1. How many grams of gas are present in 1.50 L of hydrogen peroxide, H 2 O 2 (g), at STP?

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1 Chemistry 11 Fall 2010 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. How many grams of gas are present in 1.50 L of hydrogen peroxide, H 2 O 2 (g), at STP? A g B g C g D g E g 2. Each of these flasks (equal volume) contains the same number of gas molecules. In which flask would the pressure be highest? A. Flask 1 B. Flask 2 C. Flask 3 D. Flask 4 E. Pressure would be the same in all the flasks 3. How many moles of glucose, C 6 H 12 O 6, are in a sample which weighs 75.5 g? A mol B mol C mol D mol E. None of the above 1

2 4. Which of the following is expected to be completely miscible in cold water, C 6 H 5 COOH or CH 3 COOH? A. Both are miscible in cold water to the same extent B. CH 3 COOH C. C 6 H 5 COOH D. Neither of them is miscible in cold water E. C 6 H 5 COOH is more miscible in cold water than CH 3 COOH 5. Which of the following is not an Arrhenius base? A. LiOH B. Al(OH) 3 C. N(CH 3 ) 3 D. water E. Ca(OH) 2 6. Which of the following is the strongest intermolecular interaction? A. covalent bonding B. dipole-dipole interactions C. London dispersion forces D. hydrogen bonding E. ionic bonding 7. The process of inhaling and exhaling is explained by Boyle s Law. According to this law, if the pressure on a gas sample is halved, what will happen to the volume? A. It will double B. It will increase by a small amount C. It will decrease by a small amount D. It will be halved E. It will remain the same 8. What is the weight (in g) of 4.25 x molecules of diethyl ether (C 2 H 5 ) 2O? A x g B g C g D x g E x g 2

3 9. Which of the following statements is INCORRECT? A. A patient with stage 2 hypertension should take more than one medication. B. The lowest pressure reached when determining blood pressure is termed systolic. C. A buffer resists drastic changes in ph. D. One symptom associated with acidosis is a feeling of tiredness. E. ph measures the hydronium ion concentration. 10. What is the ph of a M HCl solution? A. ph = 5.99 B. ph = 2.50 x 10-3 C. ph = 2.60 D. ph = 1.00 E. ph = A person at rest breathes about 80. ml of air per second. Assuming this air is at 25 C and 755 mmhg, how many moles of air does s/he breath per second? A moles B moles C moles D. 3.1 x 10 2 moles E moles 12. Which of the following could be a Brønsted-Lowry acid? I. H 2 O II. - NO 3 III. HNO 2 IV. 2- CO 3 A. I, III, and IV B. II and III C. I and II D. I and III E. III and IV 3

4 13. What is the ph of a 1.5 x 10-2 M CsOH solution? A. ph = 1.52 B. ph = C. ph = D. ph = E. ph = The following reaction takes place in termites as they digest wood. Solid glucose, C 6 H 12 O 6, and liquid water react to produce aqueous acetic acid (HC 2 H 3 O 2 ), carbon dioxide, and hydrogen gas. When the equation is balanced using smallest whole number coefficients, how many moles of carbon dioxide gas are required? C 6 H 12 O 6 (s) + 4H 2 O(l) HC 2 H 3 O 2 (aq) + 4CO 2 (g) + 8H 2 (g) A. 3 B. 5 C. 1 D. 2 E Which of the following can experience intermolecular forces other than London dispersion forces? A. white phosphorus (P 4 ) B. fluorine gas C. oxygen gas D. liquid carbon dioxide E. carbon monoxide gas 16. How many molecules of ZnSO4 are contained in x 10 2 g ZnSO4? A x molecules ZnSO4 B x molecules ZnSO4 C x molecules ZnSO4 D x molecules ZnSO4 E x molecules ZnSO4 17. The observation can be made that many of the anions that form water-soluble salts also form STRONG acids when paired with hydrogen. Which of these anions would be an exception to this observation? A. nitrate B. sulfate C. acetate D. chloride E. perchlorate (ClO - 4 ) 4

5 18. Typically, when a person coughs, he or she first inhales about 2.0 L of air at 1.0 atm and 25 C. The epiglottis and the vocal cords then shut, trapping the air in the lungs, where it is warmed to 37 C and compressed to a volume of about 1.7 L by the action of the diaphragm and chest muscles. The sudden opening of the epiglottis and vocal cords releases this air explosively. Just prior to this release, what is the approximate pressure of the gas inside the lungs? A. 1.0 atm B atm C. 1.7 atm D. 3.7 x 10-5 atm E. 1.2 atm 19. Consider CH 3 CH 2 OH and CH 3 OCH 3. Which statement(s) is/are correct? I. At the same temperature, CH 3 OCH 3 has a higher vapor pressure than CH 3 CH 2 OH II. Both CH 3 OCH 3 and CH 3 CH 2 OH exhibit London Dispersion Force and so their vapor pressure and boiling point must be the same. III. Because these substances have the same molar mass, they have the same forces of attraction. IV. Both of these substances are capable of intermolecular hydrogen bonding. V. CH 3 CH 3 OH has a higher boiling point than CH 3 OCH 3. A. I only B. II and III C. IV only D. I and V E. V only 20. Evaporation of ml of 0.50 M NaCl must continue to what final volume to achieve a concentration of 3.6 M? A. 16 ml B ml C. 24 ml D. 14 ml E. 720 ml 5

