Chem 1411 Practice Exam 2

Chem 1411 Practice Exam 2

Instructions 1. Write your name on your exam. 2. You may use only the scratch paper and periodic table provided with the exam. You may also use a calculator, provided it cannot communicate with other devices. 3. When completed, turn in the exam, answer sheet, and all scratch paper, periodic tables, etc. This is a 50 minute exam with 16 questions. Good luck! Constants Avogadro s Constant 6.022 141 29 10 23 mol 1 Gas Constant 0.082 057 46 L atm/k mol 8.314 J/K mol 8314 g m 2 /K mol s 2 1 atm 1.013 25 10 5 Pa 760 mmhg 760 Torr 14.7 psi 1.013 45 bar 1 cal 4.184 J Formulas P V nrt ( ( n ) ) 2 P + a (V nb) nrt V M 1 V 1 M 2 V 2 P A P tot χ A P total P A + P B +... V rms 3RT M rate 2 M1 rate 1 M 2 Data Vapor Pressure of Water Temp ( C) P H2 O (mm Hg) 20 17.3 21 18.8 22 19.5 23 21.0 24 22.5 25 24.0 100 760.0

Solubility Rules Ion Solubility Exceptions Alkali Metals, Nitrates Soluble None Ammonium Soluble None Acetates, Chlorates, Perchlorates Soluble None Chlorides, Bromides, Iodides Soluble Ag +, Hg2 2+ are insoluble. PbCl 2, PbBr 2, PbI 2, and HgBr 2 are slightly soluble. Sulfates Soluble Sr 2+, Ba 2+, Pb 2+, Hg2 2+ are insoluble. CaSO 4 and Ag 2 SO 4 are slightly soluble. Hydroxides Insoluble Alkali metals, Ba 2+ are soluble. Sr(OH) 2 and Ca(OH) 2 are slightly soluble. Sulfides, Carbonates, Phosphates Insoluble Alkali metals, NH +, CaS, SrS, BaS are soluble.

Chem 1411-03 Practice Exam 2 1 Ch. 4 Aqueous Reactions 1. 10.00 g of CuCl 2 (s) is dissolved in 1.500 L of water. What is the concentration of Cl (aq)? A. 0.074 14 M B. 0.099 17 M C. 0.049 58 M D. 0.024 79 M E. 0.033 67 M 10.00 g 1 mol 134.45 g 2 Cl 0.148 75 mol 1 CuCl 2 0.148 75 mol 1.500 L 0.0992 M 2. What is the molarity of Ca(NO 3 ) 2 (aq) when 40 ml of 2.0 M Ca(NO 3 ) 2 (aq) is diluted to a volume of 60 ml? A. 0.000 21 M B. 0.076 M C. 0.78 M D. 0.96 M E. 1.3 M M 1 V 1 M 2 V 2 M 2 M 1V 1 V 2 (2.0 M)(40 ml) (60 ml) 1.33 M 3. If Na 2 SO 4 (aq), Ba(OH) 2 (aq), and Ca(NO 3 ) 2 (aq) are added to water, the precipitates will be

