Physical 10

TECHNOLOGICAL INSTITUTE OF TH EPHILIPPINES COMPETENCY EXAM IN PHYSICAL CHEMISTRY STUDENT NUMBER __________________________________DATE__January 24, 2012___________ Direction: Write the letter that corresponds to the correct answer. 1. An aqueous solution of CuSO4 was electrolyzed between Cu electrodes. On the cathode , 0.300 grams of Cu was deposited. The solution in the anode compartment contained 1.43 grams of Cu after electrolysis and the same weight of water contained 1.2140 grams before electrolysis. Calculate the transference number of Cu +2 a. 0.18 b. 0.23 c. 0.28 d. 0.31 2. Assuming ideal gas behavior, which of the following gases would have the lowest density at standard temperature and pressure? a. SF6 b. CF2Cl2 c. CO2 d. N2 e. Kr 3. A current of electricity is passed successively through the ffg. Solutions: a) NaCl between inert electrodes b) AgNO3 between Ag electrodes c) Sulfuric acid between inert electrodes d) KOH between inert electrodes. Ten liters of H2 measured at STP are produced at the cathode in the 3 rd solution. The amount of substance liberated at the positive electrode in the first cell is a. 0.89 g H2 b. 0.89 g of Cl2 c. 31.6 g of O2 d. 31.6 g of Cl2 4. The amount of substance produced in the fourth cell at the positive electrode is a. 0.89 g H2 b. 0.89 g of O2 c. 7.12 g of O2 d. 31.6 g of H2 5. In liquids, the attractive intermolecular forces are __________. a. very weak compared with kinetic energies of the molecules b. strong enough to hold molecules relatively close together c. strong enough to keep the molecules confined to vibrating about their fixed lattice points d. not strong enough to keep molecules from moving past each other e. strong enough to hold molecules relatively close together but not strong enough to keep molecules from moving past each other 4 6. Calculate the freezing point of 0.01 M acetic acid solution, a weak electrolyte . Ka = 1.8 x 10 - 5 5 a. - 0.12 ºC b. – 0.02 ºC c. – 0.30 ºC d. – 0.03 ºC 6 7. Calculate the ionic strength of 0.001 M of K2SO4 7 a. 0.003 b. 0.002 c. 0.001 d. 0.01 8 8. The boiling point of a 2% solution of an unknown compound in benzene is 3 ºC higher than the boiling point of pure benzene. What is the molecular weight of the compound? Tf = 5.5 ºC, Tb = 80.2 ºC ; kf = 5.12 ºC /m; kb = 2.53 ºC/m 9 a. 17 g/mole b. 24.2 g/mole c. 33 g/mole d. 36 g/mole 9. Volatility and vapor pressure are __________. a. inversely proportional to one another b. directly proportional to one another c. not related d. the same thing e. both independent of temperature 10.A urea solution freezes at - 2.0 ºC. How much glucose should be added to 100 grams of urea solution to lower the freezing point of solution to – 3.0 ºC ºC? a. 16 grams b. 1.6 grams c. 24 grams 2.4 grams 11. If 0.0346 grams of gas dissolved in 600 ml of water at 20 ºC and 1 atm. What will be the concentration of a solution of oxygen in water at 20 ºC if the gas exerts a pressure of 400 mmHg. The vapour pressure of water at 20 ºC is 18mmHg. a. 3.11 x 10 -5 g/ml b. 3.25 x 10 – 5 g/ml c. 4.21 x 10 – 5 g/ml d. 4.58 x 10 -5 g/ml 12. On a phase diagram, the critical pressure is __________. a. the pressure required to melt a solid b. the pressure below which a substance is a solid at all temperatures c. the pressure above which a substance is a liquid at all temperatures d. the pressure at which a liquid changes to a gas e. the pressure required to liquefy a gas at its critical temperature 13. In an isotopic enrichment effusion apparatus, 238UF6 and 235UF6 gases at 23°C escape from a small hole into a vacuum. If the initial mole fraction ratio of the two gases is 1:1 , calculate the mole fraction ratio 238 UF6/235UF6 in the escaping gases.

a. 1.0086 c. 0.99147 b. 1.0043 d. 0.98740 14. All of the following are true about the speed of a gas according to the kinetic theory EXCEPT a. The root-mean-square speed of a gas depends on the pressure b. The particles move at different speeds. c. The root mean square speed of a gas is proportional to the square root of the temperature. d. Particles with high molar masses in a gas mixture move more slowly than those with low molecular masses. 15. An aniline and hexane pair at 30 ºC gives 2layers, one 21.9 % aniline and the other 89.9% aniline. What will be the weight of the 2 layers when 50 grams of aniline and 50 grams of hexane are mixed at 30 ºC? a. 50 grams hexane layer b. 75 grams hexane c. grams hexane d. 34 grams hexane 50 grams aniline 25 grams aniline 81 grams aniline 76 grams aniline 16. NH4HS dissociates as follows: NH4HS (s) ↔ NH3(g) + H2S (g). At 25 ºC, the dissociation pressure of the pure solid is 500 mmHg, Calculate the total pressure at equilibrium when 300 mmHg of NH3 is introduced into a flask containing solid NH4HS. a. 467 mmHg b. 503 mmHg c. 584 mmHg d. 750 mmHg 17. Which of the following will cause the density of a fixed mass of a gas to increase? a. Increasing its pressure (temperature held constant) b. Increasing its volume (temperature held constant) c. Increasing its temperature (pressure held constant) d. Increasing its temperature (volume held constant) 18. Which of the following is true regarding the reason that isotopes such as 16O and 17O are considered to be the same element? a) They have the same number of protons and protons determine the chemistry of an atom. b) They have the same number of neutrons and neutrons determine the chemistry of an atom. c) They have the same number of electrons and electrons determine the chemistry of an atom. d) The give off the same emissions when they undergo nuclear decay 19.The standard free energy of formation of HCl (g) at 25 ºC is - 22,770 cal/mole. Calculate the thermodynamic equilibrium constant for the dissociation of HCl into its elements at 25ºC. a. 5.02 x 10 – 16 b. 2 x 10 – 17 c. 3.21 x 10 – 18 d. 3.57 x 10 – 18 20.The amount of heat absorbed (or evolved) when 1 mole of a substance is formed is equal to the amount of heat evolved (or absorbed) when 1 mole of the same substance is decomposed. a. Hess Law of aHeat Summation b. Law of Lavoisier and Laplace c. Law of Lavoisier

d. Clausius - Clapeyron Equation