1. A 2.48 g sample of a noble gas is stored in a 3.50 L vessel at 157 torr and 25 ºC. What is the identity of the gas?

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1 hemistry 11 Spring 2008 Examination #2 ANSWER KEY For the first portion of this exam, select the best answer choice for the questions below and mark the answers on your scantron. Then answer the free response questions that follow (100 pts. total; multiple choice 2 pts. each). 1. A 2.48 g sample of a noble gas is stored in a 3.50 L vessel at 157 torr and 25 º. What is the identity of the gas? A. e B. Ne. Ar D. Kr E. Xe 2. When a liquid is in dynamic equilibrium with its vapor in a closed container: A. a change in temperature will not change the pressure in the container. B. the amount of gas in the container must exactly equal the amount of liquid.. molecules cannot completely go from the liquid phase to the gas phase because the amount of liquid in the container is constant. D. the vapor will gradually change back to the liquid state; that is, no vapor will be left. E. the rate at which molecules from the liquid phase enter the gas phase exactly equals the rate at which molecules from the gas phase pass into the liquid phase. 3. Determine the mass (in g) of 2.71 x atoms of sulfur. A. 144 B D E When pure water is heated to 100 º, bubbles form in the water. Is this evidence of a chemical reaction? A. Yes, the formation of a gas is proof a new compound has been made. B. No, the formation of gas bubbles is a secondary chemical reaction which is ignored.. Yes, the formation of a gas is evidence of a chemical reaction. D. No, boiling water is a physical change. E. None of the above

2 5. What is the theoretical yield of a reaction if 25.0 grams of product were produced from a reaction that has an 88% yield? A g B g g D. 352 g E g 6. When the equation below is balanced using smallest whole number integers, determine the sum of the coefficients: A. 11 B D. 19 E. 21 Al(s) + l(aq) All 3 (aq) + 2 (g) 7. Which of the following compounds is most miscible in water? A. butyl alcohol ( O) B. ethylene glycol (O 2 2 O). hexane ( ) D. carbon dioxide (O 2 ) E. iodine (I 2 ) 8. ow many grams of oxygen atoms are found in 1.00 x 10 2 g of K 2 r 2 O 7? A g B g g D g E g 9. A solution prepared by dissolving 3.00 g NaBr in 12.0 g 2 O is said to be: A. 6.67% (w/w) NaBr by mass B. 8.30% (w/w) NaBr by mass. 20.0% (w/w) NaBr by mass D. 25.0% (w/w) NaBr by mass E. 33.3% (w/w) NaBr by mass

3 10. onsider the molecular equation shown below: Nal(aq) + AgNO 3 (aq) Agl(s) + NaNO 3 (aq) If 45.8 ml of 3.14 M Nal(aq) is titrated with 50.0 ml of AgNO 3 (aq), what is the molarity of AgNO 3 (aq)? A M B M M D M E M For Questions 11 12, consider the following: 6.0 M 2 SO 4 (aq) of unknown volume is required for the preparation of ml of a 0.30 M 2 SO 4 solution. 11. What volume (in ml) is initially required of the more concentrated solution? A ml B ml ml D ml E ml 12. Determine how much water must be added to the 6.0 M solution in order to make the required dilution. A ml B ml ml D ml E ml 13. According to the kinetic molecular theory of gases, molecules of different gases at the same temperature always have the same. A. molecular mass B. pressure. average kinetic energy D. volume E. average density

4 14. Two identical, open beakers at 1 atm and 25 º initially contain the same volume of liquid unknowns. One beaker contains unknown compound X; the other beaker contains unknown compound Y. Over time, the beaker with compound X has a smaller volume than the beaker with compound Y. Based on this information, one can assume that compound X: A. is less volatile, has a lower vapor pressure, and possesses weaker intermolecular forces than compound Y. B. is more volatile, has a higher vapor pressure, and possesses stronger intermolecular forces than compound Y.. is less volatile, has a lower vapor pressure, and possesses stronger intermolecular forces than compound Y. D. is more volatile, has a higher vapor pressure, and possesses weaker intermolecular forces than compound Y. E. is the same as compound Y. 15. A sample of a gas originally at 25 º and 1.00 atm pressure in a 2.5 L container is allowed to expand until the pressure is 86.1 kpa and the temperature is 15 º. Determine the final volume of the gas (in L). A. 3.0 B D. 2.1 E onsider the structure of the benzene ( 6 6 ) molecule shown below: benzene = Which of the following substances is most miscible in benzene? A. 2 SO 4 B. Mgl 2. Br 3 D. F E. 2 4

