Chemistry Lab Fairfax High School Invitational January 7, 2017 Team Number: High School: Team Members Names: Reference Values: Gas Constant, R = 8.314 J mol -1 K -1 Gas Constant, R = 0.08206 L atm mol -1 K -1 Gas Constant, R = 62.36 L torr mol -1 K -1 1 atm = 760 mmhg = 760 torr = 101.3 kpa Heat of Fusion of Water = 0.334 kj/g Heat of Vaporization of Water = 2.26 kj/g Specific Heat of Liquid Water = 4.18 J/g C Specific Heat of Ice = 2.03 J/g C 1 P age
Part 1: Multiple Choice 1. The density of fluorine gas at STP, in grams per liter, is approximately: (a) 0.40 (b) 0.85 (c) 1.7 (d) 19 (e) 38 2. A sample of nitrogen occupies 5.50 liters under a pressure of 900. mmhg at 25.0 o C. At what temperature will it occupy 10.0 liters at the same pressure? (a) 32.0 o C (b) -109 o C (c) 154 o C (d) 269 o C (e) 370. o C 3. Under conditions of fixed temperature and amount of gas, Boyle's law requires that I. P 1 V 1 = P 2 V 2 II. PV = constant III. P 1 /P 2 = V 2 /V 1 (a) I only (b) II only (c) III only (d) I, II, and III (e) another combination 4. The volume of a sample of nitrogen is 6.00 liters at 35.0 o C and 0.974 atm. What volume will it occupy at STP? (a) 6.59 L (b) 5.46 L (c) 6.95 L (d) 5.67 L (e) 5.18 L 5. Which statement is false? (a) The density of a gas is constant as long as its temperature remains constant. (b) Gases can be expanded without limit. (c) Gases diffuse into each other and mix almost immediately when put into the same container. (d) The molecular weight of a gaseous compound is a non-variable quantity. (e) Pressure must be exerted on a sample of a gas in order to confine it. 6. What pressure (in atm) would be exerted by 284 g of chlorine gas in a 1.50 liter vessel at -37 o C? (a) 26 atm (b) 52 atm (c) 103 atm 2 P age
(d) 216 atm (e) 3700 atm 7. A container with volume 71.9 ml contains water vapor at a pressure of 10.4 atm and a temperature of 465 o C. How many grams of the gas are in the container? (a) 0.421 g (b) 0.183 g (c) 0.129 g (d) 0.363 g (e) 0.222 g 8. A 0.290 g sample of a compound containing only carbon and hydrogen contains 0.240 g of carbon and 0.050 g of hydrogen. At STP, 33.6 ml of the gas has a mass of 0.087 g. What is the molecular formula for the compound? (a) CH 3 (b) C 2 H 6 (c) C 2 H 5 (d) C 4 H 10 (e) C 4 H 12 9. A flask contains 16.0 g of SO 2(g), 16.0 g of O 2(g), and 8.0 g of CH 4(g). The total pressure of the gases in the flask is 800 mm Hg. What is the parital pressure of the SO 2(g) in the flask? (A) 800 mm Hg (B) 600 mm Hg (C) 250 mm Hg (D) 200 mm Hg (E) 160 mm Hg 10. A sample of hydrogen gas collected by displacement of water occupied 30.0 ml at 24 o C on a day when the barometric pressure was 98.1 kpa. What volume would the hydrogen occupy if it were dry and at STP? The vapor pressure of water at 24.0 o C is 2.99 kpa. (a) 32.4 ml (b) 21.6 ml (c) 36.8 ml (d) 25.9 ml (e) 27.6 ml 11. A mixture of 0.50 mol He (g) and 0.50 mol Ar (g) is introduced into a 15.0 liter container having a pinhole leak at 30 o C. After a period of time, which of the following is true? (a) The partial pressure of He exceeds that of Ar in the container. (b) The partial pressure of Ar exceeds that of He in the container. (c) The partial pressures of the two gases remain equal. (d) The partial pressures of both gases increase above their initial values. (e) The partial pressure of He in the container increases above the initial value. 12. At 25 C, a sample of NH 3 effuses at the rate of 0.050 moles per minute. Under the same conditions, which of the following gases effuses at approximately one-half that rate? (a) O 2 (b) He (c) CO 2 (d) Cl 2 (e) CH 4 13. What total gas volume (in liters) at 520 o C and 880 torr would result from the decomposition of 33 g of potassium bicarbonate according to the equation: 2KHCO 3 (s)! K 2 CO 3 (s) + CO 2 (g) + H 2 O(g) (a) 56 L (b) 37 L (c) 10 L (d) 19 L (e) 12 L 14. NH 4 NO 3(s)! N 2 O (g) + 2 H 2 O (g) (Container Volume = 1.0 L) 3 P age
