Chemistry 11 Spring 2011 Examination #2 ANSWER KEY

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1 Chemistry 11 Spring 2011 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. Determine the mass (in g) of moles of Na 2 S. A g B g C g D g E x 10-1 g 2. Of the following, which would be most immiscible in decane? A. NH 3 B. CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 C. CO 2 D. I 2 E. BF 3 3. Calculate the number of chromium atoms in g of K 2 Cr 2 O 7. A x Cr atoms B x Cr atoms C x Cr atoms D x Cr atoms E x Cr atoms 4. Which of the following compounds is a weak electrolyte? A. HNO 3 (aq) B. HCl(aq) C. HF(aq) D. Ba(OH) 2 (aq) E. NaOH(aq) 1

2 5. Consider the following liquids with similar molar masses. Predict which has the weakest intermolecular attractions based on the vapor pressure data provided below at 20 ºC: A. acetic acid (vapor pressure = 14 mm Hg) B. ethyl chloride (vapor pressure = 1050 mm Hg) C. ethyl methyl ether (vapor pressure = 1260 mm Hg) D. butane (vapor pressure = 1550 mm Hg) E. isopropyl alcohol (vapor pressure = 35 mm Hg) 6. In the complete combustion of 19.8 g of octane (C 8 H 18 ), what mass (in g) of H 2 O is produced? Hint: begin with the balanced chemical equation! A g B g C g D. 139 g E g 7. Which intermolecular force found in CH 2 Br 2 is the strongest? A. London dispersion forces B. Dipole-dipole forces C. Hydrogen bonding D. Van der Waals forces E. None of the above 8. A solution has a [H + ] of 1.0 x 10-6 M. What is its poh? A B C D E. Cannot be determined with the information given 9. In which state of matter are the attractive forces between molecules the weakest? A. solid B. liquid C. gaseous D. Both liquid and gaseous states exhibit same attractive forces between molecules E. none, the attractive forces between molecules are the same in all of them 2

3 10. At constant temperature the pressure on a 10.0 liter sample of gas is changed from 1.00 atm to 1140 torr. What is the new volume of the gas sample? A liters B liters C liters D. 114 liters E liters 11. Blowing air into a balloon is an example of which gas law? A. Boyle s Law B. Charles Law C. Gay-Lussac s Law D. Avogadro s Law E. Dalton s Law 12. If a solution is prepared by dissolving 7.7 g of lithium iodide, LiI, in enough water to make 400 ml of solution, what is the % (w/v) of LiI? A. 0.96% B. 1.9% C. 3.9% D. 7.7% E. 30.8% 13. Which of the following statements are false? 1. Liquids with large intermolecular forces tend to have very low boiling points 2. Liquids with large intermolecular forces tend to have considerable surface tension 3. When a substance changes from a solid to a liquid, the molecules remain intact (unbroken or whole) 4. Liquids with large intermolecular forces tend to have very high vapor pressure A. 1 and 4 B. 3 and 4 C. 2 and 4 D. 1 and 3 E. 2 and 3 3

4 For Questions 14 15, consider the following: a 5.00 M solution HNO 3 of unknown volume is diluted to make 4.50 L of a 1.75 M solution. 14. Determine the volume of the 5.00 M solution needed for the dilution. A L B L C. 635 ml D L E L 15. How much water must be added to the 5.00 M solution in order to make the dilution? A L B L C L D L E L 16. Which of the following species can be characterized as amphiprotic? A. H 2 O B. - H 2 PO 4 C. 2- HPO 4 D. - HCO 3 E. All of them 17. In a particular titration experiment a 25.0 ml sample of an unknown diprotic acid required 30.0 ml of M NaOH for the end point to be reached. What is the concentration of the acid? A M B M C M D M E M 4

5 For Questions 18 20, consider the following: When solutions of AgNO 3 and NaOH react, the UNBALANCED molecular equation is: 2AgNO 3 (aq) + 2NaOH(aq) Ag 2 O(s) + 2NaNO 3 (aq) + H 2 O(l) 18. What is the sum of the coefficients of this reaction? A. 2 B. 3 C. 4 D. 5 E How much Ag 2 O is produced when g of AgNO 3 and g of NaOH react? A g B g C g D g E g 20. What is the % yield of Ag 2 O if the actual yield is g? A % B. 88% C. 113% D. 88.2% E % 21. The equivalence point of a titration corresponds to which of the following? A. the point where equal volumes of acid and base have been used B. the point where a ph indicator changes color C. Equivalence point is the same as end point D. the point where the acid and base have been added in proper stoichiometric amounts E. All of the above 5

6 22. Suppose a balloon is filled so that its volume is 2.00 L when the pressure is 750. torr and the temperature is 24 C. What volume will it occupy if it rises to an elevation where the pressure is 375 torr and the temperature is 12 C? A L B L C L D L E L 23. If one has a 200. L container filled with nitrogen at a pressure of 1.00 atm, how many moles of nitrogen are present at 25ºC? A moles B moles C moles D. 19 moles E. none of the above 24. Arrange the following in the order of increasing intermolecular forces of attraction: A. C 2 H 6 < C 3 H 8 < I 2 < HF < ICl B. C 2 H 6 < C 3 H 8 < I 2 < ICl < HF C. HF < ICl < I 2 < C 3 H 8 < C 2 H 6 D. HF < ICl < C 3 H 8 < C 2 H 6 < I 2 E. I 2 < C 2 H 6 < C 3 H 8 < ICl < HF 25. What intermolecular force is responsible for the fact that ice is less dense than liquid water? A. London dispersion forces B. Dipole-dipole forces C. Ionic bonding D. Hydrogen bonding E. Ion-dipole forces END OF MULTIPLE CHOICE 6