5 17. Which of the following represents the expected trend in increasing boiling points of the liquid states for the chemical species shown? A. e < O < 2 O < SO 2 < Nal B. e < O < SO 2 < 2 O < Nal. Nal < SO 2 < 2 O < O < e D. SO 2 < Nal < 2 O < O < e E. O < e < SO 2 < Nal < 2 O 18. Determine the p of a 2.8 x 10-3 M NaO(aq) solution. A B D E When the electron cloud of an atom is easily distorted, the atom has a high? A. dipole moment B. polarity. polarizability D. vapor pressure E. surface tension 20. Which of the following INORRETLY describes an ideal gas? A. An ideal gas is one whose pressure, volume, and temperature behavior can be completely described by the equation PV = nrt. B. Attractive and repulsive forces between gas molecules are significant only at short distances.. The volume of all molecules of the gas is negligible compared to the total volume in which the gas is contained. D. Gases consist of large numbers of molecules that are in continuous, random motion. E. Gases behave ideally under conditions of low pressure and high temperature. 21. Which of the following is NOT a strong electrolyte? A. NaO(aq) B. l(aq). Mg(O) 2 (aq) D. 2 SO 4 (aq) E. Nal(aq)

6 22. Determine the FALSE statement about buffer solutions: A. A buffer solution is one that resists a drastic change in p when either an acid or a base is added. B. The most important example of an acid/base buffer system in the body is carbonic acid/sodium bicarbonate.. The second most important example of an acid/base buffer system in the body is a phosphate buffer made up of hydrogen phosphate ion, PO 4-2, and dihydrogen phosphate ion, 2 PO 4 -. D. A blood p between 7.0 and 7.3 is called alkalosis, which causes the person to feel tired and disoriented and have difficulty in breathing. E. A buffer solution consists of a weak acid and its salt or a weak base and its salt. 23. hoose the TRUE statement below: A. lo 3 (aq) and lo 4 (aq) are equally strong acids. B. Blood pressure is measured at the pulmonary artery in the arm using a sphygmomanometer.. As blood moves down the arteries and the heart prepares for another beat, the blood pressure drops temporarily, and the lowest pressure reached is called the systolic pressure. D. A blood pressure reading of 152/96 indicates pre-hypertension. E. When the temperature is raised to the point at which the vapor pressure is equal to the atmospheric pressure, vaporization occurs throughout a liquid. 24. Which of the following will react with l(aq) to produce a gas? A. Fe, Al, and u B. u, Ag, and g. Pb, Na, and Ag D. Li, K, and Sn E. g, Au, and Ni 25. What volume of 0.11 M 2 SO 4 (aq) is required to exactly neutralize 10. ml of M NaO(aq)? A. 7.7 ml B. 1.9 ml ml D. 3.9 ml E ml

