if g of NaH is required to neutralize ml of the acid.

2 7. Balance the following redox reaction: N + H HN + N For the following reaction, the pressures listed below the reactants and products are the pressures observed. Calculate the K for the reaction. N 2(g) + 3H 2(g) 2NH atm 0.42 atm 0.11 atm 9. Calculate the enthalpy of the following reaction: 2C H H(l) + 7 (g) 4C (g) + 6H (g) H f (C2H5H(l)) = kj mol fh (C 2(g)) = kj mol H (H (g)) = kj mol f For the following reaction tell what would happen if one were to 1) increase the Cl 2 pressure, 2) increase the overall pressure and 3) increase the temperature. PCl 3 + Cl 2 PCl5 rh = 08 kj mol ) What is the molar solubility of AgBr in pure water? The K sp for AgBr is ) How many grams of calcium fluoride, CaF 2, can dissolve in a solution that contains M 1 sodium fluoride, NaF? (K (CaF ) = ) sp ) What is the ph of a solution that has a total H concentration of ? 4 14) What is the ph of a 0.10 M solution of HCH. (K a (HCH) = ) 15) Using the standard potential tables, determine the potential for the following reaction: 2PbS 4 + 2H2 Pb + Pb 2 + 2H2S4

3 Answer Sheet Team Name (PRINT NEATLY) School ) The reaction shifts to the 2) The reaction shifts to the 3) The reaction shifts to the Bonus Question answer:

4 Bonus Question Name (print neatly) School Answer the following question showing all your work NEATLY. In a titration of acetic acid (CH3CH) with NaH, the ph of the solution was measured when ml of NaH was added to ml of CH3CH. The concentration of the NaH was M and the concentration of the CH3CH was M. What was the ph? (K a for 5 CH CH is ) Give your answer to the nearest 0.01 ph unit. 3

5 Periodic Chart of the Elements s electrons H p electrons He Li Be d electrons B C N F Ne Na Mg Al Si P S Cl Ar K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr Rb Sr Y Zr Nb Mo 43Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe Cs Ba * Lu Hf Ta W Re Ir s Pt Au Hg Tl Pb Bi 84Po 85At 86Rn 87Fr 88Ra ** Lr 104Rf 105Db 106Sg 107Bh 108Hs 109Mt 110Ds f electrons The Lanthanide and Actinide Series (4f and 5f) * 4f La Ce Pr Nd 61Pm Sm Eu Gd Tb Dy Ho Er Tm Yb ** 5f 89Ac Th 91Pa U 93Np 94Pu 95Am 96Cm 97Bk 98Cf 99Es 100Fm 101Md 102No

6 The EMF Series - Standard Potentials The Electromotive Series (Redox Potentials). Reduction Reaction* Standard xidation Reaction Potential E (volts) Li + e Li(s) K + e K(s) Ca + 2e Ca(s) Na + e Na(s) Al + 3e Al(s) Mn + 2e Mn(s) Cd(H) 2(s) + 2e Cd(s) + 2H Zn + 2e Zn(s) Cr + 3e Cr(s) Fe + 2e Fe(s) PbS 4(s) + 2e Pb(s) + S Ni + 2e Ni(s) Sn + 2e Sn(s) Pb + 2e Pb(s) H + 2e H 2(g) Sn + 2e Sn I 3 + 2H2 +4e I + 4H S + 2- S 4 + 4H + 2e H2 3 H Cu + 2e Cu(s) (g) + 2H2(l) + 4e 4H I + H2 + 2e I + 2H Ni 2(s) + 2H2 + 2e Ni(H) 2(s) + 2H I 2(s) + 2e 2I Fe + e Fe Ag + e Ag(s) Cl + H2(l) + 2e Cl + 2H N 3 + 4H - + 3e N(g) + 2H2(l) Br 2(l) + 2e 2Br (g) + 4H + 4e 2H2(l) Cl 2 + 2e 2Cl Mn 4 + 8H - + 5e Mn + 4H Au + e Au(s) Pb 2(s) + 4H + S e PbS 4(s) + 2H2(l) F (g) + 2e 2F Notes: All ions are 1.0 M aqueous. (g) = gas at 1 atmosphere. (s) = solid and (l) = liquid. *Reversing the reaction and changing the sign of the potential gives the oxidation reaction and the oxidation potential. The international convention of the reduction potential as the standard is followed. Source: CRC Handbook of Chemistry and Physics, 54th Edition, CRC Press, Inc. Boca Raton, FL, p D120.

7 The EMF Series - Standard Potentials Answer Sheet Team Name (PRINT NEATLY) School g L ml L N 7. 3N 2 2 HN 3 + N (0.27) kj mol 10. 1) The reaction shifts to the right 2) The reaction shifts to the right 3) The reaction shifts to the left V Bonus: 4.82 ( the 1:1 buffer is 4.76 ) partial credit if the got to a reasonable distance: Starting amounts: mmoles of NaH mmol of CH3CH mmol Ending amounts: mmoles of NaCH mmol of CH CH mmol 3 3