Chemistry 4 (Practice) MIDTERM EXAM II 009 November (a) Before starting, please check to see that your exam has 5 pages, which includes the periodic table. (b) (c) Fill in your name, section, and student number on Side of the Answer Sheet. To receive credit, you must mark Test Version B on Side of the answer sheet. (d) When you are done with the exam, hand the Answer Sheet to a TA at the exit of the room. Please take the questions with you. (e) (e) room. The exam is over at 9:0 AM. No answer sheet will be accepted after 9:0 AM. Our final exam is scheduled for MONDAY, DECEMBER 6 at 8:30 AM in this
Chem 4 Midterm II 009 November Page To receive credit you must mark version X on side of the Answer Sheet.. (0 points) Methane, CH 4 (g) (molar mass = 6.04 g/mol), reacts with steam to give synthesis gas, a mixture of carbon monoxide and hydrogen, which is used as starting material for the synthesis of a number of organic and inorganic compounds. CH 4 (g) + H O(g) CO(g) + 3 H (g) What mass of hydrogen is formed if 75 L of methane (measured at STP) is converted to synthesis gas? a. 74. g b..3 g c. 4.7 g d. 49.4 g e. None of the above. (0 points) Which of the following molecular gases effuses most rapidly? a. ammonia b. nitrogen c. oxygen d. hydrogen chloride e. They all effuse at the same rate 3. (0 points) Consider the reaction: CaCl (s) + H O(g) CaCl H O(s) The equilibrium constant for the reaction as written as: a. [CaCl H O] K = [H O] b. [CaCl H O] K = [CaCl ][H O] c. K = d. K = [H O] e. K = [H O]
Chem 4 Midterm II 009 November Page 3 4. (0 points) The reaction N (g) + 3H (g) NH 3 (g) takes place in a.0-l vessel initially filled with an equimolar mixture of N and H at a pressure of.0 atm. When equilibrium is reached, the partial pressure of H is 3.0 atm. Determine the value of K p for this reaction. a. 0.030 b. 0.95 c. 0.33 d. 0.333 5. (0 points) Nitric oxide, an important air pollutant, is formed from the elements nitrogen and oxygen at high temperatures, such as those obtained when gasoline burns in an automobile engine. At 000 C, K C = 0.0 for the reaction N (g) + O (g) NO(g) Predict the direction in which the system will move to reach equilibrium at 000 C if 0.4 moles of N, 0. moles of O, and 0.08 moles of NO are placed in a.0-liter container. a. The system remains unchanged. b. The concentration of NO will decrease; the concentrations of N and O will remain unchanged. c. The concentration of NO will decrease; the concentrations of N and O will increase. d. The concentration of NO will increase; the concentrations of N and O will decrease. e. More information is necessary. 6. (9 points) To increase the value of K for the following familiar exothermic reaction H (g) + O (g) H O(g) a) decrease the temperature. b) decrease the total pressure. c) increase the total pressure. d) increase the temperature. e) Two of the above.
Chem 4 Midterm II 009 November Page 4 7. (0 points) HCl gas is in a. liter cylinder at 0.870 atm and 8.0 C. This gas is dissolved in 750.0 ml water. Calculate the ph of this solution (assume no volume change). a. 0.950 b..5 c..37 d..5 8. (0 points) The hydrogen sulfate ion (also known as the bisulfate ion) HSO 4 can act as either an acid or a base in water solution. In which of the following equations does HSO 4 act as an acid? a. HSO 4 + H O SO 4 + H 3 O + b. HSO 4 + H O H SO 4 + OH d. HSO 4 + H 3 O + SO 3 + H O d. HSO 4 + OH H SO 4 + O e. none of thes 9. (0 points) For nitrous acid, HNO, K a = 4.0 x 0 4. Calculate the ph of 0.5 M HNO. a) 3.70 b).00 c).70 d).30 e) none of these 0. (0 points) Calculate the [H + ] in.0 M solution of Na CO 3 (for H CO 3, K a = 4.3 0 7 ; K a = 5.6 0 ). a. 7.5 0 3 M b. 7.5 0 6 M c. 6.6 0 4 M d..3 0 M