A 0.03 mol sample of NH 4 NO 3(s) decomposes completely according to the balanced equation above. The total pressure in the flask measured at 400 K is closest to which of the following? (A) 3 atm (B) 1 atm (C) 0.5 atm (D) 0.1 atm (E) 0.03 atm 15. The ideal gas law predicts that the molar volume (volume of one mole) of gas equals: (a) grt/pv (b) (MW)P/RT (c) 1/2ms -2 (d) RT/P (e) 22.4 L at any temperature and pressure 16. A 2 L container will hold about 4 g of which of the following gases at 0 C and 1 atm? (A) SO 2 (B) N 2 (C) CO 2 (D) C 4 H 8 (E) NH 3 17. A hydrocarbon gas with an empirical formula CH 2 has a density of 1.88 grams per liter at 0 C and 1.00 atmospheres. A possible formula for the hydrocarbon is (A) CH 2 (B) C 2 H 4 (C) C 3 H 6 (D) C 4 H 8 (E) C 5 H 10 18. Complete combustion of a sample of a hydrocarbon in excess oxygen produces equimolar quantities of carbon dioxide and water. Which of the following could be the formula of the compound? (A) C 2 H 2 (B) C 2 H 6 (C) C 4 H 8 (D) C 6 H 6 (E) C 3 H 5 19. Below is the equation for the decomposition of phosphorous pentachloride. If a sample of PCl 5 with a total pressure of 0.50 atm was allowed to completely decompose, what would be the total pressure in the container? PCl 5 (g)! PCl 3 (g) + Cl 2 (g) (A) 0.50 atm (B) 1.0 atm (C) 1.5 atm (D) 2.0 atm (E) 3.0 atm 20. Which of the following chemicals is responsible for the depletion of the ozone layer? (A) CHCl 2 -CHF 2 (B) CO (C) CO 2 (D) NO (E) NH 3 21. Which of the following chemicals is responsible for photochemical smog? (A) CHCl 2 -CHF 2 (B) CO (C) CO 2 (D) NO (E) SO 2 22. What is the immediate harm from the depletion of the Earth s ozone layer? (A) The average temperature of the Earth will increase gradually (B) The oxygen content of the atmosphere will decrease (C) An increased amount of ultraviolet radiation will reach Earth s surface (D) Sea levels will rise (E) Polar ice caps will melt 23. Which of the following is not a source of the greenhouse gas carbon dioxide? (A) respiration (B) burning fossil fuels (C) volcanic eruptions (D) deforestration (E) lightning 24. Which of the following describes an effect of burning sulfur waste material? (A) photochemical smog (B) acid rain (C) damage ozone layer (D) nerve damage in humans 25. Assertion: Carbon dioxide is one of the most important greenhouse gases. Reason: It is produced largely by the respiratory function of animals and plants (A) Both assertion and reason are correct, and the reason correctly explains the assertion (B) Both assertion and reason are correct, but the reason does not correctly explain the assertion (C) Both assertion and reason are not correct. 4 P age
(D) Assertion is not correct, but reason is correct. 5 P age
26. Calculate the enthalpy of combustion of C 3 H 6 : C 3 H 6 (g) + 9/2O 2 (g)! 3CO 2 + 3H 2 O using the following data: 3C(s) + 3H 2 (g)! C 3 H 6 (g) C(s) + O 2 (g)! CO 2 (g) H 2 (g) + 1/2O 2 (g)! H 2 O(l) H= 53.3 kj H=-394 kj H=-286 kj (A) -1517 kj (B) 1304 kj (C) -626 kj (D) -2093 kj 27. In which of the following processes does a gas change directly to a solid? (A) condensation (B) sublimation (C) deposition (D) freezing 28. Two containers are filled with diatomic hydrogen gas and diatomic oxygen gas. The gases have the same temperature. Compare the average speed of hydrogen molecules to the average speed of oxygen molecules. (A) 4/1 (B) 1/4 (C) 16/1 (D) 1/2 (E) They have the same speed. For questions 29-32, determine if the following are 29. Sunlight + 6CO 2 (g) + H 2 O(l)! C 6 H 12 O 6 (aq) + 6O 2 (g) (A) endothermic or (B) exothermic 30. 31. Boiling water 32. Freezing water 33. Consider the thermal energy transfer during a chemical process. When heat is transferred from the system to the surroundings, the process is said to be and the sign of H is. (A) exothermic, positive (B) endothermic, negative (C) exothermic, negative (D) endothermic, positive 34. What amount of heat will change 30.0 g of ice at -40.0 C to liquid water at 70.0 C? (A) 21.2kJ (B) 112000 J (C) 13800J (D) 10.0 kj 35. Calculate the standard entropy change for the following reaction, Cu(s) + ½ O 2 (g)! CuO(s), given that S[Cu(s)] = 33.15 J/K mol S[O 2 (g)] = 205.14 J/K mol S[CuO(s)] = 42.63 J/K mol A) 195.66 J/K (B) 93.09 J/K (C) -45.28 J/K (D) -93.09 J/K (E) 195.66 J/K 36. The normal boiling point of water is 100.0 C and its molar enthalpy of vaporization is 40.67 kj/mol. What is the change in entropy in the system in J/K when 39.3 grams of steam at 1 atm condenses to a liquid at the normal boiling point? (A) 88.8 (B) -88.8 (C) -238 6 P age