Chem 1411-03 Practice Exam 2 2 A. Ba 2 SO 4 (s),baoh (s), CaOH (s), CaSO 4 (s) B. Ba 2 SO 4 (s), Ca(OH) 2 (s), CaSO 4 (s) C. Ba 2 SO 4 (s), Ca(OH) 2 (s) D. Ba(OH) 2 (s), Ca 2 SO 4 (s) E. Na 2 SO 4 (s), Ba(OH) 2 (s), Ca(NO 3 ) 2 (s) Consulting the solubility chart, substances involving Na + or NO 3 are soluble. Ca 2+ can combine with OH or SO4 2, both of which make insoluble products. Besides nitrate, Ba 2+ can combine with SO4 2, also generating an insoluble product. 4. An Arrhenius base A. Forms insoluble compounds when reacted with an Arrhenius acid. B. Is a source of electrons. C. Generates OH in aqueous solution. D. Is covalently bonded to hydroxide. E. Reacts endothermically with water. This is the definition of an Arrhenius base. 5. Which is the correct reaction of H 2 SO 4 (aq) and NaOH (aq)? A. H 2 SO 4 (aq) + NaOH (aq) H 3 NaSO 5 (s) B. H 2 SO 4 (aq) + 2 NaOH (aq) Na 2 SO 4 (aq) + 2 H 2 O (l) C. H 2 SO 4 (aq) + NaOH (aq) NaSO 4 (aq) + H 2 O (l) D. H 2 SO 4 (aq) + NaOH (aq) NaH 2 (s) + HSO 4 (aq) E. H 2 SO 4 (aq) + NaOH (aq) NaSO 4 (aq) + H 2 (g) + O 2 (g) SO 2 4 has a -2 charge, Na + has a +1 charge. The products are thus Na 2 SO 4 (aq) and H 2 O (l). H 2 SO 4 (aq) + 2 NaOH (aq) Na 2 SO 4 (aq) + 2 H 2 O (l) is the balanced reaction. 6. If CaCl 2 (s) and Na 2 CO 3 (s) are added to a solution, the result would be A. CaCl 2 (s) and Na 2 CO 3 (s) B. CaCO 3 (s) and NaCl (s)

Chem 1411-03 Practice Exam 2 3 C. Na + (aq), CO 2 3 (aq), and CaCl 2 (s) D. Na + (aq), Cl (aq), and CaCO 3 (s) E. Ca 2+ (aq), Cl (aq) and Na 2 CO 3 (s) According to the solubility rules, chloride compounds are soluble, alkali metal compounds are soluble, and carbonate compounds are insoluble (an exception being if there is an alkali metal). Thus, CaCO 3 (s) will precipitate, and everything else will remain in solution. 7. Which of the following is a weak acid? A. HClO 4 B. HCl C. H 2 SO 4 D. HCOOH E. HBr HCOOH is the weak acid because it is not one of the known strong acids. 8. A 10.0 ml sample of H 2 SO 4 (aq) of unknown concentration is titrated with 0.200 M NaOH in presence of an indicator. The indicator changes color when 10.0 ml of NaOH (aq) have been added. What was the concentration of the H 2 SO 4 (aq) sample? A. 0.250 M B. 0.500 M C. 0.100 M D. 0.200 M E. 0.400 M The balanced equation is H 2 SO 4 (aq) + 2 NaOH (aq) Na 2 SO 4 (aq) + H 2 O (l) There are 0.200 moles NaOH liter 0.010 L NaOH 1 H 2SO 4 2 NaOH 0.001 moles H 2SO 4 which means the concentration of the original sample was 0.001 moles 0.010 L 0.10 M

Chem 1411-03 Practice Exam 2 4 Ch. 5 Gases 9. What is an ideal gas? A. A gas in molecules have no volume or chemical interactions and undergo elastic collisions. B. A fluid which takes the shape of its container. C. A gas in which the type of gas determines how pressure, volume, moles, and temperature are related. D. A gas which condenses into a liquid as the gas cools. E. A gas for which the properties must be determined by experiment. These characteristics define an ideal gas. 10. What would be a valid equation relating a change in the number of moles of gas to its change in volume? A. V 1 n 1 V 2 n 2 B. V 1 n 2 V 2 n 1 C. P 1 V 1 n 1 P 2 V 2 n 2 D. n P V/RT E. P 1 + P 2 (n 1 + n 2 )RT/V P V 1 n 1 RT P V 2 n 2 RT P V 1 n 1RT P V 2 n 2 RT V 1 V 2 n 1 n 2 V 1 n 2 V 2 n 1 11. The equivalence point is where A. All of the acid dissolves. B. Just enough acid or base has been added to neutralize the solution.

