I just wanted to clarify the final set of questions.

#36 The decomposition of silver chloride. This is exactly like the problems in class. You get the balanced equation (2AgCl –> 2 Ag + Cl2) which allows you to relate the unknown (moles of chlorine gas) to the moles of known (silver chloride). Moles of silver chloride is determined by molar mass from the mass given. Volume of gas is determined from the moles of chlorine gas and the ideal gas equation.

#37 Again a simple input out put problem. The idea was a double displacement equation that produced lead (II) chloride as the insoluble product (the other option was ammonium nitrate and that is definitely soluble). Then you use molarity to find the limiting reagent between the two inputs, followed by stoichiometry, then molar mass to get grams.

#38. The water vessel question. There are two ways to solve this question (which was in the practice problems). The first way was to solve it using the idea of partial pressures and solving for the number of moles, then back calculating the volume using the ideal gas law. This is the way I used in the answer key and it works just fine. However, there is a much more simple solution. The system has a constant volume and temperature, the only thing that affects the pressure is the number of particles in the system. As Avagadro showed us, the nature of particles is irrelevant when observed in mass, just the number. In absolute terms the final state of the system has two-thirds the number of particles as the initial state. Since all gases are ideal in the system and ideal means there are linear relationships between the gas properties you can find the final pressure by multiplying the initial pressure (1.5 atm) by 2/3 (ratio of final to initial) to get a final pressure of 1.00 atm.

#39 This relates back to Avagadro’s Hypothesis (#13 on the exam) and the idea of what an ideal gas means. The answer is it is irrelevant whether it is butane, xenon, or any other ideal gas, given a system with the same conditions all ideal gases have the same volume. I’ll give you partial credit if you picked one and gave me some decent justification for your wrong answer.