(D) 373 (E) -40.7 For Questions 37-39 below, please refer to the diagram. 37. At which number will Condensation be occurring? (A) 1 (B) 2 (C) 3 (D) 4 (E) 5 38. At which number will the Triple Point be found? (A) 1 (B) 2 (C) 3 (D) 4 (E) 5 39. Would the solid of this substance be more dense or less dense than the liquid? (A) More dense (B) Less dense (C) Cannot be determined 1 3 2 4 5 40. A 1.50 kg sample of Au is heated using 400.0 J of energy. If the initial temperature of gold is 25.0 C, what is the final temperature? The specific heat of Au is 0.130 J/g C. (A)103 C (B) 25.5 C (C)230. C (D) 27.1 C (E) 82.1 C For Question 41, refer to phase diagram. 41. What is the freezing point of this substance? (A) 10 C (B) 20 C (C) 40 C (D) 59 C (E) 60 C For Questions 42-43, use the following data. Mass of Water 25.0 g Mass of Metal 17.6 g Initial Temp. of Water 19.2 C Initial Temp. Metal 98.1 C Final Temp. of Water 24.8 C Final Temp. Metal 24.8 C 42. Which of the following can be concluded from the experiment? (A) The metal had a greater temperature change than the water, therefore a greater quantity of thermal energy was lost. (B) The metal had a greater temperature change than the water, but it lost the same quantity of thermal energy. (C) The metal had a greater temperature change than the water, therefore it has a greater specific heat. (D) The final temperature is less than the average starting temperature of the metal and the water, so the total thermal energy of the system decreased. 43. Calculate the specific heat of the metal and identify it. (A) Aluminum, 0.897 J/g C (B) Copper, 0.387 J/g C (C) Iron, 0.450 J/g C (D) Lithium, 3.57 J/g C 44. For the reaction below H = -1516 kj and S = -432.8 J/K at 25 C. This reaction is spontaneous. SiH 4 (g) + 2O 2 (g)! SiO 2 (s) + 2H 2 O (l) 7 P age
(A) Cannot tell from given information (B) at no temperature (C) at all temperatures (D) Only below a certain temperature (E) Only above a certain temperature 45. Joseph Priestly prepared oxygen by heating mercury (II) oxide. The compound is stable at room temperature, but decomposes into its elements at high temperatures. What conclusions can be drawn about H and S for this decomposition reaction? (A) H is positive and S is positive (B) H is negative and S is positive (C) H is negative and S is negative (D) H becomes negative at high temperatures (E) H is positive a S is negative 46. What is the standard heat of formation for ethene, H f C 2 H 4 (g), as calculated from the given data. C 2 H 4 (g) + 3 O 2 (g)! 2CO 2 (g) + 2H 2 O (g) H rxn = -1411 kj H f H 2 O (g) = -241.8 kj/mole H f CO 2 (g) = -393.3 kj/mole (A) -775.9 kj/mol (B) -107.5 kj/mol (C) 140.8 J/mol (D) -140.8 kj/mol (E) 775.9 kj/mol 47. What is the change in energy for a system which has the following two steps: Step 1: The system absorbs 60 J of heat while 40J of work are performed on it Step 2: The system releases 30 J of heat while doing 70 J of work. (A) 100 J (B) 90 J (C) 30 J (D) 0 J (E) 110 J 48. Consider the conversion of a substance from liquid to gas: Liquid "! Gas At 1 atmosphere and at the boiling point of the substance, for the process. (A) S = 0 (B) G = 0 (C) H = 0 (D) E = 0 49. The standard molar enthalpy of combustion is -1277.3 kj for the combustion of ethanol, C 2 H 5 OH. Calculate the standard molar enthalpy of formation for ethanol based on the following standard enthalpies of formation: H f CO 2 (g) = -393.5 kj/mole H f H 2 O (g) = -241.8 kj/mole (A)-642.7 kj/mol (B) -235.1 kj/mol (C) 235.1 kj/mol (D) 642.7 kj/mol (E) -635.3 kj/mol 50. What is the molar enthalpy of reaction for the combustion of methane given the following: (A) 80 kj/mole (B) -284 kj/mole (C) 668 kj/mol (D) -668 kj/mol 51. When a gas in a thermally insulated cylinder is suddenly compressed, the change in state is (A) adiabatic (B) isothermal (C)isobaric (D) isochoric 52. A substance changes from solid to liquid at its normal melting temperature. What change, if any occurs in the average kinetic energy and the average potential energy of its molecules? (A) Average kinetic energy is constant, average potential energy is constant. 8 P age