7 26. (16 pts. total) In a particular oganic synthesis, one of the series of chemical reactions conducted in the laboratory involves combusting a mass of 15.1 g glucose ( 6 12 O 6 ) with 16.0 g of oxygen. A. (3 pts.) Write the balanced chemical equation for this process O 6 (s) + 6O 2 (g) 6O 2 (g) O(g) B. (10 pts.) ow many grams of carbon dioxide can be produced from this reaction? Identify BOT your limiting and excess reagents. g O 2 = 15.1 g glucose x 1 mol glucose x 6 mol O 2 x 44.0 g O g glucose 1 mol glucose 1 mol O 2 = 22.1 g O 2 g O 2 = 16.0 g O 2 x 1 mol O 2 x 6 mol O 2 x 44.0 g O 2 32 g O 2 6 mol O 2 1 mol O 2 = 22.0 g O 2 The limiting reagent is oxygen; the excess reagent is glucose.. (3 pts.) If 31.8 g of O 2 are obtained by a particular student in this step of the experiment, what is the percentage yield? ow can this outcome be justified? % Yield = 100 * (Actual/Theoretical) = 100 * (31.8 g/22.0 g) = 145% A carbon-containing contaminant or impurity must have been initially mixed to result in a percentage yield higher than 100% when this particular student conducted the experiment! 27. (20 pts. total; 4 pts. each) Write BALANED equations (net ionic where appropriate) for each laboratory situation. Assume that solutions are aqueous unless otherwise indicated. Write NR if no reaction occurs. A. alcium metal is immersed in zinc chloride solution. a(s) + Znl 2 (aq) al 2 (aq) + Zn(s) a(s) + Zn +2 (aq) a +2 (aq) + Zn(s) B. Ammonium phosphate is combined with mercury(ii) sulfate. 2(N 4 ) 3 PO 4 (aq) + 3gSO 4 (aq) 3(N 4 ) 2 SO 4 (aq) + g 3 (PO 4 ) 2 (s) 2PO 4-3 (aq) + 3g +2 (aq) g 3 (PO 4 ) 2 (s)

8 . Nitric acid (NO 3 ) is mixed with strontium hydroxide. 2NO 3 (aq) + Sr(O) 2 (aq) 2 2 O(l) + Sr(NO 3 ) 2 (aq) + (aq) + O - (aq) 2 O(l) D. Solid aluminum is reacted with hydrochloric acid (l). 2Al(s) + 6l(aq) 2All 3 (aq) (g) 2Al(s) (aq) 2Al +3 (aq) (g) E. Methane gas ( 4 ) is burned in air. 4 (g) + 2O 2 (g) O 2 (g) O(g) 28. (8 pts.) Briefly explain the phenomenon of inhalation. Your description should include the following terms: diaphragm, rib cage, thoracic cavity, pressure gradient. The process of taking a breath of air begins when the diaphragm contracts, the rib cage expands, causing an increase in the volume of the thoracic cavity. The elasticity of the lungs allows them to expand when the thoracic cavity expands. According to Boyle s law, the pressure inside the lungs will decrease when their volume increases. This causes the pressure inside the lungs to fall below the pressure of the atmosphere. This causes a pressure gradient, where molecules flow from an area of greater pressure to an area of lower pressure. Thus, we inhale as air flows into the lungs until the pressure within the lungs becomes equal to the pressure of the atmosphere. 29. (6 pts. total; 2 pts. each) ircle the substance below within each given pair which most appropriately matches the listed description, and briefly explain your selection utilizing the appropriate chemical principles. A. least volatile: l 4 2 l 2 Volatility increases with weaker intermolecular forces. The selected molecule is polar, exhibiting dipole-dipole interactions in addition to London dispersion forces, thereby making it less volatile compared to the first molecule (which only exhibits LDF).

9 B. most soluble in fatty tissue of the body: Vitamin K 1 O Vitamin B 2 N N O N N O O 2 2 O O O 2 =( 3 ) ( 3 ) ( 3 ) ( 3 ) 2 O Vitamin K 1 is more soluble in the fatty tissue of the body (which is predominantly nonpolar) as it consists of a long-chain hydrocarbon with only slightly polar components within the structure.. greatest surface tension: 3 2 O O 2 2 O The greater number of -O groups on this molecule increases the hydrogen bonding, resulting in greater surface tension compared to the first molecule.

1. A sample of He(g) occupies 57.9 L at 300. K and 1.00 atm. Determine the volume (in ml) of this sample at 150. ºC and 201 kpa. (101.

1. A sample of He(g) occupies 57.9 L at 300. K and 1.00 atm. Determine the volume (in ml) of this sample at 150. ºC and 201 kpa. (101. Chemistry 11 SPRING 2013 Examination #2 ANSWER KEY For the first portion of this exam, select the best answer choice for the questions below and mark the answers on your scantron. Then answer the free