Midterm 1A

# Midterm 1A - Midterm I 150 points Version A 1 Which of the...

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Page 1 Midterm I - 150 points - 10/18/2007 — Version A 1. Which of the following acids has the lowest pH? 0.1 M HBO, p K a = 2.43 0.1 M HA, p K a = 4.55 0.1 M HMO, p K a = 8.23 0.1 M HST, p K a = 11.89 pure water A. HA B. HST C. HMO D. HBO E. pure water 2. Consider the reactions of cadmium with the thiosulfate anion. Cd 2+ ( aq ) + S 2 O 3 2- ( aq ) Cd(S 2 O 3 )( aq ); K 1 = 8.3 × 10 3 Cd(S 2 O 3 )( aq ) + S 2 O 3 2- ( aq ) Cd(S 2 O 3 ) 2 2- ( aq ); K 2 = 2.5 × 10 2 What is the value for the equilibrium constant for the following reaction? Cd 2+ ( aq ) + 2S 2 O 3 2- ( aq ) Cd(S 2 O 3 ) 2 2- ( aq ) A. 0.030 B. 33 C. 8.1 × 10 3 D. 8.6 × 10 3 E. 2.1 × 10 6

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Page 2 3. A mixture 0.500 mole of carbon monoxide and 0.400 mole of bromine was placed into a rigid 1.00-L container and the system was allowed to come to equilibrium. The equilibrium concentration of COBr 2 was 0.233 M. What is the value of K c for this reaction? CO( g ) + Br 2 ( g ) COBr 2 ( g ) A. 5.23 B. 1.22 C. 1.165 D. 0.858 E. 0.191 4. Lactic acid has a p K a of 3.08. What is the approximate degree of dissociation of a 0.35 M solution of lactic acid? A. 1.1% B. 2.2% C. 4.8% D. 14% E. none of these choices is correct 5. At 850°C, the equilibrium constant K p for the reaction C( s ) + CO 2 ( g ) 2CO( g ) has a value of 10.7. If the total pressure in the system at equilibrium is 1.000 atm, what is the partial pressure of carbon monoxide? A. 0.362 atm B. 0.489 atm C. 0.667 atm D. 0.915 atm E. 0.921 atm
Page 3 6. Arsenic acid, H 3 AsO 4 , is used industrially to manufacture insecticides. Arsenic acid is a polyprotic acid with K 1 = 2.5 × 10 -4 , K 2 = 5.6 × 10 -8 , and K 3 = 3 × 10 -13 . What is the concentration of the HAsO 4 2- in a solution whose initial arsenic acid concentration was 0.35 M ? A. 9.4 × 10 -3 M B. 2.5 × 10 -4 M C. 8.8 × 10 -5 M D. 5.6 × 10 -8 M E. none of these choices is correct 7. When a chemical system is at equilibrium, A. the concentrations of the reactants are equal to the concentrations of the products. B. the concentrations of the reactants and products have reached constant values. C. the forward and reverse reactions have stopped. D. the reaction quotient, Q , has reached a maximum. E. the reaction quotient, Q , has reached a minimum. 8. The reaction system CS 2 ( g ) + 4H 2 ( g ) CH 4 ( g ) + 2H 2 S( g ) is at equilibrium. Which of the following statements describes the behavior of the system if the partial pressure of hydrogen is doubled? A. As equilibrium is reestablished, the partial pressure of carbon disulfide increases. B. As equilibrium is reestablished, the partial pressure of methane, CH 4 , decreases. C. As equilibrium is reestablished, the partial pressure of hydrogen decreases. D.

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## This note was uploaded on 06/07/2009 for the course CHEM 01c taught by Professor Schoeller during the Spring '09 term at UC Riverside.

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Midterm 1A - Midterm I 150 points Version A 1 Which of the...

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