Chem 1411-03 Practice Exam 2 5 C. The indicator is least likely to change color. D. Any solids become soluble. E. The same volume of acid and base have been added to the solution. This is the definition of the equivalence point. 12. A light bulb contains argon gas and has a temperature of 260 C when turned on. What is the average velocity of an argon gas atom in the light bulb? A. 18.2 m/s B. 314 m/s C. 403 m/s D. 576 m/s E. 871 m/s 3RT V rms M 3(8314 m 2 g/s 2 mol K)(260 + 273.15 K) 39.948 g/mol 576 m/s 13. Which is not a property of an ideal gas? A. Gas molecules are chemically attracted to each other. B. Gas pressure is proportional to the number of molecules. C. It expands to fill the volume of its container. D. Gas molecules collide elastically. E. Its volume decreases with temperature. An ideal gas is defined to be a gas without intermolecular interactions and whose molecules collide elastically. 14. A four quart saucepan holds 210 moles of H 2 O. If the water evaporates into a gas, what volume will it occupy? The outside pressure is 732 mm Hg, and the temperature is 300 K.

Chem 1411-03 Practice Exam 2 6 A. 7.06 L B. 168 L C. 1557 L D. 4600 L E. 5370 L P V nrt V nrt P (210 mol)(0.082 06 L atm/k mol)(300 K) ( ) 1 atm 732 mm Hg 760 mm Hg 5367 L 15. A syringe has a plunger which can freely move. It initially contains 5.0 ml of oxygen. It is cooled from 98 C to 15 C. What is the new volume of the oxygen? A. 0.8 ml B. 3.9 ml C. 4.7 ml D. 6.4 ml E. 8.7 ml P V nrt V 1 T 1 V 2 T 2 ( ) T2 V 2 V 1 5 ml T 1 3.88 ml ( ) 288 k 371 k

Chem 1411-03 Practice Exam 2 7 16. A balloon is filled to 100.0 L at 739 mm Hg and 22.0 C and is allowed to ascend to an altitude where the pressure is 362 mm Hg and the temperature is 15.3 C. What is the final volume of the balloon? A. 25.7 L B. 71.9 L C. 127 L D. 179 L E. 246 L P V nrt P 1 V 1 T 1 P 2V 2 T 2 V 2 P 1V 1 T 2 T 1 P 2 (739 mm Hg)(100.0 L)(258 K) (295 K)(362 mm Hg) 178.5 L 17. It takes 1 hour for a tire filled with CO 2 (g) to deflate. How much more quickly does this happen if the tire is filled with H 2 (g)? A. 0.21 as quickly B. 4.67 as quickly C. 18.1 as quickly D. 45.1 as quickly E. 96.2 as quickly

Chem 1411-03 Practice Exam 2 8 rate 2 M1 rate 1 M 2 44.01 g/mol 2.02 g/mol 4.67 18. In which of the following cases would the ideal gas approximation be least valid? A. Calculating the number of moles of gas in an open room on earth s surface. B. A hot, low pressure gas. C. A single molecule in a large container. D. A gas for which molecular interactions were very small and the temperature was not too large. E. A very cold, high pressure gas, made of large molecules. Under these conditions, the ideal gas assumption of no molecular interactions becomes a poor one. Having a high pressure and large molecules also undermines the ideal gas assumption of no molecular volume. 19. A reaction produces H 2 (g), which is collected over water in an inverted beaker. 740 ml of volume are displaced. The temperature is 24.0 C and the pressure in the room is 768 mm Hg. How many moles of H 2 were produced by the reaction? A. 0.0298 mol B. 0.0306 mol C. 0.369 mol D. 0.379 mol E. 0.798 mol P H2 P total P H2 O 768 mm Hg 22.5 mm Hg 1 atm 745.5 mm Hg 760 mm Hg 0.9809 atm

Chem 1411-03 Practice Exam 2 9 P V nrt n P V RT (0.9809 atm)(0.740 L) (0.082 06 L atm/k mol)(24.0 + 273.15 K) 0.029 77 mol 20. In the van der Waals equation ( ( n ) ) 2 P + a (V nb) nrt V the term nb represents A. The reduction in pressure due to intermolecular attractions. B. The kinetic energy of the gas molecules. C. The concentration of the gas. D. The volume occupied by the molecules of the gas. E. The increase in pressure due to intermolecular attractions. Real gases have molecules with volume, and the remaining free volume of the container is equal to (V nb) where nb accounts for volume taken up by the gas molecules themselves. Please turn in your exam, answer sheet, periodic table, all other papers used, and clear your calculator.