Chemistry 121 Fall 2000 Oregon State University
Exam 2 November 16, 2000 Dr. Richard Nafshun
Dr. Carroll DeKock
DO NOT OPEN
THIS EXAM UNTIL INSTRUCTED.
CALCULATORS ARE
NOT TO BE SHARED.
Instructions: You should have with you several number two pencils, an eraser, your 3" x 5" notecard, and your University ID Card. You may use a TI-25X Solar calculator if you wish. If you have notes with you, place them in a sealed backpack and place the backpack OUT OF SIGHT. Or place the notes directly on the table at the front of the room.
Fill in the front page of the Scantron answer sheet with your last name, first name, middle initial, and student identification number. Leave the class section number and the test form number blank.
This exam consists of 18 multiple-choice questions and 6 open-ended questions. Each multiple-choice question has four points associated with it. Select the best answer by filling in the corresponding circle on the rear page of the answer sheet. If you have any questions before the exam, please ask. If you have any questions during the exam, please raise your hand to attract the attention of a proctor. The proctor will come to you. Open and start this exam when instructed. Present your ID card when submitting the exam. Place your open-ended portion of this exam in the appropriate stack. Place your 3" x 5" notecard in the appropriate stack. You may keep the multi-choice portion of this exam, so please mark the answers you selected on it.
NA = 6.02 x 1023 R = 0.0821 L·atm/mol·K
1. A student places 96.256 grams of methane in a cylinder.
(a) There is one mole of methane of present.
(b) There are two moles of methane present.
(c) There are four moles of methane present..
(d) There are five moles of methane present.
(e) There are six moles of methane present.
2. A student places three moles of MgCl2 into a beaker.
(a) There are 1.81 x 1024 chloride ions in the beaker.
(b) There are 3.61 x 1024 chloride ions in the beaker.
(c) There are 3.60 x 1025 chloride ions in the beaker.
(d) There are 5.73 x 1025 chloride ions in the beaker.
(e)
There are 1.08 x 1026 chloride ions in the beaker.
3. Consider the CORRECTLY BALANCED reaction for the complete combustion of C5H12 in oxygen to produce carbon dioxide and water. When one mole of C5H12 is combusted,
(a) 3 moles of CO2 are produced.
(b) 4 moles of CO2 are produced.
(c) 5 moles of CO2 are produced.
(d) 8 moles of CO2 are produced.
(e) 10 moles of CO2 are produced.
4. A student calculates the theoretical yield of lithium fluoride produced from a process to be 435.0 grams. She actually obtains 156.0 grams. Her percent yield is:
(a) 7.03 %.
(b) 12.50 %.
(c) 35.86 %.
(d) 55.91 %.
(e) 278.8 %.
5. The molarity of the nitrate ion in a solution that is one molar (1.0 M) in Al(NO3)3 is:
(a) 0.5 M.
(b) 1.0 M.
(c) 2.0 M.
(d) 3.0 M.
(e) 4.0 M.
6. Which of the following is NOT soluble in water?
(a) NaNO3.
(b) KNO3.
(c) Mg(NO3)2.
(d) MgCO3.
(e) (NH4)2CO3.
7. A student places one mole of sodium chloride into a two liter volumetric flask and fills to the mark with water. The molarity of sodium chloride is:
(a) 0.500 M.
(b) 1.000 M.
(c) 2.000 M.
(d) 0.0171 M.
(e) 0.00856 M.
8. A student pours 25.00 mL of a 1.500 M NaOH solution into a 2.000-L volumetric flask and fills to the mark with water. What is the concentration of the new solution?
(a) 0.120 M.
(b) 0.0375 M.
(c) 0.0188 M.
(d) 0.0750 M.
(e) 75.0 M.
9. A student places 32.00 grams of oxygen gas (O2) into a 1.000-L flask at 273.15 K. The pressure inside the flask is:
(a) 513.4 atm.
(b) 35.03 atm.
(c) 22.43 atm.
(d) 7.978 atm.
(e) 0.2493 atm.
10. Consider a fixed amount of gas. Which of the following is FALSE?
(a) When the volume is increased at constant temperature, the pressure increases.
(b) When the temperature is increased at constant volume, the pressure increases.
(c) When the temperature is decreased at constant pressure, the volume decreases.
(d) When the pressure is increased at constant temperature, the volume decreases.
11. A student places a gas into a 20.000-L flask at a temperature of 18.45 °C and a pressure of 0.9875 atm. When the temperature of the gas is reduced to -80.12 °C, the pressure is:
(a) 4.288 atm.
(b) - 4.288 atm.
(c) 3.939 atm.
(d) 1.530 atm.
