7. Calculate the density of nitrogen at STP.
(A)0.312 g/L
(B)0.625 g/L
(C)0.800 g/L
(D) 1.25 g/L
(E) 1.60 g/L

3.The atomic mass of rhenium is 186.2. Given that 37.1% of natural rhenium is rhenuim-185,what is the other stable isotope? (A)(B)(C)(D)(E)

4. The following reactions are examples of (A)precipitation reactions. (B)redox, precipitation, and acid-base, respectively. (C)precipitation (two) and acid-base reactions, respectively. (D) redox reactions. (E) none ofthese 75 Re , D) 7s Re

5. A 0.307-g sample of an unknown triprotic acid is titrated to the third equivalence point using 35.2 mL of 0.106 M NaOH. Calculate the molar mass of the acid. (A)247 g/mol (B)171g/mol (C)165 g/mol (D) 151 gmol (E) 82.7gmol

6. Consider two organic molecules, ethanol and benzene. One dissolves in water and the other does not. Why? (A)They have different molar masses. (B)One is ionic, the other is not. (C)One is an electrolyte, the other is not. (D) Ethanol contains a polar O–H bond, and benzene does not. (E) Two ofthese.

8. The van der Waals equation, , incorporates corrections to the ideal gas law in order to account for the properties of real gases. One of the corrections accounts for (A) the possibility of chemical reaction between molecules. (B) the finite volume of molecules. (C)the quantum behavior of molecules. (D) the fact that average kinetic energy is inversely proportional to temperature. (E) the possibility of phase changes when the temperature is decreased or the pressure is increased.

9. A 25.0 g piece of aluminum (which has a molar heat capacity of 24.03J/℃mol) is heated to 82.4*C and dropped into a calorimeter containing water (specific heat capacity of water is 4.18J/g℃initially at 22.3C. The final temperature of the water is 24.9℃. Calculate the mass of water in the calorimeter. (A)118 g(B)6.57g (C)3180g (D) 2120g (E) none of these

10. Calculate the lattice energy for MgO(s) using a Bomn-Haber cycle and the following information: (A)+1842 kJ/mol (B)+2444 kJ/mol (C)+3844 kJ/mol (D) +4108 kJ/mol

11. While mercury is very useful in barometers, mercury vapor is toxic. Given that mercury has a △Hvap of 59.11 kJ/mol and its normal boiling point is 356.7℃, calculate the vapor pressure in mm Hg at room temperature, 25℃. (A) mm Hg (B)2.99 mm Hg (C)372 mm Hg (D) 753 mm Hg

12.At a given temperature the vapor pressures of benzene and toluene are 183 mm Hg and 59.2 mm Hg, respectively. Calculate the total vapor pressure over a solution of benzene and toluene with (A)110 mm Hg (B)133 mm Hg (C)109 mm Hg (D) 242 mm Hg 

13.A concentration-time study of the gas phase reaction produced the data in the table below. What is the average rate of formation of A2 in the time interval 20-30 seconds? (A)(B)(C)(D)