Chem 4 Midterm II 009 November Page 5 Chemistry 4 MIDTERM EXAM II (PRACTICE) KEY: DO NOT LOOK AT THIS UNTIL YOU HAVE DONE THE PRACTICE 009 November. (0 points) Methane, CH 4 (g), reacts with steam to give synthesis gas, a mixture of carbon monoxide and hydrogen, which is used as starting material for the synthesis of a number of organic and inorganic compounds. CH 4 (g) + H O(g) CO(g) + 3 H (g) What mass of hydrogen is formed if 75 L of methane (measured at STP) is converted to synthesis gas? a. 74. g b..3 g c. 4.7 g d. 49.4 g e. None of the above n(ch 4 ) = PV/RT = atm 75 L/(0.08 73K) =.3 mol molh =.3 mol CH 4 3 mol H / mol CH 4 = 36.8 mol g H = 36.8 mol.06 g/mol = 74.5 g. (0 points) Which of the following molecular gases effuses most rapidly? a. ammonia N molar mass = 8 g/mol b. nitrogen O molar mass = 3 g/mol c. oxygen HCl molar mass = 36.5 g/mol d. hydrogen chloride NH 3 molar mass = 7 g/mol e. They all effuse at the same Effusion rate is proportional to (molar mass) -/, rate NH 3 has the lowest mass and the fastest effusion 3. (0 points) Consider the reaction: CaCl (s) + H O(g) CaCl H O(s) The equilibrium constant for the reaction as written as: [CaCl H O] In this reaction, only the concentration of water a. K = [H O] vapor can change, so only water appears in the equilibrium equation. In the reaction, water [CaCl H O] b. K = appears as a reactant, so its concentration appears [CaCl ][H O] in the denominator of the equilibrium constant. c. Two moles of water react in this equation, so its K = concentration is squared. d. K = [H O] e. K = [H O] 4. (0 points) The reaction N (g) + 3H (g) NH 3 (g)
Chem 4 Midterm II 009 November Page 6 takes place in a.0-l vessel initially filled with an equimolar mixture of N and H at a pressure of.0 atm. When equilibrium is reached, the partial pressure of H is 3.0 atm. Determine the value of K p for this reaction. a. 0.030 b. 0.95 c. 0.33 d. 0.333 N H NH 3 P start 6 atm 6 atm 0 P -x -3x +x P end 6-x 6-3x=3atm x From the pressure of hydrogen, x =, P N = 5 atm, P NH3 = atm K p = /(3 3 5) = 0.030 5. (0 points) Nitric oxide, an important air pollutant, is formed from the elements nitrogen and oxygen at high temperatures, such as those obtained when gasoline burns in an automobile engine. At 000 C, K = 0.0 for the reaction N (g) + O (g) NO(g) Predict the direction in which the system will move to reach equilibrium at 000 C if 0.4 moles of N, 0. moles of O, and 0.08 moles of NO are placed in a.0-liter container. a. The system remains unchanged. b. The concentration of NO will decrease; the concentrations of N and O will remain unchanged. c. The concentration of NO will decrease; the concentrations of N and O will increase. d. The concentration of NO will increase; the concentrations of N and O will decrease. e. More information is necessary. Calculate the reaction quotient. [ NO] Q = ( = 0.08) [ N ] [ O ] 0.4 0. = 0.6 > K initial since Q is greater than K, the reaction will proceed to remove products and form reactants. 6. (9 points) To increase the value of K for the following familiar exothermic reaction H (g) + O (g) H O(g) a) decrease the temperature. H (g) + O (g) H O(g)+ energy b) decrease the total pressure. to increase the equilibrium constant, remove c) increase the total pressure. energy from the system by decreasing d) increase the temperature. temperature. e) Two of the above. 7. (0 points) HCl gas is in a. liter cylinder at 0.870 atm and 8.0 C. This gas is dissolved in 750.0 ml water. Calculate the ph of this solution (assume no volume change).
Chem 4 Midterm II 009 November Page 7 a. 0.950 b..5 c..37 d..5 n = P V RT = 0.870 atm. L 0.08 L atm /mol K 30K = 4.6 0 M [ H + ]= 4.6 0 M 0.7500L ph =.5 = 5.68 0 M 8. (0 points) The hydrogen sulfate ion (also known as the bisulfate ion) HSO 4 can act as either an acid or a base in water solution. In which of the following equations does HSO 4 act as an acid? a. HSO 4 + H O SO 4 + H 3 O + b. HSO 4 + H O H SO 4 + OH c. HSO 4 + H 3 O + SO 3 + H O d. HSO 4 + OH H SO 4 + O The only case where HSO 4 - acts as a proton donor is HSO 4 + H O SO 4 + H 3 O +
Chem 4 Midterm II 009 November Page 8 9. (0 points) For nitrous acid, HNO, K a = 4.0 x 0 4. Calculate the ph of 0.5 M HNO. a) 3.70 HNO (aq) H + (aq) + NO - (aq) b).00 HNO H + - NO c).70 start 0.5 0 0 d).30 [ ] -x x x e) none of these end 0.5-x x x assume 0.5 x x [ K a = H + ]NO [ ] = x = 4.0 0 4 [ HNO ] 0.5 x =.0 0-4 ; x = [H + ] =.0 0 - M; ph =.00 0. (0 points) Calculate the [H + ] in.0 M solution of Na CO 3 (for H CO 3, K a = 4.3 0 7 ; K a = 5.6 0 ). a. 7.5 0 3 M CO - 3 (aq) + H O(l) HCO - 3 (aq) + OH - (aq) b. 7.5 0 6 - - M CO 3 HCO 3 OH - c. 6.6 0 4 M start.00 0 0 d..3 0 M [ ] -x x x end.00-x x x assume.00 x x K b = K w.0 0 4 = K a 5.6 0 =.8 0 4 = HCO 3 [ ] OH [ ] [ CO 3 ] x =.8 0-4 ; x = [OH - ] =.3 0 - ; [H + ] =.0 0-4 /[OH - ]= 7. 5 0-3 M = x