6 21. Which of the substances (a, b, c, d, e) shown is the most volatile at low temperatures? A. a B. b C. c D. d E. e 22. Which of the following change in a dilution process? I. the volume of the solution II. the numbers of moles of solute III. the concentration of the solute A. I only B. I and III C. I, II, and III D. I and II E. II and III 6

7 23. How many grams of solute are needed to prepare 250. ml of 2.50 M K 2 Cr 2 O 7 solution? A. 735 g K 2 Cr 2 O 7 B x 10 3 g K 2 Cr 2 O 7 C g K 2 Cr 2 O 7 D. 184 g K 2 Cr 2 O 7 E. 625 g K 2 Cr 2 O What is the mass percent (w/w) concentration of ethylene glycol solution prepared from 4.5 L ethylene glycol (d = g/ml) in 6.5 L of propylene glycol (d = g/ml)? A. 74% (w/w) B. 52% (w/w) C. 39% (w/w) D. 57% (w/w) E. 43% (w/w) 25. A solution is prepared by dissolving 4.40 g of KSCN in enough water to make ml of solution. What is the concentration of the solution? A M B M C M D M E M 26. Which of the following statements regarding surface tension is CORRECT? A. The surface of a liquid with high surface tension does not appear stretched B. Intermolecular forces tend to pull the molecules together and outward C. Stronger the intermolecular forces, weaker the surface tension D. (CH 3 ) 2 CHOH has a lower surface tension than HOCH 2 CH 2 CH 2 OH E. C 8 H 18 has a higher surface tension than C 8 H 17 OH 27. Which of the following statements is CORRECT? A. Gases behave ideally under conditions of high pressure and temperature. B. A dynamic equilibrium is established when a system is open. C. A stock solution of 12.0 M sulfuric acid is safer than 0.10 M sulfuric acid. D. The ph of blood in the arteries is normally 7.6. E. Combustion reactions are usually exothermic and typically give off heat. 7

8 28. A stockroom attendant has a 15.0% (w/v) solution of KOH. What volume of this solution should she use if she needs to prepare 20.0 ml of a 10.0% (w/v) solution? A ml B ml C ml D ml E. None of the above 29. In a particular titration experiment 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. 2 x 10-1 M 30. Which of the following is NOT a buffer solution? A. CH 3 COOH and CH 3 COONa B. NaH 2 PO 4 and H 3 PO 4 C. H 2 CO 3 and NaHCO 3 D. HNO 3 and NaNO 3 E. All of them are buffer solutions END OF MULTIPLE CHOICE 8

9 31. (16 pts. total) Consider the mixing of 2.00 g sample of ammonia with 4.00 g of oxygen. The unbalanced equation for the reaction is given below: 4NH 3 (g) + 5O 2 (g) 4NO(g) + 6H 2 O(g) A. (3 pts.) Write the balanced chemical equation for the process described. see above B. (8 pts.) How much NO is produced in this reaction? Determine the limiting and excess reagents g NH 3 x 1 mol NH 3 x 4 mol NO x g NO = 3.52 g NO g NH 3 4 mol NH 3 1 mol NO 4.00 g O 2 x 1 mol O 2 x 4 mol NO x g NO = 3.00 g NO g O 2 5 mol O 1 mol NO Limiting reagent is oxygen; excess reagent is ammonia C. (5 pts.) If a student obtains 2.50 g of NO in the laboratory, what is the percentage yield in the experiment? % yield = Actual x 100 = 2.50 g NO x 100 = 83.3 % Theoretical 3.00 g NO 32. (16 pts. total; 4 pts. each) Write BALANCED equations (net ionic where appropriate) for each laboratory situation. Assume all reactants are present in aqueous solution unless otherwise indicated. Write NR if no reaction occurs. A. Solid magnesium is mixed with water. Mg(s) + 2H 2 O(l) Mg(OH) 2 (s) + H 2 (g) B. Lead(II) nitrate is reacted with potassium iodide. Pb 2+ (aq) + 2I - (aq) PbI 2 (s) C. Sodium hydroxide reacts with hydrobromic acid. H + (aq) + OH - (aq) H 2 O (l) D. Liquid ethane (C 2 H 6 ) is burned in air. 2C 2 H 6 (l) + 7O 2 (g) 4CO 2 (g) + 6H 2 O(g) 9

10 33. (8 pts. total; 4 pts. each) Define the following terms and give an example of each: A. Neutralization Reaction - the reaction of an acid and a base to give salt and water. For example, see #32C above. B. Weak electrolyte - a substance that does not completely dissociate or completely ionize in solution. For example, consider acetic acid, tap water, ammonium hydroxide. 10