7 26. (24 pts. total; 4 pts. each) Write BALANCED equations (net ionic where appropriate) for each laboratory situation. Assume that solutions are aqueous unless otherwise indicated. Write NR if no reaction occurs. A. Combustion of liquid xylene (C 8 H 10 ). 2C 8 H 10(l) + 21O 2 (g) 16CO 2(g) + 10H 2 O(g) B. Barium hydroxide is reacted with hydrochloric acid. Ba(OH) 2(aq) + 2HCl (aq) BaCl 2(aq) + 2H 2 O(l) H + (aq) + OH - (aq) H 2 O(l) C. Lithium nitrate is reacted with aluminum phosphate. NR D. Iron metal is reacted with sulfuric acid. Fe (s) + H 2 SO 4 (aq) FeSO 4(aq) + H 2 (g) Fe (s) + 2H + (aq) Fe 2+ (aq) + H 2 (g) E. Silver metal is added to a solution of copper(ii) acetate. NR F. Lead(II) nitrate is added to a solution of magnesium bromide. Pb(NO 3 ) 2(aq) + MgBr 2 (aq) PbBr 2(s) + Mg(NO 3 ) 2(aq) Pb 2+ (aq) + 2Br 1- PbBr 2(s) 27. (8 pts.) How would you prepare 2.00 L of 3% (v/v) sodium hypochlorite (bleach) and water solution? You have only a measuring cup. Your answer should include cup(s) of bleach and water. (1 oz = 30 ml and 1 cup = 8 oz) 2.00 L sol x 1000 ml x 3 ml bleach x 1 oz x 1 cup = cups bleach 1 L 100 ml sol 30 ml 8 oz The solution is 97% water 2.00 L sol x 1000 ml x 97 ml water x 1 oz x 1 cup = 8.08 cups water (8 cups OK) 1L 100 ml sol 30 ml 8 oz 7

8 28. (18 pts. total) SHORT ANSWERS! A. (4 pts.) What is a buffer? Give an example of the most important buffer system in our body. A buffer solution is a solution that resists drastic changes in ph caused by the addition of acid or base. Buffers are either acidic buffers or basic buffers. Acidic buffers comprise of a weak acid and its salt. Acetic acid/sodium acetate is an example of an acidic buffer. Basic buffers are comprised of a weak base and its salt. Aqueous ammonia (ammonium hydroxide)/ammonium chloride is an example of a basic buffer. The most important buffer in the human body is carbonic acid/sodium bicarbonate buffer. B. (4 pts.) What are the four main postulates of the kinetic Molecular Theory of gases? 1. Gases consist of large numbers of molecules that are in continuous, random motion. 2. The volume of all molecules of the gas is negligible compared to the total volume in which the gas is contained. 3. Attractive and repulsive forces between gas molecules are negligible. 4. Energy can be transferred between molecules during collisions, but the average kinetic energy of the molecules does NOT change with time as long as the temperature remains constant. Moreover, an increase in temperature results in an increase in the speed that the particles move. C. (4 pts.) What is a neutralization reaction? Give an example using an equation. In a neutralization reaction, an acid reacts with a base in stoichiometrically equivalent amounts to give salt and water as the products. NaOH + HCl NaCl + H 2 O An antacid (base) works by neutralizing acid and coating the stomach. 8

9 D. (6 pts.) What is high blood pressure? How is blood pressure recorded? What are the blood pressure measurements at different stages of hypertension? What must one do to adopt a healthy lifestyle in each of these stages of blood pressure? High blood pressure or hypertension is when the blood exerts above normal pressure on the walls of blood vessels. Blood pressure is recorded using a sphygmomanometer. The systolic pressure is read when the heart muscles contract and blood is pushed into the arteries causing a temporary increase in blood pressure. This reading corresponds to the pressure in the arteries when the heart beats. The diastolic pressure is the pressure in the arteries between heart beats. At this stage, the heart muscle is resting between beats and refilling with blood. There are three different stages of hypertension. Pre-hypertension is when the systolic pressure is between mm Hg and diastolic pressure is between One should adopt a healthy lifestyle by exercising and eating right. Stage 1 hypertension is indicated by a systolic pressure reading between mm Hg and diastolic pressure reading between mm Hg. Exercise, a healthy diet, plus one medication is usually recommended. Stage 2 hypertension is indicated by a systolic pressure reading above 160 mm Hg and diastolic pressure reading above 100 mm Hg. Exercise, a healthy diet, plus more than one medication is usually recommended. 9

(50 pts.) 26. (24 pts.) 27. (8 pts.) 28. (18 pts.) TOTAL (100 points)

(50 pts.) 26. (24 pts.) 27. (8 pts.) 28. (18 pts.) TOTAL (100 points) Moorpark College Chemistry 11 Spring 2011 Instructor: Professor Torres Examination #2: Section Two March 12, 2011 Name: (print) Name: (sign) Directions: Make sure your examination contains ELEVEN total