(B) Average kinetic energy increases, average potential energy is constant (C) Average kinetic energy is increases, average potential energy is decreases (D) Average kinetic energy is constant, average potential energy is increases 53. A beaker contains water at a higher temperature than its surroundings. Which of the following correctly describes the entropy change in the water and in the surroundings as the water cools? (A) Entropy of water decreases and entropy of the surroundings decreases. (B) Entropy of water decreases and entropy of the surroundings increases. (C) Entropy of water increases and entropy of the surroundings decreases. (D) Entropy of water increases and entropy of the surroundings increases. 54. The work done by an ideal gas as it expands isothermically from a state of volume 1 to volume 2 is W. The work done by the gas as it expands adiabatically from the same initial state to a state of volume 2 is: (A) zero (B) less than W but not zero. (C) W (D) greater than W 55. One liter of a gas contains 4 g at STP. From this fact it follows that (A) the gas is helium (B) the molar mass of the gas is 89.6 g/mol (C) the molar mass of the gas is 4 g/mol (D) 6 x 10 23 molecules of the gas have a mass of 4 g (E) there are two atoms in each molecule of the gas 56. Under the same conditions of temperature and pressure a liter of hydrogen compared to a liter of oxygen contains (A) more molecules than the liter of oxygen (B) fewer molecules than the liter of oxygen (C) the same molecules as a liter of oxygen (D) molecules with lower average velocity than the oxygen molecules (E) the same total mass of gas as the liter of oxygen 57. If each gas is at STP, 2.02 grams of hydrogen gas contains the same number of molecules as (A) 16 grams of oxygen gas (B) 16 grams of nitrogen gas (C) 2 moles of helium (D) 22.4 L of oxygen (E) 2.02 g of oxygen 58. When ice melts at its normal melting point and 1 atm, which of the following is true for the process. (A) H <0, S >0, V>0 (B) H <0, S <0, V>0 (C) H >0, S <0, V<0 (D) H >0, S >0, V>0 (E) H >0, S >0, V<0 59. What is the order of increasing rate of effusion for the following gases? Ar, CO 2, He, N 2 (A) N 2 < Ar < CO 2 < He (B) Ar < CO 2 < He< N 2 (C) Ar < He < CO 2 < N 2 (D) CO 2 < N 2 < Ar < He (E) CO 2 < Ar < N 2 < He 60. The specific latent heat of vaporization of a substance is greater than its specific latent heat of fusion because (A) boiling takes place at a higher temperature than melting 9 P age
(B) thermal energy is required to raise the temperature from the melting point to the boiling point (C) the volume of the substance decreases on freezing but increases when boiling (D) the increase in potential energy of the molecules is greater on boiling than on melting. Part 2: Lab Thermodynamics Task: Determine the heat of combustion in kj/gram of the candle. General Procedure (does not include measurements you need to take!): 1. Obtain a soda can and ring stand. 2. Add water to the soda can and suspend it from the ring stand. 3. Light the candle and use it to heat the sample of water. 4. Blow out the candle and clean up. Data Table (10 points) Measurement Data Analysis/Calculations 1. Determine the heat of combustion of the candle in kj/gram. (12 points) 2. A) Write the balanced equation for the combustion of a candle made from C 25 H 52. (4 points) B) If 2.00 grams of C 25 H 52 are burned, how many grams of oxygen are required? (4 points) C) If 2.00 grams of C 25 H 52, how many total ml of product will be produced at 1.10 atm and 22.0 C? (5 points) 10 P age
Gas Laws Task: A compound contains only C, H, and N. It was analyzed by an extraordinary Science Olympiad team. They burned a 35.0 mg sample of the compound completely and 33.3 mg of CO 2 was collected. The water portion of this analysis was accidentally dumped down the sink. Fortunately they also analyzed the sample for nitrogen by the Dumas method. They used a 65.2 mg sample at 740 torr and 25 C and collected 35.7 ml of N 2 gas. Finally, they measured the effusion rate of the compound and found that the compound effused at a rate of 24.6 ml/min while Argon effused at a rate of 26.4 ml/min under the same conditions. A) Determine the % C, % H, and % N in the compound (9 pts) B) Find the empirical formula of the compound. (2 pts) C) What is the molar mass of the compound? (2 pts) D) What is the molecular formula of the compound? (2 pts) 11 P age