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NAME: ______Section:_____ Form 1 (blue)

October 3, 2001 QUIZ #2 CHEM 101 1) Bowmanics has just dumped enough barium nitrate into your 40,000. L fish pond to make the concentration of barium nitrate = 2.345 x 10-3 M. Your job is too add enough of one of the following agents to precipitate all the barium out of solution to save your family who use this water and to prove that your education was worth it! a) Which of the following solids can be added to the pond to precipitate all the Ba assuming that the reaction goes to completion (circle one): KNO3 MgS Na2SO4

b) Write down the net ionic reaction for the precipitation reaction. 2+ 2- Ba (aq) + SO4 (aq) !BaSO4(s)

c) How many kg of the reagent you chose in a) will you need to precipitate all the barium nitrate assuming complete reaction? mol of Ba2+ = 2.345 x 10-3 mol Ba2=/L x 40,000. L = 93.80 mol Ba2+

2+ 2- mol Ba = mol SO4 = mol Na2SO4 = 93.80 mol

93.80 mol Na2SO4 x 142.02 g Na2SO4/mol x 1 kg/1000 g= 13.32 kg Na2SO4

2) Which of the following are oxidation/reduction () reactions? In those that are redox reactions identify the oxidating agent and the . - - a) AgNO3(aq) + Cl (aq) ! AgCl(s) + NO3 (aq) Not a redox reaction b) 2Cr2O3(s) + 3Si(s) ! 4Cr(s) + 3SiO2(s) oxidation # (+3) (-2) (0) (0) (+4) (-2) Oxidizing agent: Cr2O3 Reducing agent: Si

3) is used to purify drinking water. Too much chlorine is harmful to humans. The excess chlorine is often used removed by treatment with dioxide (SO2). Balance the following equation in an acidic solution which represents this procedure:

- 2- Cl2 + SO2 ! Cl + SO4 oxidation no: 0 +4 -2 -1 +6 -2 Half-reactions: 2- Oxidation: SO2 ! SO4 - Reduction: Cl2 ! Cl Balanced half-reactions: 2- + - Oxidation: 2H2O + SO2 ! SO4 + 4H + 2e - - Reduction: 2e + Cl2 ! 2Cl Balanced reaction: 2- - + 2H2O + SO2 + Cl2 ! SO4 + 2Cl + 4H

4) A dented (but not punctured) ping pong ball often can be restored to its initial shape by immersing it in hot water. Referring to the ideal gas law explain this observation. P is proportional to T. Increase in temperature of the gas inside the ball increases the pressure causing the ping pong ball to expand against the dent and push it out. NAME: ______Section:_____ Form 2 (yellow)

October 3, 2001 QUIZ #2 CHEM 101 1) Bowmanics has just dumped enough barium nitrate into your 60,000. L fish pond to make the concentration of barium nitrate = 5.432 x 10-3 M. Your job is too add enough of one of the following agents to precipitate all the barium out of solution to save your family who use this water and to prove that your education was worth it! a) Which of the following solids can be added to the pond to precipitate all the Ba assuming that the reaction goes to completion (circle one): KNO3 Na2SO4 MgS

b) Write down the net ionic reaction for the precipitation reaction. 2+ 2- Ba (aq) + SO4 (aq) !BaSO4(s)

c) How many kg of the reagent you chose in a) will you need to precipitate all the barium nitrate assuming complete reaction? mol of Ba2+ = 5.432 x 10-3 mol Ba2=/L x 60,000. L = 325.9 mol Ba2+

2+ 2- mol Ba = mol SO4 = mol Na2SO4 = 325.9 mol

325.9 mol Na2SO4 x 142.02 g Na2SO4/mol x 1 kg/1000 g= 46.28 kg Na2SO4

2) Which of the following are oxidation/reduction (redox) reactions? In those that are redox reactions identify the oxidation agent and the reducing agent. a) 2Fe2O3(s) + 3C(s) ! 4Fe(s) + 3CO2(g) oxidation # (+3) (-2) (0) (0) (+4) (-2) Oxidizing agent: Fe2O3 Reducing agent: C - - b) Pb(NO3)2(aq) + 2Cl (aq) ! PbCl2(s) + 2NO3 (aq) Not a redox reaction

3) is used to purify drinking water. Too much bromine is harmful to humans. The excess bromine is often used removed by treatment with (SO2). Balance the following equation in an acidic solution which represents this procedure:

- 2- Br2 + SO2 ! Br + SO4 oxidation no: 0 +4 -2 -1 +6 -2 Half-reactions: 2- Oxidation: SO2 ! SO4 - Reduction: Br2 ! Br Balanced half-reactions: 2- + - Oxidation: 2H2O + SO2 ! SO4 + 4H + 2e - - Reduction: 2e + Br2 ! 2Br Balanced reaction: 2- - + 2H2O + SO2 + Br2 ! SO4 + 2Br + 4H

4) A dented (but not punctured) ping pong ball often can be restored to its initial shape by immersing it in hot water. Referring to the ideal gas law explain this observation. P is proportional to T. Increase in temperature of the gas inside the ball increases the pressure causing the ping pong ball to expand against the dent and push it out.