Question

Page 2 5. How many grams of NaCl are contained in 300 mL of a 0.250 M solution of sodium chloride? a) 3.65 g b) 4.38 8 c) 10.4 g d) 14.6 g e) 29.9 g 6. Consider three identical 1 L flasks at STP. Flask A contains NH3 gas, flask B contains NO2 gas, flask C contains N2 gas. Which contains the largest number of molecules a) flask A b) flask B c) flask C d) each flask contains the same number of molecules e) more information is needed 7. Which of the following processes always results in a decrease in the energy of a systems a) The system loses heat and does work on the surroundings. b) The system gains heat and does work on the surroundings c) The system loses heat and has work done on it by the surroundings. d) The system gains heat and has work done on it by the surroundings. e) None of these is always true. The system loses heat and has work 8. BF3 NF3 The molecules NF2, BFand BrF3 have similar molecular formulas but different molecular geo Use VSEPR theory to predict their molecular shapes. BrF3 a) trigonal pyramidal trigonal planar T-shaped b) T-shaped trigonal planar trigonal pyramidal c) trigonal planar T-shaped trigonal pyramidal d) T-shaped trigonal pyramidal trigonal planar e) trigonal pyramidal T-shaped trigonal planar 9. Sideways overlap of two p orbitals as shown below results in formation of a a) b) c) d) single bond double bond (sigma) bond (pi) bond Lilit

Answer 1

5. The mass can be calculated as:

m = M.V(L).mmolar = 0.250 -.0.300L - 58.44 = 4.38 g

6. If we consider the gases as ideal, same V, p and T force the number of moles to be the same in the 3 cases, so the correct answer is d) each flask contains the same number of molecules.

7. The internal energy is defined as:

m +b= n

Where q is heat (positive when heat is added and negative when heat is lost) an w is work (positive when it is done TO the system and negative when it is done BY the system). So the process that always results in a decrease of energy is losing heat and doing work, so option a.

8. NF₃ is trigonal pyramidal, BF₃ is trigonal planar and BrF₃ is T-shaped. option a is correct.

9. The parallele overlap of p orbitals results in pi bonding; option d.