Laude’s CH302 Practice test 3 key Use the values below on test questions Half reaction Eo (V) Half reaction Eo (V) Cu+2 + 2e-= Cu +0.34 Zn+2 + 2e-= Zn -0.76 Mg+2 + 2e- = Mg -2.38 Pb+2 + 2e-= Pb -0.13 2H+ + e-= H2 0.00 Sn+2 + 2e-= Sn -0.14 Ag+ + e- = Ag +0.80 Pt2+ + 2e- = Pt +1.20 1. Consider a reaction happening in a cell: Mg(s) + HCl ↔ MgCl2 + H2(g) What kind of cell is it? Calculate the value of ∆G for the reaction that occurs when current is drawn from this cell. a. Voltaic, 2.38 V b. Voltaic, -457 kJ Correct c. Electrolytic, -457 kJ d. Electrolytic, 457 kJ 2. Consider a reaction happening in a cell: Cu (s) + HCl ↔ CuCl2 + H2(g) What is the equilibrium constant of the new reaction? (all reaction happens at standard condition, 273K and 1atm) a. 63920 J b. – 63920 J c.3.18 e-13 d.5.8 e-13 Correct 3. Consider this reaction happening in acidic solution: CuS + HNO3 ↔ CuSO4 + NO (g) + H2O If you balance the reaction, the coefficient for HNO3 is: a.1 b. 2 c. 4 d. 8 correct 4. Rank the following reducing agents from weakest to strongest using the table of standard potentials above: a. Ag<Sn<Mg Correct b. Sn<Ag<Mg c. Mg<Sn<Ag d. Mg<Ag<Sn 5. Rank the same three compound from the weakest to the strongest in terms of their potential to be oxidized (that was a pun): a. Ag<Sn<Mg Correctb. Sn<Ag<Mg c. Mg<Sn<Ag d. Mg<Ag<Sn6. A scientist decided to save money in buying his lover gifts by covering a cheap zinc bracelet with Pt. The estimated amount of Pt required to cover this bracelet with a very thin layer of Pt is 3.22 mg. How much time should he run this electrolytic cell at 1mA of current? (Pt = 195g/mol) a. 3170 hours b. .88 hours Correct c. 3.17 hours d. 3303 seconds 7. Consider this conventional electrochemical cell diagram: Pt| Fe | Fe3+ || Br2 | Br- | Pt What are the anode and cathode, respectively? a. Pt and Pt2+ b. Pt and Br2 c. Br2 and Fe d. Fe and Br2 Correct 8. What does the || sign indicate, and by convention, what reaction occurs on the right side of the || sign: a. salt bridge, reduction Correctb. separation between reactant and product, reduction c. wire connecting two cell chambers, oxidation d. separation between two cell chambers, oxidation e. a. salt bridge, oxidation 9. If you were to construct a galvanic cell with lead and silver solution using platinum wire to connect them, after a while, would the platinum wire be covered in lead or in silver? a. lead b. silver Correct c. a bit of both d. none of them e. I have absolutely no idea. 10. What is true for a standard reduction potential: I electromotive force is measured II strength of the current generated is constant III the half reaction process is cathodic IV conditions are 0 K and 1atm a. all of the above b. I, III and IV c. I, II Correct d. I, II, III 11. Calculate the potential for the standard cell indicated: Zn | Zn 2+ || Cu2+ | Cu(s) What are the sign of the anode and the direction of electron flow? a. - , anode-> cathode correct b. +, anode-> cathode c. -, cathode -> anode d. +, cathode -> anode 12. If the concentration of Zn2+ and Cu2+ in the above cell is .15M and 1.5 M respectively, what is the cell potential? a. 1.07 Vb. -1.07 V c.1.13 V Correct d. -1.13 V 13. What is the potential of the reaction below reaction, which takes place in a standard electrochemical cell: Sn2+ + Pb ↔ Sn + Pb2+ a. -.01 Correct b. + .01 c. -.02 d. +.1 14. Which of these batteries is used in your car: a. zinc-carbon battery b. Nickel-cadmium battery c. Lead-acid battery Correct d. Lithium-ion battery 15. Which of these batteries is used in your cell phone: a. zinc-carbon battery b. Nickel-cadmium battery c. Lead-acid battery d. Lithium-ion battery Correct 16. Consider this reaction: H2 + N2 ↔ NH3 What is the rate expression in terms of H2? a. - ∆ H2/ ∆t b. -∆H2/3∆t Correct c. ∆H2/3∆t d. -∆H2/2t 17. The unit of the rate constant of this reaction is: 2 Cl ↔ Cl2 Rate = k [Cl]2 a. s-1 b. liter mole -1 s-1 correctc. s-1 mole liter-1 d. s mole liter-1 18. Consider this reaction: 2A + 3B ↔ C + 2D Trial [A] [B] Initial rate 1 .2M .1M 3 e-2 2 .4M .1M .12 3 .2M .6M 3 e-2 What is the overall order of the reaction: a. 1 b. 2 correct c. 3 d. 019. The conversion from 14C to N which happens in nature is a first order reaction. 14C Æ N + β The haft life of carbon 14 is about 5500 years. A fossil was discovered to have only 3.125% of the normal amount of 14C. How old is this fossil? a. 27500 yrs correct b. 1100 yrs c. 11000 yrs d. 7971 yrs 20. Supposing 14C degradation is a second order reaction with k = 1.5 e-5 year-1mg-1. The rate law would be rate = k [14C]2 How old is the above fossil, if there is 1 mg of 14C left? a. 13000 yrs b. 65000 yrs correct c. .65 yrs d. 1.3 yrs 21. What is the amount of 14C left if the fossil is only 2000 years old? a. 16.3 mg correct b. 8.16 mg c. 3.16 mg d. 27.5 mg 22. Consider this reaction 2A + B ↔ 3C This is the plot of concentration of A vs. time: What is the order of this reaction: a. 0 b. 1 correct c. 2 d. Can’t determine from the information given 23. The collision kinetic theory states that in order for a reaction to occur: a. the reactant molecules must have the right orientation when they contact each other correct b. the reactant molecules must have enough energy when they contact each other c. the temperature of the reacting environment must be high enough d. catalysts much be present24. The transition state kinetic theory states that in order for a reaction to occur: a. the reactant molecules must have the right orientation when they contact each other b. the reactant molecules must have enough energy when they contact each other correct c. the reaction must be exothermic d. catalysts much be present 25. What is the change in temperature for a reaction happening at 25°C, activation energy 2000 J to increase its reaction rate
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