(e) 0.6537 atm.
12. A student places 0.050 mol of CO and 0.025 mol of CO2 into a 1.0 liter balloon at 20 °C.
(a) The partial pressure of the CO is LESS THAN the partial pressure of CO2.
(b) The partial pressure of the CO is THE SAME AS the partial pressure of CO2.
(c) The partial pressure of the CO is GREATER THAN the partial pressure of CO2.
(d) The mole fraction of CO is LESS THAN the mole fraction the mole fraction of CO2.
13. A student places 2.00 moles of O2 (g) and 1.00 mole of CH4 (g) into a 22.4-L flask at 273 K. The pressure of O2 (g) is:
(a) 1/3 atm.
(b) 2/3 atm.
(c) 1.00 atm.
(d) 2.00 atm.
(e) 3.00 atm.
14. Consider the following five gases: O 2 (g) Br2 (g) C2H6 (g) H2 (g) CO (g)
Of these, the gas molecule with the greatest velocity at room temperature is:
(a) O2 (g).
(b) Br2 (g).
(c) C2H6 (g).
(d) H2 (g).
(e) CO (g).
15. Which of the following processes is EXOTHERMIC?
(a) CO2(g) ® C(s) + O2 (g)
(b) H2O (l) ® H2 (g) + ½ O2 (g).
(c) 6CO2(g) + 6 H2O(l) ® C6H12O6 + 6 O2(g).
(d) CH4 (g) + 2 O2 (g) ® CO2 (g) + 2 H2O (l).
16. A system does 60 kJ of work and gives off 40 kJ of heat. The change in the internal energy of the system is:
(a) 20 kJ.
(b) 100 kJ.
(c) -20 kJ.
(d) -100 kJ.
(e) -40 kJ.
17. The energy required to heat 100 g of silver metal [cp = 0.235 J/g°C] from 20 °C to 140 °C is:
(a) 100 J.
(b) 120 J.
(c) 12,000 J.
(d) 2820 J
(e) 1.2 J.
18. When the following reaction is carried out in a flask (the system), the flask feels COLD when held in the hands: NH4NO3 (s) + (H2O) ® NH4+ (aq) + NO3- (aq)
Which of the following is TRUE?
(a) Heat is transferred from the flask to the hand; this is an exothermic process.
(b) Heat is transferred from the flask to the hand; this is an endothermic process.
(c) Heat is transferred from the hand to the flask; this is an exothermic process.
(d) Heat is transferred from the hand to the flask; this is an endothermic process.
Chemistry 121
Fall 2000
Oregon State University
Exam 2
November 16, 2000
Student's Name
__________________________________________
ID Number
__________________________________________
Lecture Instructor (Circle
One)
Dr. Richard Nafshun
Dr. Carroll DeKock
Recitation Day (Circle One)
M/W
T/R
Recitation Time (Circle One)
0800
0900
1000
1100
1200
1300
1400
1500
1600
YOU MUST SHOW ALL WORK ON NUMERICAL PROBLEMS TO RECEIVE CREDIT
1. [4 points] Assume that the reaction given below occurs at STP (standard temperature and pressure.)
What volume of CO2(g) at STP is produced when 13.0 g of C2H2(g) are combusted?
C2H2(g) + 5/2 O2(g) → 2CO2(g) + H2O(l)
Answer:_______________
2. [6 Points] Calculate the enthalpy of combustion for one mole of methanol at standard conditions:
CH3OH (l) + 3/2 O2 (g) → CO2 (g) + 2 H2O (l)
Compound ΔHfº kJ/mol
CH3OH (l) -238.7
CO2 (g) -393.5
H2O (l) -285.8
Answer:________________
3. [6 Points] Write each of the following equations in ionic form and balance. Show a down arrow↓
next to any precipitate that forms. If no reaction occurs write N.R. on the right side.
Example: NaOH + Fe(NO3)3 →
3Na+ + 3OH- + Fe3+ + 3NO3- → Fe(OH)3↓ + 3Na+ + 3 NO3-
In this
example above, circle the ions
which are spectator ions.
(a) Ca(NO3)2 + K2CO3 →
(b) (NH4)2SO4 + NaCl →
4. [4 Points] Calculate the density (g/L) of O2 (g) at STP.
Answer:______________
5. [6 Points] Given the reaction S(s) + 3 F2(g) → SF6(g). How many grams of F2 are required to
react with 16.0 g of S to yield SF6? (Atomic masses: S=32.0 g/mole; F=19.0 g/mole)
Answer:________________
6. [2 Points] The heat of formation of C2H5OH is -277.7 kJ. Write the chemical equation associated
with this heat of formation.